[PATCH 2/3] Support for partial HTTP transfers

@@ -13,8 +13,12 @@
 #define curl_global_init(a) do { /* nothing */ } while(0)
 #endif
 
+#define PREV_BUF_SIZE 4096
+#define RANGE_HEADER_SIZE 30
+
 static CURL *curl;
 static struct curl_slist *no_pragma_header;
+static struct curl_slist *no_range_header;
 
 static char *initial_base;
 

@@ -351,14 +355,26 @@ int fetch_object(struct alt_base *repo, 
 	char *filename = sha1_file_name(sha1);
 	unsigned char real_sha1[20];
 	char tmpfile[PATH_MAX];
+	char prevfile[PATH_MAX];
 	int ret;
 	char *url;
 	char *posn;
+	int prevlocal;
+	unsigned char prev_buf[PREV_BUF_SIZE];
+	ssize_t prev_read = 0;
+	long prev_posn = 0;
+	char range[RANGE_HEADER_SIZE];
+	struct curl_slist *range_header = NULL;
+	CURLcode curl_result;
+
+	snprintf(tmpfile, sizeof(tmpfile), "%s.temp", filename);
+	snprintf(prevfile, sizeof(prevfile), "%s.prev", filename);
+	unlink(prevfile);
+	rename(tmpfile, prevfile);
+	unlink(tmpfile);
 
-	snprintf(tmpfile, sizeof(tmpfile), "%s/obj_XXXXXX",
-		 get_object_directory());
+	local = open(tmpfile, O_WRONLY | O_CREAT | O_EXCL, 0666);
 
-	local = mkstemp(tmpfile);
 	if (local < 0)
 		return error("Couldn't create temporary file %s for %s: %s\n",
 			     tmpfile, filename, strerror(errno));

@@ -386,8 +402,52 @@ int fetch_object(struct alt_base *repo, 
 
 	curl_easy_setopt(curl, CURLOPT_URL, url);
 
-	if (curl_easy_perform(curl)) {
-		unlink(filename);
+	/* If a previous temp file is present, process what was already
+	   fetched. */
+	prevlocal = open(prevfile, O_RDONLY);
+	if (prevlocal != -1) {
+		do {
+			prev_read = read(prevlocal, prev_buf, PREV_BUF_SIZE);
+			if (prev_read>0) {
+				if (fwrite_sha1_file(prev_buf,
+						     1,
+						     prev_read,
+						     NULL) == prev_read) {
+					prev_posn += prev_read;
+				} else {
+					prev_read = -1;
+				}
+			}
+		} while (prev_read > 0);
+		close(prevlocal);
+	}
+	unlink(prevfile);
+
+	/* Reset inflate/SHA1 if there was an error reading the previous temp
+	   file; also rewind to the beginning of the local file. */
+	if (prev_read == -1) {
+		memset(&stream, 0, sizeof(stream));
+		inflateInit(&stream);
+		SHA1_Init(&c);
+		if (prev_posn>0) {
+			prev_posn = 0;
+			lseek(local, SEEK_SET, 0);
+		}
+	}
+
+	/* If we have successfully processed data from a previous fetch
+	   attempt, only fetch the data we don't already have. */
+	if (prev_posn>0) {
+		sprintf(range, "Range: bytes=%ld-", prev_posn);
+		range_header = curl_slist_append(range_header, range);
+		curl_easy_setopt(curl, CURLOPT_HTTPHEADER, range_header);
+	}
+
+	/* Clear out the Range: header after performing the request, so
+	   other curl requests don't inherit inappropriate header data */
+	curl_result = curl_easy_perform(curl);
+	curl_easy_setopt(curl, CURLOPT_HTTPHEADER, no_range_header);
+	if (curl_result != 0) {
 		return -1;
 	}
 

@@ -517,6 +577,7 @@ int main(int argc, char **argv)
 
 	curl = curl_easy_init();
 	no_pragma_header = curl_slist_append(no_pragma_header, "Pragma:");
+	no_range_header = curl_slist_append(no_range_header, "Range:");
 
         /* Set SSL parameters if they were provided */
 	if (ssl_cert != NULL) {

@@ -549,6 +610,7 @@ int main(int argc, char **argv)
 		return 1;
 
 	curl_slist_free_all(no_pragma_header);
+	curl_slist_free_all(no_range_header);
 	curl_global_cleanup();
 	return 0;
 }