Start parsing remote git repository addresses

This doesn't really usefully work, but I'm committing it to have git
diff and history.  It also insanely hardcodes the git-repo cache
directory, because right now it's purely useful for development.

The big missing pieces are:

 - progress information
 - credential callbacks not implemented

where the first one makes the user interface horrible (long delays with
nothing visibly going on), and the second one makes ssh logins etc not
work.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

git-access.c

@@ -11,6 +11,205 @@
 #include <git2.h>
 
 #include "dive.h"
+#include "membuffer.h"
+
+/*
+ * The libgit2 people are incompetent at making libraries. They randomly change
+ * the interfaces, often just renaming things without any sane way to know which
+ * version you should check for etc etc. It's a disgrace.
+ */
+#if !LIBGIT2_VER_MAJOR && LIBGIT2_VER_MINOR < 22
+  #define git_remote_lookup(res, repo, name) git_remote_load(res, repo, name)
+  #define git_remote_fetch(remote, refspecs, signature, reflog) git_remote_fetch(remote, signature, reflog)
+#endif
+
+static const char *system_git_dir(void)
+{
+	static char pathname[PATH_MAX];
+
+	if (!*pathname) {
+		// This doesn't work on Windows, crap that it is. Somebody needs to fix it.
+		snprintf(pathname, PATH_MAX, "%s/git-caches", system_default_directory());
+		mkdir(pathname, 0777);
+	}
+	return pathname;
+}
+
+static char *get_local_dir(const char *remote, const char *branch)
+{
+	SHA_CTX ctx;
+	unsigned char hash[20];
+
+	// That zero-byte update is so that we don't get hash
+	// collisions for "repo1 branch" vs "repo 1branch".
+	SHA1_Init(&ctx);
+	SHA1_Update(&ctx, remote, strlen(remote));
+	SHA1_Update(&ctx, "", 1);
+	SHA1_Update(&ctx, branch, strlen(branch));
+	SHA1_Final(hash, &ctx);
+
+	return format_string("%s/%02x%02x%02x%02x%02x%02x%02x%02x",
+			system_git_dir(),
+			hash[0], hash[1], hash[2], hash[3],
+			hash[4], hash[5], hash[6], hash[7]);
+}
+
+static int check_clean(const char *path, unsigned int status, void *payload)
+{
+	status &= ~GIT_STATUS_CURRENT | GIT_STATUS_IGNORED;
+	if (!status)
+		return 0;
+	report_error("WARNING: Git cache directory modified (path %s)", path);
+	return 1;
+}
+
+static int try_to_update(git_repository *rep, git_reference *local, git_reference *remote)
+{
+	if (!git_reference_cmp(local, remote))
+		return 0;
+	return report_error("Local and remote do not match, not updating");
+}
+
+static git_repository *update_local_repo(const char *localdir, const char *remote, const char *branch)
+{
+	int error;
+	git_repository *repo = NULL;
+	git_remote *origin;
+	git_reference *local_ref, *remote_ref;
+
+	error = git_repository_open(&repo, localdir);
+	if (error) {
+		report_error("Unable to open git cache repository at %s: %s",
+			localdir, giterr_last()->message);
+		return NULL;
+	}
+
+	/*
+	 * NOTE! Remote errors are reported, but are nonfatal:
+	 * we still successfully return the local repository.
+	 */
+	error = git_remote_lookup(&origin, repo, "origin");
+	if (error) {
+		report_error("Repository '%s' origin lookup failed (%s)",
+			remote, giterr_last()->message);
+		return repo;
+	}
+
+	// NOTE! A fetch error is not fatal, we just report it
+	error = git_remote_fetch(origin, NULL, NULL, NULL);
+	git_remote_free(origin);
+	if (error) {
+		report_error("Unable to update cache for remote '%s'", remote);
+		return repo;
+	}
+
+	// Dirty modified state in the working tree? We're not going
+	// to tru to update
+	if (git_status_foreach(repo, check_clean, NULL))
+		return repo;
+
