plz.el

plz is an HTTP library for Emacs. It uses curl as a backend, which avoids some of the issues with using Emacs’s built-in url library. It supports both synchronous and asynchronous requests. Its API is intended to be simple, natural, and expressive. Its code is intended to be simple and well-organized. Every feature is tested against httpbin.

Contents

Installation

GNU ELPA

plz is available in GNU ELPA. It may be installed in Emacs using the package-install command.

Manual

plz has no dependencies other than Emacs and curl. It’s known to work on Emacs 26.3 or later. To install it manually, simply place plz.el in your load-path and (require 'plz).

Usage

The main public function is plz, which sends an HTTP request and returns either the result of the specified type (for a synchronous request), or the curl process object (for asynchronous requests). For asynchronous requests, callback, error-handling, and finalizer functions may be specified, as well as various other options.

Examples

Synchronously GET a URL and return the response body as a decoded string (here, raw JSON):

(plz 'get "https://httpbin.org/user-agent")

#+RESULTS[47fef7e4780e9fac6c99d7661c29de580bf0fa14]:

"{\n \"user-agent\": \"curl/7.35.0\"\n}\n"

Synchronously GET a URL that returns a JSON object, and parse and return it as an alist:

(plz 'get "https://httpbin.org/get" :as #'json-read)

#+RESULTS[a117174ba62b2be3ea3f23e5c43662047b81bccf]:

((args)
 (headers
  (Accept . "*/*")
  (Accept-Encoding . "deflate, gzip")
  (Host . "httpbin.org")
  (User-Agent . "curl/7.35.0"))
 (url . "https://httpbin.org/get"))

Asynchronously POST a JSON object in the request body, then parse a JSON object from the response body, and call a function with the result:

(plz 'post "https://httpbin.org/post"
  :headers '(("Content-Type" . "application/json"))
  :body (json-encode '(("key" . "value")))
  :as #'json-read
  :then (lambda (alist)
          (message "Result: %s" (alist-get 'data alist))))

#+RESULTS[3f4fdd16c4980bf36c3930e91f69cc379cca4a35]:

Result: {"key":"value"}

Synchronously download a JPEG file, then create an Emacs image object from the data:

(let ((jpeg-data (plz 'get "https://httpbin.org/image/jpeg" :as 'binary)))
  (create-image jpeg-data nil 'data))

#+RESULTS[fbe8a6c8cb097ac08e992ea90bdbd50e7337a385]:

(image :type jpeg :data ""ÿØÿà^@^PJFIF...")

Functions

plz(method url &key headers body else finally noquery (as ‘string) (then ‘sync) (body-type ‘text) (decode t decode-s) (connect-timeout plz-connect-timeout) (timeout plz-timeout))

Request METHOD from URL with curl. Return the curl process object or, for a synchronous request, the selected result.

HEADERS may be an alist of extra headers to send with the request.

BODY-TYPE may be text to send BODY as text, or binary to send it as binary.

AS selects the kind of result to pass to the callback function THEN, or the kind of result to return for synchronous requests. It may be:

• buffer to pass the response buffer.
• binary to pass the response body as an undecoded string.
• string to pass the response body as a decoded string.
• response to pass a plz-response struct.
• A function, to pass its return value; it is called in the response buffer, which is narrowed to the response body (suitable for, e.g. json-read).
• file to pass a temporary filename to which the response body has been saved without decoding.
• (file FILENAME) to pass FILENAME after having saved the response body to it without decoding. FILENAME must be a non-existent file; if it exists, it will not be overwritten, and an error will be signaled.

If DECODE is non-nil, the response body is decoded automatically. For binary content, it should be nil. When AS is binary, DECODE is automatically set to nil.

THEN is a callback function, whose sole argument is selected above with AS. Or THEN may be sync to make a synchronous request, in which case the result is returned directly.

ELSE is an optional callback function called when the request fails (i.e. if curl fails, or if the HTTP response has a non-2xx status code). It is called with one argument, a plz-error structure. If ELSE is nil, an error is signaled when the request fails, either plz-curl-error or plz-http-error as appropriate, with a plz-error structure as the error data. For synchronous requests, this argument is ignored.

FINALLY is an optional function called without argument after THEN or ELSE, as appropriate. For synchronous requests, this argument is ignored.

CONNECT-TIMEOUT and TIMEOUT are a number of seconds that limit how long it takes to connect to a host and to receive a response from a host, respectively.

NOQUERY is passed to make-process, which see.

Queueing

plz provides a simple system for queueing HTTP requests. First, make a plz-queue struct by calling make-plz-queue. Then call plz-queue with the struct as the first argument, and the rest of the arguments being the same as those passed to plz. Then call plz-run to run the queued requests.

All of the queue-related functions return the queue as their value, making them easy to use. For example:

(defvar my-queue (make-plz-queue :limit 2))

(plz-run
 (plz-queue my-queue
   'get "https://httpbin.org/get?foo=0"
   :then (lambda (body) (message "%s" body))))

(let ((queue (make-plz-queue :limit 2))
      (urls '("https://httpbin.org/get?foo=0"
              "https://httpbin.org/get?foo=1")))
  (plz-run
   (dolist (url urls queue)
     (plz-queue queue 'get url
       :then (lambda (body) (message "%s" body))))))

You may also clear a queue with plz-clear, which cancels any active or queued requests and calls their :else functions. And plz-length returns the number of a queue’s active and queued requests.

• You can customize settings in the plz group, but this can only be used to adjust a few defaults. It’s not intended that changing or binding global variables be necessary for normal operation.

Changelog

Additions

• Support for HTTP HEAD requests. (Thanks to USHIN, Inc. for sponsoring.)

Changes

• Allow sending POST and PUT requests without bodies. (#16. Thanks to Joseph Turner for reporting. Thanks to USHIN, Inc. for sponsoring.)

Fixes

• All 2xx HTTP status codes are considered successful. (#17. Thanks to Joseph Turner for reporting. Thanks to USHIN, Inc. for sponsoring.)
• Errors are signaled with error data correctly.

Internal

• Test suite explicitly tests with both HTTP/1.1 and HTTP/2.
• Test suite also tests with Emacs versions 27.2, 28.1, and 28.2.

Additions

• Handle HTTP proxy headers from Curl. (#2. Thanks to Alan Third and Sawyer Zheng for reporting.)

Fixes

• Replaced words not in Ispell’s default dictionaries (so checkdoc linting succeeds).

0.2.1

Fixes

• Handle when Curl process is interrupted.

Added

• Simple request queueing.

Initial release.

Credits

• Thanks to Chris Wellons, author of the Elfeed feed reader and the popular blog null program, for his invaluable advice, review, and encouragement.

Development

Bug reports, feature requests, suggestions — oh my!

Note that plz is a young library, and its only client so far is Ement.el. There are a variety of HTTP and curl features it does not yet support, since they have not been needed by the author. Patches are welcome, as long as they include passing tests.

Copyright assignment

This package is part of GNU Emacs, being distributed in GNU ELPA. Contributions to this project must follow GNU guidelines, which means that, as with other parts of Emacs, patches of more than a few lines must be accompanied by having assigned copyright for the contribution to the FSF. Contributors who wish to do so may contact [email protected] to request the assignment form.

License

GPLv3