curl_ngtcp2.c

/***************************************************************************
 *                                  _   _ ____  _
 *  Project                     ___| | | |  _ \| |
 *                             / __| | | | |_) | |
 *                            | (__| |_| |  _ <| |___
 *                             \___|\___/|_| \_\_____|
 *
 * Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
 *
 * This software is licensed as described in the file COPYING, which
 * you should have received as part of this distribution. The terms
 * are also available at https://curl.se/docs/copyright.html.
 *
 * You may opt to use, copy, modify, merge, publish, distribute and/or sell
 * copies of the Software, and permit persons to whom the Software is
 * furnished to do so, under the terms of the COPYING file.
 *
 * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
 * KIND, either express or implied.
 *
 * SPDX-License-Identifier: curl
 *
 ***************************************************************************/

#include "curl_setup.h"

#if defined(USE_NGTCP2) && defined(USE_NGHTTP3)
#include <ngtcp2/ngtcp2.h>
#include <nghttp3/nghttp3.h>

#ifdef USE_OPENSSL
#include <openssl/err.h>
#ifdef OPENSSL_IS_BORINGSSL
#include <ngtcp2/ngtcp2_crypto_boringssl.h>
#else
#include <ngtcp2/ngtcp2_crypto_openssl.h>
#endif
#include "vtls/openssl.h"
#elif defined(USE_GNUTLS)
#include <ngtcp2/ngtcp2_crypto_gnutls.h>
#include "vtls/gtls.h"
#elif defined(USE_WOLFSSL)
#include <ngtcp2/ngtcp2_crypto_wolfssl.h>
#include "vtls/wolfssl.h"
#endif

#include "urldata.h"
#include "sendf.h"
#include "strdup.h"
#include "rand.h"
#include "multiif.h"
#include "strcase.h"
#include "cfilters.h"
#include "cf-socket.h"
#include "connect.h"
#include "progress.h"
#include "strerror.h"
#include "dynbuf.h"
#include "http1.h"
#include "select.h"
#include "vquic.h"
#include "vquic_int.h"
#include "vtls/keylog.h"
#include "vtls/vtls.h"
#include "curl_ngtcp2.h"

#include "warnless.h"

/* The last 3 #include files should be in this order */
#include "curl_printf.h"
#include "curl_memory.h"
#include "memdebug.h"


#define H3_ALPN_H3_29 "\x5h3-29"
#define H3_ALPN_H3 "\x2h3"

#define QUIC_MAX_STREAMS (256*1024)
#define QUIC_MAX_DATA (1*1024*1024)
#define QUIC_IDLE_TIMEOUT (60*NGTCP2_SECONDS)
#define QUIC_HANDSHAKE_TIMEOUT (10*NGTCP2_SECONDS)

/* A stream window is the maximum amount we need to buffer for
 * each active transfer. We use HTTP/3 flow control and only ACK
 * when we take things out of the buffer.
 * Chunk size is large enough to take a full DATA frame */
#define H3_STREAM_WINDOW_SIZE (128 * 1024)
#define H3_STREAM_CHUNK_SIZE   (16 * 1024)
/* The pool keeps spares around and half of a full stream windows
 * seems good. More does not seem to improve performance.
 * The benefit of the pool is that stream buffer to not keep
 * spares. So memory consumption goes down when streams run empty,
 * have a large upload done, etc. */
#define H3_STREAM_POOL_SPARES \
          (H3_STREAM_WINDOW_SIZE / H3_STREAM_CHUNK_SIZE ) / 2
/* Receive and Send max number of chunks just follows from the
 * chunk size and window size */
#define H3_STREAM_RECV_CHUNKS \
          (H3_STREAM_WINDOW_SIZE / H3_STREAM_CHUNK_SIZE)
#define H3_STREAM_SEND_CHUNKS \
          (H3_STREAM_WINDOW_SIZE / H3_STREAM_CHUNK_SIZE)


#ifdef USE_OPENSSL
#define QUIC_CIPHERS                                                          \
  "TLS_AES_128_GCM_SHA256:TLS_AES_256_GCM_SHA384:TLS_CHACHA20_"               \
  "POLY1305_SHA256:TLS_AES_128_CCM_SHA256"
#define QUIC_GROUPS "P-256:X25519:P-384:P-521"
#elif defined(USE_GNUTLS)
#define QUIC_PRIORITY \
  "NORMAL:-VERS-ALL:+VERS-TLS1.3:-CIPHER-ALL:+AES-128-GCM:+AES-256-GCM:" \
  "+CHACHA20-POLY1305:+AES-128-CCM:-GROUP-ALL:+GROUP-SECP256R1:" \
  "+GROUP-X25519:+GROUP-SECP384R1:+GROUP-SECP521R1:" \
  "%DISABLE_TLS13_COMPAT_MODE"
#elif defined(USE_WOLFSSL)
#define QUIC_CIPHERS                                                          \
  "TLS_AES_128_GCM_SHA256:TLS_AES_256_GCM_SHA384:TLS_CHACHA20_"               \
  "POLY1305_SHA256:TLS_AES_128_CCM_SHA256"
#define QUIC_GROUPS "P-256:P-384:P-521"
#endif


/*
 * Store ngtcp2 version info in this buffer.
 */
void Curl_ngtcp2_ver(char *p, size_t len)
{
  const ngtcp2_info *ng2 = ngtcp2_version(0);
  const nghttp3_info *ht3 = nghttp3_version(0);
  (void)msnprintf(p, len, "ngtcp2/%s nghttp3/%s",
                  ng2->version_str, ht3->version_str);
}

struct cf_ngtcp2_ctx {
  struct cf_quic_ctx q;
  ngtcp2_path connected_path;
  ngtcp2_conn *qconn;
  ngtcp2_cid dcid;
  ngtcp2_cid scid;
  uint32_t version;
  ngtcp2_settings settings;
  ngtcp2_transport_params transport_params;
  ngtcp2_ccerr last_error;
  ngtcp2_crypto_conn_ref conn_ref;
#ifdef USE_OPENSSL
  SSL_CTX *sslctx;
  SSL *ssl;
#elif defined(USE_GNUTLS)
  struct gtls_instance *gtls;
#elif defined(USE_WOLFSSL)
  WOLFSSL_CTX *sslctx;
  WOLFSSL *ssl;
#endif
  struct cf_call_data call_data;
  nghttp3_conn *h3conn;
  nghttp3_settings h3settings;
  struct curltime started_at;        /* time the current attempt started */
  struct curltime handshake_at;      /* time connect handshake finished */
  struct curltime first_byte_at;     /* when first byte was recvd */
  struct curltime reconnect_at;      /* time the next attempt should start */
  struct bufc_pool stream_bufcp;     /* chunk pool for streams */
  size_t max_stream_window;          /* max flow window for one stream */
  int qlogfd;
  BIT(got_first_byte);               /* if first byte was received */
};

/* How to access `call_data` from a cf_ngtcp2 filter */
#undef CF_CTX_CALL_DATA
#define CF_CTX_CALL_DATA(cf)  \
  ((struct cf_ngtcp2_ctx *)(cf)->ctx)->call_data

/**
 * All about the H3 internals of a stream
 */
struct h3_stream_ctx {
  int64_t id; /* HTTP/3 protocol identifier */
  struct bufq sendbuf;   /* h3 request body */
  struct bufq recvbuf;   /* h3 response body */
  size_t sendbuf_len_in_flight; /* sendbuf amount "in flight" */
  size_t upload_blocked_len; /* the amount written last and EGAINed */
  size_t recv_buf_nonflow; /* buffered bytes, not counting for flow control */
  uint64_t error3; /* HTTP/3 stream error code */
  curl_off_t upload_left; /* number of request bytes left to upload */
  int status_code; /* HTTP status code */
  bool resp_hds_complete; /* we have a complete, final response */
  bool closed; /* TRUE on stream close */
  bool reset;  /* TRUE on stream reset */
  bool send_closed; /* stream is local closed */
};

#define H3_STREAM_CTX(d)  ((struct h3_stream_ctx *)(((d) && (d)->req.p.http)? \
                           ((struct HTTP *)(d)->req.p.http)->h3_ctx \
                             : NULL))
#define H3_STREAM_LCTX(d) ((struct HTTP *)(d)->req.p.http)->h3_ctx
#define H3_STREAM_ID(d)   (H3_STREAM_CTX(d)? \
                           H3_STREAM_CTX(d)->id : -2)

static CURLcode h3_data_setup(struct Curl_cfilter *cf,
                              struct Curl_easy *data)
{
  struct cf_ngtcp2_ctx *ctx = cf->ctx;
  struct h3_stream_ctx *stream = H3_STREAM_CTX(data);

  if(!data || !data->req.p.http) {
    failf(data, "initialization failure, transfer not http initialized");
    return CURLE_FAILED_INIT;
  }

  if(stream)
    return CURLE_OK;

  stream = calloc(1, sizeof(*stream));
  if(!stream)
    return CURLE_OUT_OF_MEMORY;

  stream->id = -1;
  /* on send, we control how much we put into the buffer */
  Curl_bufq_initp(&stream->sendbuf, &ctx->stream_bufcp,
                  H3_STREAM_SEND_CHUNKS, BUFQ_OPT_NONE);
  stream->sendbuf_len_in_flight = 0;
  /* on recv, we need a flexible buffer limit since we also write
   * headers to it that are not counted against the nghttp3 flow limits. */
  Curl_bufq_initp(&stream->recvbuf, &ctx->stream_bufcp,
                  H3_STREAM_RECV_CHUNKS, BUFQ_OPT_SOFT_LIMIT);
  stream->recv_buf_nonflow = 0;

  H3_STREAM_LCTX(data) = stream;
  DEBUGF(LOG_CF(data, cf, "data setup"));
  return CURLE_OK;
}

static void h3_data_done(struct Curl_cfilter *cf, struct Curl_easy *data)
{
  struct h3_stream_ctx *stream = H3_STREAM_CTX(data);

  (void)cf;
  if(stream) {
    DEBUGF(LOG_CF(data, cf, "[h3sid=%"PRId64"] easy handle is done",
                  stream->id));
    Curl_bufq_free(&stream->sendbuf);
    Curl_bufq_free(&stream->recvbuf);
    free(stream);
    H3_STREAM_LCTX(data) = NULL;
  }
}

/* ngtcp2 default congestion controller does not perform pacing. Limit
   the maximum packet burst to MAX_PKT_BURST packets. */
#define MAX_PKT_BURST 10

struct pkt_io_ctx {
  struct Curl_cfilter *cf;
  struct Curl_easy *data;
  ngtcp2_tstamp ts;
  size_t pkt_count;
  ngtcp2_path_storage ps;
};

static ngtcp2_tstamp timestamp(void)
{
  struct curltime ct = Curl_now();
  return ct.tv_sec * NGTCP2_SECONDS + ct.tv_usec * NGTCP2_MICROSECONDS;
}

static void pktx_init(struct pkt_io_ctx *pktx,
                      struct Curl_cfilter *cf,
                      struct Curl_easy *data)
{
  pktx->cf = cf;
  pktx->data = data;
  pktx->ts = timestamp();
  pktx->pkt_count = 0;
  ngtcp2_path_storage_zero(&pktx->ps);
}

static CURLcode cf_progress_ingress(struct Curl_cfilter *cf,
                                    struct Curl_easy *data,
                                    struct pkt_io_ctx *pktx);
static CURLcode cf_progress_egress(struct Curl_cfilter *cf,
                                   struct Curl_easy *data,
                                   struct pkt_io_ctx *pktx);
static int cb_h3_acked_req_body(nghttp3_conn *conn, int64_t stream_id,
                                   uint64_t datalen, void *user_data,
                                   void *stream_user_data);

static ngtcp2_conn *get_conn(ngtcp2_crypto_conn_ref *conn_ref)
{
  struct Curl_cfilter *cf = conn_ref->user_data;
  struct cf_ngtcp2_ctx *ctx = cf->ctx;
  return ctx->qconn;
}

#ifdef DEBUG_NGTCP2
static void quic_printf(void *user_data, const char *fmt, ...)
{
  struct Curl_cfilter *cf = user_data;
  struct cf_ngtcp2_ctx *ctx = cf->ctx;

