cli: introduce the concept of user defined hooks

Add mechanism for running user defined hooks. Hooks are executables or
symlinks to executables stored under the new notmuch hooks directory,
<database-path>/.notmuch/hooks.

No hooks are introduced here, but adding support for a hook is now a simple
matter of calling the new notmuch_run_hook() function at an appropriate
location with the hook name.

Signed-off-by: Jani Nikula <jani@nikula.org>

Makefile.local

@@ -299,6 +299,7 @@ notmuch_client_srcs =		\
 	debugger.c		\
 	gmime-filter-reply.c	\
 	gmime-filter-headers.c	\
+	hooks.c			\
 	notmuch.c		\
 	notmuch-config.c	\
 	notmuch-count.c		\

hooks.c

@@ -0,0 +1,93 @@
+/* notmuch - Not much of an email program, (just index and search)
+ *
+ * This file is part of notmuch.
+ *
+ * Copyright © 2011 Jani Nikula
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see http://www.gnu.org/licenses/ .
+ *
+ * Author: Jani Nikula <jani@nikula.org>
+ */
+
+#include "notmuch-client.h"
+#include <sys/wait.h>
+
+int
+notmuch_run_hook (const char *db_path, const char *hook)
+{
+    char *hook_path;
+    int status = 0;
+    pid_t pid;
+
+    hook_path = talloc_asprintf (NULL, "%s/%s/%s/%s", db_path, ".notmuch",
+				 "hooks", hook);
+    if (hook_path == NULL) {
+	fprintf (stderr, "Out of memory\n");
+	return 1;
+    }
+
+    /* Check access before fork() for speed and simplicity of error handling. */
+    if (access (hook_path, X_OK) == -1) {
+	/* Ignore ENOENT. It's okay not to have a hook, hook dir, or even
+	 * notmuch dir. Dangling symbolic links also result in ENOENT, but
+	 * we'll ignore that too for simplicity. */
+	if (errno != ENOENT) {
+	    fprintf (stderr, "Error: %s hook access failed: %s\n", hook,
+		     strerror (errno));
+	    status = 1;
+	}
+	goto DONE;
+    }
+
+    pid = fork();
+    if (pid == -1) {
+	fprintf (stderr, "Error: %s hook fork failed: %s\n", hook,
+		 strerror (errno));
+	status = 1;
+	goto DONE;
+    } else if (pid == 0) {
+	execl (hook_path, hook_path, NULL);
+	/* Same as above for ENOENT, but unlikely now. Indicate all other errors
+	 * to parent through non-zero exit status. */
+	if (errno != ENOENT) {
+	    fprintf (stderr, "Error: %s hook execution failed: %s\n", hook,
+		     strerror (errno));
+	    status = 1;
+	}
+	exit (status);
+    }
+
+    if (waitpid (pid, &status, 0) == -1) {
+	fprintf (stderr, "Error: %s hook wait failed: %s\n", hook,
+		 strerror (errno));
+	status = 1;
+	goto DONE;
+    }
+
+    if (!WIFEXITED (status) || WEXITSTATUS (status)) {
+	if (WIFEXITED (status)) {
+	    fprintf (stderr, "Error: %s hook failed with status %d\n",
+		     hook, WEXITSTATUS (status));
+	} else if (WIFSIGNALED (status)) {
+	    fprintf (stderr, "Error: %s hook terminated with signal %d\n",
+		     hook, WTERMSIG (status));
+	}
+	status = 1;
+    }
+
+  DONE:
+    talloc_free (hook_path);
+
+    return status;
+}

notmuch-client.h

@@ -235,6 +235,9 @@ void
 notmuch_config_set_maildir_synchronize_flags (notmuch_config_t *config,
 					      notmuch_bool_t synchronize_flags);
 
+int
+notmuch_run_hook (const char *db_path, const char *hook);
+
 notmuch_bool_t
 debugger_is_active (void);