[RFC 2/2] Add Git-aware CGI for Git-aware smart HTTP transport
This CGI can be loaded into an Apache server using ScriptAlias, such as with the following configuration:
LoadModule cgi_module /usr/libexec/apache2/mod_cgi.so
LoadModule alias_module /usr/libexec/apache2/mod_alias.so
ScriptAlias /git/ /usr/libexec/git-core/git-http-backend/
Repositories are accessed via the translated PATH_INFO.
The CGI is backwards compatible with the dumb client, allowing the client to detect the server's smarts by looking at the content-type returned from "GET /repo.git/info/refs". If the returned content type is the magic application/x-git-refs type then the client can assume the server is Git-aware.
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
---
.gitignore | 1 +
Documentation/technical/http-protocol.txt | 88 +++++++++
Makefile | 1 +
http-backend.c | 302 +++++++++++++++++++++++++++++
4 files changed, 392 insertions(+), 0 deletions(-)
create mode 100644 Documentation/technical/http-protocol.txt
create mode 100644 http-backend.c
diff --git a/.gitignore b/.gitignore
index a213e8e..02eaf3a 100644
--- a/.gitignore
+++ b/.gitignore
@@ -51,6 +51,7 @@ git-gc
git-get-tar-commit-id
git-grep
git-hash-object
+git-http-backend
git-http-fetch
git-http-push
git-imap-send
diff --git a/Documentation/technical/http-protocol.txt b/Documentation/technical/http-protocol.txt
new file mode 100644
index 0000000..6cb96f3
--- /dev/null
+++ b/Documentation/technical/http-protocol.txt
@@ -0,0 +1,88 @@
+Smart HTTP transfer protocols
+=============================
+
+Git supports two HTTP based transfer protocols. A "dumb" protocol
+which requires only a standard HTTP server on the server end of the
+connection, and a "smart" protocol which requires a Git aware CGI
+(or server module). This document describes the "smart" protocol.
+
+As a design feature smart servers automatically degrade to the
+dumb protocol when speaking with a dumb client. This may cause
+more load to be placed on the server as the file GET requests are
+handled by a CGI rather than the server itself.
+
+
+Authentication
+--------------
+
+Standard HTTP authentication is used, and must be configured and
+enforced by the HTTP server software.
+
+Chunked Transfer Encoding
+-------------------------
+
+For performance reasons the HTTP/1.1 chunked transfer encoding is
+used frequently to transfer variable length objects. This avoids
+needing to produce large results in memory to compute the proper
+content-length.
+
+Detecting Smart Servers
+-----------------------
+
+HTTP clients can detect a smart Git-aware server by sending the
+/info/refs request (below) to the server. If the response has a
+status of 200 and the magic application/x-git-refs content type
+then the server can be assumed to be a smart Git-aware server.
+
+
+Show Refs
+---------
+
+Obtains the available refs from the remote repository. The response
+is a sequence of refs, one per line. The actual format matches that
+of the $GIT_DIR/info/refs file normally used by a "dumb" protocol.
+
+ C: GET /path/to/repository.git/info/refs HTTP/1.0
+
+ S: HTTP/1.1 200 OK
+ S: Content-Type: application/x-git-refs
+ S: Transfer-Encoding: chunked
+ S:
+ S: 62
+ S: 95dcfa3633004da0049d3d0fa03f80589cbcaf31 refs/heads/maint
+ S:
+ S: 63
+ S: d049f6c27a2244e12041955e262a404c7faba355 refs/heads/master
+ S:
+ S: 59
+ S: 2cb58b79488a98d2721cea644875a8dd0026b115 refs/heads/pu
+ S:
+
+Push Pack
+---------
+
+Uploads a pack and updates refs. The start of the stream is the
+commands to update the refs and the remainder of the stream is the
+pack file itself. See git-receive-pack and its network protocol
+in pack-protocol.txt, as this is essentially the same.
+
+ C: POST /path/to/repository.git/receive-pack HTTP/1.0
+ C: Content-Type: application/x-git-receive-pack
+ C: Transfer-Encoding: chunked
+ C:
+ C: 103
+ C: 006395dcfa3633004da0049d3d0fa03f80589cbcaf31 d049f6c27a2244e12041955e262a404c7faba355 refs/heads/maint
+ C: 4
+ C: 0000
+ C: 12
+ C: PACK
+ ...
+ C: 0
+
+ S: HTTP/1.0 200 OK
+ S: Content-type: application/x-git-receive-pack-status
+ S: Transfer-Encoding: chunked
+ S:
+ S: ...<output of receive-pack>...
