Merge branch 'gb/shell-ext'

* gb/shell-ext:
  shell: Display errors from improperly-formatted command lines
  shell: Rewrite documentation and improve error message
  Add sample commands for git-shell
  Add interactive mode to git-shell for user-friendliness
  Allow creation of arbitrary git-shell commands

Documentation/git-shell.txt

@@ -3,24 +3,30 @@ git-shell(1)
 
 NAME
 ----
-git-shell - Restricted login shell for GIT-only SSH access
+git-shell - Restricted login shell for Git-only SSH access
 
 
 SYNOPSIS
 --------
-'$(git --exec-path)/git-shell' -c <command> <argument>
+'git shell' [-c <command> <argument>]
 
 DESCRIPTION
 -----------
-This is meant to be used as a login shell for SSH accounts you want
-to restrict to GIT pull/push access only. It permits execution only
-of server-side GIT commands implementing the pull/push functionality.
-The commands can be executed only by the '-c' option; the shell is not
-interactive.
-
-Currently, only four commands are permitted to be called, 'git-receive-pack'
-'git-upload-pack' and 'git-upload-archive' with a single required argument, or
-'cvs server' (to invoke 'git-cvsserver').
+
+A login shell for SSH accounts to provide restricted Git access. When
+'-c' is given, the program executes <command> non-interactively;
+<command> can be one of 'git receive-pack', 'git upload-pack', 'git
+upload-archive', 'cvs server', or a command in COMMAND_DIR. The shell
+is started in interactive mode when no arguments are given; in this
+case, COMMAND_DIR must exist, and any of the executables in it can be
+invoked.
+
+'cvs server' is a special command which executes git-cvsserver.
+
+COMMAND_DIR is the path "$HOME/git-shell-commands". The user must have
+read and execute permissions to the directory in order to execute the
+programs in it. The programs are executed with a cwd of $HOME, and
+<argument> is parsed as a command-line string.
 
 Author
 ------

contrib/git-shell-commands/README

+Sample programs callable through git-shell.  Place a directory named
+'git-shell-commands' in the home directory of a user whose shell is
+git-shell.  Then anyone logging in as that user will be able to run
+executables in the 'git-shell-commands' directory.
+
+Provided commands:
+
+help: Prints out the names of available commands.  When run
+interactively, git-shell will automatically run 'help' on startup,
+provided it exists.
+
+list: Displays any bare repository whose name ends with ".git" under
+user's home directory.  No other git repositories are visible,
+although they might be clonable through git-shell.  'list' is designed
+to minimize the number of calls to git that must be made in finding
+available repositories; if your setup has additional repositories that
+should be user-discoverable, you may wish to modify 'list'
+accordingly.

contrib/git-shell-commands/help

+#!/bin/sh
+
+if tty -s
+then
+	echo "Run 'help' for help, or 'exit' to leave.  Available commands:"
+else
+	echo "Run 'help' for help.  Available commands:"
+fi
+
+cd "$(dirname "$0")"
+
+for cmd in *
+do
+	case "$cmd" in
+	help) ;;
+	*) [ -f "$cmd" ] && [ -x "$cmd" ] && echo "$cmd" ;;
+	esac
+done

contrib/git-shell-commands/list

+#!/bin/sh
+
+print_if_bare_repo='
+	if "$(git --git-dir="$1" rev-parse --is-bare-repository)" = true
+	then
+		printf "%s\n" "${1#./}"
+	fi
+'
+
+find -type d -name "*.git" -exec sh -c "$print_if_bare_repo" -- \{} \; -prune 2>/dev/null

shell.c

@@ -2,6 +2,10 @@
 #include "quote.h"
 #include "exec_cmd.h"
 #include "strbuf.h"
+#include "run-command.h"
+
+#define COMMAND_DIR "git-shell-commands"
+#define HELP_COMMAND COMMAND_DIR "/help"
 
 static int do_generic_cmd(const char *me, char *arg)
 {
@@ -33,6 +37,86 @@ static int do_cvs_cmd(const char *me, char *arg)
 	return execv_git_cmd(cvsserver_argv);
 }
 
