httpserver.cpp

// Copyright (c) 2015-2016 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.

#include "httpserver.h"
#include "chainparamsbase.h"
#include "config.h"
#include "net/netbase.h"
#include "rpc/http_protocol.h" // For HTTP status codes
#include "task_helpers.h"
#include "ui_interface.h"
#include "util.h"
#include "utilstrencodings.h"
#include <sys/types.h>
#include <event2/buffer.h>
#include <event2/event.h>
#include <event2/http.h>
#include <event2/keyvalq_struct.h>
#include <event2/thread.h>
#include <event2/util.h>

#ifdef EVENT__HAVE_NETINET_IN_H
#include <netinet/in.h>
#ifdef _XOPEN_SOURCE_EXTENDED
#include <arpa/inet.h>
#endif
#endif

#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <future>

/** Maximum size of http request (request line + headers) */
static const size_t MAX_HEADERS_SIZE = 8192;

/**
 * Maximum HTTP post body size. Twice the maximum block size is added to this
 * value in practice.
 */
static const size_t MIN_SUPPORTED_BODY_SIZE = 0x02000000;

struct HTTPPathHandler {
    HTTPPathHandler() {}
    HTTPPathHandler(std::string _prefix, bool _exactMatch,
                    HTTPRequestHandler _handler)
        : prefix(_prefix), exactMatch(_exactMatch), handler(_handler) {}
    std::string prefix;
    bool exactMatch;
    HTTPRequestHandler handler;
};

/** HTTP module state */

//! libevent event loop
static struct event_base *eventBase = 0;
//! HTTP server
struct evhttp *eventHTTP = 0;
//! List of subnets to allow RPC connections from
static std::vector<CSubNet> rpc_allow_subnets;
//! Work queue for handling longer requests off the event loop thread
static std::unique_ptr<CThreadPool<CQueueAdaptor>> pWorkQueue {nullptr};
//! Handlers for (sub)paths
std::vector<HTTPPathHandler> pathHandlers;
//! Bound listening sockets
std::vector<evhttp_bound_socket *> boundSockets;

/** Check if a network address is allowed to access the HTTP server */
static bool ClientAllowed(const CNetAddr &netaddr) {
    if (!netaddr.IsValid()) return false;
    for (const CSubNet &subnet : rpc_allow_subnets)
        if (subnet.Match(netaddr)) return true;
    return false;
}

/** Initialize ACL list for HTTP server */
static bool InitHTTPAllowList() {
    rpc_allow_subnets.clear();
    CNetAddr localv4;
    CNetAddr localv6;
    LookupHost("127.0.0.1", localv4, false);
    LookupHost("::1", localv6, false);
    // always allow IPv4 local subnet.
    rpc_allow_subnets.push_back(CSubNet(localv4, 8));
    // always allow IPv6 localhost.
    rpc_allow_subnets.push_back(CSubNet(localv6));
    if (gArgs.IsArgSet("-rpcallowip")) {
        for (const std::string &strAllow : gArgs.GetArgs("-rpcallowip")) {
            CSubNet subnet;
            LookupSubNet(strAllow.c_str(), subnet);
            if (!subnet.IsValid()) {
                uiInterface.ThreadSafeMessageBox(
                    strprintf("Invalid -rpcallowip subnet specification: %s. "
                              "Valid are a single IP (e.g. 1.2.3.4), a "
                              "network/netmask (e.g. 1.2.3.4/255.255.255.0) or "
                              "a network/CIDR (e.g. 1.2.3.4/24).",
                              strAllow),
                    "", CClientUIInterface::MSG_ERROR);
                return false;
            }
            rpc_allow_subnets.push_back(subnet);
        }
    }
    std::string strAllowed;
    for (const CSubNet &subnet : rpc_allow_subnets)
        strAllowed += subnet.ToString() + " ";
    LogPrint(BCLog::HTTP, "Allowing HTTP connections from: %s\n", strAllowed);
    return true;
}

/** HTTP request method as string - use for logging only */
static std::string RequestMethodString(HTTPRequest::RequestMethod m) {
    switch (m) {
        case HTTPRequest::GET:
            return "GET";
        case HTTPRequest::POST:
            return "POST";
        case HTTPRequest::HEAD:
            return "HEAD";
        case HTTPRequest::PUT:
            return "PUT";
        case HTTPRequest::OPTIONS:
            return "OPTIONS";
        default:
            return "unknown";
    }
}

