pacman downloads sometimes stall after upgrading to curl 7.79.0

[foutrelis]

After upgrading to curl 7.79.0 (from 7.78.0) I'm seeing connection stalls and dropouts in Arch Linux's package manager (pacman). The issue is reproducible when using Basic authentication against a HTTP/2 mirror. (It doesn't happen without Basic auth.)

Bisected this to commit 3cb8a74. I don't have a reliable reproducer yet; I used repeated pacman -Syy calls for testing and the issue usually occurs within the first few invocations. Each pacman -Syy call downloads 5 repositories concurrently (a few MiB each) using libcurl's multi interface.

No tangible error messages other than Operation too slow. Less than 1 bytes/sec transferred the last 10 seconds and/or transfer closed with 5472421 bytes remaining to read. Sorry for not providing a reproducer outside of pacman; I'll update this issue if I manage to come up with one.

curl/libcurl version

curl 7.79.0 (x86_64-pc-linux-gnu) libcurl/7.79.0 OpenSSL/1.1.1l zlib/1.2.11 brotli/1.0.9 zstd/1.5.0 libidn2/2.3.2 libpsl/0.21.1 (+libidn2/2.3.0) libssh2/1.9.0 nghttp2/1.44.0
Release-Date: 2021-09-15
Protocols: dict file ftp ftps gopher gophers http https imap imaps mqtt pop3 pop3s rtsp scp sftp smb smbs smtp smtps telnet tftp 
Features: alt-svc AsynchDNS brotli GSS-API HSTS HTTP2 HTTPS-proxy IDN IPv6 Kerberos Largefile libz NTLM NTLM_WB PSL SPNEGO SSL TLS-SRP UnixSockets zstd

operating system

Arch Linux x86_64

Linux notbad 5.14.3-arch1-1 #1 SMP PREEMPT Sun, 12 Sep 2021 20:51:34 +0000 x86_64 GNU/Linux

[bagder]

Can you try a patch? I immediately now spotted a mistake in that commit.

diff --git a/lib/http2.c b/lib/http2.c
index a3de607c7..6d63f4363 100644
--- a/lib/http2.c
+++ b/lib/http2.c
@@ -2219,16 +2219,10 @@ CURLcode Curl_http2_setup(struct Curl_easy *data,
   stream->upload_mem = NULL;
   stream->upload_len = 0;
   stream->mem = data->state.buffer;
   stream->len = data->set.buffer_size;
 
-  httpc->inbuflen = 0;
-  httpc->nread_inbuf = 0;
-
-  httpc->pause_stream_id = 0;
-  httpc->drain_total = 0;
-
   multi_connchanged(data->multi);
   /* below this point only connection related inits are done, which only needs
      to be done once per connection */
 
   if((conn->handler == &Curl_handler_http2_ssl) ||
@@ -2250,10 +2244,16 @@ CURLcode Curl_http2_setup(struct Curl_easy *data,
 
   conn->bits.multiplex = TRUE; /* at least potentially multiplexed */
   conn->httpversion = 20;
   conn->bundle->multiuse = BUNDLE_MULTIPLEX;
 
+  httpc->inbuflen = 0;
+  httpc->nread_inbuf = 0;
+
+  httpc->pause_stream_id = 0;
+  httpc->drain_total = 0;
+
   infof(data, "Connection state changed (HTTP/2 confirmed)");
 
   return CURLE_OK;
 }
 

[foutrelis]

Seems to have fixed it! I have pacman -Syy running in a loop for a few minutes now with no issues (whereas previously it would fail within seconds).

Many thanks!

[bagder]

Primarily due to this issue, we now plan a 7.79.1 patch release for Sep 22.