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http2: fix stream window size after unpausing

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When pausing a HTTP/2 transfer, the stream's local window size
is reduced to 0 to prevent the server from sending further data
which curl cannot write out to the application.

When unpausing again, the stream's window size was not correctly
increased again. The attempt to trigger a window update was
ignored by nghttp2, the server never received it and the transfer
stalled.

Add a debug feature to allow use of small window sizes which
reproduces this bug in test_02_21.

Fixes #16955
Closes #16960
This commit is contained in:
Stefan Eissing 2025-04-04 10:43:13 +02:00 • committed by Daniel Stenberg
parent dac78ae638
commit 5fbd78eb2d
No known key found for this signature in database
GPG key ID: 5CC908FDB71E12C2
3 changed files with 61 additions and 2 deletions
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31
lib/http2.c
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@ -44,6 +44,7 @@
#include "connect.h"
#include "rand.h"
#include "strdup.h"
#include "strparse.h"
#include "transfer.h"
#include "dynbuf.h"
#include "headers.h"
@ -141,6 +142,9 @@ struct cf_h2_ctx {
uint32_t goaway_error; /* goaway error code from server */
int32_t remote_max_sid; /* max id processed by server */
int32_t local_max_sid; /* max id processed by us */
#ifdef DEBUGBUILD
int32_t stream_win_max; /* max h2 stream window size */
#endif
BIT(initialized);
BIT(via_h1_upgrade);
BIT(conn_closed);
@ -166,6 +170,18 @@ static void cf_h2_ctx_init(struct cf_h2_ctx *ctx, bool via_h1_upgrade)
Curl_hash_offt_init(&ctx->streams, 63, h2_stream_hash_free);
ctx->remote_max_sid = 2147483647;
ctx->via_h1_upgrade = via_h1_upgrade;
#ifdef DEBUGBUILD
{
const char *p = getenv("CURL_H2_STREAM_WIN_MAX");
ctx->stream_win_max = H2_STREAM_WINDOW_SIZE_MAX;
if(p) {
curl_off_t l;
if(!Curl_str_number(&p, &l, INT_MAX))
ctx->stream_win_max = (int32_t)l;
}
}
#endif
ctx->initialized = TRUE;
}
@ -285,7 +301,15 @@ static int32_t cf_h2_get_desired_local_win(struct Curl_cfilter *cf,
* This gets less precise the higher the latency. */
return (int32_t)data->set.max_recv_speed;
}
#ifdef DEBUGBUILD
else {
struct cf_h2_ctx *ctx = cf->ctx;
CURL_TRC_CF(data, cf, "stream_win_max=%d", ctx->stream_win_max);
return ctx->stream_win_max;
}
#else
return H2_STREAM_WINDOW_SIZE_MAX;
#endif
}
static CURLcode cf_h2_update_local_win(struct Curl_cfilter *cf,
@ -302,6 +326,13 @@ static CURLcode cf_h2_update_local_win(struct Curl_cfilter *cf,
int32_t wsize = nghttp2_session_get_stream_effective_local_window_size(
ctx->h2, stream->id);
if(dwsize > wsize) {
rv = nghttp2_session_set_local_window_size(ctx->h2, NGHTTP2_FLAG_NONE,
stream->id, dwsize);
if(rv) {
failf(data, "[%d] nghttp2 set_local_window_size(%d) failed: "
"%s(%d)", stream->id, dwsize, nghttp2_strerror(rv), rv);
return CURLE_HTTP2;
}
rv = nghttp2_submit_window_update(ctx->h2, NGHTTP2_FLAG_NONE,
stream->id, dwsize - wsize);
if(rv) {