/** HTTP request callback */
static void http_request_cb(struct evhttp_request *req, void *arg) {
    Config &config = *reinterpret_cast<Config *>(arg);

    std::shared_ptr<HTTPRequest> hreq { std::make_shared<HTTPRequest>(req) };

    LogPrint(BCLog::HTTP, "Received a %s request for %s from %s\n",
             RequestMethodString(hreq->GetRequestMethod()), hreq->GetURI(),
             hreq->GetPeer().ToString());

    // Early address-based allow check
    if (!ClientAllowed(hreq->GetPeer())) {
        hreq->WriteReply(HTTP_FORBIDDEN);
        return;
    }

    // Early reject unknown HTTP methods
    if (hreq->GetRequestMethod() == HTTPRequest::UNKNOWN) {
        hreq->WriteReply(HTTP_BADMETHOD);
        return;
    }

    // Find registered handler for prefix
    std::string strURI = hreq->GetURI();
    std::string path;
    std::vector<HTTPPathHandler>::const_iterator i = pathHandlers.begin();
    std::vector<HTTPPathHandler>::const_iterator iend = pathHandlers.end();
    for (; i != iend; ++i) {
        bool match = false;
        if (i->exactMatch) {
            match = (strURI == i->prefix);
        } else {
            match = (strURI.substr(0, i->prefix.size()) == i->prefix);
        }
        if (match) {
            path = strURI.substr(i->prefix.size());
            break;
        }
    }

    // Dispatch to worker thread.
    if (i != iend) {
        size_t workQueueDepth = std::max(static_cast<size_t>(gArgs.GetArg("-rpcworkqueue", DEFAULT_HTTP_WORKQUEUE)), size_t{1});

        assert(pWorkQueue);
        if(pWorkQueue->getTaskDepth() < workQueueDepth) {
            auto handleTask = [&config, hreq = std::move(hreq), path, handler = i->handler]()
            {
                handler(config, hreq.get(), path);
            };
            make_task(*pWorkQueue, std::move(handleTask));
        }
        else {
            LogPrintf("WARNING: request rejected because http work queue depth "
                      "exceeded, it can be increased with the -rpcworkqueue= "
                      "setting\n");
            hreq->WriteReply(HTTP_INTERNAL, "Work queue depth exceeded");
        }
    } else {
        hreq->WriteReply(HTTP_NOTFOUND);
    }
}

/** Callback to reject HTTP requests after shutdown. */
static void http_reject_request_cb(struct evhttp_request *req, void *) {
    LogPrint(BCLog::HTTP, "Rejecting request while shutting down\n");
    evhttp_send_error(req, HTTP_SERVUNAVAIL, nullptr);
}

/** Event dispatcher thread */
static bool ThreadHTTP(struct event_base *base, struct evhttp *http) {
    RenameThread("http");
    LogPrint(BCLog::HTTP, "Entering http event loop\n");
    event_base_dispatch(base);
    // Event loop will be interrupted by InterruptHTTPServer()
    LogPrint(BCLog::HTTP, "Exited http event loop\n");
    return event_base_got_break(base) == 0;
}

/** Bind HTTP server to specified addresses */
static bool HTTPBindAddresses(struct evhttp *http) {
    int defaultPort = gArgs.GetArg("-rpcport", BaseParams().RPCPort());
    std::vector<std::pair<std::string, uint16_t>> endpoints;

    // Determine what addresses to bind to
    if (!gArgs.IsArgSet("-rpcallowip")) {
        // Default to loopback if not allowing external IPs.
        endpoints.push_back(std::make_pair("::1", defaultPort));
        endpoints.push_back(std::make_pair("127.0.0.1", defaultPort));
        if (gArgs.IsArgSet("-rpcbind")) {
            LogPrintf("WARNING: option -rpcbind was ignored because "
                      "-rpcallowip was not specified, refusing to allow "
                      "everyone to connect\n");
        }
    } else if (gArgs.IsArgSet("-rpcbind")) {
        // Specific bind address.
        for (const std::string &strRPCBind : gArgs.GetArgs("-rpcbind")) {
            int port = defaultPort;
            std::string host;
            SplitHostPort(strRPCBind, port, host);
            endpoints.push_back(std::make_pair(host, port));
        }
    } else {
        // No specific bind address specified, bind to any.
        endpoints.push_back(std::make_pair("::", defaultPort));
        endpoints.push_back(std::make_pair("0.0.0.0", defaultPort));
    }

