http: prefer CURLOPT_SEEKFUNCTION to CURLOPT_IOCTLFUNCTION

The IOCTLFUNCTION option has been deprecated, and generates a compiler
warning in recent versions of curl. We can switch to using SEEKFUNCTION
instead. It was added in 2008 via curl 7.18.0; our INSTALL file already
indicates we require at least curl 7.19.4.

But there's one catch: curl says we should use CURL_SEEKFUNC_{OK,FAIL},
and those didn't arrive until 7.19.5. One workaround would be to use a
bare 0/1 here (or define our own macros).  But let's just bump the
minimum required version to 7.19.5. That version is only a minor version
bump from our existing requirement, and is only a 2 month time bump for
versions that are almost 13 years old. So it's not likely that anybody
cares about the distinction.

Switching means we have to rewrite the ioctl functions into seek
functions. In some ways they are simpler (seeking is the only
operation), but in some ways more complex (the ioctl allowed only a full
rewind, but now we can seek to arbitrary offsets).

Curl will only ever use SEEK_SET (per their documentation), so I didn't
bother implementing anything else, since it would naturally be
completely untested. This seems unlikely to change, but I added an
assertion just in case.

Likewise, I doubt curl will ever try to seek outside of the buffer sizes
we've told it, but I erred on the defensive side here, rather than do an
out-of-bounds read.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

INSTALL

@@ -139,7 +139,7 @@ Issues of note:
 	  not need that functionality, use NO_CURL to build without
 	  it.
 
-	  Git requires version "7.19.4" or later of "libcurl" to build
+	  Git requires version "7.19.5" or later of "libcurl" to build
 	  without NO_CURL. This version requirement may be bumped in
 	  the future.
 

http-push.c

@@ -203,8 +203,8 @@ static void curl_setup_http(CURL *curl, const char *url,
 	curl_easy_setopt(curl, CURLOPT_INFILE, buffer);
 	curl_easy_setopt(curl, CURLOPT_INFILESIZE, buffer->buf.len);
 	curl_easy_setopt(curl, CURLOPT_READFUNCTION, fread_buffer);
-	curl_easy_setopt(curl, CURLOPT_IOCTLFUNCTION, ioctl_buffer);
-	curl_easy_setopt(curl, CURLOPT_IOCTLDATA, buffer);
+	curl_easy_setopt(curl, CURLOPT_SEEKFUNCTION, seek_buffer);
+	curl_easy_setopt(curl, CURLOPT_SEEKDATA, buffer);
 	curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_fn);
 	curl_easy_setopt(curl, CURLOPT_NOBODY, 0);
 	curl_easy_setopt(curl, CURLOPT_CUSTOMREQUEST, custom_req);

http.c

@@ -157,21 +157,19 @@ size_t fread_buffer(char *ptr, size_t eltsize, size_t nmemb, void *buffer_)
 	return size / eltsize;
 }
 
-curlioerr ioctl_buffer(CURL *handle, int cmd, void *clientp)
+int seek_buffer(void *clientp, curl_off_t offset, int origin)
 {
 	struct buffer *buffer = clientp;
 
-	switch (cmd) {
-	case CURLIOCMD_NOP:
-		return CURLIOE_OK;
-
-	case CURLIOCMD_RESTARTREAD:
-		buffer->posn = 0;
-		return CURLIOE_OK;
-
-	default:
-		return CURLIOE_UNKNOWNCMD;
+	if (origin != SEEK_SET)
+		BUG("seek_buffer only handles SEEK_SET");
+	if (offset < 0 || offset >= buffer->buf.len) {
+		error("curl seek would be outside of buffer");
+		return CURL_SEEKFUNC_FAIL;
 	}
+
+	buffer->posn = offset;
+	return CURL_SEEKFUNC_OK;
 }
 
 size_t fwrite_buffer(char *ptr, size_t eltsize, size_t nmemb, void *buffer_)

http.h

@@ -40,7 +40,7 @@ struct buffer {
 size_t fread_buffer(char *ptr, size_t eltsize, size_t nmemb, void *strbuf);
 size_t fwrite_buffer(char *ptr, size_t eltsize, size_t nmemb, void *strbuf);
 size_t fwrite_null(char *ptr, size_t eltsize, size_t nmemb, void *strbuf);
-curlioerr ioctl_buffer(CURL *handle, int cmd, void *clientp);
+int seek_buffer(void *clientp, curl_off_t offset, int origin);
 
 /* Slot lifecycle functions */
 struct active_request_slot *get_active_slot(void);

remote-curl.c

@@ -717,25 +717,23 @@ static size_t rpc_out(void *ptr, size_t eltsize,
 	return avail;
 }
 
-static curlioerr rpc_ioctl(CURL *handle, int cmd, void *clientp)
+static int rpc_seek(void *clientp, curl_off_t offset, int origin)
 {
 	struct rpc_state *rpc = clientp;
 
-	switch (cmd) {
-	case CURLIOCMD_NOP:
-		return CURLIOE_OK;
+	if (origin != SEEK_SET)
+		BUG("rpc_seek only handles SEEK_SET, not %d", origin);
 
-	case CURLIOCMD_RESTARTREAD:
-		if (rpc->initial_buffer) {
-			rpc->pos = 0;
-			return CURLIOE_OK;
+	if (rpc->initial_buffer) {
+		if (offset < 0 || offset > rpc->len) {
+			error("curl seek would be outside of rpc buffer");
+			return CURL_SEEKFUNC_FAIL;
 		}
-		error(_("unable to rewind rpc post data - try increasing http.postBuffer"));
-		return CURLIOE_FAILRESTART;
-
-	default:
-		return CURLIOE_UNKNOWNCMD;
+		rpc->pos = offset;
+		return CURL_SEEKFUNC_OK;
 	}
+	error(_("unable to rewind rpc post data - try increasing http.postBuffer"));
+	return CURL_SEEKFUNC_FAIL;
 }
 
 struct check_pktline_state {
@@ -959,8 +957,8 @@ retry:
 		rpc->initial_buffer = 1;
 		curl_easy_setopt(slot->curl, CURLOPT_READFUNCTION, rpc_out);
 		curl_easy_setopt(slot->curl, CURLOPT_INFILE, rpc);
-		curl_easy_setopt(slot->curl, CURLOPT_IOCTLFUNCTION, rpc_ioctl);
-		curl_easy_setopt(slot->curl, CURLOPT_IOCTLDATA, rpc);
+		curl_easy_setopt(slot->curl, CURLOPT_SEEKFUNCTION, rpc_seek);
+		curl_easy_setopt(slot->curl, CURLOPT_SEEKDATA, rpc);
 		if (options.verbosity > 1) {
 			fprintf(stderr, "POST %s (chunked)\n", rpc->service_name);
 			fflush(stderr);