  (void)ctx;  /* TODO: need an easy handle to infof() message */
  va_list ap;
  va_start(ap, fmt);
  vfprintf(stderr, fmt, ap);
  va_end(ap);
  fprintf(stderr, "\n");
}
#endif

static void qlog_callback(void *user_data, uint32_t flags,
                          const void *data, size_t datalen)
{
  struct Curl_cfilter *cf = user_data;
  struct cf_ngtcp2_ctx *ctx = cf->ctx;
  (void)flags;
  if(ctx->qlogfd != -1) {
    ssize_t rc = write(ctx->qlogfd, data, datalen);
    if(rc == -1) {
      /* on write error, stop further write attempts */
      close(ctx->qlogfd);
      ctx->qlogfd = -1;
    }
  }

}

static void quic_settings(struct cf_ngtcp2_ctx *ctx,
                          struct Curl_easy *data,
                          struct pkt_io_ctx *pktx)
{
  ngtcp2_settings *s = &ctx->settings;
  ngtcp2_transport_params *t = &ctx->transport_params;

  ngtcp2_settings_default(s);
  ngtcp2_transport_params_default(t);
#ifdef DEBUG_NGTCP2
  s->log_printf = quic_printf;
#else
  s->log_printf = NULL;
#endif

  (void)data;
  s->initial_ts = pktx->ts;
  s->handshake_timeout = QUIC_HANDSHAKE_TIMEOUT;
  s->max_window = 100 * ctx->max_stream_window;
  s->max_stream_window = ctx->max_stream_window;

  t->initial_max_data = 10 * ctx->max_stream_window;
  t->initial_max_stream_data_bidi_local = ctx->max_stream_window;
  t->initial_max_stream_data_bidi_remote = ctx->max_stream_window;
  t->initial_max_stream_data_uni = ctx->max_stream_window;
  t->initial_max_streams_bidi = QUIC_MAX_STREAMS;
  t->initial_max_streams_uni = QUIC_MAX_STREAMS;
  t->max_idle_timeout = QUIC_IDLE_TIMEOUT;
  if(ctx->qlogfd != -1) {
    s->qlog_write = qlog_callback;
  }
}

#ifdef USE_OPENSSL
static void keylog_callback(const SSL *ssl, const char *line)
{
  (void)ssl;
  Curl_tls_keylog_write_line(line);
}
#elif defined(USE_GNUTLS)
static int keylog_callback(gnutls_session_t session, const char *label,
                    const gnutls_datum_t *secret)
{
  gnutls_datum_t crandom;
  gnutls_datum_t srandom;

  gnutls_session_get_random(session, &crandom, &srandom);
  if(crandom.size != 32) {
    return -1;
  }

  Curl_tls_keylog_write(label, crandom.data, secret->data, secret->size);
  return 0;
}
#elif defined(USE_WOLFSSL)
#if defined(HAVE_SECRET_CALLBACK)
static void keylog_callback(const WOLFSSL *ssl, const char *line)
{
  (void)ssl;
  Curl_tls_keylog_write_line(line);
}
#endif
#endif

static int init_ngh3_conn(struct Curl_cfilter *cf);

#ifdef USE_OPENSSL
static CURLcode quic_ssl_ctx(SSL_CTX **pssl_ctx,
                             struct Curl_cfilter *cf, struct Curl_easy *data)
{
  struct connectdata *conn = cf->conn;
  CURLcode result = CURLE_FAILED_INIT;
  SSL_CTX *ssl_ctx = SSL_CTX_new(TLS_method());

  if(!ssl_ctx) {
    result = CURLE_OUT_OF_MEMORY;
    goto out;
  }

#ifdef OPENSSL_IS_BORINGSSL
  if(ngtcp2_crypto_boringssl_configure_client_context(ssl_ctx) != 0) {
    failf(data, "ngtcp2_crypto_boringssl_configure_client_context failed");
    goto out;
  }
#else
  if(ngtcp2_crypto_openssl_configure_client_context(ssl_ctx) != 0) {
    failf(data, "ngtcp2_crypto_openssl_configure_client_context failed");
    goto out;
  }
#endif

  SSL_CTX_set_default_verify_paths(ssl_ctx);

#ifdef OPENSSL_IS_BORINGSSL
  if(SSL_CTX_set1_curves_list(ssl_ctx, QUIC_GROUPS) != 1) {
    failf(data, "SSL_CTX_set1_curves_list failed");
    goto out;
  }
#else
  if(SSL_CTX_set_ciphersuites(ssl_ctx, QUIC_CIPHERS) != 1) {
    char error_buffer[256];
    ERR_error_string_n(ERR_get_error(), error_buffer, sizeof(error_buffer));
    failf(data, "SSL_CTX_set_ciphersuites: %s", error_buffer);
    goto out;
  }

  if(SSL_CTX_set1_groups_list(ssl_ctx, QUIC_GROUPS) != 1) {
    failf(data, "SSL_CTX_set1_groups_list failed");
    goto out;
  }
#endif

  /* Open the file if a TLS or QUIC backend has not done this before. */
  Curl_tls_keylog_open();
  if(Curl_tls_keylog_enabled()) {
    SSL_CTX_set_keylog_callback(ssl_ctx, keylog_callback);
  }

  result = Curl_ssl_setup_x509_store(cf, data, ssl_ctx);
  if(result)
    goto out;

  /* OpenSSL always tries to verify the peer, this only says whether it should
   * fail to connect if the verification fails, or if it should continue
   * anyway. In the latter case the result of the verification is checked with
   * SSL_get_verify_result() below. */
  SSL_CTX_set_verify(ssl_ctx, conn->ssl_config.verifypeer ?
                     SSL_VERIFY_PEER : SSL_VERIFY_NONE, NULL);

  /* give application a chance to interfere with SSL set up. */
  if(data->set.ssl.fsslctx) {
    Curl_set_in_callback(data, true);
    result = (*data->set.ssl.fsslctx)(data, ssl_ctx,
                                      data->set.ssl.fsslctxp);
    Curl_set_in_callback(data, false);
    if(result) {
      failf(data, "error signaled by ssl ctx callback");
      goto out;
    }
  }
  result = CURLE_OK;

out:
  *pssl_ctx = result? NULL : ssl_ctx;
  if(result && ssl_ctx)
    SSL_CTX_free(ssl_ctx);
  return result;
}

static CURLcode quic_set_client_cert(struct Curl_cfilter *cf,
                                     struct Curl_easy *data)
{
  struct cf_ngtcp2_ctx *ctx = cf->ctx;
  SSL_CTX *ssl_ctx = ctx->sslctx;
  const struct ssl_config_data *ssl_config;

  ssl_config = Curl_ssl_get_config(data, FIRSTSOCKET);
  DEBUGASSERT(ssl_config);

  if(ssl_config->primary.clientcert || ssl_config->primary.cert_blob
     || ssl_config->cert_type) {
    return Curl_ossl_set_client_cert(
        data, ssl_ctx, ssl_config->primary.clientcert,
        ssl_config->primary.cert_blob, ssl_config->cert_type,
        ssl_config->key, ssl_config->key_blob,
        ssl_config->key_type, ssl_config->key_passwd);
  }

  return CURLE_OK;
}

/** SSL callbacks ***/

static CURLcode quic_init_ssl(struct Curl_cfilter *cf,
                              struct Curl_easy *data)
{
  struct cf_ngtcp2_ctx *ctx = cf->ctx;
  const uint8_t *alpn = NULL;
  size_t alpnlen = 0;

  (void)data;
  DEBUGASSERT(!ctx->ssl);
  ctx->ssl = SSL_new(ctx->sslctx);

  SSL_set_app_data(ctx->ssl, &ctx->conn_ref);
  SSL_set_connect_state(ctx->ssl);
  SSL_set_quic_use_legacy_codepoint(ctx->ssl, 0);

  alpn = (const uint8_t *)H3_ALPN_H3_29 H3_ALPN_H3;
  alpnlen = sizeof(H3_ALPN_H3_29) - 1 + sizeof(H3_ALPN_H3) - 1;
  if(alpn)
    SSL_set_alpn_protos(ctx->ssl, alpn, (int)alpnlen);

  /* set SNI */
  SSL_set_tlsext_host_name(ctx->ssl, cf->conn->host.name);
  return CURLE_OK;
}
#elif defined(USE_GNUTLS)
static CURLcode quic_init_ssl(struct Curl_cfilter *cf,
                              struct Curl_easy *data)
{
  struct cf_ngtcp2_ctx *ctx = cf->ctx;
  CURLcode result;
  gnutls_datum_t alpn[2];
  /* this will need some attention when HTTPS proxy over QUIC get fixed */
  const char * const hostname = cf->conn->host.name;
  long * const pverifyresult = &data->set.ssl.certverifyresult;
  int rc;

  DEBUGASSERT(ctx->gtls == NULL);
  ctx->gtls = calloc(1, sizeof(*(ctx->gtls)));
  if(!ctx->gtls)
    return CURLE_OUT_OF_MEMORY;

  result = gtls_client_init(data, &cf->conn->ssl_config, &data->set.ssl,
                            hostname, ctx->gtls, pverifyresult);
  if(result)
    return result;

  gnutls_session_set_ptr(ctx->gtls->session, &ctx->conn_ref);

  if(ngtcp2_crypto_gnutls_configure_client_session(ctx->gtls->session) != 0) {
    DEBUGF(LOG_CF(data, cf,
                  "ngtcp2_crypto_gnutls_configure_client_session failed\n"));
    return CURLE_QUIC_CONNECT_ERROR;
  }

  rc = gnutls_priority_set_direct(ctx->gtls->session, QUIC_PRIORITY, NULL);
  if(rc < 0) {
    DEBUGF(LOG_CF(data, cf, "gnutls_priority_set_direct failed: %s\n",
                  gnutls_strerror(rc)));
    return CURLE_QUIC_CONNECT_ERROR;
  }

  /* Open the file if a TLS or QUIC backend has not done this before. */
  Curl_tls_keylog_open();
  if(Curl_tls_keylog_enabled()) {
    gnutls_session_set_keylog_function(ctx->gtls->session, keylog_callback);
  }

  /* strip the first byte (the length) from NGHTTP3_ALPN_H3 */
  alpn[0].data = (unsigned char *)H3_ALPN_H3_29 + 1;
  alpn[0].size = sizeof(H3_ALPN_H3_29) - 2;
  alpn[1].data = (unsigned char *)H3_ALPN_H3 + 1;
  alpn[1].size = sizeof(H3_ALPN_H3) - 2;

  gnutls_alpn_set_protocols(ctx->gtls->session,
                            alpn, 2, GNUTLS_ALPN_MANDATORY);
  return CURLE_OK;
}
#elif defined(USE_WOLFSSL)

static CURLcode quic_ssl_ctx(WOLFSSL_CTX **pssl_ctx,
                             struct Curl_cfilter *cf, struct Curl_easy *data)
{
  struct connectdata *conn = cf->conn;
  CURLcode result = CURLE_FAILED_INIT;
  WOLFSSL_CTX *ssl_ctx = wolfSSL_CTX_new(wolfTLSv1_3_client_method());

  if(!ssl_ctx) {
    result = CURLE_OUT_OF_MEMORY;
    goto out;
  }

  if(ngtcp2_crypto_wolfssl_configure_client_context(ssl_ctx) != 0) {
    failf(data, "ngtcp2_crypto_wolfssl_configure_client_context failed");
    goto out;
  }

  wolfSSL_CTX_set_default_verify_paths(ssl_ctx);

  if(wolfSSL_CTX_set_cipher_list(ssl_ctx, QUIC_CIPHERS) != 1) {
    char error_buffer[256];
    ERR_error_string_n(ERR_get_error(), error_buffer, sizeof(error_buffer));
    failf(data, "SSL_CTX_set_ciphersuites: %s", error_buffer);
    goto out;
  }

  if(wolfSSL_CTX_set1_groups_list(ssl_ctx, (char *)QUIC_GROUPS) != 1) {
    failf(data, "SSL_CTX_set1_groups_list failed");
    goto out;
  }

