[PATCH v2 1/5] remote-curl: avoid hang if curl asks for more data after eof
- From
Jiří Hruška <jirka@fud.cz>
- Date
- Nov 15, 2023, 03:34 UTC
- Message-ID
- <CAGE_+C4JWA0DrcV4rT7J6hXsbYPL2Po31wFPvLESe_sKq_16FQ@mail.gmail.com>
- In-Reply-To
- <20231115033121.939-1-jirka@fud.cz>
It has been observed that under some circumstances, libcurl can call our `CURLOPT_READFUNCTION` callback `rpc_out()` again even after already getting a return value of zero (EOF) back once before.
Because `rpc->flush_read_but_not_sent` is reset to false immediately the first time an EOF is returned, the repeated call goes again to `rpc_read_from_out()`, which tries to read more from the child process pipe and the whole operation gets stuck - the child process is already trying to read a response back and will not write anything to the output pipe anymore, while the parent/remote process is now blocked waiting to read more too and never even finishes sending the request.
The bug is fixed by moving the reset of the `flush_read_but_not_sent` flag to `post_rpc()`, only before `rpc_out()` would be potentially used the next time. This makes the callback behave like fread() and return a zero any number of times at the end of a finished upload.
Signed-off-by: Jiri Hruska <jirka@fud.cz> --- remote-curl.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/remote-curl.c b/remote-curl.c index ef05752ca5..199c4615a5 100644 --- a/remote-curl.c +++ b/remote-curl.c @@ -705,9 +705,10 @@ static size_t rpc_out(void *ptr, size_t eltsize, * The line length either does not need to be sent at * all or has already been completely sent. Now we can * return 0, indicating EOF, meaning that the flush has - * been fully sent. + * been fully sent. It is important to keep returning 0 + * as long as needed in that case, as libcurl invokes + * the callback multiple times at EOF sometimes. */ - rpc->flush_read_but_not_sent = 0; return 0; } /* @@ -963,6 +964,7 @@ static int post_rpc(struct rpc_state *rpc, int stateless_connect, int flush_rece */ headers = curl_slist_append(headers, "Transfer-Encoding: chunked"); rpc->initial_buffer = 1; + rpc->flush_read_but_not_sent = 0; curl_easy_setopt(slot->curl, CURLOPT_READFUNCTION, rpc_out); curl_easy_setopt(slot->curl, CURLOPT_INFILE, rpc); curl_easy_setopt(slot->curl, CURLOPT_SEEKFUNCTION, rpc_seek);
-- 2.42.1.5.g2f21867bd5