[PATCH v2] http.c: use CURLOPT_RANGE for range requests

[David Turner <dturner@twopensource.com>]

A HTTP server is permitted to return a non-range response to a HTTP
range request (and Apache httpd in fact does this in some cases).
While libcurl knows how to correctly handle this (by skipping bytes
before and after the requested range), it only turns on this handling
if it is aware that a range request is being made.  By manually
setting the range header instead of using CURLOPT_RANGE, we were
hiding the fact that this was a range request from libcurl.  This
could cause corruption.

Signed-off-by: David Turner <dturner@twopensource.com>
---

This version applies on top of pu.  It also catches all of the range
requests instead of just the one that I happened to notice.

---
 http.c | 24 ++++++++----------------
 http.h |  1 -
 2 files changed, 8 insertions(+), 17 deletions(-)

diff --git a/http.c b/http.c
index 6b89dea..16610b9 100644
--- a/http.c
+++ b/http.c
@@ -30,7 +30,7 @@ static CURL *curl_default;
 #endif
 
 #define PREV_BUF_SIZE 4096
-#define RANGE_HEADER_SIZE 30
+#define RANGE_HEADER_SIZE 17
 
 char curl_errorstr[CURL_ERROR_SIZE];
 
@@ -1213,8 +1213,9 @@ static int http_request(const char *url,
 			curl_easy_setopt(slot->curl, CURLOPT_WRITEFUNCTION,
 					 fwrite);
 			if (posn > 0) {
-				strbuf_addf(&buf, "Range: bytes=%ld-", posn);
-				headers = curl_slist_append(headers, buf.buf);
+				strbuf_addf(&buf, "%ld-", posn);
+				curl_easy_setopt(slot->curl, CURLOPT_RANGE,
+						 &buf.buf);
 				strbuf_reset(&buf);
 			}
 		} else
@@ -1526,10 +1527,6 @@ void release_http_pack_request(struct http_pack_request *preq)
 		fclose(preq->packfile);
 		preq->packfile = NULL;
 	}
-	if (preq->range_header != NULL) {
-		curl_slist_free_all(preq->range_header);
-		preq->range_header = NULL;
-	}
 	preq->slot = NULL;
 	free(preq->url);
 	free(preq);
@@ -1631,10 +1628,8 @@ struct http_pack_request *new_http_pack_request(
 			fprintf(stderr,
 				"Resuming fetch of pack %s at byte %ld\n",
 				sha1_to_hex(target->sha1), prev_posn);
-		xsnprintf(range, sizeof(range), "Range: bytes=%ld-", prev_posn);
-		preq->range_header = curl_slist_append(NULL, range);
-		curl_easy_setopt(preq->slot->curl, CURLOPT_HTTPHEADER,
-			preq->range_header);
+		xsnprintf(range, sizeof(range), "%ld-", prev_posn);
+		curl_easy_setopt(preq->slot->curl, CURLOPT_RANGE, range);
 	}
 
 	return preq;
@@ -1685,7 +1680,6 @@ struct http_object_request *new_http_object_request(const char *base_url,
 	ssize_t prev_read = 0;
 	long prev_posn = 0;
 	char range[RANGE_HEADER_SIZE];
-	struct curl_slist *range_header = NULL;
 	struct http_object_request *freq;
 
 	freq = xcalloc(1, sizeof(*freq));
@@ -1791,10 +1785,8 @@ struct http_object_request *new_http_object_request(const char *base_url,
 			fprintf(stderr,
 				"Resuming fetch of object %s at byte %ld\n",
 				hex, prev_posn);
-		xsnprintf(range, sizeof(range), "Range: bytes=%ld-", prev_posn);
-		range_header = curl_slist_append(range_header, range);
-		curl_easy_setopt(freq->slot->curl,
-				 CURLOPT_HTTPHEADER, range_header);
+		xsnprintf(range, sizeof(range), "%ld-", prev_posn);
+		curl_easy_setopt(freq->slot->curl, CURLOPT_RANGE, range);
 	}
 
 	return freq;
diff --git a/http.h b/http.h
index 49afe39..4f97b60 100644
--- a/http.h
+++ b/http.h
@@ -190,7 +190,6 @@ struct http_pack_request {
 	struct packed_git **lst;
 	FILE *packfile;
 	char tmpfile[PATH_MAX];
-	struct curl_slist *range_header;
 	struct active_request_slot *slot;
 };
 
-- 
2.4.2.691.g714732c-twtrsrc