  /* Open the file if a TLS or QUIC backend has not done this before. */
  Curl_tls_keylog_open();
  if(Curl_tls_keylog_enabled()) {
#if defined(HAVE_SECRET_CALLBACK)
    wolfSSL_CTX_set_keylog_callback(ssl_ctx, keylog_callback);
#else
    failf(data, "wolfSSL was built without keylog callback");
    goto out;
#endif
  }

  if(conn->ssl_config.verifypeer) {
    const char * const ssl_cafile = conn->ssl_config.CAfile;
    const char * const ssl_capath = conn->ssl_config.CApath;

    wolfSSL_CTX_set_verify(ssl_ctx, SSL_VERIFY_PEER, NULL);
    if(conn->ssl_config.CAfile || conn->ssl_config.CApath) {
      /* tell wolfSSL where to find CA certificates that are used to verify
         the server's certificate. */
      if(!wolfSSL_CTX_load_verify_locations(ssl_ctx, ssl_cafile, ssl_capath)) {
        /* Fail if we insist on successfully verifying the server. */
        failf(data, "error setting certificate verify locations:"
              "  CAfile: %s CApath: %s",
              ssl_cafile ? ssl_cafile : "none",
              ssl_capath ? ssl_capath : "none");
        goto out;
      }
      infof(data, " CAfile: %s", ssl_cafile ? ssl_cafile : "none");
      infof(data, " CApath: %s", ssl_capath ? ssl_capath : "none");
    }
#ifdef CURL_CA_FALLBACK
    else {
      /* verifying the peer without any CA certificates won't work so
         use wolfssl's built-in default as fallback */
      wolfSSL_CTX_set_default_verify_paths(ssl_ctx);
    }
#endif
  }
  else {
    wolfSSL_CTX_set_verify(ssl_ctx, SSL_VERIFY_NONE, NULL);
  }

  /* give application a chance to interfere with SSL set up. */
  if(data->set.ssl.fsslctx) {
    Curl_set_in_callback(data, true);
    result = (*data->set.ssl.fsslctx)(data, ssl_ctx,
                                      data->set.ssl.fsslctxp);
    Curl_set_in_callback(data, false);
    if(result) {
      failf(data, "error signaled by ssl ctx callback");
      goto out;
    }
  }
  result = CURLE_OK;

out:
  *pssl_ctx = result? NULL : ssl_ctx;
  if(result && ssl_ctx)
    SSL_CTX_free(ssl_ctx);
  return result;
}

/** SSL callbacks ***/

static CURLcode quic_init_ssl(struct Curl_cfilter *cf,
                              struct Curl_easy *data)
{
  struct cf_ngtcp2_ctx *ctx = cf->ctx;
  const uint8_t *alpn = NULL;
  size_t alpnlen = 0;
  /* this will need some attention when HTTPS proxy over QUIC get fixed */
  const char * const hostname = cf->conn->host.name;

  (void)data;
  DEBUGASSERT(!ctx->ssl);
  ctx->ssl = wolfSSL_new(ctx->sslctx);

  wolfSSL_set_app_data(ctx->ssl, &ctx->conn_ref);
  wolfSSL_set_connect_state(ctx->ssl);
  wolfSSL_set_quic_use_legacy_codepoint(ctx->ssl, 0);

  alpn = (const uint8_t *)H3_ALPN_H3_29 H3_ALPN_H3;
  alpnlen = sizeof(H3_ALPN_H3_29) - 1 + sizeof(H3_ALPN_H3) - 1;
  if(alpn)
    wolfSSL_set_alpn_protos(ctx->ssl, alpn, (int)alpnlen);

  /* set SNI */
  wolfSSL_UseSNI(ctx->ssl, WOLFSSL_SNI_HOST_NAME,
                 hostname, (unsigned short)strlen(hostname));

  return CURLE_OK;
}
#endif /* defined(USE_WOLFSSL) */

static int cb_handshake_completed(ngtcp2_conn *tconn, void *user_data)
{
  (void)user_data;
  (void)tconn;
  return 0;
}

static void report_consumed_data(struct Curl_cfilter *cf,
                                 struct Curl_easy *data,
                                 size_t consumed)
{
  struct h3_stream_ctx *stream = H3_STREAM_CTX(data);
  struct cf_ngtcp2_ctx *ctx = cf->ctx;

  if(!stream)
    return;
  /* the HTTP/1.1 response headers are written to the buffer, but
   * consuming those does not count against flow control. */
  if(stream->recv_buf_nonflow) {
    if(consumed >= stream->recv_buf_nonflow) {
      consumed -= stream->recv_buf_nonflow;
      stream->recv_buf_nonflow = 0;
    }
    else {
      stream->recv_buf_nonflow -= consumed;
      consumed = 0;
    }
  }
  if(consumed > 0) {
    DEBUGF(LOG_CF(data, cf, "[h3sid=%" PRId64 "] consumed %zu DATA bytes",
                  stream->id, consumed));
    ngtcp2_conn_extend_max_stream_offset(ctx->qconn, stream->id,
                                         consumed);
    ngtcp2_conn_extend_max_offset(ctx->qconn, consumed);
  }
}

static int cb_recv_stream_data(ngtcp2_conn *tconn, uint32_t flags,
                               int64_t stream_id, uint64_t offset,
                               const uint8_t *buf, size_t buflen,
                               void *user_data, void *stream_user_data)
{
  struct Curl_cfilter *cf = user_data;
  struct cf_ngtcp2_ctx *ctx = cf->ctx;
  nghttp3_ssize nconsumed;
  int fin = (flags & NGTCP2_STREAM_DATA_FLAG_FIN) ? 1 : 0;
  struct Curl_easy *data = stream_user_data;
  (void)offset;
  (void)data;

  nconsumed =
    nghttp3_conn_read_stream(ctx->h3conn, stream_id, buf, buflen, fin);
  DEBUGF(LOG_CF(data, cf, "[h3sid=%" PRId64 "] read_stream(len=%zu) -> %zd",
                stream_id, buflen, nconsumed));
  if(nconsumed < 0) {
    ngtcp2_ccerr_set_application_error(
      &ctx->last_error,
      nghttp3_err_infer_quic_app_error_code((int)nconsumed), NULL, 0);
    return NGTCP2_ERR_CALLBACK_FAILURE;
  }

  /* number of bytes inside buflen which consists of framing overhead
   * including QPACK HEADERS. In other words, it does not consume payload of
   * DATA frame. */
  ngtcp2_conn_extend_max_stream_offset(tconn, stream_id, nconsumed);
  ngtcp2_conn_extend_max_offset(tconn, nconsumed);

  return 0;
}

static int
cb_acked_stream_data_offset(ngtcp2_conn *tconn, int64_t stream_id,
                            uint64_t offset, uint64_t datalen, void *user_data,
                            void *stream_user_data)
{
  struct Curl_cfilter *cf = user_data;
  struct cf_ngtcp2_ctx *ctx = cf->ctx;
  int rv;
  (void)stream_id;
  (void)tconn;
  (void)offset;
  (void)datalen;
  (void)stream_user_data;

  rv = nghttp3_conn_add_ack_offset(ctx->h3conn, stream_id, datalen);
  if(rv) {
    return NGTCP2_ERR_CALLBACK_FAILURE;
  }

  return 0;
}

static int cb_stream_close(ngtcp2_conn *tconn, uint32_t flags,
                           int64_t stream3_id, uint64_t app_error_code,
                           void *user_data, void *stream_user_data)
{
  struct Curl_cfilter *cf = user_data;
  struct Curl_easy *data = stream_user_data;
  struct cf_ngtcp2_ctx *ctx = cf->ctx;
  int rv;

  (void)tconn;
  (void)data;
  /* stream is closed... */

  if(!(flags & NGTCP2_STREAM_CLOSE_FLAG_APP_ERROR_CODE_SET)) {
    app_error_code = NGHTTP3_H3_NO_ERROR;
  }

  rv = nghttp3_conn_close_stream(ctx->h3conn, stream3_id,
                                 app_error_code);
  DEBUGF(LOG_CF(data, cf, "[h3sid=%" PRId64 "] quic close(err=%"
                PRIu64 ") -> %d", stream3_id, app_error_code, rv));
  if(rv) {
    ngtcp2_ccerr_set_application_error(
      &ctx->last_error, nghttp3_err_infer_quic_app_error_code(rv), NULL, 0);
    return NGTCP2_ERR_CALLBACK_FAILURE;
  }

  return 0;
}

static int cb_stream_reset(ngtcp2_conn *tconn, int64_t stream_id,
                           uint64_t final_size, uint64_t app_error_code,
                           void *user_data, void *stream_user_data)
{
  struct Curl_cfilter *cf = user_data;
  struct cf_ngtcp2_ctx *ctx = cf->ctx;
  struct Curl_easy *data = stream_user_data;
  int rv;
  (void)tconn;
  (void)final_size;
  (void)app_error_code;
  (void)data;

  rv = nghttp3_conn_shutdown_stream_read(ctx->h3conn, stream_id);
  DEBUGF(LOG_CF(data, cf, "[h3sid=%" PRId64 "] reset -> %d", stream_id, rv));
  if(rv) {
    return NGTCP2_ERR_CALLBACK_FAILURE;
  }

  return 0;
}

static int cb_stream_stop_sending(ngtcp2_conn *tconn, int64_t stream_id,
                                  uint64_t app_error_code, void *user_data,
                                  void *stream_user_data)
{
  struct Curl_cfilter *cf = user_data;
  struct cf_ngtcp2_ctx *ctx = cf->ctx;
  int rv;
  (void)tconn;
  (void)app_error_code;
  (void)stream_user_data;

  rv = nghttp3_conn_shutdown_stream_read(ctx->h3conn, stream_id);
  if(rv) {
    return NGTCP2_ERR_CALLBACK_FAILURE;
  }

  return 0;
}

static int cb_extend_max_local_streams_bidi(ngtcp2_conn *tconn,
                                            uint64_t max_streams,
                                            void *user_data)
{
  (void)tconn;
  (void)max_streams;
  (void)user_data;

  return 0;
}

static int cb_extend_max_stream_data(ngtcp2_conn *tconn, int64_t stream_id,
                                     uint64_t max_data, void *user_data,
                                     void *stream_user_data)
{
  struct Curl_cfilter *cf = user_data;
  struct cf_ngtcp2_ctx *ctx = cf->ctx;
  int rv;
  (void)tconn;
  (void)max_data;
  (void)stream_user_data;

  rv = nghttp3_conn_unblock_stream(ctx->h3conn, stream_id);
  if(rv) {
    return NGTCP2_ERR_CALLBACK_FAILURE;
  }

  return 0;
}

static void cb_rand(uint8_t *dest, size_t destlen,
                    const ngtcp2_rand_ctx *rand_ctx)
{
  CURLcode result;
  (void)rand_ctx;

  result = Curl_rand(NULL, dest, destlen);
  if(result) {
    /* cb_rand is only used for non-cryptographic context.  If Curl_rand
       failed, just fill 0 and call it *random*. */
    memset(dest, 0, destlen);
  }
}

static int cb_get_new_connection_id(ngtcp2_conn *tconn, ngtcp2_cid *cid,
                                    uint8_t *token, size_t cidlen,
                                    void *user_data)
{
  CURLcode result;
  (void)tconn;
  (void)user_data;

  result = Curl_rand(NULL, cid->data, cidlen);
  if(result)
    return NGTCP2_ERR_CALLBACK_FAILURE;
  cid->datalen = cidlen;

  result = Curl_rand(NULL, token, NGTCP2_STATELESS_RESET_TOKENLEN);
  if(result)
    return NGTCP2_ERR_CALLBACK_FAILURE;

  return 0;
}

static int cb_recv_rx_key(ngtcp2_conn *tconn, ngtcp2_encryption_level level,
                          void *user_data)
{
  struct Curl_cfilter *cf = user_data;
  (void)tconn;

  if(level != NGTCP2_ENCRYPTION_LEVEL_1RTT) {
    return 0;
  }

  if(init_ngh3_conn(cf) != CURLE_OK) {
    return NGTCP2_ERR_CALLBACK_FAILURE;
  }

  return 0;
}

static ngtcp2_callbacks ng_callbacks = {
  ngtcp2_crypto_client_initial_cb,
  NULL, /* recv_client_initial */
  ngtcp2_crypto_recv_crypto_data_cb,
  cb_handshake_completed,
  NULL, /* recv_version_negotiation */
  ngtcp2_crypto_encrypt_cb,
  ngtcp2_crypto_decrypt_cb,
  ngtcp2_crypto_hp_mask_cb,
  cb_recv_stream_data,
  cb_acked_stream_data_offset,
  NULL, /* stream_open */
  cb_stream_close,
  NULL, /* recv_stateless_reset */
  ngtcp2_crypto_recv_retry_cb,
  cb_extend_max_local_streams_bidi,
  NULL, /* extend_max_local_streams_uni */
  cb_rand,
  cb_get_new_connection_id,
  NULL, /* remove_connection_id */
  ngtcp2_crypto_update_key_cb, /* update_key */
  NULL, /* path_validation */
  NULL, /* select_preferred_addr */
  cb_stream_reset,
  NULL, /* extend_max_remote_streams_bidi */
  NULL, /* extend_max_remote_streams_uni */
  cb_extend_max_stream_data,
  NULL, /* dcid_status */
  NULL, /* handshake_confirmed */
  NULL, /* recv_new_token */
  ngtcp2_crypto_delete_crypto_aead_ctx_cb,
  ngtcp2_crypto_delete_crypto_cipher_ctx_cb,
  NULL, /* recv_datagram */
  NULL, /* ack_datagram */
  NULL, /* lost_datagram */
  ngtcp2_crypto_get_path_challenge_data_cb,
  cb_stream_stop_sending,
  NULL, /* version_negotiation */
  cb_recv_rx_key,
  NULL, /* recv_tx_key */
  NULL, /* early_data_rejected */
};

