#+TITLE: plz.el

#+PROPERTY: LOGGING nil

# NOTE: It would be preferable to put these at the bottom of the file under the export options heading, but it seems that "TEXINFO_DIR_CATEGORY" only works at the top of the file.
#+EXPORT_FILE_NAME: plz.texi
#+TEXINFO_DIR_CATEGORY: Emacs
#+TEXINFO_DIR_TITLE: Plz: (plz)
#+TEXINFO_DIR_DESC: HTTP library using Curl as a backend

# Note: This readme works with the org-make-toc <https://github.com/alphapapa/org-make-toc> package, which automatically updates the table of contents.

[[http://elpa.gnu.org/packages/plz.html][file:http://elpa.gnu.org/packages/plz.svg]]

#+HTML: <img src="images/mascot.png" align="right">

~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 [[https://httpbin.org/][httpbin]].

* Contents                                                         :noexport:
:PROPERTIES:
:TOC:      :include siblings
:END:
:CONTENTS:
- [[#installation][Installation]]
- [[#usage][Usage]]
  - [[#examples][Examples]]
  - [[#functions][Functions]]
  - [[#queueing][Queueing]]
- [[#changelog][Changelog]]
- [[#credits][Credits]]
- [[#development][Development]]
  - [[#copyright-assignment][Copyright assignment]]
:END:

* Installation
:PROPERTIES:
:TOC:      :depth 0
:END:

** GNU ELPA

~plz~ is available in [[http://elpa.gnu.org/packages/plz.html][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
:PROPERTIES:
:TOC:      :depth 1
:END:

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):

#+BEGIN_SRC elisp :exports both :results value code :cache yes
  (plz 'get "https://httpbin.org/user-agent")
#+END_SRC

#+RESULTS[47fef7e4780e9fac6c99d7661c29de580bf0fa14]:
#+begin_src elisp
  "{\n \"user-agent\": \"curl/7.35.0\"\n}\n"
#+end_src

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

#+BEGIN_SRC elisp :exports both :results value code :cache yes
  (plz 'get "https://httpbin.org/get" :as #'json-read)
#+END_SRC

#+RESULTS[a117174ba62b2be3ea3f23e5c43662047b81bccf]:
#+begin_src elisp
  ((args)
   (headers
    (Accept . "*/*")
    (Accept-Encoding . "deflate, gzip")
    (Host . "httpbin.org")
    (User-Agent . "curl/7.35.0"))
   (url . "https://httpbin.org/get"))
#+end_src

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:

#+BEGIN_SRC elisp :exports both :cache yes
  (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))))
#+END_SRC

#+RESULTS[3f4fdd16c4980bf36c3930e91f69cc379cca4a35]:
: Result: {"key":"value"}

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

#+BEGIN_SRC elisp :exports both :cache yes
  (let ((jpeg-data (plz 'get "https://httpbin.org/image/jpeg" :as 'binary)))
    (create-image jpeg-data nil 'data))
#+END_SRC

#+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~ may be a string, a buffer, or a list like ~(file FILENAME)~ to upload a file from disk.

   ~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, which will be narrowed to the response body and decoded according to ~DECODE~.
   - ~binary~ to pass the response body as an un-decoded string.
   - ~string~ to pass the response body as a decoded string.
   - ~response~ to pass a ~plz-response~ structure.
   - ~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.  ~FILENAME~ is passed through ~expand-file-name~, which see.
   - A function, which is called in the response buffer with it narrowed to the response body (suitable for, e.g. ~json-read~).

   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~; if the request fails and no ~ELSE~ function is given (see below), the argument will be a ~plz-error~ structure describing the error.  Or ~THEN~ may be ~sync~ to make a synchronous request, in which case the result is returned directly from this function.

   ~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, a ~plz-curl-error~ or ~plz-http-error~ is signaled when the request fails, with a ~plz-error~ structure as the error data.  For synchronous requests, this argument is ignored.

   ~NOTE~: In v0.8 of ~plz~, only one error will be signaled: ~plz-error~.  The existing errors, ~plz-curl-error~ and ~plz-http-error~, inherit from ~plz-error~ to allow applications to update their code while using v0.7 (i.e. any ~condition-case~ forms should now handle only ~plz-error~, not the other two).

   ~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.

   ~FILTER~ is an optional function to be used as the process filter for the curl process.  It can be used to handle HTTP responses in a streaming way.  The function must accept 2 arguments, the process object running curl, and a string which is output received from the process.  The default process filter inserts the output of the process into the process buffer.  The provided ~FILTER~ function should at least insert output up to the HTTP body into the process buffer.