+
+
diff --git a/Makefile b/Makefile
index 52c67c1..3a93bf6 100644
--- a/Makefile
+++ b/Makefile
@@ -298,6 +298,7 @@ PROGRAMS += git-unpack-file$X
PROGRAMS += git-update-server-info$X
PROGRAMS += git-upload-pack$X
PROGRAMS += git-var$X
+PROGRAMS += git-http-backend$X
# List built-in command $C whose implementation cmd_$C() is not in
# builtin-$C.o but is linked in as part of some other command.
diff --git a/http-backend.c b/http-backend.c
new file mode 100644
index 0000000..a498f89
--- /dev/null
+++ b/http-backend.c
@@ -0,0 +1,302 @@
+#include "cache.h"
+#include "refs.h"
+#include "pkt-line.h"
+#include "object.h"
+#include "tag.h"
+#include "exec_cmd.h"
+#include "run-command.h"
+
+static const char content_type[] = "Content-Type";
+static const char content_length[] = "Content-Length";
+
+static int can_chunk;
+static char buffer[1000];
+
+static void send_status(unsigned code, const char *msg)
+{
+ size_t n;
+
+ n = snprintf(buffer, sizeof(buffer), "Status: %u %s\r\n", code, msg);
+ if (n >= sizeof(buffer))
+ die("protocol error: impossibly long header");
+ safe_write(1, buffer, n);
+}
+
+static void send_header(const char *name, const char *value)
+{
+ size_t n;
+
+ n = snprintf(buffer, sizeof(buffer), "%s: %s\r\n", name, value);
+ if (n >= sizeof(buffer))
+ die("protocol error: impossibly long header");
+ safe_write(1, buffer, n);
+}
+
+static void end_headers(void)
+{
+ safe_write(1, "\r\n", 2);
+}
+
+static void send_nocaching(void)
+{
+ const char *proto = getenv("SERVER_PROTOCOL");
+ if (!proto || !strcmp(proto, "HTTP/1.0"))
+ send_header("Expires", "Mon, 17 Sep 2001 00:00:00 GMT");
+ else
+ send_header("Cache-Control", "no-cache");
+}
+
+static void send_connection_close(void)
+{
+ send_header("Connection", "close");
+}
+
+static void enable_chunking(void)
+{
+ const char *proto = getenv("SERVER_PROTOCOL");
+
+ can_chunk = proto && strcmp(proto, "HTTP/1.0");
+ if (can_chunk)
+ send_header("Transfer-Encoding", "chunked");
+ else
+ send_connection_close();
+}
+
+#define hex(a) (hexchar[(a) & 15])
+static void chunked_write(const char *fmt, ...)
+{
+ static const char hexchar[] = "0123456789abcdef";
+ va_list args;
+ unsigned n;
+
+ va_start(args, fmt);
+ n = vsnprintf(buffer + 6, sizeof(buffer) - 8, fmt, args);
+ va_end(args);
+ if (n >= sizeof(buffer) - 8)
+ die("protocol error: impossibly long line");
+
+ if (can_chunk) {
+ unsigned len = n + 4, b = 4;
+
+ buffer[4] = '\r';
+ buffer[5] = '\n';
+ buffer[n + 6] = '\r';
+ buffer[n + 7] = '\n';
+
+ while (n > 0) {
+ buffer[--b] = hex(n);
+ n >>= 4;
+ len++;
+ }
+
+ safe_write(1, buffer + b, len);
+ } else
+ safe_write(1, buffer + 6, n);
+}
+
+static void end_chunking(void)
+{
+ static const char flush_chunk[] = "0\r\n\r\n";
+ if (can_chunk)
+ safe_write(1, flush_chunk, strlen(flush_chunk));
+}
+
+static void NORETURN invalid_request(const char *msg)
+{
+ static const char header[] = "error: ";
+
+ send_status(400, "Bad Request");
+ send_header(content_type, "text/plain");
+ end_headers();
+
+ safe_write(1, header, strlen(header));
+ safe_write(1, msg, strlen(msg));
+ safe_write(1, "\n", 1);
+
+ exit(0);
+}
+
+static void not_found(void)
+{
+ send_status(404, "Not Found");
+ end_headers();
+}
+
+static void server_error(void)
+{
+ send_status(500, "Internal Error");
+ end_headers();
+}
+
+static void require_content_type(const char *need_type)
+{
+ const char *input_type = getenv("CONTENT_TYPE");
+ if (!input_type || strcmp(input_type, need_type))
+ invalid_request("Unsupported content-type");
+}
+
+static void do_GET_any_file(char *name)
+{
+ const char *p = git_path("%s", name);
+ struct stat sb;
+ uintmax_t remaining;
