run-command: expose is_executable function

Move the logic for 'is_executable()' from help.c to run_command.c and
expose it so that callers from outside help.c can access the function.
This is to enable run-command to be able to query if a file is
executable in a future patch.

Signed-off-by: Brandon Williams <bmwill@google.com>
Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 42 insertions, 0 deletions

diff --git a/run-command.c b/run-command.c
index a97d7bf9f..2ffbd7e67 100644
--- a/run-command.c
+++ b/run-command.c
@@ -117,6 +117,48 @@ static inline void close_pair(int fd[2])
 	close(fd[1]);
 }
 
+int is_executable(const char *name)
+{
+	struct stat st;
+
+	if (stat(name, &st) || /* stat, not lstat */
+	    !S_ISREG(st.st_mode))
+		return 0;
+
+#if defined(GIT_WINDOWS_NATIVE)
+	/*
+	 * On Windows there is no executable bit. The file extension
+	 * indicates whether it can be run as an executable, and Git
+	 * has special-handling to detect scripts and launch them
+	 * through the indicated script interpreter. We test for the
+	 * file extension first because virus scanners may make
+	 * it quite expensive to open many files.
+	 */
+	if (ends_with(name, ".exe"))
+		return S_IXUSR;
+
+{
+	/*
+	 * Now that we know it does not have an executable extension,
+	 * peek into the file instead.
+	 */
+	char buf[3] = { 0 };
+	int n;
+	int fd = open(name, O_RDONLY);
+	st.st_mode &= ~S_IXUSR;
+	if (fd >= 0) {
+		n = read(fd, buf, 2);
+		if (n == 2)
+			/* look for a she-bang */
+			if (!strcmp(buf, "#!"))
+				st.st_mode |= S_IXUSR;
+		close(fd);
+	}
+}
+#endif
+	return st.st_mode & S_IXUSR;
+}
+
 static char *locate_in_PATH(const char *file)
 {
 	const char *p = getenv("PATH");