** 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:

#+begin_src elisp :exports code
  (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))))
#+end_src

Or:

#+begin_src elisp :exports code
  (let ((queue (make-plz-queue :limit 2
                               :finally (lambda ()
                                          (message "Queue empty."))))
        (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))))))
#+end_src

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.

** Tips
:PROPERTIES:
:TOC:      :ignore (this)
:END:

+ 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
:PROPERTIES:
:TOC:      :depth 0
:END:

** 0.9.1

*Fixes*

+ Expand filenames when downloading to files (which was already applied to filenames passed for uploading).  (Thanks to [[https://github.com/josephmturner][Joseph Turner]].)  

** 0.9

*Compatibility*

+ The minimum supported Emacs version is now 27.1.  (It is no longer practical to test ~plz~ with Emacs versions older than 27.1.  For Emacs 26.3, an earlier version of ~plz~ may be used, or this version might be compatible, with or without minor changes, which the maintainer cannot offer support for.)

*Changes*

+ Option ~plz-timeout~ is removed.  (It was the default value for ~plz~'s ~:timeout~ argument, which is passed to Curl as its ~--max-time~ argument, limiting the total duration of a request operation.  This argument should be unset by default, because larger or slower downloads might not finish within a certain duration, and it is surprising to the user to have this option set by default, potentially causing requests to timeout unnecessarily.)
+ Using arguments ~:as 'file~ or ~:as '(file FILENAME)~ now passes the filename to Curl, allowing it to write the data to the file itself (rather than receiving the data into an Emacs buffer and then writing it to a file.  This improves performance when downloading large files, significantly reducing Emacs's CPU and memory usage).

*Fixes*

+ Improve workaround for Emacs's process sentinel-related issues.  (Don't try to process response a second time if Emacs calls the sentinel after ~plz~ has returned for a synchronous request.  See [[https://github.com/alphapapa/plz.el/issues/53][#53]].  Thanks to [[https://github.com/josephmturner][Joseph Turner]] for extensive help debugging, and to [[https://ushin.org/][USHIN]] for sponsoring some of this work.)
+ Inhibit buffer hooks when calling ~generate-new-buffer~ (as extra protection against "kill buffer?" prompts in case of errors).  (See [[https://github.com/alphapapa/plz.el/pull/52][#52]].  Thanks to [[https://github.com/mkcms][Michał Krzywkowski]].)
  - Avoid "kill buffer?" prompts in case of errors on Emacs versions before 28.  (See [[https://github.com/alphapapa/plz.el/pull/52][#52]] and [[https://github.com/alphapapa/plz.el/issues/57][#57]].  Thanks to [[https://github.com/mkcms][Michał Krzywkowski]].)  

*Development*

+ ~plz~ is now automatically tested against Emacs versions 27.1, 27.2, 28.1, 28.2, 29.1, 29.2, 29.3, and a recent snapshot of the ~master~ branch (adding 29.2 and 29.3).

** 0.8

*Additions*

+ Function ~plz~ now accepts a ~:filter~ argument which can be used to override the default process filter (e.g. for streaming responses).  ([[https://github.com/alphapapa/plz.el/pull/43][#43]], [[https://github.com/alphapapa/plz.el/pull/50][#50]].  Thanks to [[https://github.com/r0man][Roman Scherer]].)

** 0.7.3

*Fixes*
+ Info manual generation on GNU ELPA.  (Also, the Info manual is no longer committed to Git.)

** 0.7.2

*Fixes*
+ Don't delete preexisting files when downloading to a file.  ([[https://github.com/alphapapa/plz.el/pull/41][#41]]. Thanks to [[https://github.com/josephmturner][Joseph Turner]].)

** 0.7.1

*Fixes*
+ Handle HTTP 303 redirects.  (Thanks to [[https://github.com/hubisan][Daniel Hubmann]] for reporting.)

** 0.7

*Changes*
+ A new error signal, ~plz-error~, is defined.  The existing signals, ~plz-curl-error~ and ~plz-http-error~, inherit from it, so handling ~plz-error~ catches both.

  *NOTE:* The existing signals, ~plz-curl-error~ and ~plz-http-error~, are hereby deprecated, and they will be removed in v0.8.  Applications should be updated while using v0.7 to only expect ~plz-error~.