/**
 * Connection maintenance like timeouts on packet ACKs etc. are done by us, not
 * the OS like for TCP. POLL evenets on the socket therefore are not
 * sufficient.
 * ngtcp2 tells us when it wants to be invoked again. We handle that via
 * the `Curl_expire()` mechanisms.
 */
static CURLcode check_and_set_expiry(struct Curl_cfilter *cf,
                                     struct Curl_easy *data,
                                     struct pkt_io_ctx *pktx)
{
  struct cf_ngtcp2_ctx *ctx = cf->ctx;
  struct pkt_io_ctx local_pktx;
  ngtcp2_tstamp expiry;
  ngtcp2_duration timeout;

  if(!pktx) {
    pktx_init(&local_pktx, cf, data);
    pktx = &local_pktx;
  }
  else {
    pktx->ts = timestamp();
  }

  expiry = ngtcp2_conn_get_expiry(ctx->qconn);
  if(expiry != UINT64_MAX) {
    if(expiry <= pktx->ts) {
      CURLcode result;
      int rv = ngtcp2_conn_handle_expiry(ctx->qconn, pktx->ts);
      if(rv) {
        failf(data, "ngtcp2_conn_handle_expiry returned error: %s",
              ngtcp2_strerror(rv));
        ngtcp2_ccerr_set_liberr(&ctx->last_error, rv, NULL, 0);
        return CURLE_SEND_ERROR;
      }
      timeout = 0;
      result = cf_progress_ingress(cf, data, pktx);
      if(result)
        return result;
      result = cf_progress_egress(cf, data, pktx);
      if(result)
        return result;
      /* ask again, things might have changed */
      expiry = ngtcp2_conn_get_expiry(ctx->qconn);
    }

    if(expiry > pktx->ts) {
      timeout = expiry - pktx->ts;
      if(timeout % NGTCP2_MILLISECONDS) {
        timeout += NGTCP2_MILLISECONDS;
      }
      Curl_expire(data, timeout / NGTCP2_MILLISECONDS, EXPIRE_QUIC);
    }
  }
  return CURLE_OK;
}

static int cf_ngtcp2_get_select_socks(struct Curl_cfilter *cf,
                                      struct Curl_easy *data,
                                      curl_socket_t *socks)
{
  struct cf_ngtcp2_ctx *ctx = cf->ctx;
  struct SingleRequest *k = &data->req;
  int rv = GETSOCK_BLANK;
  struct h3_stream_ctx *stream = H3_STREAM_CTX(data);
  struct cf_call_data save;

  CF_DATA_SAVE(save, cf, data);
  socks[0] = ctx->q.sockfd;

  /* in HTTP/3 we can always get a frame, so check read */
  rv |= GETSOCK_READSOCK(0);

  /* we're still uploading or the HTTP/2 layer wants to send data */
  if((k->keepon & KEEP_SENDBITS) == KEEP_SEND &&
     ngtcp2_conn_get_cwnd_left(ctx->qconn) &&
     ngtcp2_conn_get_max_data_left(ctx->qconn) &&
     stream && nghttp3_conn_is_stream_writable(ctx->h3conn, stream->id))
    rv |= GETSOCK_WRITESOCK(0);

  /* DEBUGF(LOG_CF(data, cf, "get_select_socks -> %x (sock=%d)",
                rv, (int)socks[0])); */
  CF_DATA_RESTORE(cf, save);
  return rv;
}

static void h3_drain_stream(struct Curl_cfilter *cf,
                            struct Curl_easy *data)
{
  struct h3_stream_ctx *stream = H3_STREAM_CTX(data);
  unsigned char bits;

  (void)cf;
  bits = CURL_CSELECT_IN;
  if(stream && stream->upload_left && !stream->send_closed)
    bits |= CURL_CSELECT_OUT;
  if(data->state.dselect_bits != bits) {
    data->state.dselect_bits = bits;
    Curl_expire(data, 0, EXPIRE_RUN_NOW);
  }
}

static int cb_h3_stream_close(nghttp3_conn *conn, int64_t stream_id,
                              uint64_t app_error_code, void *user_data,
                              void *stream_user_data)
{
  struct Curl_cfilter *cf = user_data;
  struct Curl_easy *data = stream_user_data;
  struct h3_stream_ctx *stream = H3_STREAM_CTX(data);
  (void)conn;
  (void)stream_id;
  (void)app_error_code;
  (void)cf;

  /* we might be called by nghttp3 after we already cleaned up */
  if(!stream)
    return 0;

  DEBUGF(LOG_CF(data, cf, "[h3sid=%" PRId64 "] h3 close(err=%" PRId64 ")",
                stream_id, app_error_code));
  stream->closed = TRUE;
  stream->error3 = app_error_code;
  if(app_error_code == NGHTTP3_H3_INTERNAL_ERROR) {
    stream->reset = TRUE;
    stream->send_closed = TRUE;
  }
  h3_drain_stream(cf, data);
  return 0;
}

/*
 * write_resp_raw() copies response data in raw format to the `data`'s
  * receive buffer. If not enough space is available, it appends to the
 * `data`'s overflow buffer.
 */
static CURLcode write_resp_raw(struct Curl_cfilter *cf,
                               struct Curl_easy *data,
                               const void *mem, size_t memlen,
                               bool flow)
{
  struct h3_stream_ctx *stream = H3_STREAM_CTX(data);
  CURLcode result = CURLE_OK;
  ssize_t nwritten;

  (void)cf;
  if(!stream) {
    return CURLE_RECV_ERROR;
  }
  nwritten = Curl_bufq_write(&stream->recvbuf, mem, memlen, &result);
  /* DEBUGF(LOG_CF(data, cf, "[h3sid=%" PRId64 "] add recvbuf(len=%zu) "
                "-> %zd, %d", stream->id, memlen, nwritten, result));
   */
  if(nwritten < 0) {
    return result;
  }

  if(!flow)
    stream->recv_buf_nonflow += (size_t)nwritten;

  if((size_t)nwritten < memlen) {
    /* This MUST not happen. Our recbuf is dimensioned to hold the
     * full max_stream_window and then some for this very reason. */
    DEBUGASSERT(0);
    return CURLE_RECV_ERROR;
  }
  return result;
}

static int cb_h3_recv_data(nghttp3_conn *conn, int64_t stream3_id,
                           const uint8_t *buf, size_t buflen,
                           void *user_data, void *stream_user_data)
{
  struct Curl_cfilter *cf = user_data;
  struct Curl_easy *data = stream_user_data;
  CURLcode result;

  (void)conn;
  (void)stream3_id;

  result = write_resp_raw(cf, data, buf, buflen, TRUE);
  h3_drain_stream(cf, data);
  return result? -1 : 0;
}

static int cb_h3_deferred_consume(nghttp3_conn *conn, int64_t stream3_id,
                                  size_t consumed, void *user_data,
                                  void *stream_user_data)
{
  struct Curl_cfilter *cf = user_data;
  struct cf_ngtcp2_ctx *ctx = cf->ctx;
  (void)conn;
  (void)stream_user_data;

  /* nghttp3 has consumed bytes on the QUIC stream and we need to
   * tell the QUIC connection to increase its flow control */
  ngtcp2_conn_extend_max_stream_offset(ctx->qconn, stream3_id, consumed);
  ngtcp2_conn_extend_max_offset(ctx->qconn, consumed);
  return 0;
}

static int cb_h3_end_headers(nghttp3_conn *conn, int64_t stream_id,
                             int fin, void *user_data, void *stream_user_data)
{
  struct Curl_cfilter *cf = user_data;
  struct Curl_easy *data = stream_user_data;
  struct h3_stream_ctx *stream = H3_STREAM_CTX(data);
  CURLcode result = CURLE_OK;
  (void)conn;
  (void)stream_id;
  (void)fin;
  (void)cf;

  if(!stream)
    return 0;
  /* add a CRLF only if we've received some headers */
  result = write_resp_raw(cf, data, "\r\n", 2, FALSE);
  if(result) {
    return -1;
  }

  DEBUGF(LOG_CF(data, cf, "[h3sid=%" PRId64 "] end_headers(status_code=%d",
                stream_id, stream->status_code));
  if(stream->status_code / 100 != 1) {
    stream->resp_hds_complete = TRUE;
  }
  h3_drain_stream(cf, data);
  return 0;
}

static int cb_h3_recv_header(nghttp3_conn *conn, int64_t stream_id,
                             int32_t token, nghttp3_rcbuf *name,
                             nghttp3_rcbuf *value, uint8_t flags,
                             void *user_data, void *stream_user_data)
{
  struct Curl_cfilter *cf = user_data;
  nghttp3_vec h3name = nghttp3_rcbuf_get_buf(name);
  nghttp3_vec h3val = nghttp3_rcbuf_get_buf(value);
  struct Curl_easy *data = stream_user_data;
  struct h3_stream_ctx *stream = H3_STREAM_CTX(data);
  CURLcode result = CURLE_OK;
  (void)conn;
  (void)stream_id;
  (void)token;
  (void)flags;
  (void)cf;

  /* we might have cleaned up this transfer already */
  if(!stream)
    return 0;

  if(token == NGHTTP3_QPACK_TOKEN__STATUS) {
    char line[14]; /* status line is always 13 characters long */
    size_t ncopy;

    result = Curl_http_decode_status(&stream->status_code,
                                     (const char *)h3val.base, h3val.len);
    if(result)
      return -1;
    ncopy = msnprintf(line, sizeof(line), "HTTP/3 %03d \r\n",
                      stream->status_code);
    DEBUGF(LOG_CF(data, cf, "[h3sid=%" PRId64 "] status: %s",
                  stream_id, line));
    result = write_resp_raw(cf, data, line, ncopy, FALSE);
    if(result) {
      return -1;
    }
  }
  else {
    /* store as an HTTP1-style header */
    DEBUGF(LOG_CF(data, cf, "[h3sid=%" PRId64 "] header: %.*s: %.*s",
                  stream_id, (int)h3name.len, h3name.base,
                  (int)h3val.len, h3val.base));
    result = write_resp_raw(cf, data, h3name.base, h3name.len, FALSE);
    if(result) {
      return -1;
    }
    result = write_resp_raw(cf, data, ": ", 2, FALSE);
    if(result) {
      return -1;
    }
    result = write_resp_raw(cf, data, h3val.base, h3val.len, FALSE);
    if(result) {
      return -1;
    }
    result = write_resp_raw(cf, data, "\r\n", 2, FALSE);
    if(result) {
      return -1;
    }
  }
  return 0;
}

static int cb_h3_stop_sending(nghttp3_conn *conn, int64_t stream_id,
                              uint64_t app_error_code, void *user_data,
                              void *stream_user_data)
{
  struct Curl_cfilter *cf = user_data;
  struct cf_ngtcp2_ctx *ctx = cf->ctx;
  int rv;
  (void)conn;
  (void)stream_user_data;

  rv = ngtcp2_conn_shutdown_stream_read(ctx->qconn, 0, stream_id,
                                        app_error_code);
  if(rv && rv != NGTCP2_ERR_STREAM_NOT_FOUND) {
    return NGTCP2_ERR_CALLBACK_FAILURE;
  }

  return 0;
}

static int cb_h3_reset_stream(nghttp3_conn *conn, int64_t stream_id,
                              uint64_t app_error_code, void *user_data,
                              void *stream_user_data) {
  struct Curl_cfilter *cf = user_data;
  struct cf_ngtcp2_ctx *ctx = cf->ctx;
  struct Curl_easy *data = stream_user_data;
  int rv;
  (void)conn;
  (void)data;

  rv = ngtcp2_conn_shutdown_stream_write(ctx->qconn, 0, stream_id,
                                         app_error_code);
  DEBUGF(LOG_CF(data, cf, "[h3sid=%" PRId64 "] reset -> %d", stream_id, rv));
  if(rv && rv != NGTCP2_ERR_STREAM_NOT_FOUND) {
    return NGTCP2_ERR_CALLBACK_FAILURE;
  }