+	if (git_branch_lookup(&local_ref, repo, branch, GIT_BRANCH_LOCAL)) {
+		report_error("Git cache branch %s no longer exists", branch);
+		return repo;
+	}
+
+	if (git_branch_upstream(&remote_ref, local_ref)) {
+		report_error("Git cache branch %s no longer has an upstream branch", branch);
+		git_reference_free(local_ref);
+		return repo;
+	}
+
+	try_to_update(repo, local_ref, remote_ref);
+	git_reference_free(local_ref);
+	git_reference_free(remote_ref);
+	return repo;
+}
+
+static git_repository *create_local_repo(const char *localdir, const char *remote, const char *branch)
+{
+	int error;
+	git_repository *cloned_repo = NULL;
+	git_clone_options opts = GIT_CLONE_OPTIONS_INIT;
+
+	opts.checkout_branch = branch;
+	error = git_clone(&cloned_repo, remote, localdir, &opts);
+	if (error) {
+		report_error("git clone of %s failed (%s)", remote, giterr_last()->message);
+		return NULL;
+	}
+	return cloned_repo;
+}
+
+static struct git_repository *get_remote_repo(const char *localdir, const char *remote, const char *branch)
+{
+	struct stat st;
+
+	/* Do we already have a local cache? */
+	if (!stat(localdir, &st)) {
+		if (!S_ISDIR(st.st_mode)) {
+			report_error("local git cache at '%s' is corrupt");
+			return NULL;
+		}
+		return update_local_repo(localdir, remote, branch);
+	}
+	return create_local_repo(localdir, remote, branch);
+}
+
+/*
+ * This turns a remote repository into a local one if possible.
+ *
+ * The recognized formats are
+ *    git://host/repo[branch]
+ *    ssh://host/repo[branch]
+ *    http://host/repo[branch]
+ *    https://host/repo[branch]
+ *    file://repo[branch]
+ */
+static struct git_repository *is_remote_git_repository(const char *remote, const char *branch)
+{
+	char c, *localdir;
+	const char *p = remote;
+
+	while ((c = *p++) >= 'a' && c <= 'z')
+		/* nothing */;
+	if (c != ':')
+		return NULL;
+	if (*p++ != '/' || *p++ != '/')
+		return NULL;
+
+	/* Special-case "file://", since it's already local */
+	if (!strncmp(remote, "file://", 7))
+		remote += 7;
+
+	/*
+	 * Ok, we found "[a-z]*://", we've simplified the
+	 * local repo case (because libgit2 is insanely slow
+	 * for that), and we think we have a real "remote
+	 * git" format.
+	 *
+	 * We now create the SHA1 hash of the whole thing,
+	 * including the branch name. That will be our unique
+	 * unique local repository name.
+	 *
+	 * NOTE! We will create a local repository per branch,
+	 * because
+	 *
+	 *  (a) libgit2 remote tracking branch support seems to
+	 *      be a bit lacking
+	 *  (b) we'll actually check the branch out so that we
+	 *      can do merges etc too.
+	 *
+	 * so even if you have a single remote git repo with
+	 * multiple branches for different people, the local
+	 * caches will sadly force that to split into multiple
+	 * individual repositories.
+	 */
+	localdir = get_local_dir(remote, branch);
+	if (!localdir)
+		return NULL;
+
+	return get_remote_repo(localdir, remote, branch);
+}
 
 /*
  * If it's not a git repo, return NULL. Be very conservative.
@@ -31,6 +230,10 @@ struct git_repository *is_git_repository(const char *filename, const char **bran
 	while (flen && filename[--flen] != '[')
 		blen++;
 
+	/* Ignore slashes at the end of the repo name */
+	while (flen && filename[flen-1] == '/')
+		flen--;
+
 	if (!flen)
 		return NULL;
 
@@ -59,6 +262,13 @@ struct git_repository *is_git_repository(const char *filename, const char **bran
 		return dummy_git_repository;
 	}
 
+	repo = is_remote_git_repository(loc, branch);
+	if (repo) {
+		free(loc);
+		*branchp = branch;
+		return repo;
+	}
+
 	if (stat(loc, &st) < 0 || !S_ISDIR(st.st_mode)) {
 		free(loc);
 		free(branch);