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.
plz
is available in GNU ELPA. It may be installed in Emacs using the package-install
command.
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)
.
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.
Synchronously GET
a URL and return the response body as a decoded string (here, raw JSON):
(plz 'get "https://httpbin.org/user-agent")
"{\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)
((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))))
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))
(image :type jpeg :data ""ÿØÿà^@^PJFIF...")
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
fromURL
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 betext
to sendBODY
as text, orbinary
to send it as binary.AS
selects the kind of result to pass to the callback functionTHEN
, 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 aplz-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 passFILENAME
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. WhenAS
isbinary
,DECODE
is automatically set to nil.THEN
is a callback function, whose sole argument is selected above withAS
. OrTHEN
may besync
to make a synchronous request, in which case the result is returned directly.ELSE
is an optional callback function called when the request fails with one argument, aplz-error
struct. IfELSE
is nil, an error is signaled when the request fails, eitherplz-curl-error
orplz-http-error
as appropriate, with aplz-error
struct as the error data. For synchronous requests, this argument is ignored.FINALLY
is an optional function called without argument afterTHEN
orELSE
, as appropriate. For synchronous requests, this argument is ignored.CONNECT-TIMEOUT
andTIMEOUT
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 tomake-process
, which see.
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))))
Or:
(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.
Fixes
- Handle when Curl process is interrupted.
Added
- Simple request queueing.
Initial release.
- Thanks to Chris Wellons, author of the Elfeed feed reader and the popular blog null program, for his invaluable advice, review, and encouragement.
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.
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 emacs-devel@gnu.org to request the assignment form.
GPLv3