[PATCH 2/5] emacs: Utilities to manage asynchronous notmuch processes

[Mark Walters]

Hi

I am working my way through this set. 

On Sat, 18 May 2013, Austin Clements <amdragon at MIT.EDU> wrote:
> This provides a new notmuch-lib utility to start an asynchronous
> notmuch process that handles redirecting of stderr and checking of the
> exit status.  This is similar to `notmuch-call-notmuch-json', but for
> asynchronous processes (and it leaves output processing to the
> caller).
> ---
>  emacs/notmuch-lib.el |   73 +++++++++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 69 insertions(+), 4 deletions(-)
>
> diff --git a/emacs/notmuch-lib.el b/emacs/notmuch-lib.el
> index 59b1ce3..a543471 100644
> --- a/emacs/notmuch-lib.el
> +++ b/emacs/notmuch-lib.el
> @@ -383,18 +383,21 @@ signaled error.  This function does not return."
>    (error "%s" (concat msg (when extra
>  			    " (see *Notmuch errors* for more details)"))))
>  
> -(defun notmuch-check-async-exit-status (proc msg)
> +(defun notmuch-check-async-exit-status (proc msg &optional command err-file)
>    "If PROC exited abnormally, pop up an error buffer and signal an error.
>  
>  This is a wrapper around `notmuch-check-exit-status' for
>  asynchronous process sentinels.  PROC and MSG must be the
> -arguments passed to the sentinel."
> +arguments passed to the sentinel.  COMMAND and ERR-FILE, if
> +provided, are passed to `notmuch-check-exit-status'.  If COMMAND
> +is not provided, it is taken from `process-command'."
>    (let ((exit-status
>  	 (case (process-status proc)
>  	   ((exit) (process-exit-status proc))
>  	   ((signal) msg))))
>      (when exit-status
> -      (notmuch-check-exit-status exit-status (process-command proc)))))
> +      (notmuch-check-exit-status exit-status (or command (process-command proc))
> +				 nil err-file))))
>  
>  (defun notmuch-check-exit-status (exit-status command &optional output err-file)
>    "If EXIT-STATUS is non-zero, pop up an error buffer and signal an error.
> @@ -448,7 +451,7 @@ You may need to restart Emacs or upgrade your notmuch package."))
>  	))))
>  
>  (defun notmuch-call-notmuch-json (&rest args)
> -  "Invoke `notmuch-command' with `args' and return the parsed JSON output.
> +  "Invoke `notmuch-command' with ARGS and return the parsed JSON output.
>  
>  The returned output will represent objects using property lists
>  and arrays as lists.  If notmuch exits with a non-zero status,

I think I would prefer that this patch is split here. The stuff above is
"obviously correct" and could go in independently of the rest.
 
> @@ -469,6 +472,68 @@ an error."
>  	      (json-read)))
>  	(delete-file err-file)))))
>  
> +(defun notmuch-start-notmuch (name buffer sentinel &rest args)
> +  "Start and return an asynchronous notmuch command.
> +
> +This starts and returns an asynchronous process running
> +`notmuch-command' with ARGS.  The exit status is checked via
> +`notmuch-check-async-exit-status'.  Output written to stderr is
> +redirected and displayed when the process exits (even if the
> +process exits successfully).  NAME and BUFFER are the same as in
> +`start-process'.  SENTINEL is a process sentinel function to call
> +when the process exits, or nil for none.  The caller must *not*
> +invoke `set-process-sentinel' directly on the returned process,
> +as that will interfere with the handling of stderr and the exit
> +status."
> +
> +  ;; There is no way (as of Emacs 24.3) to capture stdout and stderr
> +  ;; separately for asynchronous processes, or even to redirect stderr
> +  ;; to a file, so we use a trivial shell wrapper to send stderr to a
> +  ;; temporary file and clean things up in the sentinel.
> +  (let* ((err-file (make-temp-file "nmerr"))
> +	 ;; Use a pipe
> +	 (process-connection-type nil)
> +	 (proc (apply #'start-process name buffer
> +		      "sh" "-c"
> +		      "ERR=\"$1\"; shift; exec \"$0\" \"$@\" 2>\"$ERR\""
> +		      notmuch-command err-file args)))

I would like some other people to look at this carefully as I won't spot
errors in quoting or shell side effects or whether PATH is the same as
emacs would use etc.

> +    (process-put proc 'err-file err-file)
> +    (process-put proc 'sub-sentinel sentinel)
> +    (process-put proc 'real-command (cons notmuch-command args))
> +    (set-process-sentinel proc #'notmuch-start-notmuch-sentinel)
> +    proc))
> +
> +(defun notmuch-start-notmuch-sentinel (proc event)
> +  (let ((err-file (process-get proc 'err-file))
> +	(sub-sentinel (process-get proc 'sub-sentinel))
> +	(real-command (process-get proc 'real-command)))
> +    (condition-case-unless-debug err
> +	(progn
> +	  ;; Invoke the sub-sentinel, if any
> +	  (when sub-sentinel
> +	    (funcall sub-sentinel proc event))
> +	  ;; Check the exit status.  This will signal an error if the
> +	  ;; exit status is non-zero.
> +	  (notmuch-check-async-exit-status proc event real-command err-file)
> +	  ;; If that didn't signal an error, then any error output was
> +	  ;; really warning output.  Show warnings, if any.
> +	  (let ((warnings
> +		 (with-temp-buffer
> +		   (unless (= (second (insert-file-contents err-file)) 0)
> +		     (end-of-line)
> +		     ;; Show first line; stuff remaining lines in the
> +		     ;; errors buffer.
> +		     (let ((l1 (buffer-substring (point-min) (point))))
> +		       (skip-chars-forward "\n")
> +		       (cons l1 (unless (eobp)
> +				  (buffer-substring (point) (point-max)))))))))
> +	    (when warnings
> +	      (notmuch-logged-error (car warnings) (cdr warnings)))))
> +      (error
> +       ;; Don't signal an error from a sentinel

I found this comment confusing as I was thinking of signal in the
non-technical sense of "tell the user".

Best wishes

Mark
> +       (message "%s" (error-message-string err))))
> +    (ignore-errors (delete-file err-file))))
> +
>  ;; This variable is used only buffer local, but it needs to be
>  ;; declared globally first to avoid compiler warnings.
>  (defvar notmuch-show-process-crypto nil)
> -- 
> 1.7.10.4