[PATCH] Add support for alternates in HTTP

This tries .../objects/info/http-alternates and then
.../objects/info/alternates, looking for a file which specifies where
else to download objects and packs from.

It currently only supports absolute paths, and doesn't support full URLs.

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

http-fetch.c

@@ -16,7 +16,17 @@
 static CURL *curl;
 static struct curl_slist *no_pragma_header;
 
-static char *base;
+static char *initial_base;
+
+struct alt_base
+{
+	char *base;
+	int got_indices;
+	struct packed_git *packs;
+	struct alt_base *next;
+};
+
+struct alt_base *alt = NULL;
 
 static SHA_CTX c;
 static z_stream stream;
@@ -72,11 +82,9 @@ void prefetch(unsigned char *sha1)
 {
 }
 
-static int got_indices = 0;
+static int got_alternates = 0;
-
-static struct packed_git *packs = NULL;
 
-static int fetch_index(unsigned char *sha1)
+static int fetch_index(struct alt_base *repo, unsigned char *sha1)
 {
 	char *filename;
 	char *url;
@@ -90,9 +98,9 @@ static int fetch_index(unsigned char *sha1)
 		fprintf(stderr, "Getting index for pack %s\n",
 			sha1_to_hex(sha1));
 	
-	url = xmalloc(strlen(base) + 64);
+	url = xmalloc(strlen(repo->base) + 64);
 	sprintf(url, "%s/objects/pack/pack-%s.idx",
-		base, sha1_to_hex(sha1));
+		repo->base, sha1_to_hex(sha1));
 	
 	filename = sha1_pack_index_name(sha1);
 	indexfile = fopen(filename, "w");
@@ -114,22 +122,92 @@ static int fetch_index(unsigned char *sha1)
 	return 0;
 }
 
-static int setup_index(unsigned char *sha1)
+static int setup_index(struct alt_base *repo, unsigned char *sha1)
 {
 	struct packed_git *new_pack;
 	if (has_pack_file(sha1))
 		return 0; // don't list this as something we can get
 
-	if (fetch_index(sha1))
+	if (fetch_index(repo, sha1))
 		return -1;
 
 	new_pack = parse_pack_index(sha1);
-	new_pack->next = packs;
+	new_pack->next = repo->packs;
-	packs = new_pack;
+	repo->packs = new_pack;
 	return 0;
 }
 
-static int fetch_indices(void)
+static int fetch_alternates(char *base)
+{
+	int ret = 0;
+	struct buffer buffer;
+	char *url;
+	char *data;
+	int i = 0;
+	if (got_alternates)
+		return 0;
+	data = xmalloc(4096);
+	buffer.size = 4096;
+	buffer.posn = 0;
+	buffer.buffer = data;
+
+	if (get_verbosely)
+		fprintf(stderr, "Getting alternates list\n");
+	
+	url = xmalloc(strlen(base) + 31);
+	sprintf(url, "%s/objects/info/http-alternates", base);
+
+	curl_easy_setopt(curl, CURLOPT_FILE, &buffer);
+	curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, fwrite_buffer);
+	curl_easy_setopt(curl, CURLOPT_URL, url);
+
+	if (curl_easy_perform(curl) || !buffer.posn) {
+		sprintf(url, "%s/objects/info/alternates", base);
+		
+		curl_easy_setopt(curl, CURLOPT_FILE, &buffer);
+		curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, fwrite_buffer);
+		curl_easy_setopt(curl, CURLOPT_URL, url);
+		
+		if (curl_easy_perform(curl)) {
+			return 0;
+		}
+	}
+
+	while (i < buffer.posn) {
+		int posn = i;
+		while (posn < buffer.posn && data[posn] != '\n')
+			posn++;
+		if (data[posn] == '\n') {
+			if (data[i] == '/') {
+				int serverlen = strchr(base + 8, '/') - base;
+				// skip 'objects' at end
+				char *target = 
+					xmalloc(serverlen + posn - i - 6);
+				struct alt_base *newalt;
+				strncpy(target, base, serverlen);
+				strncpy(target + serverlen, data + i,
+					posn - i - 7);
+				target[serverlen + posn - i - 7] = '\0';
+				if (get_verbosely)
+					fprintf(stderr, 
+						"Also look at %s\n", target);
+				newalt = xmalloc(sizeof(*newalt));
+				newalt->next = alt;
+				newalt->base = target;
+				newalt->got_indices = 0;
+				newalt->packs = NULL;
+				alt = newalt;
+				ret++;
+			}
+		}
+		i = posn + 1;
+	}
+	got_alternates = 1;
+	
+	return ret;
+}
+
+static int fetch_indices(struct alt_base *repo)
 {
 	unsigned char sha1[20];
 	char *url;
@@ -137,7 +215,7 @@ static int fetch_indices(void)
 	char *data;
 	int i = 0;
 
-	if (got_indices)
+	if (repo->got_indices)
 		return 0;
 
 	data = xmalloc(4096);
@@ -148,8 +226,8 @@ static int fetch_indices(void)
 	if (get_verbosely)
 		fprintf(stderr, "Getting pack list\n");
 	