    // Bind addresses
    for (std::vector<std::pair<std::string, uint16_t>>::iterator i =
             endpoints.begin();
         i != endpoints.end(); ++i) {
        LogPrint(BCLog::HTTP, "Binding RPC on address %s port %i\n", i->first,
                 i->second);
        evhttp_bound_socket *bind_handle = evhttp_bind_socket_with_handle(
            http, i->first.empty() ? nullptr : i->first.c_str(), i->second);
        if (bind_handle) {
            boundSockets.push_back(bind_handle);
        } else {
            LogPrintf("Binding RPC on address %s port %i failed.\n", i->first,
                      i->second);
        }
    }
    return !boundSockets.empty();
}

/** libevent event log callback */
static void libevent_log_cb(int severity, const char *msg) {
#ifndef EVENT_LOG_WARN
// EVENT_LOG_WARN was added in 2.0.19; but before then _EVENT_LOG_WARN existed.
#define EVENT_LOG_WARN _EVENT_LOG_WARN
#endif
    // Log warn messages and higher without debug category.
    if (severity >= EVENT_LOG_WARN) {
        LogPrintf("libevent: %s\n", msg);
    } else {
        LogPrint(BCLog::LIBEVENT, "libevent: %s\n", msg);
    }
}

ev_ssize_t GetMaxBodySizeSafe(uint64_t maxBlockSize)
{    
    ev_ssize_t maxBodySize{ 0 };
    constexpr auto maxSsize = std::numeric_limits<ev_ssize_t>::max();
    if (maxBlockSize > (maxSsize / 2 - MIN_SUPPORTED_BODY_SIZE))
    {
        maxBodySize = maxSsize;
    }
    else
    {
        maxBodySize = MIN_SUPPORTED_BODY_SIZE + 2 * maxBlockSize;
    }
    return maxBodySize;
}

bool InitHTTPServer(Config &config) {
    struct evhttp *http = 0;
    struct event_base *base = 0;

    if (!InitHTTPAllowList()) return false;

    if (gArgs.GetBoolArg("-rpcssl", false)) {
        uiInterface.ThreadSafeMessageBox(
            "SSL mode for RPC (-rpcssl) is no longer supported.", "",
            CClientUIInterface::MSG_ERROR);
        return false;
    }

    // Redirect libevent's logging to our own log
    event_set_log_callback(&libevent_log_cb);
#if LIBEVENT_VERSION_NUMBER >= 0x02010100
    // If -debug=libevent, set full libevent debugging.
    // Otherwise, disable all libevent debugging.
    if (LogAcceptCategory(BCLog::LIBEVENT)) {
        event_enable_debug_logging(EVENT_DBG_ALL);
    } else {
        event_enable_debug_logging(EVENT_DBG_NONE);
    }
#endif
#ifdef WIN32
    evthread_use_windows_threads();
#else
    evthread_use_pthreads();
#endif

    // XXX RAII
    base = event_base_new();
    if (!base) {
        LogPrintf("Couldn't create an event_base: exiting\n");
        return false;
    }

    /* Create a new evhttp object to handle requests. */
    // XXX RAII
    http = evhttp_new(base);
    if (!http) {
        LogPrintf("couldn't create evhttp. Exiting.\n");
        event_base_free(base);
        return false;
    }

    evhttp_set_timeout(
        http, gArgs.GetArg("-rpcservertimeout", DEFAULT_HTTP_SERVER_TIMEOUT));
    evhttp_set_max_headers_size(http, MAX_HEADERS_SIZE);
    evhttp_set_max_body_size(http, GetMaxBodySizeSafe(config.GetMaxBlockSize()));
    evhttp_set_gencb(http, http_request_cb, &config);

    // Only POST and OPTIONS are supported, but we return HTTP 405 for the
    // others
    evhttp_set_allowed_methods(http,
                               EVHTTP_REQ_GET | EVHTTP_REQ_POST |
                                   EVHTTP_REQ_HEAD | EVHTTP_REQ_PUT |
                                   EVHTTP_REQ_DELETE | EVHTTP_REQ_OPTIONS);

    if (!HTTPBindAddresses(http)) {
        LogPrintf("Unable to bind any endpoint for RPC server\n");
        evhttp_free(http);
        event_base_free(base);
        return false;
    }

    eventBase = base;
    eventHTTP = http;
    LogPrint(BCLog::HTTP, "Initialized HTTP server\n");

    int rpcThreads = std::max(static_cast<long>(gArgs.GetArg("-rpcthreads", DEFAULT_HTTP_THREADS)), 1L);
    LogPrintf("HTTP: creating work queue with %d threads\n", rpcThreads);
    pWorkQueue = std::make_unique<CThreadPool<CQueueAdaptor>>(true, "HTTPServer", rpcThreads);

