Windows: Wrap execve so that shell scripts can be invoked.

When an external git command is invoked, it can be a Bourne shell script.
This patch looks into the command file to see whether it is one.
In this case, the command line is rearranged to invoke the shell
with the proper arguments.

With this change, scripted git commands work. Command line arguments
to those scripts cannot be complex (contain spaces or double-quotes), yet.

Signed-off-by: Johannes Sixt <johannes.sixt@telecom.at>

2 files changed, 187 insertions, 0 deletions

diff --git a/compat/mingw.c b/compat/mingw.c
index 3ffff75ba..89b29c55e 100644
--- a/compat/mingw.c
+++ b/compat/mingw.c
@@ -86,6 +86,190 @@ char *mingw_getcwd(char *pointer, int len)
 	return ret;
 }
 
+static const char *parse_interpreter(const char *cmd)
+{
+	static char buf[100];
+	char *p, *opt;
+	int n, fd;
+
+	/* don't even try a .exe */
+	n = strlen(cmd);
+	if (n >= 4 && !strcasecmp(cmd+n-4, ".exe"))
+		return NULL;
+
+	fd = open(cmd, O_RDONLY);
+	if (fd < 0)
+		return NULL;
+	n = read(fd, buf, sizeof(buf)-1);
+	close(fd);
+	if (n < 4)	/* at least '#!/x' and not error */
+		return NULL;
+
+	if (buf[0] != '#' || buf[1] != '!')
+		return NULL;
+	buf[n] = '\0';
+	p = strchr(buf, '\n');
+	if (!p)
+		return NULL;
+
+	*p = '\0';
+	if (!(p = strrchr(buf+2, '/')) && !(p = strrchr(buf+2, '\\')))
+		return NULL;
+	/* strip options */
+	if ((opt = strchr(p+1, ' ')))
+		*opt = '\0';
+	return p+1;
+}
+
+/*
+ * Splits the PATH into parts.
+ */
+static char **get_path_split(void)
+{
+	char *p, **path, *envpath = getenv("PATH");
+	int i, n = 0;
+
+	if (!envpath || !*envpath)
+		return NULL;
+
+	envpath = xstrdup(envpath);
+	p = envpath;
+	while (p) {
+		char *dir = p;
+		p = strchr(p, ';');
+		if (p) *p++ = '\0';
+		if (*dir) {	/* not earlier, catches series of ; */
+			++n;
+		}
+	}
+	if (!n)
+		return NULL;
+
+	path = xmalloc((n+1)*sizeof(char*));
+	p = envpath;
+	i = 0;
+	do {
+		if (*p)
+			path[i++] = xstrdup(p);
+		p = p+strlen(p)+1;
+	} while (i < n);
+	path[i] = NULL;
+
+	free(envpath);
+
+	return path;
+}
+
+static void free_path_split(char **path)
+{
+	if (!path)
+		return;
+
+	char **p = path;
+	while (*p)
+		free(*p++);
+	free(path);
+}
+
+/*
+ * exe_only means that we only want to detect .exe files, but not scripts
+ * (which do not have an extension)
+ */
+static char *lookup_prog(const char *dir, const char *cmd, int isexe, int exe_only)
+{
+	char path[MAX_PATH];
+	snprintf(path, sizeof(path), "%s/%s.exe", dir, cmd);
+
+	if (!isexe && access(path, F_OK) == 0)
+		return xstrdup(path);
+	path[strlen(path)-4] = '\0';
+	if ((!exe_only || isexe) && access(path, F_OK) == 0)
+		return xstrdup(path);
+	return NULL;
+}
+
+/*
+ * Determines the absolute path of cmd using the the split path in path.
+ * If cmd contains a slash or backslash, no lookup is performed.
+ */
+static char *path_lookup(const char *cmd, char **path, int exe_only)
+{
+	char *prog = NULL;
+	int len = strlen(cmd);
+	int isexe = len >= 4 && !strcasecmp(cmd+len-4, ".exe");
+
+	if (strchr(cmd, '/') || strchr(cmd, '\\'))
+		prog = xstrdup(cmd);
+
+	while (!prog && *path)
+		prog = lookup_prog(*path++, cmd, isexe, exe_only);
+
+	return prog;
+}
+
+static int try_shell_exec(const char *cmd, char *const *argv, char **env)
+{
+	const char *interpr = parse_interpreter(cmd);
+	char **path;
+	char *prog;
+	int pid = 0;
+
+	if (!interpr)
+		return 0;
+	path = get_path_split();
+	prog = path_lookup(interpr, path, 1);
+	if (prog) {
+		int argc = 0;
+		const char **argv2;
+		while (argv[argc]) argc++;
+		argv2 = xmalloc(sizeof(*argv) * (argc+2));
+		argv2[0] = (char *)interpr;
+		argv2[1] = (char *)cmd;	/* full path to the script file */
+		memcpy(&argv2[2], &argv[1], sizeof(*argv) * argc);
+		pid = spawnve(_P_NOWAIT, prog, argv2, (const char **)env);
+		if (pid >= 0) {
+			int status;
+			if (waitpid(pid, &status, 0) < 0)
+				status = 255;
+			exit(status);
+		}
+		pid = 1;	/* indicate that we tried but failed */
+		free(prog);
+		free(argv2);
+	}
+	free_path_split(path);
+	return pid;
+}
+
+static void mingw_execve(const char *cmd, char *const *argv, char *const *env)
+{
+	/* check if git_command is a shell script */
+	if (!try_shell_exec(cmd, argv, (char **)env)) {
+		int pid, status;
+
+		pid = spawnve(_P_NOWAIT, cmd, (const char **)argv, (const char **)env);
+		if (pid < 0)
+			return;
+		if (waitpid(pid, &status, 0) < 0)
+			status = 255;
+		exit(status);
+	}
+}
+
+void mingw_execvp(const char *cmd, char *const *argv)
+{
+	char **path = get_path_split();
+	char *prog = path_lookup(cmd, path, 0);
+
+	if (prog) {
+		mingw_execve(prog, argv, environ);
+		free(prog);
+	} else
+		errno = ENOENT;
+
+	free_path_split(path);
+}
+
 #undef rename
 int mingw_rename(const char *pold, const char *pnew)
 {
diff --git a/compat/mingw.h b/compat/mingw.h
index a369ade9e..3ddef11ed 100644
--- a/compat/mingw.h
+++ b/compat/mingw.h
@@ -154,6 +154,9 @@ char *mingw_getcwd(char *pointer, int len);
 int mingw_rename(const char*, const char*);
 #define rename mingw_rename
 
+void mingw_execvp(const char *cmd, char *const *argv);
+#define execvp mingw_execvp
+
 sig_handler_t mingw_signal(int sig, sig_handler_t handler);
 #define signal mingw_signal