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CURLOPT_WS_OPTIONS(3) documents that in raw mode (CURLWS_RAW_MODE), libcurl does not handle pings or any other frame for the application. Previously, auto_pong only checked !data->set.ws_no_auto_pong, ignoring data->set.ws_raw_mode. As a result, receiving a PING in raw mode caused libcurl to intercept the frame, discard it from the application stream, and queue an automatic PONG into ws->pending. When sending raw data via curl_ws_send(), ws_flush() would inject this unexpected PONG control frame into the application's raw stream, corrupting message framing. Disable auto_pong whenever ws_raw_mode is active.
bagder
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Sep 22, 2026
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🟡 Changes recommended
The connect-only raw-mode regression needs automated test coverage.
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Review effort: Balanced
Findings: 1
What changed in this PR
Prevents automatic WebSocket PONG handling in raw mode.
Changes:
- Disables auto-PONG in callback and
curl_ws_recv()paths when raw mode is enabled.
| File | Description |
|---|---|
lib/ws.c |
Adds raw-mode checks to auto-PONG logic. |
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| struct ws_collect *ctx = userp; | ||
| struct Curl_easy *data = ctx->data; | ||
| bool auto_pong = !data->set.ws_no_auto_pong; | ||
| bool auto_pong = !data->set.ws_raw_mode && !data->set.ws_no_auto_pong; |
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Summary
According to
CURLOPT_WS_OPTIONS(3):However, in
lib/ws.c(ws_cw_dec_next()andws_client_collect()),auto_pongwas computed as:which omitted checking
data->set.ws_raw_mode.Consequence
When receiving a WebSocket
PINGframe whileCURLWS_RAW_MODEis enabled:auto_pongevaluates totrue, causing libcurl to intercept thePINGframe and discard it from the application stream (ctx.writtenremains unset).PONGintows->pending.curl_ws_recv(), line 1689 checksif(!data->set.ws_raw_mode && ws->pending.type), intentionally skipping flushing pending control frames in raw mode. Consequently, the peer never receives a pong reply and may timeout.curl_ws_send(),ws_flush()callsws_enc_add_pending(), injecting the queuedPONGcontrol frame directly into the application's raw stream, corrupting user frame boundaries and protocol state.Fix
Disable
auto_pongwheneverws_raw_modeis active:Verified with
checksrc.pl(0 warnings).