[PATCH v2 01/16] 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  | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 util/search-path.h  | 24 +++++++++++++++++++++++
 3 files changed, 80 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..5eac367
--- /dev/null
+++ b/util/search-path.c
@@ -0,0 +1,55 @@
+#include "search-path.h"
+#include <stdlib.h>
+#include <talloc.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 *c = NULL, *save = NULL, *tok;
+    size_t n;
+    int dfd = -1;
+    notmuch_bool_t ret = FALSE;
+
+    if (strchr(exename, '/')) {
+	if (0 == access(exename, X_OK))
+	    return TRUE;
+	else
+	    return FALSE;
+    }
+    
+    c = getenv("PATH");
+    if (c)
+	c = talloc_strdup(NULL, c);
+    else {
+	n = confstr(_CS_PATH, NULL, 0);
+	c = (char*)talloc_size(NULL, n);
+	if (!c)
+	    return FALSE;
+	confstr(_CS_PATH, c, n);
+    }
+
+    tok = strtok_r(c, ":", &save);
+    while (tok) {
+	dfd = open(tok, O_DIRECTORY | O_RDONLY);
+	if (dfd != -1) {
+	    if (!faccessat(dfd, exename, X_OK, 0)) {
+		ret = TRUE;
+		goto done;
+	    }
+	    close(dfd);
+	}
+	tok = strtok_r(NULL, ":", &save);
+    }
+done:
+    if (dfd != -1)
+	close(dfd);
+    if (c)
+	talloc_free(c);
+    return ret;
+}
diff --git a/util/search-path.h b/util/search-path.h
new file mode 100644
index 0000000..727d0b3
--- /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.rc3