+static int is_valid_cmd_name(const char *cmd)
+{
+	/* Test command contains no . or / characters */
+	return cmd[strcspn(cmd, "./")] == '\0';
+}
+
+static char *make_cmd(const char *prog)
+{
+	char *prefix = xmalloc((strlen(prog) + strlen(COMMAND_DIR) + 2));
+	strcpy(prefix, COMMAND_DIR);
+	strcat(prefix, "/");
+	strcat(prefix, prog);
+	return prefix;
+}
+
+static void cd_to_homedir(void)
+{
+	const char *home = getenv("HOME");
+	if (!home)
+		die("could not determine user's home directory; HOME is unset");
+	if (chdir(home) == -1)
+		die("could not chdir to user's home directory");
+}
+
+static void run_shell(void)
+{
+	int done = 0;
+	static const char *help_argv[] = { HELP_COMMAND, NULL };
+	/* Print help if enabled */
+	run_command_v_opt(help_argv, RUN_SILENT_EXEC_FAILURE);
+
+	do {
+		struct strbuf line = STRBUF_INIT;
+		const char *prog;
+		char *full_cmd;
+		char *rawargs;
+		char *split_args;
+		const char **argv;
+		int code;
+		int count;
+
+		fprintf(stderr, "git> ");
+		if (strbuf_getline(&line, stdin, '\n') == EOF) {
+			fprintf(stderr, "\n");
+			strbuf_release(&line);
+			break;
+		}
+		strbuf_trim(&line);
+		rawargs = strbuf_detach(&line, NULL);
+		split_args = xstrdup(rawargs);
+		count = split_cmdline(split_args, &argv);
+		if (count < 0) {
+			fprintf(stderr, "invalid command format '%s': %s\n", rawargs,
+				split_cmdline_strerror(count));
+			free(split_args);
+			free(rawargs);
+			continue;
+		}
+
+		prog = argv[0];
+		if (!strcmp(prog, "")) {
+		} else if (!strcmp(prog, "quit") || !strcmp(prog, "logout") ||
+			   !strcmp(prog, "exit") || !strcmp(prog, "bye")) {
+			done = 1;
+		} else if (is_valid_cmd_name(prog)) {
+			full_cmd = make_cmd(prog);
+			argv[0] = full_cmd;
+			code = run_command_v_opt(argv, RUN_SILENT_EXEC_FAILURE);
+			if (code == -1 && errno == ENOENT) {
+				fprintf(stderr, "unrecognized command '%s'\n", prog);
+			}
+			free(full_cmd);
+		} else {
+			fprintf(stderr, "invalid command format '%s'\n", prog);
+		}
+
+		free(argv);
+		free(rawargs);
+	} while (!done);
+}
 
 static struct commands {
 	const char *name;
@@ -48,8 +132,10 @@ static struct commands {
 int main(int argc, char **argv)
 {
 	char *prog;
+	const char **user_argv;
 	struct commands *cmd;
 	int devnull_fd;
+	int count;
 
 	/*
 	 * Always open file descriptors 0/1/2 to avoid clobbering files
@@ -66,17 +152,28 @@ int main(int argc, char **argv)
 	/*
 	 * Special hack to pretend to be a CVS server
 	 */
-	if (argc == 2 && !strcmp(argv[1], "cvs server"))
+	if (argc == 2 && !strcmp(argv[1], "cvs server")) {
 		argv--;
+	} else if (argc == 1) {
+		/* Allow the user to run an interactive shell */
+		cd_to_homedir();
+		if (access(COMMAND_DIR, R_OK | X_OK) == -1) {
+			die("Interactive git shell is not enabled.\n"
+			    "hint: ~/" COMMAND_DIR " should exist "
+			    "and have read and execute access.");
+		}
+		run_shell();
+		exit(0);
+	} else if (argc != 3 || strcmp(argv[1], "-c")) {
+		/*
+		 * We do not accept any other modes except "-c" followed by
+		 * "cmd arg", where "cmd" is a very limited subset of git
+		 * commands or a command in the COMMAND_DIR
+		 */
+		die("Run with no arguments or with -c cmd");
+	}
 
-	/*
-	 * We do not accept anything but "-c" followed by "cmd arg",
-	 * where "cmd" is a very limited subset of git commands.
-	 */
-	else if (argc != 3 || strcmp(argv[1], "-c"))
-		die("What do you think I am? A shell?");
-
-	prog = argv[2];
+	prog = xstrdup(argv[2]);
 	if (!strncmp(prog, "git", 3) && isspace(prog[3]))
 		/* Accept "git foo" as if the caller said "git-foo". */
 		prog[3] = '-';
@@ -99,5 +196,21 @@ int main(int argc, char **argv)
 		}
 		exit(cmd->exec(cmd->name, arg));
 	}
-	die("unrecognized command '%s'", prog);
+
+	cd_to_homedir();
+	count = split_cmdline(prog, &user_argv);
+	if (count >= 0) {
+		if (is_valid_cmd_name(user_argv[0])) {
+			prog = make_cmd(user_argv[0]);
+			user_argv[0] = prog;
+			execv(user_argv[0], (char *const *) user_argv);
+		}
+		free(prog);
+		free(user_argv);
+		die("unrecognized command '%s'", argv[2]);
+	} else {
+		free(prog);
+		die("invalid command format '%s': %s", argv[2],
+		    split_cmdline_strerror(count));
+	}
 }