Re: [RFC PATCH 2/4] Git-aware CGI to provide dumb HTTP transport

> The git-http-backend CGI can be configured into any 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 all
> older HTTP clients to continue to download repositories which are
> managed by the CGI.
> 
> Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
> ---
>  .gitignore     |    1 +
>  Makefile       |    1 +
>  http-backend.c |  261 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 263 insertions(+), 0 deletions(-)
>  create mode 100644 http-backend.c
> 
> diff --git a/.gitignore b/.gitignore
> index 51a37b1..353d22f 100644
> --- a/.gitignore
> +++ b/.gitignore
> @@ -55,6 +55,7 @@ git-get-tar-commit-id
>  git-grep
>  git-hash-object
>  git-help
> +git-http-backend
>  git-http-fetch
>  git-http-push
>  git-imap-send
> diff --git a/Makefile b/Makefile
> index dd3d520..c80fb56 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -361,6 +361,7 @@ PROGRAMS += git-show-index$X
>  PROGRAMS += git-unpack-file$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..39cfd25
> --- /dev/null
> +++ b/http-backend.c
> @@ -0,0 +1,261 @@
> +#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 char buffer[1024];
> +
> +static const char *http_date(unsigned long time)
> +{
> +	return show_date(time, 0, DATE_RFC2822);
> +}
> +
> +static void format_write(const char *fmt, ...)
> +{
> +	va_list args;
> +	unsigned n;
> +
> +	va_start(args, fmt);
> +	n = vsnprintf(buffer, sizeof(buffer), fmt, args);
> +	va_end(args);
> +	if (n >= sizeof(buffer))
> +		die("protocol error: impossibly long line");
> +
> +	safe_write(1, buffer, n);
> +}
> +
> +static void write_status(unsigned code, const char *msg)
> +{
> +	format_write("Status: %u %s\r\n", code, msg);
> +}
> +
> +static void write_header(const char *name, const char *value)
> +{
> +	format_write("%s: %s\r\n", name, value);
> +}
> +
> +static void end_headers(void)
> +{
> +	safe_write(1, "\r\n", 2);
> +}
> +
> +static void write_nocache(void)
> +{
> +	write_header("Expires", "Fri, 01 Jan 1980 00:00:00 GMT");
> +	write_header("Pragma", "no-cache");
> +	write_header("Cache-Control", "no-cache, max-age=0, must-revalidate");
> +}
> +
> +static void write_cache_forever(void)
> +{
> +	unsigned long now = time(NULL);
> +	write_header("Date", http_date(now));
> +	write_header("Expires", http_date(now + 31536000));
> +	write_header("Cache-Control", "public, max-age=31536000");
> +}
> +
> +static NORETURN void not_found(const char *err, ...)
> +{
> +	va_list params;
> +
> +	write_status(404, "Not Found");
> +	write_nocache();
> +	end_headers();
> +
> +	va_start(params, err);
> +	if (err && *err) {
> +		vsnprintf(buffer, sizeof(buffer), err, params);
> +		fprintf(stderr, "%s\n", buffer);
> +	}
> +	va_end(params);
> +	exit(0);
> +}
> +
> +static void write_file(const char *the_type, const char *name)
> +{
> +	const char *p = git_path("%s", name);
> +	int fd;
> +	struct stat sb;
> +	uintmax_t remaining;
> +
> +	fd = open(p, O_RDONLY);
> +	if (fd < 0)
> +		not_found("Cannot open '%s': %s", p, strerror(errno));
> +	if (fstat(fd, &sb) < 0)
> +		die_errno("Cannot stat '%s'", p);
> +	remaining = (uintmax_t)sb.st_size;
> +
> +	write_header(content_type, the_type);
> +	write_header("Last-Modified", http_date(sb.st_mtime));
> +	format_write("Content-Length: %" PRIuMAX "\r\n", remaining);
> +	end_headers();
> +
> +	while (remaining) {
> +		ssize_t n = xread(fd, buffer, sizeof(buffer));
> +		if (n < 0)
> +			die_errno("Cannot read '%s'", p);
> +		n = safe_write(1, buffer, n);
> +		if (n <= 0)
> +			break;
> +	}
> +	close(fd);
> +}
> +
> +static void get_text_file(char *name)
> +{
> +	write_nocache();