  return 0;
}

static nghttp3_callbacks ngh3_callbacks = {
  cb_h3_acked_req_body, /* acked_stream_data */
  cb_h3_stream_close,
  cb_h3_recv_data,
  cb_h3_deferred_consume,
  NULL, /* begin_headers */
  cb_h3_recv_header,
  cb_h3_end_headers,
  NULL, /* begin_trailers */
  cb_h3_recv_header,
  NULL, /* end_trailers */
  cb_h3_stop_sending,
  NULL, /* end_stream */
  cb_h3_reset_stream,
  NULL, /* shutdown */
  NULL /* recv_settings */
};

static int init_ngh3_conn(struct Curl_cfilter *cf)
{
  struct cf_ngtcp2_ctx *ctx = cf->ctx;
  CURLcode result;
  int rc;
  int64_t ctrl_stream_id, qpack_enc_stream_id, qpack_dec_stream_id;

  if(ngtcp2_conn_get_streams_uni_left(ctx->qconn) < 3) {
    return CURLE_QUIC_CONNECT_ERROR;
  }

  nghttp3_settings_default(&ctx->h3settings);

  rc = nghttp3_conn_client_new(&ctx->h3conn,
                               &ngh3_callbacks,
                               &ctx->h3settings,
                               nghttp3_mem_default(),
                               cf);
  if(rc) {
    result = CURLE_OUT_OF_MEMORY;
    goto fail;
  }

  rc = ngtcp2_conn_open_uni_stream(ctx->qconn, &ctrl_stream_id, NULL);
  if(rc) {
    result = CURLE_QUIC_CONNECT_ERROR;
    goto fail;
  }

  rc = nghttp3_conn_bind_control_stream(ctx->h3conn, ctrl_stream_id);
  if(rc) {
    result = CURLE_QUIC_CONNECT_ERROR;
    goto fail;
  }

  rc = ngtcp2_conn_open_uni_stream(ctx->qconn, &qpack_enc_stream_id, NULL);
  if(rc) {
    result = CURLE_QUIC_CONNECT_ERROR;
    goto fail;
  }

  rc = ngtcp2_conn_open_uni_stream(ctx->qconn, &qpack_dec_stream_id, NULL);
  if(rc) {
    result = CURLE_QUIC_CONNECT_ERROR;
    goto fail;
  }

  rc = nghttp3_conn_bind_qpack_streams(ctx->h3conn, qpack_enc_stream_id,
                                       qpack_dec_stream_id);
  if(rc) {
    result = CURLE_QUIC_CONNECT_ERROR;
    goto fail;
  }

  return CURLE_OK;
fail:

  return result;
}

static ssize_t recv_closed_stream(struct Curl_cfilter *cf,
                                  struct Curl_easy *data,
                                  struct h3_stream_ctx *stream,
                                  CURLcode *err)
{
  ssize_t nread = -1;

  (void)cf;
  if(stream->reset) {
    failf(data,
          "HTTP/3 stream %" PRId64 " reset by server", stream->id);
    *err = CURLE_PARTIAL_FILE;
    DEBUGF(LOG_CF(data, cf, "[h3sid=%" PRId64 "] cf_recv, was reset -> %d",
                  stream->id, *err));
    goto out;
  }
  else if(stream->error3 != NGHTTP3_H3_NO_ERROR) {
    failf(data,
          "HTTP/3 stream %" PRId64 " was not closed cleanly: "
          "(err %"PRId64")", stream->id, stream->error3);
    *err = CURLE_HTTP3;
    DEBUGF(LOG_CF(data, cf, "[h3sid=%" PRId64 "] cf_recv, closed uncleanly"
                  " -> %d", stream->id, *err));
    goto out;
  }

  if(!stream->resp_hds_complete) {
    failf(data,
          "HTTP/3 stream %" PRId64 " was closed cleanly, but before getting"
          " all response header fields, treated as error",
          stream->id);
    *err = CURLE_HTTP3;
    DEBUGF(LOG_CF(data, cf, "[h3sid=%" PRId64 "] cf_recv, closed incomplete"
                  " -> %d", stream->id, *err));
    goto out;
  }
  else {
    DEBUGF(LOG_CF(data, cf, "[h3sid=%" PRId64 "] cf_recv, closed ok"
                  " -> %d", stream->id, *err));
  }
  *err = CURLE_OK;
  nread = 0;

out:
  return nread;
}

/* incoming data frames on the h3 stream */
static ssize_t cf_ngtcp2_recv(struct Curl_cfilter *cf, struct Curl_easy *data,
                              char *buf, size_t len, CURLcode *err)
{
  struct cf_ngtcp2_ctx *ctx = cf->ctx;
  struct h3_stream_ctx *stream = H3_STREAM_CTX(data);
  ssize_t nread = -1;
  struct cf_call_data save;
  struct pkt_io_ctx pktx;

  (void)ctx;

  CF_DATA_SAVE(save, cf, data);
  DEBUGASSERT(cf->connected);
  DEBUGASSERT(ctx);
  DEBUGASSERT(ctx->qconn);
  DEBUGASSERT(ctx->h3conn);
  *err = CURLE_OK;

  pktx_init(&pktx, cf, data);

  if(!stream) {
    *err = CURLE_RECV_ERROR;
    goto out;
  }

  if(!Curl_bufq_is_empty(&stream->recvbuf)) {
    nread = Curl_bufq_read(&stream->recvbuf,
                           (unsigned char *)buf, len, err);
    DEBUGF(LOG_CF(data, cf, "[h3sid=%" PRId64 "] read recvbuf(len=%zu) "
                  "-> %zd, %d", stream->id, len, nread, *err));
    if(nread < 0)
      goto out;
    report_consumed_data(cf, data, nread);
  }

  if(cf_progress_ingress(cf, data, &pktx)) {
    *err = CURLE_RECV_ERROR;
    nread = -1;
    goto out;
  }

  /* recvbuf had nothing before, maybe after progressing ingress? */
  if(nread < 0 && !Curl_bufq_is_empty(&stream->recvbuf)) {
    nread = Curl_bufq_read(&stream->recvbuf,
                           (unsigned char *)buf, len, err);
    DEBUGF(LOG_CF(data, cf, "[h3sid=%" PRId64 "] read recvbuf(len=%zu) "
                  "-> %zd, %d", stream->id, len, nread, *err));
    if(nread < 0)
      goto out;
    report_consumed_data(cf, data, nread);
  }

  if(nread > 0) {
    h3_drain_stream(cf, data);
  }
  else {
    if(stream->closed) {
      nread = recv_closed_stream(cf, data, stream, err);
      goto out;
    }
    *err = CURLE_AGAIN;
    nread = -1;
  }

out:
  if(cf_progress_egress(cf, data, &pktx)) {
    *err = CURLE_SEND_ERROR;
    nread = -1;
  }
  else {
    CURLcode result2 = check_and_set_expiry(cf, data, &pktx);
    if(result2) {
      *err = result2;
      nread = -1;
    }
  }
  DEBUGF(LOG_CF(data, cf, "[h3sid=%" PRId64 "] cf_recv(len=%zu) -> %zd, %d",
                stream? stream->id : -1, len, nread, *err));
  CF_DATA_RESTORE(cf, save);
  return nread;
}

static int cb_h3_acked_req_body(nghttp3_conn *conn, int64_t stream_id,
                                uint64_t datalen, void *user_data,
                                void *stream_user_data)
{
  struct Curl_cfilter *cf = user_data;
  struct Curl_easy *data = stream_user_data;
  struct h3_stream_ctx *stream = H3_STREAM_CTX(data);
  size_t skiplen;

  (void)cf;
  if(!stream)
    return 0;
  /* The server acknowledged `datalen` of bytes from our request body.
   * This is a delta. We have kept this data in `sendbuf` for
   * re-transmissions and can free it now. */
  if(datalen >= (uint64_t)stream->sendbuf_len_in_flight)
    skiplen = stream->sendbuf_len_in_flight;
  else
    skiplen = (size_t)datalen;
  Curl_bufq_skip(&stream->sendbuf, skiplen);
  stream->sendbuf_len_in_flight -= skiplen;

  /* Everything ACKed, we resume upload processing */
  if(!stream->sendbuf_len_in_flight) {
    int rv = nghttp3_conn_resume_stream(conn, stream_id);
    if(rv) {
      return NGTCP2_ERR_CALLBACK_FAILURE;
    }
    if((data->req.keepon & KEEP_SEND_HOLD) &&
       (data->req.keepon & KEEP_SEND)) {
      data->req.keepon &= ~KEEP_SEND_HOLD;
      h3_drain_stream(cf, data);
      DEBUGF(LOG_CF(data, cf, "[h3sid=%" PRId64 "] unpausing acks",
                    stream_id));
    }
  }
  return 0;
}

static nghttp3_ssize
cb_h3_read_req_body(nghttp3_conn *conn, int64_t stream_id,
                    nghttp3_vec *vec, size_t veccnt,
                    uint32_t *pflags, void *user_data,
                    void *stream_user_data)
{
  struct Curl_cfilter *cf = user_data;
  struct Curl_easy *data = stream_user_data;
  struct h3_stream_ctx *stream = H3_STREAM_CTX(data);
  ssize_t nwritten = 0;
  size_t nvecs = 0;
  (void)cf;
  (void)conn;
  (void)stream_id;
  (void)user_data;
  (void)veccnt;

  if(!stream)
    return NGHTTP3_ERR_CALLBACK_FAILURE;
  /* nghttp3 keeps references to the sendbuf data until it is ACKed
   * by the server (see `cb_h3_acked_req_body()` for updates).
   * `sendbuf_len_in_flight` is the amount of bytes in `sendbuf`
   * that we have already passed to nghttp3, but which have not been
   * ACKed yet.
   * Any amount beyond `sendbuf_len_in_flight` we need still to pass
   * to nghttp3. Do that now, if we can. */
  if(stream->sendbuf_len_in_flight < Curl_bufq_len(&stream->sendbuf)) {
    nvecs = 0;
    while(nvecs < veccnt &&
          Curl_bufq_peek_at(&stream->sendbuf,
                            stream->sendbuf_len_in_flight,
                            (const unsigned char **)&vec[nvecs].base,
                            &vec[nvecs].len)) {
      stream->sendbuf_len_in_flight += vec[nvecs].len;
      nwritten += vec[nvecs].len;
      ++nvecs;
    }
    DEBUGASSERT(nvecs > 0); /* we SHOULD have been be able to peek */
  }

  if(nwritten > 0 && stream->upload_left != -1)
    stream->upload_left -= nwritten;

  /* When we stopped sending and everything in `sendbuf` is "in flight",
   * we are at the end of the request body. */
  if(stream->upload_left == 0) {
    *pflags = NGHTTP3_DATA_FLAG_EOF;
    stream->send_closed = TRUE;
  }
  else if(!nwritten) {
    /* Not EOF, and nothing to give, we signal WOULDBLOCK. */
    DEBUGF(LOG_CF(data, cf, "[h3sid=%" PRId64 "] read req body -> AGAIN",
                  stream->id));
    return NGHTTP3_ERR_WOULDBLOCK;
  }

  DEBUGF(LOG_CF(data, cf, "[h3sid=%" PRId64 "] read req body -> "
                          "%d vecs%s with %zu (buffered=%zu, left=%"
                          CURL_FORMAT_CURL_OFF_T ")",
                stream->id, (int)nvecs,
                *pflags == NGHTTP3_DATA_FLAG_EOF?" EOF":"",
                nwritten, Curl_bufq_len(&stream->sendbuf),
                stream->upload_left));
  return (nghttp3_ssize)nvecs;
}

/* Index where :authority header field will appear in request header
   field list. */
#define AUTHORITY_DST_IDX 3

static ssize_t h3_stream_open(struct Curl_cfilter *cf,
                              struct Curl_easy *data,
                              const void *buf, size_t len,
                              CURLcode *err)
{
  struct cf_ngtcp2_ctx *ctx = cf->ctx;
  struct h3_stream_ctx *stream = NULL;
  struct h1_req_parser h1;
  struct dynhds h2_headers;
  size_t nheader;
  nghttp3_nv *nva = NULL;
  int rc = 0;
  unsigned int i;
  ssize_t nwritten = -1;
  nghttp3_data_reader reader;
  nghttp3_data_reader *preader = NULL;

