[PATCH v4] add util/search-path.{c, h} to test for executables in $PATH

[Daniel Kahn Gillmor <dkg@fifthhorseman.net>]

This is a utility function we can use to see whether an executable is
available.
---
 util/Makefile.local |  2 +-
 util/search-path.c  | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++
 util/search-path.h  | 24 ++++++++++++++++++++++++
 3 files changed, 75 insertions(+), 1 deletion(-)
 create mode 100644 util/search-path.c
 create mode 100644 util/search-path.h

diff --git a/util/Makefile.local b/util/Makefile.local
index 905f237..8b2b91b 100644
--- a/util/Makefile.local
+++ b/util/Makefile.local
@@ -5,7 +5,7 @@ extra_cflags += -I$(srcdir)/$(dir)
 
 libutil_c_srcs := $(dir)/xutil.c $(dir)/error_util.c $(dir)/hex-escape.c \
 		  $(dir)/string-util.c $(dir)/talloc-extra.c $(dir)/zlib-extra.c \
-		$(dir)/util.c
+		$(dir)/util.c $(dir)/search-path.c
 
 libutil_modules := $(libutil_c_srcs:.c=.o)
 
diff --git a/util/search-path.c b/util/search-path.c
new file mode 100644
index 0000000..9da21cb
--- /dev/null
+++ b/util/search-path.c
@@ -0,0 +1,50 @@
+#include "search-path.h"
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+
+
+notmuch_bool_t
+test_for_executable (const char *exename)
+{
+    char *path = NULL, *save = NULL, *tok;
+    notmuch_bool_t ret = FALSE;
+
+    if (strchr (exename, '/')) {
+	if (0 == access (exename, X_OK))
+	    return TRUE;
+	else
+	    return FALSE;
+    }
+
+    path = getenv ("PATH");
+    if (path)
+	path = strdup (path);
+    else {
+	size_t n = confstr (_CS_PATH, NULL, 0);
+	path = (char *) malloc (n);
+	if (! path)
+	    return FALSE;
+	confstr (_CS_PATH, path, n);
+    }
+
+    tok = strtok_r (path, ":", &save);
+    while (tok) {
+	int dir_fd = open (tok, O_DIRECTORY | O_RDONLY);
+	if (dir_fd != -1) {
+	    int access = faccessat (dir_fd, exename, X_OK, 0);
+	    close (dir_fd);
+	    if (access == 0) {
+		ret = TRUE;
+		break;
+	    }
+	}
+	tok = strtok_r (NULL, ":", &save);
+    }
+    if (path)
+	free (path);
+    return ret;
+}
diff --git a/util/search-path.h b/util/search-path.h
new file mode 100644
index 0000000..14c4d14
--- /dev/null
+++ b/util/search-path.h
@@ -0,0 +1,24 @@
+#ifndef _SEARCH_PATH_H
+#define _SEARCH_PATH_H
+
+#include "notmuch.h"
+
+/* can an executable be found with the given name?
+ *
+ * Return TRUE only if we can find something to execute with the
+ * associated name.
+ *
+ * if the name has a '/' in it, we look for it directly with
+ * access(exename, X_OK).
+ *
+ * otherwise, we look for it in $PATH (or in confstr(_CS_PATH), if
+ * $PATH is unset).
+ *
+ * This should match the logic for execvp (as well as matching user
+ * expectations, hopefully).
+ */
+
+notmuch_bool_t
+test_for_executable (const char *exename);
+
+#endif
-- 
2.7.0