> +	write_file("text/plain; charset=utf-8", name);
> +}
> +
> +static void get_loose_object(char *name)
> +{
> +	write_cache_forever();
> +	write_file("application/x-git-loose-object", name);
> +}
> +
> +static void get_pack_file(char *name)
> +{
> +	write_cache_forever();
> +	write_file("application/x-git-packed-objects", name);
> +}
> +
> +static void get_idx_file(char *name)
> +{
> +	write_cache_forever();
> +	write_file("application/x-git-packed-objects-toc", name);
> +}
> +
> +static int show_text_ref(const char *name, const unsigned char *sha1,
> +	int flag, void *cb_data)
> +{
> +	struct object *o = parse_object(sha1);
> +	if (!o)
> +		return 0;
> +
> +	format_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;
> +		format_write("%s\t%s^{}\n", sha1_to_hex(o->sha1), name);
> +	}
> +
> +	return 0;
> +}
> +
> +static void get_info_refs(char *arg)
> +{
> +	write_nocache();
> +	write_header(content_type, "text/plain; charset=utf-8");
> +	end_headers();
> +
> +	for_each_ref(show_text_ref, NULL);
> +}
> +
> +static void get_info_packs(char *arg)
> +{
> +	size_t objdirlen = strlen(get_object_directory());
> +	struct packed_git *p;
> +
> +	write_nocache();
> +	write_header(content_type, "text/plain; charset=utf-8");
> +	end_headers();
> +
> +	prepare_packed_git();
> +	for (p = packed_git; p; p = p->next) {
> +		if (!p->pack_local)
> +			continue;
> +		format_write("P %s\n", p->pack_name + objdirlen + 6);
> +	}
> +	safe_write(1, "\n", 1);
> +}
> +
> +static NORETURN void die_webcgi(const char *err, va_list params)
> +{
> +	write_status(500, "Internal Server Error");
> +	write_nocache();
> +	end_headers();
> +
> +	vsnprintf(buffer, sizeof(buffer), err, params);
> +	fprintf(stderr, "fatal: %s\n", buffer);
> +	exit(0);
> +}
> +
> +static struct service_cmd {
> +	const char *method;
> +	const char *pattern;
> +	void (*imp)(char *);
> +} services[] = {
> +	{"GET", "/HEAD$", get_text_file},
> +	{"GET", "/info/refs$", get_info_refs},
> +	{"GET", "/objects/info/packs$", get_info_packs},
> +	{"GET", "/objects/info/[^/]*$", get_text_file},
> +	{"GET", "/objects/[0-9a-f]{2}/[0-9a-f]{38}$", get_loose_object},
> +	{"GET", "/objects/pack/pack-[0-9a-f]{40}\\.pack$", get_pack_file},
> +	{"GET", "/objects/pack/pack-[0-9a-f]{40}\\.idx$", get_idx_file}
> +};
> +
> +int main(int argc, char **argv)
> +{
> +	char *dir = getenv("PATH_TRANSLATED");
> +	char *input_method = getenv("REQUEST_METHOD");
> +	struct service_cmd *cmd = NULL;
> +	char *cmd_arg = NULL;
> +	int i;
> +
> +	set_die_routine(die_webcgi);
> +
> +	if (!dir)
> +		die("No PATH_TRANSLATED from server");
> +	if (!input_method)
> +		die("No REQUEST_METHOD from server");
> +	if (!strcmp(input_method, "HEAD"))
> +		input_method = "GET";
> +
> +	for (i = 0; i < ARRAY_SIZE(services); i++) {
> +		struct service_cmd *c = &services[i];
> +		regex_t re;
> +		regmatch_t out[1];
> +
> +		if (regcomp(&re, c->pattern, REG_EXTENDED))
> +			die("Bogus regex in service table: %s", c->pattern);
> +		if (!regexec(&re, dir, 1, out, 0)) {
> +			size_t n = out[0].rm_eo - out[0].rm_so;
> +
> +			if (strcmp(input_method, c->method)) {
> +				const char *proto = getenv("SERVER_PROTOCOL");
> +				if (proto && !strcmp(proto, "HTTP/1.1"))
> +					write_status(405, "Method Not Allowed");
> +				else
> +					write_status(400, "Bad Request");
> +				write_nocache();
> +				end_headers();
> +				return 0;
> +			}
> +
> +			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)
> +		not_found("Request not supported: '%s'", dir);
> +
> +	setup_path();
> +	if (!enter_repo(dir, 0))
> +		not_found("Not a git repository: '%s'", dir);
> +
> +	cmd->imp(cmd_arg);
> +	return 0;
> +}