  Curl_h1_req_parse_init(&h1, H1_PARSE_DEFAULT_MAX_LINE_LEN);
  Curl_dynhds_init(&h2_headers, 0, DYN_HTTP_REQUEST);

  *err = h3_data_setup(cf, data);
  if(*err)
    goto out;
  stream = H3_STREAM_CTX(data);
  DEBUGASSERT(stream);

  rc = ngtcp2_conn_open_bidi_stream(ctx->qconn, &stream->id, NULL);
  if(rc) {
    failf(data, "can get bidi streams");
    *err = CURLE_SEND_ERROR;
    goto out;
  }

  nwritten = Curl_h1_req_parse_read(&h1, buf, len, NULL, 0, err);
  if(nwritten < 0)
    goto out;
  DEBUGASSERT(h1.done);
  DEBUGASSERT(h1.req);

  *err = Curl_http_req_to_h2(&h2_headers, h1.req, data);
  if(*err) {
    nwritten = -1;
    goto out;
  }

  nheader = Curl_dynhds_count(&h2_headers);
  nva = malloc(sizeof(nghttp3_nv) * nheader);
  if(!nva) {
    *err = CURLE_OUT_OF_MEMORY;
    nwritten = -1;
    goto out;
  }

  for(i = 0; i < nheader; ++i) {
    struct dynhds_entry *e = Curl_dynhds_getn(&h2_headers, i);
    nva[i].name = (unsigned char *)e->name;
    nva[i].namelen = e->namelen;
    nva[i].value = (unsigned char *)e->value;
    nva[i].valuelen = e->valuelen;
    nva[i].flags = NGHTTP3_NV_FLAG_NONE;
  }

  switch(data->state.httpreq) {
  case HTTPREQ_POST:
  case HTTPREQ_POST_FORM:
  case HTTPREQ_POST_MIME:
  case HTTPREQ_PUT:
    /* known request body size or -1 */
    if(data->state.infilesize != -1)
      stream->upload_left = data->state.infilesize;
    else
      /* data sending without specifying the data amount up front */
      stream->upload_left = -1; /* unknown */
    break;
  default:
    /* there is not request body */
    stream->upload_left = 0; /* no request body */
    break;
  }

  stream->send_closed = (stream->upload_left == 0);
  if(!stream->send_closed) {
    reader.read_data = cb_h3_read_req_body;
    preader = &reader;
  }

  rc = nghttp3_conn_submit_request(ctx->h3conn, stream->id,
                                   nva, nheader, preader, data);
  if(rc) {
    switch(rc) {
    case NGHTTP3_ERR_CONN_CLOSING:
      DEBUGF(LOG_CF(data, cf, "h3sid[%"PRId64"] failed to send, "
                    "connection is closing", stream->id));
      break;
    default:
      DEBUGF(LOG_CF(data, cf, "h3sid[%"PRId64"] failed to send -> %d (%s)",
                    stream->id, rc, ngtcp2_strerror(rc)));
      break;
    }
    *err = CURLE_SEND_ERROR;
    nwritten = -1;
    goto out;
  }

  infof(data, "Using HTTP/3 Stream ID: %" PRId64, stream->id);
  DEBUGF(LOG_CF(data, cf, "[h3sid=%" PRId64 "] opened for %s",
                stream->id, data->state.url));

out:
  free(nva);
  Curl_h1_req_parse_free(&h1);
  Curl_dynhds_free(&h2_headers);
  return nwritten;
}

static ssize_t cf_ngtcp2_send(struct Curl_cfilter *cf, struct Curl_easy *data,
                              const void *buf, size_t len, CURLcode *err)
{
  struct cf_ngtcp2_ctx *ctx = cf->ctx;
  struct h3_stream_ctx *stream = H3_STREAM_CTX(data);
  ssize_t sent = 0;
  struct cf_call_data save;
  struct pkt_io_ctx pktx;
  CURLcode result;

  CF_DATA_SAVE(save, cf, data);
  DEBUGASSERT(cf->connected);
  DEBUGASSERT(ctx->qconn);
  DEBUGASSERT(ctx->h3conn);
  pktx_init(&pktx, cf, data);
  *err = CURLE_OK;

  result = cf_progress_ingress(cf, data, &pktx);
  if(result) {
    *err = result;
    sent = -1;
  }

  if(!stream || stream->id < 0) {
    sent = h3_stream_open(cf, data, buf, len, err);
    if(sent < 0) {
      DEBUGF(LOG_CF(data, cf, "failed to open stream -> %d", *err));
      goto out;
    }
  }
  else if(stream->upload_blocked_len) {
    /* the data in `buf` has alread been submitted or added to the
     * buffers, but have been EAGAINed on the last invocation. */
    DEBUGASSERT(len >= stream->upload_blocked_len);
    if(len < stream->upload_blocked_len) {
      /* Did we get called again with a smaller `len`? This should not
       * happend. We are not prepared to handle that. */
      failf(data, "HTTP/3 send again with decreased length");
      *err = CURLE_HTTP3;
      sent = -1;
      goto out;
    }
    sent = (ssize_t)stream->upload_blocked_len;
    stream->upload_blocked_len = 0;
  }
  else if(stream->closed) {
    *err = CURLE_HTTP3;
    sent = -1;
    goto out;
  }
  else {
    sent = Curl_bufq_write(&stream->sendbuf, buf, len, err);
    DEBUGF(LOG_CF(data, cf, "[h3sid=%" PRId64 "] cf_send, add to "
                  "sendbuf(len=%zu) -> %zd, %d",
                  stream->id, len, sent, *err));
    if(sent < 0) {
      goto out;
    }

    (void)nghttp3_conn_resume_stream(ctx->h3conn, stream->id);
  }

  result = cf_progress_egress(cf, data, &pktx);
  if(result) {
    *err = result;
    sent = -1;
  }

  if(stream && sent > 0 && stream->sendbuf_len_in_flight) {
    /* We have unacknowledged DATA and cannot report success to our
     * caller. Instead we EAGAIN and remember how much we have already
     * "written" into our variour internal connection buffers.
     * We put the stream upload on HOLD, until this gets ACKed. */
    stream->upload_blocked_len = sent;
    DEBUGF(LOG_CF(data, cf, "[h3sid=%" PRId64 "] cf_send(len=%zu), "
                  "%zu bytes in flight -> EGAIN", stream->id, len,
                  stream->sendbuf_len_in_flight));
    *err = CURLE_AGAIN;
    sent = -1;
    data->req.keepon |= KEEP_SEND_HOLD;
  }

out:
  result = check_and_set_expiry(cf, data, &pktx);
  if(result) {
    *err = result;
    sent = -1;
  }
  CF_DATA_RESTORE(cf, save);
  return sent;
}

static CURLcode qng_verify_peer(struct Curl_cfilter *cf,
                                struct Curl_easy *data)
{
  struct cf_ngtcp2_ctx *ctx = cf->ctx;
  CURLcode result = CURLE_OK;
  const char *hostname, *disp_hostname;
  int port;
  char *snihost;

  Curl_conn_get_host(data, cf->sockindex, &hostname, &disp_hostname, &port);
  snihost = Curl_ssl_snihost(data, hostname, NULL);
  if(!snihost)
    return CURLE_PEER_FAILED_VERIFICATION;

  cf->conn->bits.multiplex = TRUE; /* at least potentially multiplexed */
  cf->conn->httpversion = 30;
  cf->conn->bundle->multiuse = BUNDLE_MULTIPLEX;

  if(cf->conn->ssl_config.verifyhost) {
#ifdef USE_OPENSSL
    X509 *server_cert;
    server_cert = SSL_get_peer_certificate(ctx->ssl);
    if(!server_cert) {
      return CURLE_PEER_FAILED_VERIFICATION;
    }
    result = Curl_ossl_verifyhost(data, cf->conn, server_cert);
    X509_free(server_cert);
    if(result)
      return result;
#elif defined(USE_GNUTLS)
    result = Curl_gtls_verifyserver(data, ctx->gtls->session,
                                    &cf->conn->ssl_config, &data->set.ssl,
                                    hostname, disp_hostname,
                                    data->set.str[STRING_SSL_PINNEDPUBLICKEY]);
    if(result)
      return result;
#elif defined(USE_WOLFSSL)
    if(wolfSSL_check_domain_name(ctx->ssl, snihost) == SSL_FAILURE)
      return CURLE_PEER_FAILED_VERIFICATION;
#endif
    infof(data, "Verified certificate just fine");
  }
  else
    infof(data, "Skipped certificate verification");
#ifdef USE_OPENSSL
  if(data->set.ssl.certinfo)
    /* asked to gather certificate info */
    (void)Curl_ossl_certchain(data, ctx->ssl);
#endif
  return result;
}

static CURLcode recv_pkt(const unsigned char *pkt, size_t pktlen,
                         struct sockaddr_storage *remote_addr,
                         socklen_t remote_addrlen, int ecn,
                         void *userp)
{
  struct pkt_io_ctx *pktx = userp;
  struct cf_ngtcp2_ctx *ctx = pktx->cf->ctx;
  ngtcp2_pkt_info pi;
  ngtcp2_path path;
  int rv;

  ++pktx->pkt_count;
  ngtcp2_addr_init(&path.local, (struct sockaddr *)&ctx->q.local_addr,
                   ctx->q.local_addrlen);
  ngtcp2_addr_init(&path.remote, (struct sockaddr *)remote_addr,
                   remote_addrlen);
  pi.ecn = (uint32_t)ecn;

  rv = ngtcp2_conn_read_pkt(ctx->qconn, &path, &pi, pkt, pktlen, pktx->ts);
  if(rv) {
    DEBUGF(LOG_CF(pktx->data, pktx->cf, "ingress, read_pkt -> %s",
                  ngtcp2_strerror(rv)));
    if(!ctx->last_error.error_code) {
      if(rv == NGTCP2_ERR_CRYPTO) {
        ngtcp2_ccerr_set_tls_alert(&ctx->last_error,
                                   ngtcp2_conn_get_tls_alert(ctx->qconn),
                                   NULL, 0);
      }
      else {
        ngtcp2_ccerr_set_liberr(&ctx->last_error, rv, NULL, 0);
      }
    }

    if(rv == NGTCP2_ERR_CRYPTO)
      /* this is a "TLS problem", but a failed certificate verification
         is a common reason for this */
      return CURLE_PEER_FAILED_VERIFICATION;
    return CURLE_RECV_ERROR;
  }

  return CURLE_OK;
}

static CURLcode cf_progress_ingress(struct Curl_cfilter *cf,
                                    struct Curl_easy *data,
                                    struct pkt_io_ctx *pktx)
{
  struct cf_ngtcp2_ctx *ctx = cf->ctx;
  struct pkt_io_ctx local_pktx;
  size_t pkts_chunk = 128, i;
  size_t pkts_max = 10 * pkts_chunk;
  CURLcode result = CURLE_OK;

  if(!pktx) {
    pktx_init(&local_pktx, cf, data);
    pktx = &local_pktx;
  }
  else {
    pktx->ts = timestamp();
  }

  for(i = 0; i < pkts_max; i += pkts_chunk) {
    pktx->pkt_count = 0;
    result = vquic_recv_packets(cf, data, &ctx->q, pkts_chunk,
                                recv_pkt, pktx);
    if(result) /* error */
      break;
    if(pktx->pkt_count < pkts_chunk) /* got less than we could */
      break;
    /* give egress a chance before we receive more */
    result = cf_progress_egress(cf, data, pktx);
    if(result) /* error */
      break;
  }
  return result;
}

/**
 * Read a network packet to send from ngtcp2 into `buf`.
 * Return number of bytes written or -1 with *err set.
 */
static ssize_t read_pkt_to_send(void *userp,
                                unsigned char *buf, size_t buflen,
                                CURLcode *err)
{
  struct pkt_io_ctx *x = userp;
  struct cf_ngtcp2_ctx *ctx = x->cf->ctx;
  nghttp3_vec vec[16];
  nghttp3_ssize veccnt;
  ngtcp2_ssize ndatalen;
  uint32_t flags;
  int64_t stream_id;
  int fin;
  ssize_t nwritten, n;
  veccnt = 0;
  stream_id = -1;
  fin = 0;

