Open the data at the HTTP server as a Prolog stream. URL is
either an atom specifying a URL or a list representing a
broken-down URL as specified below. After this predicate
succeeds the data can be read from Stream. After completion this
stream must be closed using the built-in Prolog predicate
close/1. Options provides additional options:
true), do not try to automatically
authenticate the client if a 401 (Unauthorized) status code
- Send authorization. See also http_set_authorization/2. Supported
- basic(+User, +Password)
- HTTP Basic authentication.
- HTTP Bearer authentication.
- digest(+User, +Password)
- HTTP Digest authentication. This option is only provided
if the plugin library(http/http_digest) is also loaded.
- Connect to the given Unix domain socket. In this scenario
the host name and port or ignored. If the server replies
with a redirect message and the host differs from the
original host as normal TCP connection is used to handle
the redirect. This option is inspired by
- Specify the
Connection header. Default is
Keep-alive. This maintains a pool of
available connections as determined by keep_connection/1.
Keep-alive connections can be closed explicitly using
http_close_keep_alive/1. Keep-alive connections may
significantly improve repetitive requests on the same server,
especially if the IP route is long, HTTPS is used or the
connection uses a proxy.
- Unify FinalURL with the final destination. This differs from
the original URL if the returned head of the original
indicates an HTTP redirect (codes 301, 302 or 303). Without a
redirect, FinalURL is the same as URL if URL is an atom, or a
URL constructed from the parts.
- header(Name, -AtomValue)
- If provided, AtomValue is unified with the value of the
indicated field in the reply header. Name is matched
case-insensitive and the underscore (_) matches the hyphen
(-). Multiple of these options may be provided to extract
multiple header fields. If the header is not available
AtomValue is unified to the empty atom ('').
- If provided, List is unified with a list of Name(Value) pairs
corresponding to fields in the reply header. Name and Value
follow the same conventions used by the
option. A pseudo header
status_code(Code) is added to provide
the HTTP status as an integer. See also
which provides the entire HTTP reply header in unparsed
- One of
head message can be
used in combination with the
header(Name, Value) option to
access information on the resource without actually fetching
the resource itself. The returned stream must be closed
post(Data) is provided, the default is
- Size is unified with the integer value of
in the reply header.
- Version is a pair
Major-Minor, where Major and Minor
are integers representing the HTTP version in the reply header.
- Ask for partial content. Range is a term Unit(From,To),
where From is an integer and To is either an integer or
end. HTTP 1.1 only supports Unit =
to ask for bytes 1000-1999, use the option
- Do not install a decoding filter for Encoding. For example,
raw_encoding('applocation/gzip') the system will not
decompress the stream if it is compressed using
- Unify Lines with a list of strings that represents the complete
reply header returned by the server. See also
true), do not automatically redirect
if a 3XX code is received. Must be combined with
status_code(Code) and one of the header options to read the
redirect reply. In particular, without
redirect is mapped to an exception.
- If this option is present and Code unifies with the HTTP
status code, do not translate errors (4xx, 5xx) into an
exception. Instead, http_open/3 behaves as if 2xx (success) is
returned, providing the application to read the error document
from the returned stream.
- Unify the output stream with Out and do not close it. This can
be used to upgrade a connection.
- If provided, set a timeout on the stream using set_stream/2.
With this option if no new data arrives within Timeout seconds
the stream raises an exception. Default is to wait forever
- Issue a
POST request on the HTTP server. Data is
handed to http_post_data/3.
- Use an HTTP proxy to connect to the outside world. See also
socket:proxy_for_url/3. This option overrules the proxy
specification defined by socket:proxy_for_url/3.
- proxy(+Host, +Port)
- Synonym for
- Send authorization to the proxy. Otherwise the same as the
true, bypass proxy hooks. Default is
- Additional name-value parts are added in the order of
appearance to the HTTP request header. No interpretation is
- Sets the maximum length of a redirection chain. This is needed
for some IRIs that redirect indefinitely to other IRIs without
looping (e.g., redirecting to IRIs with a random element in them).
Max must be either a non-negative integer or the atom
The default value is
- Defines the value of the
User-Agent field of the HTTP
header. Default is
The hook http:open_options/2 can be used to provide default
options based on the broken-down URL. The option
status_code(-Code) is particularly useful to query REST
interfaces that commonly return status codes other than
that need to be be processed by the client code.
|URL||- is either an atom or string (url) or a list of parts.
When provided, this list may contain the fields
query_string (whose argument is an atom)
search (whose argument is a list of
Name=Value compound terms).
host is mandatory. The example below opens the
Note that values must not be quoted because the
library inserts the required quotes.
search([ q='Hello world',
error(existence_error(url, Id),Context) is raised if the
HTTP result code is not in the range 200..299. Context has the
context(Message, status(Code, TextCode)), where Code is the
numeric HTTP code and TextCode is the textual description thereof
provided by the server. Message may provide additional details or
may be unbound.
- See also
- - ssl_context/3 for SSL related options if
library(http/http_ssl_plugin) is loaded.