cgit - Web front-end for git that you're looking at right now. Might have had a few additions from upstream.

	Commit message (Expand)	Author	Age
...
*	Move global variables + callback functions into shared.c	Lars Hjemli	2006-12-11
/* ui-snapshot.c: generate snapshot of a commit
 *
 * Copyright (C) 2006 Lars Hjemli
 *
 * Licensed under GNU General Public License v2
 *   (see COPYING for full license text)
 */

#include "cgit.h"
#include "html.h"
#include "ui-shared.h"

static int write_compressed_tar_archive(struct archiver_args *args,const char *filter)
{
	int rw[2];
	pid_t gzpid;
	int stdout2;
	int status;
	int rv;

	stdout2 = chk_non_negative(dup(STDIN_FILENO), "Preserving STDOUT before compressing");
	chk_zero(pipe(rw), "Opening pipe from compressor subprocess");
	gzpid = chk_non_negative(fork(), "Forking compressor subprocess");
	if(gzpid==0) {
		/* child */
		chk_zero(close(rw[1]), "Closing write end of pipe in child");
		chk_zero(close(STDIN_FILENO), "Closing STDIN");
		chk_non_negative(dup2(rw[0],STDIN_FILENO), "Redirecting compressor input to stdin");
		execlp(filter,filter,NULL);
		_exit(-1);
	}
	/* parent */
	chk_zero(close(rw[0]), "Closing read end of pipe");
	chk_non_negative(dup2(rw[1],STDOUT_FILENO), "Redirecting output to compressor");

	rv = write_tar_archive(args);

	chk_zero(close(STDOUT_FILENO), "Closing STDOUT redirected to compressor");
	chk_non_negative(dup2(stdout2,STDOUT_FILENO), "Restoring uncompressed STDOUT");
	chk_zero(close(stdout2), "Closing uncompressed STDOUT");
	chk_zero(close(rw[1]), "Closing write end of pipe in parent");
	chk_positive(waitpid(gzpid,&status,0), "Waiting on compressor process");
	if(! ( WIFEXITED(status) && WEXITSTATUS(status)==0 ) )
		cgit_print_error("Failed to compress archive");

	return rv;
}

static int write_tar_gzip_archive(struct archiver_args *args)
{
	return write_compressed_tar_archive(args,"gzip");
}

static int write_tar_bzip2_archive(struct archiver_args *args)
{
	return write_compressed_tar_archive(args,"bzip2");
}

const struct cgit_snapshot_format cgit_snapshot_formats[] = {
	{ ".zip", "application/x-zip", write_zip_archive, 0x1 },
	{ ".tar.gz", "application/x-tar", write_tar_gzip_archive, 0x2 },
	{ ".tar.bz2", "application/x-tar", write_tar_bzip2_archive, 0x4 },
	{ ".tar", "application/x-tar", write_tar_archive, 0x8 },
	{}
};

static const struct cgit_snapshot_format *get_format(const char *filename)
{
	const struct cgit_snapshot_format *fmt;
	int fl, sl;

	fl = strlen(filename);
	for(fmt = cgit_snapshot_formats; fmt->suffix; fmt++) {
		sl = strlen(fmt->suffix);
		if (sl >= fl)
			continue;
		if (!strcmp(fmt->suffix, filename + fl - sl))
			return fmt;
	}
	return NULL;
}

static int make_snapshot(const struct cgit_snapshot_format *format,
			 const char *hex, const char *prefix,
			 const char *filename)
{
	struct archiver_args args;
	struct commit *commit;
	unsigned char sha1[20];

	if(get_sha1(hex, sha1)) {
		cgit_print_error(fmt("Bad object id: %s", hex));
		return 1;
	}
	commit = lookup_commit_reference(sha1);
	if(!commit) {
		cgit_print_error(fmt("Not a commit reference: %s", hex));
		return 1;
	}
	memset(&args, 0, sizeof(args));
	if (prefix) {
		args.base = fmt("%s/", prefix);
		args.baselen = strlen(prefix) + 1;
	} else {
		args.base = "";
		args.baselen = 0;
	}
	args.tree = commit->tree;
	args.time = commit->date;
	ctx.page.mimetype = xstrdup(format->mimetype);
	ctx.page.filename = xstrdup(filename);
	cgit_print_http_headers(&ctx);
	format->write_func(&args);
	return 0;
}

char *dwim_filename = NULL;
const char *dwim_refname = NULL;

static int ref_cb(const char *refname, const unsigned char *sha1, int flags,
		  void *cb_data)
{
	const char *r = refname;
	while (r && *r) {
		fprintf(stderr, "  cmp %s with %s:", dwim_filename, r);
		if (!strcmp(dwim_filename, r)) {
			fprintf(stderr, "MATCH!\n");
			dwim_refname = refname;
			return 1;
		}
		fprintf(stderr, "no match\n");
		if (isdigit(*r))
			break;
		r++;
	}
	return 0;
}

/* Try to guess the requested revision by combining repo name and tag name
 * and comparing this to the requested snapshot name. E.g. the requested
 * snapshot is "cgit-0.7.2.tar.gz" while repo name is "cgit" and tag name
 * is "v0.7.2". First, the reponame is stripped off, leaving "-0.7.2.tar.gz".
 * Next, any '-' and '_' characters are stripped, leaving "0.7.2.tar.gz".
 * Finally, the requested format suffix is removed and we end up with "0.7.2".
 * Then we test each tag against this dwimmed filename, and for each tag
 * we even try to remove any leading characters which are non-digits. I.e.
 * we first compare with "v0.7.2", then with "0.7.2" and we've got a match.
 */
static const char *get_ref_from_filename(const char *url, const char *filename,
					 const struct cgit_snapshot_format *fmt)
{
	const char *reponame = cgit_repobasename(url);
	fprintf(stderr, "reponame=%s, filename=%s\n", reponame, filename);
	if (prefixcmp(filename, reponame))
		return NULL;
	filename += strlen(reponame);
	while (filename && (*filename == '-' || *filename == '_'))
		filename++;
	dwim_filename = xstrdup(filename);
	dwim_filename[strlen(filename) - strlen(fmt->suffix)] = '\0';
	for_each_tag_ref(ref_cb, NULL);
	return dwim_refname;
}

void cgit_print_snapshot(const char *head, const char *hex, const char *prefix,
			 const char *filename, int snapshots, int dwim)
{
	const struct cgit_snapshot_format* f;

	f = get_format(filename);
	if (!f) {
		ctx.page.mimetype = "text/html";
		cgit_print_http_headers(&ctx);
		cgit_print_docstart(&ctx);
		cgit_print_pageheader(&ctx);
		cgit_print_error(fmt("Unsupported snapshot format: %s", filename));
		cgit_print_docend();
		return;
	}

	if (!hex && dwim)
		hex = get_ref_from_filename(ctx.repo->url, filename, f);

	if (!hex)
		hex = head;

	make_snapshot(f, hex, prefix, filename);
}