The url library defines the following three functions for
retrieving the data specified by a URL. The actual retrieval protocol
depends on the URL’s URI scheme, and is performed by lower-level
scheme-specific functions. (Those lower-level functions are not
documented here, and generally should not be called directly.)
In each of these functions, the url argument can be either a
string or a parsed URL structure. If it is a string, that string is
passed through url-encode-url before using it, to ensure that
it is properly URI-encoded (see URI Encoding).
This function synchronously retrieves the data specified by url,
and returns a buffer containing the data. The return value is
nil if there is no data associated with the URL (as is the case
for dired, info, and mailto URLs).
If the optional argument silent is non-nil, progress
messages are suppressed. If the optional argument no-cookies is
non-nil, cookies are not stored or sent. If the optional
argument timeout is non-nil, it should be a number that
says (in seconds) how long to wait for a response before giving up.
This function retrieves url asynchronously, calling the function
callback when the object has been completely retrieved. The
return value is the buffer into which the data will be inserted, or
nil if the process has already completed.
The callback function is called this way:
(apply callback status cbargs)
where status is a plist representing what happened during the retrieval, with most recent events first, or an empty list if no events have occurred. Each pair in the plist is one of:
(:redirect redirected-to)This means that the request was redirected to the URL redirected-to.
(:error (error-symbol . data))This means that an error occurred. If so desired, the error can be
signaled with (signal error-symbol data).
When the callback function is called, the current buffer is the one containing the retrieved data (if any). The buffer also contains any MIME headers associated with the data retrieval.
If the optional argument silent is non-nil, progress
messages are suppressed. If the optional argument no-cookies is
non-nil, cookies are not stored or sent.
This function acts like url-retrieve, but with limits on the
number of concurrently-running network processes. The option
url-queue-parallel-processes controls the number of concurrent
processes, and the option url-queue-timeout sets a timeout in
seconds.
To use this function, you must (require 'url-queue).
The value of this option is an integer specifying the maximum number
of concurrent url-queue-retrieve network processes. If the
number of url-queue-retrieve calls is larger than this number,
later ones are queued until earlier ones are finished.
The value of this option is a number specifying the maximum lifetime
of a url-queue-retrieve network process, once it is started.
If a process is not finished by then, it is killed and removed from
the queue.