    return true;
}

std::thread threadHTTP;
std::future<bool> threadResult;

bool StartHTTPServer() {
    LogPrint(BCLog::HTTP, "Starting HTTP server\n");
    std::packaged_task<bool(event_base *, evhttp *)> task(ThreadHTTP);
    threadResult = task.get_future();
    threadHTTP = std::thread(std::move(task), eventBase, eventHTTP);

    return true;
}

void InterruptHTTPServer() {
    LogPrint(BCLog::HTTP, "Interrupting HTTP server\n");
    if (eventHTTP) {
        // Unlisten sockets
        for (evhttp_bound_socket *socket : boundSockets) {
            evhttp_del_accept_socket(eventHTTP, socket);
        }
        // Reject requests on current connections
        evhttp_set_gencb(eventHTTP, http_reject_request_cb, nullptr);
    }

    if (pWorkQueue)
        pWorkQueue->pause();
}

void StopHTTPServer() {
    LogPrint(BCLog::HTTP, "Stopping HTTP server\n");
    if (pWorkQueue) {
        LogPrint(BCLog::HTTP, "Waiting for HTTP worker threads to exit\n");
        pWorkQueue.reset();
    }
    if (eventBase) {
        LogPrint(BCLog::HTTP, "Waiting for HTTP event thread to exit\n");
        // Give event loop a few seconds to exit (to send back last RPC
        // responses), then break it. Before this was solved with
        // event_base_loopexit, but that didn't work as expected in at least
        // libevent 2.0.21 and always introduced a delay. In libevent master
        // that appears to be solved, so in the future that solution could be
        // used again (if desirable).
        // (see discussion in https://github.com/bitcoin/bitcoin/pull/6990)
        if (threadResult.valid() &&
            threadResult.wait_for(std::chrono::milliseconds(2000)) ==
                std::future_status::timeout) {
            LogPrintf("HTTP event loop did not exit within allotted time, "
                      "sending loopbreak\n");
            event_base_loopbreak(eventBase);
        }
        threadHTTP.join();
    }
    if (eventHTTP) {
        evhttp_free(eventHTTP);
        eventHTTP = 0;
    }
    if (eventBase) {
        event_base_free(eventBase);
        eventBase = 0;
    }
    LogPrint(BCLog::HTTP, "Stopped HTTP server\n");
}

struct event_base *EventBase() {
    return eventBase;
}

// this callback is called after successful or failed transmission
static void httpevent_callback_fn(evutil_socket_t, short, void *data) {
    // Static handler: simply call inner handler
    HTTPEvent *self = ((HTTPEvent *)data);
    self->handler();
    if (self->deleteWhenTriggered) delete self;
}

HTTPEvent::HTTPEvent(struct event_base *base, bool _deleteWhenTriggered,
                     const std::function<void(void)> &_handler)
    : deleteWhenTriggered(_deleteWhenTriggered), handler(_handler) {
    ev = event_new(base, -1, 0, httpevent_callback_fn, this);
    assert(ev);
}
HTTPEvent::~HTTPEvent() {
    event_free(ev);
}
void HTTPEvent::trigger(struct timeval *tv) {
    if (tv == nullptr) {
        // Immediately trigger event in main thread.
        event_active(ev, 0, 0);
    } else {
        // Trigger after timeval passed.
        evtimer_add(ev, tv);
    }
}
HTTPRequest::HTTPRequest(struct evhttp_request *_req)
    : req(_req), replySent(false) {}
HTTPRequest::~HTTPRequest() {
    if (!replySent) {
        // Keep track of whether reply was sent to avoid request leaks
        LogPrintf("%s: Unhandled request\n", __func__);
        WriteReply(HTTP_INTERNAL, "Unhandled request");
    }
    // evhttpd cleans up the request, as long as a reply was sent.
}

std::pair<bool, std::string> HTTPRequest::GetHeader(const std::string &hdr) {
    const struct evkeyvalq *headers = evhttp_request_get_input_headers(req);
    assert(headers);
    const char *val = evhttp_find_header(headers, hdr.c_str());
    if (val)
        return std::make_pair(true, val);
    else
        return std::make_pair(false, "");
}

