[PATCH v2 1/2] cli: introduce the concept of user defined hooks

[Austin Clements]

I like it.  See below for some nits.

Quoth Jani Nikula on Dec 04 at  1:16 am:
> 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 at nikula.org>
> 
> ---
> 
> v2: Switch to git style hooks in a hook directory as suggested by Austin
> Clements in IRC. Update manpage and add polish.
> ---
>  Makefile.local   |    1 +
>  notmuch-client.h |    3 ++
>  notmuch-hook.c   |   63 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 67 insertions(+), 0 deletions(-)
>  create mode 100644 notmuch-hook.c
> 
> diff --git a/Makefile.local b/Makefile.local
> index c94402b..a1665e1 100644
> --- a/Makefile.local
> +++ b/Makefile.local
> @@ -302,6 +302,7 @@ notmuch_client_srcs =		\
>  	notmuch-config.c	\
>  	notmuch-count.c		\
>  	notmuch-dump.c		\
> +	notmuch-hook.c		\
>  	notmuch-new.c		\
>  	notmuch-reply.c		\
>  	notmuch-restore.c	\
> diff --git a/notmuch-client.h b/notmuch-client.h
> index b50cb38..a91ad6c 100644
> --- a/notmuch-client.h
> +++ b/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);
>  
> diff --git a/notmuch-hook.c b/notmuch-hook.c
> new file mode 100644
> index 0000000..fc32044
> --- /dev/null
> +++ b/notmuch-hook.c
> @@ -0,0 +1,63 @@
> +/* 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 at nikula.org>
> + */
> +
> +#include "notmuch-client.h"
> +
> +int
> +notmuch_run_hook (const char *db_path, const char *hook)
> +{
> +    char *hook_path;
> +    int status = 0;

You use status as both a notmuch_status_t and for generic C library
results.  This seems a little weird.  You may or may not want to do
anything about it.

> +
> +    if (asprintf (&hook_path, "%s/%s/%s/%s", db_path, ".notmuch", "hooks",
> +		  hook) == -1)

asprintf isn't very portable.  Perhaps talloc_asprintf would be
better?  (And more idiomatic.)

> +	return NOTMUCH_STATUS_OUT_OF_MEMORY;
> +
> +    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 = NOTMUCH_STATUS_FILE_ERROR;
> +	}
> +	goto DONE;
> +    }
> +
> +    status = system (hook_path);

It would probably be better to fork/execl.  system is sensitive to all
sorts of weird things because it invokes the shell (e.g., spaces or
funny characters in db_path) and it plays funny games with signals.

Really proper error handling with fork/exec is a pain, but I think you
can get away with something simpler and even get rid of the access
call in the process.  Something like

ret = fork();
if (ret < 0) ...
else if (ret == 0) {
  ret = execl(hook_path, hook_path, NULL);
  if (ret != ENOENT && ret != EACCESS)
    print a real error message
  exit(0);
} else {
  waitpid(ret, &status, 0);
  if (status) .. checks you do now ..
}

I guess this wastes a fork if there is no hook script, so maybe the
access call is worth doing anyway.

> +    if (status) {
> +	if (WIFSIGNALED(status))
> +	    fprintf(stderr, "Error: %s hook terminated with signal %d\n", hook,
> +		    WTERMSIG(status));
> +	else
> +	    fprintf(stderr, "Error: %s hook failed with status %d\n", hook,
> +		    WEXITSTATUS(status));
> +
> +	status = NOTMUCH_STATUS_FILE_ERROR; /* Close enough */
> +    }
> +
> +  DONE:
> +    free (hook_path);
> +
> +    return status;
> +}