-	url = xmalloc(strlen(base) + 21);
+	url = xmalloc(strlen(repo->base) + 21);
-	sprintf(url, "%s/objects/info/packs", base);
+	sprintf(url, "%s/objects/info/packs", repo->base);
 
 	curl_easy_setopt(curl, CURLOPT_FILE, &buffer);
 	curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, fwrite_buffer);
@@ -160,7 +238,7 @@ static int fetch_indices(void)
 		return error("Unable to get pack index %s", url);
 	}
 
-	do {
+	while (i < buffer.posn) {
 		switch (data[i]) {
 		case 'P':
 			i++;
@@ -168,7 +246,7 @@ static int fetch_indices(void)
 			    !strncmp(data + i, " pack-", 6) &&
 			    !strncmp(data + i + 46, ".pack\n", 6)) {
 				get_sha1_hex(data + i + 6, sha1);
-				setup_index(sha1);
+				setup_index(repo, sha1);
 				i += 51;
 				break;
 			}
@@ -177,13 +255,13 @@ static int fetch_indices(void)
 				i++;
 		}
 		i++;
-	} while (i < buffer.posn);
+	}
 
-	got_indices = 1;
+	repo->got_indices = 1;
 	return 0;
 }
 
-static int fetch_pack(unsigned char *sha1)
+static int fetch_pack(struct alt_base *repo, unsigned char *sha1)
 {
 	char *url;
 	struct packed_git *target;
@@ -191,12 +269,11 @@ static int fetch_pack(unsigned char *sha1)
 	FILE *packfile;
 	char *filename;
 
-	if (fetch_indices())
+	if (fetch_indices(repo))
 		return -1;
-	target = find_sha1_pack(sha1, packs);
+	target = find_sha1_pack(sha1, repo->packs);
 	if (!target)
-		return error("Couldn't get %s: not separate or in any pack",
+		return -1;
-			     sha1_to_hex(sha1));
 
 	if (get_verbosely) {
 		fprintf(stderr, "Getting pack %s\n",
@@ -205,9 +282,9 @@ static int fetch_pack(unsigned char *sha1)
 			sha1_to_hex(sha1));
 	}
 
-	url = xmalloc(strlen(base) + 65);
+	url = xmalloc(strlen(repo->base) + 65);
 	sprintf(url, "%s/objects/pack/pack-%s.pack",
-		base, sha1_to_hex(target->sha1));
+		repo->base, sha1_to_hex(target->sha1));
 
 	filename = sha1_pack_name(target->sha1);
 	packfile = fopen(filename, "w");
@@ -227,7 +304,7 @@ static int fetch_pack(unsigned char *sha1)
 
 	fclose(packfile);
 
-	lst = &packs;
+	lst = &repo->packs;
 	while (*lst != target)
 		lst = &((*lst)->next);
 	*lst = (*lst)->next;
@@ -237,7 +314,7 @@ static int fetch_pack(unsigned char *sha1)
 	return 0;
 }
 
-int fetch(unsigned char *sha1)
+int fetch_object(struct alt_base *repo, unsigned char *sha1)
 {
 	char *hex = sha1_to_hex(sha1);
 	char *filename = sha1_file_name(sha1);
@@ -261,9 +338,9 @@ int fetch(unsigned char *sha1)
 	curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, fwrite_sha1_file);
 	curl_easy_setopt(curl, CURLOPT_HTTPHEADER, no_pragma_header);
 
-	url = xmalloc(strlen(base) + 50);
+	url = xmalloc(strlen(repo->base) + 50);
-	strcpy(url, base);
+	strcpy(url, repo->base);
-	posn = url + strlen(base);
+	posn = url + strlen(repo->base);
 	strcpy(posn, "objects/");
 	posn += 8;
 	memcpy(posn, hex, 2);
@@ -275,9 +352,7 @@ int fetch(unsigned char *sha1)
 
 	if (curl_easy_perform(curl)) {
 		unlink(filename);
-		if (fetch_pack(sha1))
+		return -1;
-			return error("Tried %s", url);
-		return 0;
 	}
 
 	close(local);
@@ -296,11 +371,30 @@ int fetch(unsigned char *sha1)
 	return 0;
 }
 
+int fetch(unsigned char *sha1)
+{
+	struct alt_base *altbase = alt;
+	while (altbase) {
+		if (!fetch_object(altbase, sha1))
+			return 0;
+		if (!fetch_pack(altbase, sha1))
+			return 0;
+		if (fetch_alternates(altbase->base) > 0) {
+			altbase = alt;
+			continue;
+		}
+		altbase = altbase->next;
+	}
+	return error("Unable to find %s under %s\n", sha1_to_hex(sha1), 
+		     initial_base);
+}
+
 int fetch_ref(char *ref, unsigned char *sha1)
 {
         char *url, *posn;
         char hex[42];
         struct buffer buffer;
+	char *base = initial_base;
         buffer.size = 41;
         buffer.posn = 0;
         buffer.buffer = hex;
@@ -368,7 +462,12 @@ int main(int argc, char **argv)
 	curl_easy_setopt(curl, CURLOPT_NETRC, CURL_NETRC_OPTIONAL);
 #endif
 
-	base = url;
+	alt = xmalloc(sizeof(*alt));
+	alt->base = url;
+	alt->got_indices = 0;
+	alt->packs = NULL;
+	alt->next = NULL;
+	initial_base = url;
 
 	if (pull(commit_id))
 		return 1;