  /* ngtcp2 may want to put several frames from different streams into
   * this packet. `NGTCP2_WRITE_STREAM_FLAG_MORE` tells it to do so.
   * When `NGTCP2_ERR_WRITE_MORE` is returned, we *need* to make
   * another iteration.
   * When ngtcp2 is happy (because it has no other frame that would fit
   * or it has nothing more to send), it returns the total length
   * of the assembled packet. This may be 0 if there was nothing to send. */
  nwritten = 0;
  *err = CURLE_OK;
  for(;;) {

    if(ctx->h3conn && ngtcp2_conn_get_max_data_left(ctx->qconn)) {
      veccnt = nghttp3_conn_writev_stream(ctx->h3conn, &stream_id, &fin, vec,
                                          sizeof(vec) / sizeof(vec[0]));
      if(veccnt < 0) {
        failf(x->data, "nghttp3_conn_writev_stream returned error: %s",
              nghttp3_strerror((int)veccnt));
        ngtcp2_ccerr_set_application_error(
          &ctx->last_error,
          nghttp3_err_infer_quic_app_error_code((int)veccnt), NULL, 0);
        *err = CURLE_SEND_ERROR;
        return -1;
      }
    }

    flags = NGTCP2_WRITE_STREAM_FLAG_MORE |
            (fin ? NGTCP2_WRITE_STREAM_FLAG_FIN : 0);
    n = ngtcp2_conn_writev_stream(ctx->qconn, &x->ps.path,
                                  NULL, buf, buflen,
                                  &ndatalen, flags, stream_id,
                                  (const ngtcp2_vec *)vec, veccnt, x->ts);
    if(n == 0) {
      /* nothing to send */
      *err = CURLE_AGAIN;
      nwritten = -1;
      goto out;
    }
    else if(n < 0) {
      switch(n) {
      case NGTCP2_ERR_STREAM_DATA_BLOCKED:
        DEBUGASSERT(ndatalen == -1);
        nghttp3_conn_block_stream(ctx->h3conn, stream_id);
        n = 0;
        break;
      case NGTCP2_ERR_STREAM_SHUT_WR:
        DEBUGASSERT(ndatalen == -1);
        nghttp3_conn_shutdown_stream_write(ctx->h3conn, stream_id);
        n = 0;
        break;
      case NGTCP2_ERR_WRITE_MORE:
        /* ngtcp2 wants to send more. update the flow of the stream whose data
         * is in the buffer and continue */
        DEBUGASSERT(ndatalen >= 0);
        n = 0;
        break;
      default:
        DEBUGASSERT(ndatalen == -1);
        failf(x->data, "ngtcp2_conn_writev_stream returned error: %s",
              ngtcp2_strerror((int)n));
        ngtcp2_ccerr_set_liberr(&ctx->last_error, (int)n, NULL, 0);
        *err = CURLE_SEND_ERROR;
        nwritten = -1;
        goto out;
      }
    }

    if(ndatalen >= 0) {
      /* we add the amount of data bytes to the flow windows */
      int rv = nghttp3_conn_add_write_offset(ctx->h3conn, stream_id, ndatalen);
      if(rv) {
        failf(x->data, "nghttp3_conn_add_write_offset returned error: %s\n",
              nghttp3_strerror(rv));
        return CURLE_SEND_ERROR;
      }
    }

    if(n > 0) {
      /* packet assembled, leave */
      nwritten = n;
      goto out;
    }
  }
out:
  return nwritten;
}

static CURLcode cf_progress_egress(struct Curl_cfilter *cf,
                                   struct Curl_easy *data,
                                   struct pkt_io_ctx *pktx)
{
  struct cf_ngtcp2_ctx *ctx = cf->ctx;
  ssize_t nread;
  size_t max_payload_size, path_max_payload_size, max_pktcnt;
  size_t pktcnt = 0;
  size_t gsolen = 0;  /* this disables gso until we have a clue */
  CURLcode curlcode;
  struct pkt_io_ctx local_pktx;

  if(!pktx) {
    pktx_init(&local_pktx, cf, data);
    pktx = &local_pktx;
  }
  else {
    pktx->ts = timestamp();
    ngtcp2_path_storage_zero(&pktx->ps);
  }

  curlcode = vquic_flush(cf, data, &ctx->q);
  if(curlcode) {
    if(curlcode == CURLE_AGAIN) {
      Curl_expire(data, 1, EXPIRE_QUIC);
      return CURLE_OK;
    }
    return curlcode;
  }

  /* In UDP, there is a maximum theoretical packet paload length and
   * a minimum payload length that is "guarantueed" to work.
   * To detect if this minimum payload can be increased, ngtcp2 sends
   * now and then a packet payload larger than the minimum. It that
   * is ACKed by the peer, both parties know that it works and
   * the subsequent packets can use a larger one.
   * This is called PMTUD (Path Maximum Transmission Unit Discovery).
   * Since a PMTUD might be rejected right on send, we do not want it
   * be followed by other packets of lesser size. Because those would
   * also fail then. So, if we detect a PMTUD while buffering, we flush.
   */
  max_payload_size = ngtcp2_conn_get_max_tx_udp_payload_size(ctx->qconn);
  path_max_payload_size =
      ngtcp2_conn_get_path_max_tx_udp_payload_size(ctx->qconn);
  /* maximum number of packets buffered before we flush to the socket */
  max_pktcnt = CURLMIN(MAX_PKT_BURST,
                       ctx->q.sendbuf.chunk_size / max_payload_size);

  for(;;) {
    /* add the next packet to send, if any, to our buffer */
    nread = Curl_bufq_sipn(&ctx->q.sendbuf, max_payload_size,
                           read_pkt_to_send, pktx, &curlcode);
    /* DEBUGF(LOG_CF(data, cf, "sip packet(maxlen=%zu) -> %zd, %d",
                  max_payload_size, nread, curlcode)); */
    if(nread < 0) {
      if(curlcode != CURLE_AGAIN)
        return curlcode;
      /* Nothing more to add, flush and leave */
      curlcode = vquic_send(cf, data, &ctx->q, gsolen);
      if(curlcode) {
        if(curlcode == CURLE_AGAIN) {
          Curl_expire(data, 1, EXPIRE_QUIC);
          return CURLE_OK;
        }
        return curlcode;
      }
      goto out;
    }

    DEBUGASSERT(nread > 0);
    if(pktcnt == 0) {
      /* first packet in buffer. This is either of a known, "good"
       * payload size or it is a PMTUD. We'll see. */
      gsolen = (size_t)nread;
    }
    else if((size_t)nread > gsolen ||
            (gsolen > path_max_payload_size && (size_t)nread != gsolen)) {
      /* The just added packet is a PMTUD *or* the one(s) before the
       * just added were PMTUD and the last one is smaller.
       * Flush the buffer before the last add. */
      curlcode = vquic_send_tail_split(cf, data, &ctx->q,
                                       gsolen, nread, nread);
      if(curlcode) {
        if(curlcode == CURLE_AGAIN) {
          Curl_expire(data, 1, EXPIRE_QUIC);
          return CURLE_OK;
        }
        return curlcode;
      }
      pktcnt = 0;
      continue;
    }

    if(++pktcnt >= max_pktcnt || (size_t)nread < gsolen) {
      /* Reached MAX_PKT_BURST *or*
       * the capacity of our buffer *or*
       * last add was shorter than the previous ones, flush */
      curlcode = vquic_send(cf, data, &ctx->q, gsolen);
      if(curlcode) {
        if(curlcode == CURLE_AGAIN) {
          Curl_expire(data, 1, EXPIRE_QUIC);
          return CURLE_OK;
        }
        return curlcode;
      }
      /* pktbuf has been completely sent */
      pktcnt = 0;
    }
  }

out:
  return CURLE_OK;
}

/*
 * Called from transfer.c:data_pending to know if we should keep looping
 * to receive more data from the connection.
 */
static bool cf_ngtcp2_data_pending(struct Curl_cfilter *cf,
                                   const struct Curl_easy *data)
{
  const struct h3_stream_ctx *stream = H3_STREAM_CTX(data);
  (void)cf;
  return stream && !Curl_bufq_is_empty(&stream->recvbuf);
}

static CURLcode h3_data_pause(struct Curl_cfilter *cf,
                              struct Curl_easy *data,
                              bool pause)
{
  /* TODO: there seems right now no API in ngtcp2 to shrink/enlarge
   * the streams windows. As we do in HTTP/2. */
  if(!pause) {
    h3_drain_stream(cf, data);
    Curl_expire(data, 0, EXPIRE_RUN_NOW);
  }
  return CURLE_OK;
}

static CURLcode cf_ngtcp2_data_event(struct Curl_cfilter *cf,
                                     struct Curl_easy *data,
                                     int event, int arg1, void *arg2)
{
  struct cf_ngtcp2_ctx *ctx = cf->ctx;
  CURLcode result = CURLE_OK;
  struct cf_call_data save;

  CF_DATA_SAVE(save, cf, data);
  (void)arg1;
  (void)arg2;
  switch(event) {
  case CF_CTRL_DATA_SETUP:
    break;
  case CF_CTRL_DATA_PAUSE:
    result = h3_data_pause(cf, data, (arg1 != 0));
    break;
  case CF_CTRL_DATA_DONE: {
    h3_data_done(cf, data);
    break;
  }
  case CF_CTRL_DATA_DONE_SEND: {
    struct h3_stream_ctx *stream = H3_STREAM_CTX(data);
    if(stream && !stream->send_closed) {
      stream->send_closed = TRUE;
      stream->upload_left = Curl_bufq_len(&stream->sendbuf);
      (void)nghttp3_conn_resume_stream(ctx->h3conn, stream->id);
    }
    break;
  }
  case CF_CTRL_DATA_IDLE:
    result = check_and_set_expiry(cf, data, NULL);
    break;
  default:
    break;
  }
  CF_DATA_RESTORE(cf, save);
  return result;
}

static void cf_ngtcp2_ctx_clear(struct cf_ngtcp2_ctx *ctx)
{
  struct cf_call_data save = ctx->call_data;

  if(ctx->qlogfd != -1) {
    close(ctx->qlogfd);
  }
#ifdef USE_OPENSSL
  if(ctx->ssl)
    SSL_free(ctx->ssl);
  if(ctx->sslctx)
    SSL_CTX_free(ctx->sslctx);
#elif defined(USE_GNUTLS)
  if(ctx->gtls) {
    if(ctx->gtls->cred)
      gnutls_certificate_free_credentials(ctx->gtls->cred);
    if(ctx->gtls->session)
      gnutls_deinit(ctx->gtls->session);
    free(ctx->gtls);
  }
#elif defined(USE_WOLFSSL)
  if(ctx->ssl)
    wolfSSL_free(ctx->ssl);
  if(ctx->sslctx)
    wolfSSL_CTX_free(ctx->sslctx);
#endif
  vquic_ctx_free(&ctx->q);
  if(ctx->h3conn)
    nghttp3_conn_del(ctx->h3conn);
  if(ctx->qconn)
    ngtcp2_conn_del(ctx->qconn);
  Curl_bufcp_free(&ctx->stream_bufcp);

  memset(ctx, 0, sizeof(*ctx));
  ctx->qlogfd = -1;
  ctx->call_data = save;
}

static void cf_ngtcp2_close(struct Curl_cfilter *cf, struct Curl_easy *data)
{
  struct cf_ngtcp2_ctx *ctx = cf->ctx;
  struct cf_call_data save;

  CF_DATA_SAVE(save, cf, data);
  if(ctx && ctx->qconn) {
    char buffer[NGTCP2_MAX_UDP_PAYLOAD_SIZE];
    ngtcp2_tstamp ts;
    ngtcp2_ssize rc;

    DEBUGF(LOG_CF(data, cf, "close"));
    ts = timestamp();
    rc = ngtcp2_conn_write_connection_close(ctx->qconn, NULL, /* path */
                                            NULL, /* pkt_info */
                                            (uint8_t *)buffer, sizeof(buffer),
                                            &ctx->last_error, ts);
    if(rc > 0) {
      while((send(ctx->q.sockfd, buffer, (SEND_TYPE_ARG3)rc, 0) == -1) &&
            SOCKERRNO == EINTR);
    }

    cf_ngtcp2_ctx_clear(ctx);
  }

  cf->connected = FALSE;
  CF_DATA_RESTORE(cf, save);
}

static void cf_ngtcp2_destroy(struct Curl_cfilter *cf, struct Curl_easy *data)
{
  struct cf_ngtcp2_ctx *ctx = cf->ctx;
  struct cf_call_data save;

  CF_DATA_SAVE(save, cf, data);
  DEBUGF(LOG_CF(data, cf, "destroy"));
  if(ctx) {
    cf_ngtcp2_ctx_clear(ctx);
    free(ctx);
  }
  cf->ctx = NULL;
  /* No CF_DATA_RESTORE(cf, save) possible */
  (void)save;
}