+ size_t n;
+ int fd = open(p, O_RDONLY);
+
+ if (fd < 0) {
+ not_found();
+ return;
+ }
+ if (fstat(fd, &sb) < 0) {
+ close(fd);
+ server_error();
+ die("fstat on plain file failed");
+ }
+ remaining = (uintmax_t)sb.st_size;
+
+ n = snprintf(buffer, sizeof(buffer),
+ "Content-Length: %" PRIuMAX "\r\n", remaining);
+ if (n >= sizeof(buffer))
+ die("protocol error: impossibly long header");
+ safe_write(1, buffer, n);
+ send_header(content_type, "application/octet-stream");
+ end_headers();
+
+ while (remaining) {
+ n = xread(fd, buffer, sizeof(buffer));
+ if (n < 0)
+ die("error reading from %s", p);
+ n = safe_write(1, buffer, n);
+ if (n <= 0)
+ break;
+ }
+ close(fd);
+}
+
+static int show_one_ref(const char *name, const unsigned char *sha1,
+ int flag, void *cb_data)
+{
+ struct object *o = parse_object(sha1);
+ if (!o)
+ return 0;
+
+ chunked_write("%s\t%s\n", sha1_to_hex(sha1), name);
+ if (o->type == OBJ_TAG) {
+ o = deref_tag(o, name, 0);
+ if (!o)
+ return 0;
+ chunked_write("%s\t%s^{}\n", sha1_to_hex(o->sha1), name);
+ }
+
+ return 0;
+}
+
+static void do_GET_info_refs(char *arg)
+{
+ send_header(content_type, "application/x-git-refs");
+ send_nocaching();
+ enable_chunking();
+ end_headers();
+
+ for_each_ref(show_one_ref, NULL);
+ end_chunking();
+}
+
+static void do_GET_info_packs(char *arg)
+{
+ size_t objdirlen = strlen(get_object_directory());
+ struct packed_git *p;
+
+ send_nocaching();
+ enable_chunking();
+ end_headers();
+
+ prepare_packed_git();
+ for (p = packed_git; p; p = p->next) {
+ if (!p->pack_local)
+ continue;
+ chunked_write("P %s\n", p->pack_name + objdirlen + 6);
+ }
+ chunked_write("\n");
+ end_chunking();
+}
+
+static void do_POST_receive_pack(char *arg)
+{
+ require_content_type("application/x-git-receive-pack");
+ send_header(content_type, "application/x-git-receive-pack-status");
+ send_nocaching();
+ send_connection_close();
+ end_headers();
+
+ execl_git_cmd("receive-pack",
+ "--report-status",
+ "--no-advertise-heads",
+ ".",
+ NULL);
+ die("Failed to start receive-pack");
+}
+
+static struct service_cmd {
+ const char *method;
+ const char *pattern;
+ void (*imp)(char *);
+} services[] = {
+ {"GET", "/info/refs$", do_GET_info_refs},
+ {"GET", "/objects/info/packs", do_GET_info_packs},
+
+ {"GET", "/HEAD$", do_GET_any_file},
+ {"GET", "/objects/../.{38}$", do_GET_any_file},
+ {"GET", "/objects/pack/pack-[^/]*$", do_GET_any_file},
+ {"GET", "/objects/info/[^/]*$", do_GET_any_file},
+
+ {"POST", "/receive-pack", do_POST_receive_pack}
+};
+
+int main(int argc, char **argv)
+{
+ char *input_method = getenv("REQUEST_METHOD");
+ char *dir = getenv("PATH_TRANSLATED");
+ struct service_cmd *cmd = NULL;
+ char *cmd_arg = NULL;
+ int i;
+
+ if (!input_method)
+ die("No REQUEST_METHOD from server");
+ if (!strcmp(input_method, "HEAD"))
+ input_method = "GET";
+
+ if (!dir)
+ die("No PATH_TRANSLATED from server");
+
+ for (i = 0; i < ARRAY_SIZE(services); i++) {
+ struct service_cmd *c = &services[i];
+ regex_t re;
+ regmatch_t out[1];
+
+ if (strcmp(input_method, c->method))
+ continue;
+ if (regcomp(&re, c->pattern, REG_EXTENDED))
+ die("Bogus re in service table: %s", c->pattern);
+ if (!regexec(&re, dir, 2, out, 0)) {
+ size_t n = out[0].rm_eo - out[0].rm_so;
+ cmd = c;
+ cmd_arg = xmalloc(n);
+ strncpy(cmd_arg, dir + out[0].rm_so + 1, n);
+ cmd_arg[n] = 0;
+ dir[out[0].rm_so] = 0;
+ break;
+ }
+ regfree(&re);
+ }
+
+ if (!cmd)
+ invalid_request("Unsupported query request");
+
+ setup_path();
+ if (!enter_repo(dir, 0))
+ invalid_request("Not a Git repository");
+
+ cmd->imp(cmd_arg);
+ return 0;
+}
--
1.6.0.rc1.221.g9ae23
