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A useful HTTP client

Emacs has quite a few HTTP clients but they are all rather old. This is my attempt at a modern one.

The idea is to always use callbacks to collect the response.


An interactive function is included:

M-x web-get [RET] url

I'm hoping to make this plugin to ffap.


Here's a basic example:

;; -*- lexical-binding: t -*-
(require 'web)

(let ((url "http://feeds.pinboard.in/json/u:nicferrier"))
   (lambda (httpc header my-data)
     (with-current-buffer (get-buffer-create "nicfeed")
       (goto-char (point-max))
       (insert my-data)))
   :url url))

That creates the buffer nicfeed with the downloaded contents in it.

Here's a POST:

;; -*- lexical-binding: t -*-

(require 'web)

(let ((query-data (make-hash-table :test 'equal)))
  (puthash 'name "nic" query-data)
  (puthash 'email "nic@example.com" query-data)
    (lambda (con header data)
      (message "data received is: %s" data))
    :url "http://localhost:8001/someplace"
    :data query-data))

SSL works too:

;; -*- lexical-binding: t -*-

(require 'web)

 (lambda (conn headers data)
   (message "%S %S" headers data))
 :url "https://duckduckgo.com/"
 :data '(("q" . "search+engine")))

and JSON has special support and a *different* callback form:

;; -*- lexical-binding: t -*-

(require 'web)

  (lambda (data conn headers)
     (message "%S" data))
  :url "http://someurlthatproducesjson/")

The JSON callback form allows just data to be collected:

;; -*- lexical-binding: t -*-
(require 'web)

  (lambda (data)
     (message "%S" data))
  :url "http://someurlthatproducesjson/")

and the JSON support allows the usual overriding of JSON type mappings:

;; -*- lexical-binding: t -*-
(require 'web)

  (lambda (data)
    ;; data will be a list
    (message "The car => %s" (car data)))
  :url "http://someurlthatproducesjson/"
  :json-object-type 'list)

You can also upload files with web:

;; -*- lexical-binding: t -*-
(require 'web)

(let ((myfile (get-buffer-create "my-file.txt")))
  (with-current-buffer myfile 
     (insert "hello!!!!")
     (write-file "my-file.txt"))
   (lambda (con hdr data) (message "the file was uploaded!"))
   :url "http://localhost:9020"
   :data `(("my-file" . ,myfile))
   :mime-type web-multipart-mimetype))

The request MIME type has to be set to web-multipart-mimetype which is multipart/form-data. When set like that any buffer visiting a file used as a parameter value will be uploaded as a file.

web uses Emacs' default MIME checking on files to try to establish the right content-type to send the file as.

Currently no extra encoding is done so binary files probably can't be sent.

Most wanted

I'd really like web to not have to take a callback there and then but to be able to return some sort of future. The alteration would allow things like this:

(web-json-post :future :url "http://marmalade-repo.org/login")


I keep the web package on http://marmalade-repo.org but if you want to install it manually you can just install the package file web.el.

Using elpakit you can also get testing.


web-header-parse data

Parse an HTTP response header.

Each header line is stored in the hash with a symbol form of the header name.

The status line is expected to be the first line of the data. The status is stored in the header as well with the following keys:


which are stored as symbols the same as the normal header keys.

web-http-call method callback &key url (host "localhost") (port 80) secure (path "/") extra-headers data (mime-type web/request-mimetype) (mode 'batch) logging

Make an HTTP method to the url or the host, port, path and send data.

If url is specified then it takes precedence over secure, host, port and path. url may be HTTP or HTTPS.

Important note: any query in url is currently IGNORED!

secure is nil by default but if t then SSL is used.

port is 80 by default. Even if secure it t. If you manually specify secure you should manually specify port to be 443. Using url negates the need for that, an SSL url will work correctly.

extra-headers is an alist or a hash-table of extra headers to send to the server.

data is of mime-type. We try to interpret data and mime-type usefully:

If mime-type is application/form-www-url-encoded then web-to-query-string is used to to format the data into a POST body.

When the request comes back the callback is called. callback is always passed 3 arguments: the HTTP connection which is a process object, the HTTP header which is a hash-table and data, which is normally a string. data depends somewhat on the context. See below.

mode defines what it means for the request to cause the callback to be fired. When mode is stream then the callback is called for every chunk of data received after the header has arrived. This allows streaming data to somewhere else; hence stream mode. In this mode callback's data argument is a single chunk of the stream or :done when the stream ends.

The default mode is batch which collects all the data from the response before calling callback with all the data as a string.

web-http-get callback &key url (host "localhost") (port 80) (path "/") extra-headers (mode 'batch)) (logging t)

Make a GET calling callback with the result.

For information on url or path, host, port and also extra-headers and mode see web-http-call.

The callback probably won't work unless you set lexical-binding to t.

web-http-post callback &key url host ("localhost") port (80) path ("/") extra-headers data mime-type (web/request-mimetype) mode ((quote batch)) logging (t)

Make a POST and call callback with the result.

For information on url or path, host, port and also mode see web-http-call.

The callback probably won't work unless you set lexical-binding to t.

web-json-default-expectation-failure data http-con headers

Default expectation callback for JSON expectation errors.

web-json-post callback &key url data headers json-array-type (json-array-type) json-object-type (json-object-type) json-key-type (json-key-type) expectation-failure-callback ((quote web-json-default-expectation-failure))

POST data to url expecting a JSON response sent to callback.

See web-json-expected-mimetypes-list for the list of Mime Types we accept JSON for. This may be let bound. If the expectation is not met then expectation-failure-callback is called being passed the callback parameters. By default expectation-failure-callback is web-json-default-expectation-failure.

The callback is called as:


so the function may be defined like this:

  (lambda (data &rest stuff) ...)

headers may be specified, these are treated as extra-headers to be sent with the request.

The data is sent as application/x-www-form-urlencoded.

json-array-type, json-object-type and json-key-type, if present, are used to let bind the json-read variables of the same name affecting the resulting lisp structure.

web-json/parse json-candidate-data &key json-array-type (json-array-type) json-object-type (json-object-type) json-key-type (json-key-type)

Parse DATA as JSON and return the result.

web-to-query-string object

Convert object (a hash-table or alist) to an HTTP query string.

If object is of type hash-table then the keys and values of the hash are iterated into the string depending on their types.

Keys with number and string values are encoded as "key=value" in the resulting query.

Keys with a boolean value (or any other value not already described) are encoded just as "key".

Keys may be symbols or strings.