/*
 * Might be called twice for happy eyeballs.
 */
static CURLcode cf_connect_start(struct Curl_cfilter *cf,
                                 struct Curl_easy *data,
                                 struct pkt_io_ctx *pktx)
{
  struct cf_ngtcp2_ctx *ctx = cf->ctx;
  int rc;
  int rv;
  CURLcode result;
  const struct Curl_sockaddr_ex *sockaddr;
  int qfd;

  ctx->version = NGTCP2_PROTO_VER_MAX;
  ctx->max_stream_window = H3_STREAM_WINDOW_SIZE;
  Curl_bufcp_init(&ctx->stream_bufcp, H3_STREAM_CHUNK_SIZE,
                  H3_STREAM_POOL_SPARES);

#ifdef USE_OPENSSL
  result = quic_ssl_ctx(&ctx->sslctx, cf, data);
  if(result)
    return result;

  result = quic_set_client_cert(cf, data);
  if(result)
    return result;
#elif defined(USE_WOLFSSL)
  result = quic_ssl_ctx(&ctx->sslctx, cf, data);
  if(result)
    return result;
#endif

  result = quic_init_ssl(cf, data);
  if(result)
    return result;

  ctx->dcid.datalen = NGTCP2_MAX_CIDLEN;
  result = Curl_rand(data, ctx->dcid.data, NGTCP2_MAX_CIDLEN);
  if(result)
    return result;

  ctx->scid.datalen = NGTCP2_MAX_CIDLEN;
  result = Curl_rand(data, ctx->scid.data, NGTCP2_MAX_CIDLEN);
  if(result)
    return result;

  (void)Curl_qlogdir(data, ctx->scid.data, NGTCP2_MAX_CIDLEN, &qfd);
  ctx->qlogfd = qfd; /* -1 if failure above */
  quic_settings(ctx, data, pktx);

  result = vquic_ctx_init(&ctx->q);
  if(result)
    return result;

  Curl_cf_socket_peek(cf->next, data, &ctx->q.sockfd,
                      &sockaddr, NULL, NULL, NULL, NULL);
  ctx->q.local_addrlen = sizeof(ctx->q.local_addr);
  rv = getsockname(ctx->q.sockfd, (struct sockaddr *)&ctx->q.local_addr,
                   &ctx->q.local_addrlen);
  if(rv == -1)
    return CURLE_QUIC_CONNECT_ERROR;

  ngtcp2_addr_init(&ctx->connected_path.local,
                   (struct sockaddr *)&ctx->q.local_addr,
                   ctx->q.local_addrlen);
  ngtcp2_addr_init(&ctx->connected_path.remote,
                   &sockaddr->sa_addr, sockaddr->addrlen);

  rc = ngtcp2_conn_client_new(&ctx->qconn, &ctx->dcid, &ctx->scid,
                              &ctx->connected_path,
                              NGTCP2_PROTO_VER_V1, &ng_callbacks,
                              &ctx->settings, &ctx->transport_params,
                              NULL, cf);
  if(rc)
    return CURLE_QUIC_CONNECT_ERROR;

#ifdef USE_GNUTLS
  ngtcp2_conn_set_tls_native_handle(ctx->qconn, ctx->gtls->session);
#else
  ngtcp2_conn_set_tls_native_handle(ctx->qconn, ctx->ssl);
#endif

  ngtcp2_ccerr_default(&ctx->last_error);

  ctx->conn_ref.get_conn = get_conn;
  ctx->conn_ref.user_data = cf;

  return CURLE_OK;
}

static CURLcode cf_ngtcp2_connect(struct Curl_cfilter *cf,
                                  struct Curl_easy *data,
                                  bool blocking, bool *done)
{
  struct cf_ngtcp2_ctx *ctx = cf->ctx;
  CURLcode result = CURLE_OK;
  struct cf_call_data save;
  struct curltime now;
  struct pkt_io_ctx pktx;

  if(cf->connected) {
    *done = TRUE;
    return CURLE_OK;
  }

  /* Connect the UDP filter first */
  if(!cf->next->connected) {
    result = Curl_conn_cf_connect(cf->next, data, blocking, done);
    if(result || !*done)
      return result;
  }

  *done = FALSE;
  now = Curl_now();
  pktx_init(&pktx, cf, data);

  CF_DATA_SAVE(save, cf, data);

  if(ctx->reconnect_at.tv_sec && Curl_timediff(now, ctx->reconnect_at) < 0) {
    /* Not time yet to attempt the next connect */
    DEBUGF(LOG_CF(data, cf, "waiting for reconnect time"));
    goto out;
  }

  if(!ctx->qconn) {
    ctx->started_at = now;
    result = cf_connect_start(cf, data, &pktx);
    if(result)
      goto out;
    result = cf_progress_egress(cf, data, &pktx);
    /* we do not expect to be able to recv anything yet */
    goto out;
  }

  result = cf_progress_ingress(cf, data, &pktx);
  if(result)
    goto out;

  result = cf_progress_egress(cf, data, &pktx);
  if(result)
    goto out;

  if(ngtcp2_conn_get_handshake_completed(ctx->qconn)) {
    ctx->handshake_at = now;
    DEBUGF(LOG_CF(data, cf, "handshake complete after %dms",
           (int)Curl_timediff(now, ctx->started_at)));
    result = qng_verify_peer(cf, data);
    if(!result) {
      DEBUGF(LOG_CF(data, cf, "peer verified"));
      cf->connected = TRUE;
      cf->conn->alpn = CURL_HTTP_VERSION_3;
      *done = TRUE;
      connkeep(cf->conn, "HTTP/3 default");
    }
  }

out:
  if(result == CURLE_RECV_ERROR && ctx->qconn &&
     ngtcp2_conn_in_draining_period(ctx->qconn)) {
    /* When a QUIC server instance is shutting down, it may send us a
     * CONNECTION_CLOSE right away. Our connection then enters the DRAINING
     * state.
     * This may be a stopping of the service or it may be that the server
     * is reloading and a new instance will start serving soon.
     * In any case, we tear down our socket and start over with a new one.
     * We re-open the underlying UDP cf right now, but do not start
     * connecting until called again.
     */
    int reconn_delay_ms = 200;

    DEBUGF(LOG_CF(data, cf, "connect, remote closed, reconnect after %dms",
                  reconn_delay_ms));
    Curl_conn_cf_close(cf->next, data);
    cf_ngtcp2_ctx_clear(ctx);
    result = Curl_conn_cf_connect(cf->next, data, FALSE, done);
    if(!result && *done) {
      *done = FALSE;
      ctx->reconnect_at = now;
      ctx->reconnect_at.tv_usec += reconn_delay_ms * 1000;
      Curl_expire(data, reconn_delay_ms, EXPIRE_QUIC);
      result = CURLE_OK;
    }
  }

#ifndef CURL_DISABLE_VERBOSE_STRINGS
  if(result) {
    const char *r_ip;
    int r_port;

    Curl_cf_socket_peek(cf->next, data, NULL, NULL,
                        &r_ip, &r_port, NULL, NULL);
    infof(data, "QUIC connect to %s port %u failed: %s",
          r_ip, r_port, curl_easy_strerror(result));
  }
#endif
  if(!result && ctx->qconn) {
    result = check_and_set_expiry(cf, data, &pktx);
  }
  DEBUGF(LOG_CF(data, cf, "connect -> %d, done=%d", result, *done));
  CF_DATA_RESTORE(cf, save);
  return result;
}

static CURLcode cf_ngtcp2_query(struct Curl_cfilter *cf,
                                struct Curl_easy *data,
                                int query, int *pres1, void *pres2)
{
  struct cf_ngtcp2_ctx *ctx = cf->ctx;
  struct cf_call_data save;

  switch(query) {
  case CF_QUERY_MAX_CONCURRENT: {
    const ngtcp2_transport_params *rp;
    DEBUGASSERT(pres1);

    CF_DATA_SAVE(save, cf, data);
    rp = ngtcp2_conn_get_remote_transport_params(ctx->qconn);
    if(rp)
      *pres1 = (rp->initial_max_streams_bidi > INT_MAX)?
                 INT_MAX : (int)rp->initial_max_streams_bidi;
    else  /* not arrived yet? */
      *pres1 = Curl_multi_max_concurrent_streams(data->multi);
    DEBUGF(LOG_CF(data, cf, "query max_conncurrent -> %d", *pres1));
    CF_DATA_RESTORE(cf, save);
    return CURLE_OK;
  }
  case CF_QUERY_CONNECT_REPLY_MS:
    if(ctx->got_first_byte) {
      timediff_t ms = Curl_timediff(ctx->first_byte_at, ctx->started_at);
      *pres1 = (ms < INT_MAX)? (int)ms : INT_MAX;
    }
    else
      *pres1 = -1;
    return CURLE_OK;
  case CF_QUERY_TIMER_CONNECT: {
    struct curltime *when = pres2;
    if(ctx->got_first_byte)
      *when = ctx->first_byte_at;
    return CURLE_OK;
  }
  case CF_QUERY_TIMER_APPCONNECT: {
    struct curltime *when = pres2;
    if(cf->connected)
      *when = ctx->handshake_at;
    return CURLE_OK;
  }
  default:
    break;
  }
  return cf->next?
    cf->next->cft->query(cf->next, data, query, pres1, pres2) :
    CURLE_UNKNOWN_OPTION;
}

static bool cf_ngtcp2_conn_is_alive(struct Curl_cfilter *cf,
                                    struct Curl_easy *data,
                                    bool *input_pending)
{
  bool alive = TRUE;

  *input_pending = FALSE;
  if(!cf->next || !cf->next->cft->is_alive(cf->next, data, input_pending))
    return FALSE;

  if(*input_pending) {
    /* This happens before we've sent off a request and the connection is
       not in use by any other transfer, there shouldn't be any data here,
       only "protocol frames" */
    *input_pending = FALSE;
    if(cf_progress_ingress(cf, data, NULL))
      alive = FALSE;
    else {
      alive = TRUE;
    }
  }

  return alive;
}

struct Curl_cftype Curl_cft_http3 = {
  "HTTP/3",
  CF_TYPE_IP_CONNECT | CF_TYPE_SSL | CF_TYPE_MULTIPLEX,
  0,
  cf_ngtcp2_destroy,
  cf_ngtcp2_connect,
  cf_ngtcp2_close,
  Curl_cf_def_get_host,
  cf_ngtcp2_get_select_socks,
  cf_ngtcp2_data_pending,
  cf_ngtcp2_send,
  cf_ngtcp2_recv,
  cf_ngtcp2_data_event,
  cf_ngtcp2_conn_is_alive,
  Curl_cf_def_conn_keep_alive,
  cf_ngtcp2_query,
};

CURLcode Curl_cf_ngtcp2_create(struct Curl_cfilter **pcf,
                               struct Curl_easy *data,
                               struct connectdata *conn,
                               const struct Curl_addrinfo *ai)
{
  struct cf_ngtcp2_ctx *ctx = NULL;
  struct Curl_cfilter *cf = NULL, *udp_cf = NULL;
  CURLcode result;

  (void)data;
  ctx = calloc(sizeof(*ctx), 1);
  if(!ctx) {
    result = CURLE_OUT_OF_MEMORY;
    goto out;
  }
  ctx->qlogfd = -1;
  cf_ngtcp2_ctx_clear(ctx);

  result = Curl_cf_create(&cf, &Curl_cft_http3, ctx);
  if(result)
    goto out;

  result = Curl_cf_udp_create(&udp_cf, data, conn, ai, TRNSPRT_QUIC);
  if(result)
    goto out;

  cf->conn = conn;
  udp_cf->conn = cf->conn;
  udp_cf->sockindex = cf->sockindex;
  cf->next = udp_cf;

out:
  *pcf = (!result)? cf : NULL;
  if(result) {
    if(udp_cf)
      Curl_conn_cf_discard_sub(cf, udp_cf, data, TRUE);
    Curl_safefree(cf);
    Curl_safefree(ctx);
  }
  return result;
}

bool Curl_conn_is_ngtcp2(const struct Curl_easy *data,
                         const struct connectdata *conn,
                         int sockindex)
{
  struct Curl_cfilter *cf = conn? conn->cfilter[sockindex] : NULL;

  (void)data;
  for(; cf; cf = cf->next) {
    if(cf->cft == &Curl_cft_http3)
      return TRUE;
    if(cf->cft->flags & CF_TYPE_IP_CONNECT)
      return FALSE;
  }
  return FALSE;
}

#endif