*Fixes*
+ Significant improvement in reliability by implementing failsafes and workarounds for Emacs's process-handling code.  (See [[https://github.com/alphapapa/plz.el/issues/3][#3]].)
+ STDERR output from curl processes is not included in response bodies (which sometimes happened, depending on Emacs's internal race conditions).  (Fixes [[https://github.com/alphapapa/plz.el/issues/23][#23]].)
+ Use ~with-local-quit~ for synchronous requests (preventing Emacs from complaining sometimes).  (Fixes [[https://github.com/alphapapa/plz.el/issues/26][#26]].)
+ Various fixes for ~:as 'buffer~ result type: decode body when appropriate; unset multibyte for binary; narrow to body; don't kill buffer prematurely.
+ When clearing a queue, don't try to kill finished processes.

*Internal*
+ Response processing now happens outside the process sentinel, so any errors (e.g. in user callbacks) are not signaled from inside the sentinel.  (This avoids the 2-second pause Emacs imposes in such cases.)
+ Tests run against a local instance of [[https://github.com/postmanlabs/httpbin][httpbin]] (since the ~httpbin.org~ server is often overloaded).
+ No buffer-local variables are defined anymore; process properties are used instead.

** 0.6

*Additions*
+ Function ~plz~'s ~:body~ argument now accepts a list like ~(file FILENAME)~ to upload a file from disk (by passing the filename to curl, rather than reading its content into Emacs and sending it to curl through the pipe).

*Fixes*
+ Function ~plz~'s docstring now mentions that the ~:body~ argument may also be a buffer (an intentional feature that was accidentally undocumented).
+ Handle HTTP 3xx redirects when using ~:as 'response~.

** 0.5.4

*Fixes*
+ Only run queue's ~finally~ function after queue is empty.  (New features should not be designed and released on a Friday.)

** 0.5.3

*Fixes*
+ Move new slot in ~plz-queue~ struct to end to prevent invalid byte-compiler expansions for already-compiled applications (which would require them to be recompiled after upgrading ~plz~).

** 0.5.2

*Fixes*
+ When clearing a queue, only call ~plz-queue~'s ~finally~ function when specified.

** 0.5.1

*Fixes*
+ Only call ~plz-queue~'s ~finally~ function when specified.  (Thanks to [[https://github.com/redchops][Dan Oriani]] for reporting.)

** 0.5

*Additions*
+ Struct ~plz-queue~'s ~finally~ slot, a function called when the queue is finished.

** 0.4

*Additions*
+ Support for HTTP ~HEAD~ requests.  (Thanks to [[https://ushin.org/][USHIN]] for sponsoring.)

*Changes*
+ Allow sending ~POST~ and ~PUT~ requests without bodies.  ([[https://github.com/alphapapa/plz.el/issues/16][#16]].  Thanks to [[https://github.com/josephmturner][Joseph Turner]] for reporting.  Thanks to [[https://ushin.org/][USHIN]] for sponsoring.)

*Fixes*
+ All 2xx HTTP status codes are considered successful.  ([[https://github.com/alphapapa/plz.el/issues/17][#17]].  Thanks to [[https://github.com/josephmturner][Joseph Turner]] for reporting.  Thanks to [[https://ushin.org/][USHIN]] 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.

** 0.3

*Additions*
+ Handle HTTP proxy headers from Curl. ([[https://github.com/alphapapa/plz.el/issues/2][#2]].  Thanks to [[https://github.com/alanthird][Alan Third]] and [[https://github.com/sawyerzheng][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.

** 0.2

*Added*
+ Simple request queueing.

** 0.1

Initial release.

* Credits

+  Thanks to [[https://github.com/skeeto][Chris Wellons]], author of the [[https://github.com/skeeto/elfeed][Elfeed]] feed reader and the popular blog [[https://nullprogram.com/][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 [[https://github.com/alphapapa/ement.el][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 [[https://www.gnu.org/software/emacs/][GNU Emacs]], being distributed in [[https://elpa.gnu.org/][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 [[mailto:emacs-devel@gnu.org][emacs-devel@gnu.org]] to request the assignment form.

* License
:PROPERTIES:
:TOC:      :ignore (this)
:END:

GPLv3

* COMMENT Export setup                                             :noexport:
:PROPERTIES:
:TOC:      :ignore (this descendants)
:END:

# Copied from org-super-agenda's readme, in which much was borrowed from Org's =org-manual.org=.

#+OPTIONS: broken-links:t *:t

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** File-local variables

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