std::string HTTPRequest::ReadBody() {
    struct evbuffer *buf = evhttp_request_get_input_buffer(req);
    if (!buf) return "";
    size_t size = evbuffer_get_length(buf);
    /** Trivial implementation: if this is ever a performance bottleneck,
     * internal copying can be avoided in multi-segment buffers by using
     * evbuffer_peek and an awkward loop. Though in that case, it'd be even
     * better to not copy into an intermediate string but use a stream
     * abstraction to consume the evbuffer on the fly in the parsing algorithm.
     */
    const char *data = (const char *)evbuffer_pullup(buf, size);
    // returns nullptr in case of empty buffer.
    if (!data) {
        return "";
    }
    std::string rv(data, size);
    evbuffer_drain(buf, size);
    return rv;
}

void HTTPRequest::WriteHeader(const std::string &hdr,
                              const std::string &value) {
    struct evkeyvalq *headers = evhttp_request_get_output_headers(req);
    assert(headers);
    evhttp_add_header(headers, hdr.c_str(), value.c_str());
}

/** Closure sent to main thread to request a reply to be sent to a HTTP request.
 * Replies must be sent in the main loop in the main http thread, this cannot be
 * done from worker threads.
 */
void HTTPRequest::WriteReply(int nStatus, const std::string &strReply) {
    assert(!replySent && req);
    // Send event to main http thread to send reply message
    struct evbuffer *evb = evhttp_request_get_output_buffer(req);
    assert(evb);
    evbuffer_add(evb, strReply.data(), strReply.size());
    HTTPEvent *ev =
        new HTTPEvent(eventBase, true, std::bind(evhttp_send_reply, req,
                                                 nStatus, (const char *)nullptr,
                                                 (struct evbuffer *)nullptr));
    ev->trigger(0);
    replySent = true;
    // transferred back to main thread.
    req = 0;
}

void HTTPRequest::StartWritingChunks(int nStatus) {
    HTTPEvent *ev = new HTTPEvent(eventBase, true, std::bind(evhttp_send_reply_start, req, nStatus, (const char *)nullptr));
    ev->trigger(nullptr);
}

void HTTPRequest::WriteReplyChunk(std::string_view strReply) {
    struct evbuffer *evb = evbuffer_new();
    evbuffer_add(evb, strReply.data(), strReply.length());

    // Send event to main http thread to send reply message
    HTTPEvent *ev = new HTTPEvent(eventBase, true, std::bind(evhttp_send_reply_chunk, req, evb));
    ev->trigger(nullptr);

    HTTPEvent *evDel = new HTTPEvent(eventBase, true, std::bind(evbuffer_free, evb));
    evDel->trigger(nullptr);
}

void HTTPRequest::StopWritingChunks() {
    HTTPEvent *ev = new HTTPEvent(eventBase, true, std::bind(evhttp_send_reply_end, req));
    ev->trigger(nullptr);

    replySent = true;
    req = 0;
}

CService HTTPRequest::GetPeer() {
    evhttp_connection *con = evhttp_request_get_connection(req);
    CService peer;
    if (con) {
        // evhttp retains ownership over returned address string
        char * address = nullptr;
        uint16_t port = 0;
        evhttp_connection_get_peer(con, &address, &port);
        peer = LookupNumeric(address, port);
    }
    return peer;
}

std::string HTTPRequest::GetURI() {
    return evhttp_request_get_uri(req);
}

HTTPRequest::RequestMethod HTTPRequest::GetRequestMethod() {
    switch (evhttp_request_get_command(req)) {
        case EVHTTP_REQ_GET:
            return GET;
        case EVHTTP_REQ_POST:
            return POST;
        case EVHTTP_REQ_HEAD:
            return HEAD;
        case EVHTTP_REQ_PUT:
            return PUT;
        case EVHTTP_REQ_OPTIONS:
            return OPTIONS;
        default:
            return UNKNOWN;
    }
}

void RegisterHTTPHandler(const std::string &prefix, bool exactMatch,
                         const HTTPRequestHandler &handler) {
    LogPrint(BCLog::HTTP, "Registering HTTP handler for %s (exactmatch %d)\n",
             prefix, exactMatch);
    pathHandlers.push_back(HTTPPathHandler(prefix, exactMatch, handler));
}

void UnregisterHTTPHandler(const std::string &prefix, bool exactMatch) {
    std::vector<HTTPPathHandler>::iterator i = pathHandlers.begin();
    std::vector<HTTPPathHandler>::iterator iend = pathHandlers.end();
    for (; i != iend; ++i)
        if (i->prefix == prefix && i->exactMatch == exactMatch) break;
    if (i != iend) {
        LogPrint(BCLog::HTTP,
                 "Unregistering HTTP handler for %s (exactmatch %d)\n", prefix,
                 exactMatch);
        pathHandlers.erase(i);
    }
}