From: Junio C Hamano <gitster@pobox.com>
To: Jeff King <peff@peff.net>
Cc: David Turner <dturner@twosigma.com>,
git@vger.kernel.org, spearce@spearce.org
Subject: Re: [PATCH] remote-curl: don't hang when a server dies before any output
Date: Mon, 14 Nov 2016 13:19:49 -0800 [thread overview]
Message-ID: <xmqqpolxwyh6.fsf@gitster.mtv.corp.google.com> (raw)
In-Reply-To: <20161114194049.mktpsvgdhex2f4zv@sigill.intra.peff.net> (Jeff King's message of "Mon, 14 Nov 2016 14:40:49 -0500")
Jeff King <peff@peff.net> writes:
> So something like this. It turned out to be a lot uglier than I had
> hoped because we get fed the data from curl in odd-sized chunks, so we
> need a state machine.
It is unfortunate that we have to snoop the protocol like this to
infer an error, but I do not think we can do better than that
approach. FWIW, I did not find the logic in update_pktline_state()
you wrote ugly at all.
Having to assume that the end of each round from the other end must
be a FLUSH does feel somewhat ugly and brittle, though.
> diff --git a/remote-curl.c b/remote-curl.c
> index f14c41f4c..605357d77 100644
> --- a/remote-curl.c
> +++ b/remote-curl.c
> @@ -403,6 +403,18 @@ struct rpc_state {
> struct strbuf result;
> unsigned gzip_request : 1;
> unsigned initial_buffer : 1;
> +
> + enum {
> + RPC_PKTLINE_ERROR, /* bogus hex chars in length */
> + RPC_PKTLINE_INITIAL, /* no packets received yet */
> + RPC_PKTLINE_1, /* got one hex char */
> + RPC_PKTLINE_2, /* got two hex chars */
> + RPC_PKTLINE_3, /* got three hex chars */
> + RPC_PKTLINE_DATA, /* reading data; pktline_len holds remaining */
> + RPC_PKTLINE_END_OF_PACKET, /* last packet completed */
> + RPC_PKTLINE_FLUSH, /* last packet was flush */
> + } pktline_state;
> + size_t pktline_len;
> };
>
> static size_t rpc_out(void *ptr, size_t eltsize,
> @@ -451,11 +463,77 @@ static curlioerr rpc_ioctl(CURL *handle, int cmd, void *clientp)
> }
> #endif
>
> +static void update_pktline_state(struct rpc_state *rpc,
> + const char *buf, size_t len)
> +{
> +#define READ_ONE_HEX(shift) do { \
> + int val = hexval(buf[0]); \
> + if (val < 0) { \
> + warning("error on %d", *buf); \
> + rpc->pktline_state = RPC_PKTLINE_ERROR; \
> + return; \
> + } \
> + rpc->pktline_len |= val << shift; \
> + buf++; \
> + len--; \
> +} while(0)
> +
> + while (len > 0) {
> + switch (rpc->pktline_state) {
> + case RPC_PKTLINE_ERROR:
> + /* previous error; there is no recovery */
> + return;
> +
> + /* We can start a new pktline at any of these states */
> + case RPC_PKTLINE_INITIAL:
> + case RPC_PKTLINE_FLUSH:
> + case RPC_PKTLINE_END_OF_PACKET:
> + rpc->pktline_len = 0;
> + READ_ONE_HEX(12);
> + rpc->pktline_state = RPC_PKTLINE_1;
> + break;
> +
> + case RPC_PKTLINE_1:
> + READ_ONE_HEX(8);
> + rpc->pktline_state = RPC_PKTLINE_2;
> + break;
> +
> + case RPC_PKTLINE_2:
> + READ_ONE_HEX(4);
> + rpc->pktline_state = RPC_PKTLINE_3;
> + break;
> +
> + case RPC_PKTLINE_3:
> + READ_ONE_HEX(0);
> + if (rpc->pktline_len) {
> + rpc->pktline_state = RPC_PKTLINE_DATA;
> + rpc->pktline_len -= 4;
> + } else
> + rpc->pktline_state = RPC_PKTLINE_FLUSH;
> + break;
> +
> + case RPC_PKTLINE_DATA:
> + if (len < rpc->pktline_len) {
> + rpc->pktline_len -= len;
> + len = 0;
> + } else {
> + buf += rpc->pktline_len;
> + len -= rpc->pktline_len;
> + rpc->pktline_len = 0;
> + rpc->pktline_state = RPC_PKTLINE_END_OF_PACKET;
> + }
> + break;
> + }
> + }
> +#undef READ_ONE_HEX
> +}
> +
> static size_t rpc_in(char *ptr, size_t eltsize,
> size_t nmemb, void *buffer_)
> {
> size_t size = eltsize * nmemb;
> struct rpc_state *rpc = buffer_;
> + update_pktline_state(rpc, ptr, size);
> write_or_die(rpc->in, ptr, size);
> return size;
> }
> @@ -659,6 +737,8 @@ static int post_rpc(struct rpc_state *rpc)
> curl_easy_setopt(slot->curl, CURLOPT_WRITEFUNCTION, rpc_in);
> curl_easy_setopt(slot->curl, CURLOPT_FILE, rpc);
>
> + rpc->pktline_state = RPC_PKTLINE_INITIAL;
> +
> err = run_slot(slot, NULL);
> if (err == HTTP_REAUTH && !large_request) {
> credential_fill(&http_auth);
> @@ -667,6 +747,11 @@ static int post_rpc(struct rpc_state *rpc)
> if (err != HTTP_OK)
> err = -1;
>
> + if (rpc->pktline_state != RPC_PKTLINE_FLUSH) {
> + error("invalid or truncated response from http server");
> + err = -1;
> + }
> +
> curl_slist_free_all(headers);
> free(gzip_body);
> return err;
next prev parent reply other threads:[~2016-11-14 21:19 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-09 22:18 [PATCH] remote-curl: don't hang when a server dies before any output David Turner
2016-11-14 18:24 ` Jeff King
2016-11-14 19:40 ` Jeff King
2016-11-14 21:19 ` Junio C Hamano [this message]
2016-11-14 21:33 ` Jeff King
2016-11-14 23:25 ` David Turner
2016-11-14 23:48 ` Jeff King
2016-11-15 15:45 ` David Turner
2016-11-15 0:44 ` Jeff King
2016-11-15 1:02 ` Junio C Hamano
2016-11-15 3:58 ` Jeff King
2016-11-15 17:42 ` Junio C Hamano
2016-11-18 17:01 ` Jeff King
2016-11-18 17:04 ` David Turner
2016-11-18 17:08 ` Jeff King
2016-11-18 17:48 ` David Turner
2016-11-18 18:28 ` Junio C Hamano
2016-11-15 2:40 ` Jeff King
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