[PATCH] Support alternates and http-alternates in http-fetch

This allows the remote repository to refer to additional repositories
in a file objects/info/http-alternates or
objects/info/alternates. Each line may be:

 a relative path, starting with ../, to get from the objects directory
  of the starting repository to the objects directory of the added
  repository.

 an absolute path of the objects directory of the added repository (on
  the same server).

 (only in http-alternates) a full URL of the objects directory of the
  added repository.

Signed-off-by: Daniel Barkalow <barkalow@iabervon.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

http-fetch.c

@@ -144,10 +144,11 @@ static int fetch_alternates(char *base)
 	char *url;
 	char *data;
 	int i = 0;
+	int http_specific = 1;
 	if (got_alternates)
 		return 0;
 	data = xmalloc(4096);
-	buffer.size = 4096;
+	buffer.size = 4095;
 	buffer.posn = 0;
 	buffer.buffer = data;
 
@@ -162,6 +163,8 @@ static int fetch_alternates(char *base)
 	curl_easy_setopt(curl, CURLOPT_URL, url);
 
 	if (curl_easy_perform(curl) || !buffer.posn) {
+		http_specific = 0;
+
 		sprintf(url, "%s/objects/info/alternates", base);
 
 		curl_easy_setopt(curl, CURLOPT_FILE, &buffer);
@@ -173,17 +176,45 @@ static int fetch_alternates(char *base)
 		}
 	}
 
+	data[buffer.posn] = '\0';
+
 	while (i < buffer.posn) {
 		int posn = i;
 		while (posn < buffer.posn && data[posn] != '\n')
 			posn++;
 		if (data[posn] == '\n') {
+			int okay = 0;
+			int serverlen = 0;
+			struct alt_base *newalt;
+			char *target = NULL;
 			if (data[i] == '/') {
-				int serverlen = strchr(base + 8, '/') - base;
-				// skip 'objects' at end
-				char *target = 
-					xmalloc(serverlen + posn - i - 6);
-				struct alt_base *newalt;
+				serverlen = strchr(base + 8, '/') - base;
+				okay = 1;
+			} else if (!memcmp(data + i, "../", 3)) {
+				i += 3;
+				serverlen = strlen(base);
+				while (i + 2 < posn && 
+				       !memcmp(data + i, "../", 3)) {
+					do {
+						serverlen--;
+					} while (serverlen &&
+						 base[serverlen - 1] != '/');
+					i += 3;
+				}
+				// If the server got removed, give up.
+				okay = strchr(base, ':') - base + 3 < 
+					serverlen;
+			} else if (http_specific) {
+				char *colon = strchr(data + i, ':');
+				char *slash = strchr(data + i, '/');
+				if (colon && slash && colon < data + posn &&
+				    slash < data + posn && colon < slash) {
+					okay = 1;
+				}
+			}
+			// skip 'objects' at end
+			if (okay) {
+				target = xmalloc(serverlen + posn - i - 6);
 				strncpy(target, base, serverlen);
 				strncpy(target + serverlen, data + i,
 					posn - i - 7);
@@ -235,7 +266,7 @@ static int fetch_indices(struct alt_base *repo)
 	curl_easy_setopt(curl, CURLOPT_HTTPHEADER, NULL);
 
 	if (curl_easy_perform(curl)) {
-		return error("Unable to get pack index %s", url);
+		return -1;
 	}
 
 	while (i < buffer.posn) {