Most code doesn't need to use this directly; instead use
library(http/http_server), which combines this library with the
typical HTTP libraries that most servers need.
This module adds hooks to several parts of the HTTP libraries, making
them JSON-aware. Notably:
- Make http_read_data/3 convert
application/jsonrequest content to a JSON term.
- Cause http_open/3 to accept
post(json(Term)) to issue a POST
request with JSON content.
- Provide HTTP server and client utility predicates for reading
and replying JSON:
- Reply to exceptions in the server using an JSON document rather
then HTML if the
Accept header prefers application/json over
Typically JSON is used by Prolog HTTP servers. This module supports two
JSON representations: the classical representation and the new
representation supported by the SWI-Prolog version 7 extended data
types. Below is a skeleton for handling a JSON request, answering in
JSON using the classical interface.
<compute>(PrologIn, PrologOut), % application body
When using dicts, the conversion step is generally not needed and the
This module also integrates JSON support into the http client provided
by http_client.pl. Posting a JSON query and processing the JSON reply
(or any other reply understood by http_read_data/3) is as simple as
below, where Term is a JSON term as described in json.pl and reply is of
the same format if the server replies with JSON.
http_post(URL, json(Term), Reply, )
- See also
- - JSON Requests are discussed in http://json.org/JSONRequest.html
- - json.pl describes how JSON objects are represented in Prolog terms.
- - json_convert.pl converts between more natural Prolog terms and json
- http_client:http_convert_data(+In, +Fields, -Data, +Options)[multifile]
- Hook implementation that supports reading JSON documents. It
processes the following option:
- Where As is one of
dict. If the value is
json_read_dict/3 is used.
- is_json_content_type(+ContentType) is semidet
- True if ContentType is a header value (either parsed or as
atom/string) that denotes a JSON value.
- json_type(?MediaType) is semidet[multifile]
- True if MediaType is a JSON media type. http_json:json_type/1 is
a multifile predicate and may be extended to facilitate
|MediaType||- is a term Type/SubType, where both Type and
SubType are atoms.|
- http:post_data_hook(+Data, +Out:stream, +HdrExtra) is semidet[multifile]
- Hook implementation that allows http_post_data/3 posting JSON
objects using one of the forms below.
http_post(URL, json(Term), Reply, Options)
http_post(URL, json(Term, Options), Reply, Options)
If Options are passed, these are handed to json_write/3. In
addition, this option is processed:
- If As is
dict, json_write_dict/3 is used to write the
output. This is default if
json(Dict) is passed.
- To be done
- - avoid creation of intermediate data using chunked output.
- http_read_json(+Request, -JSON) is det
- http_read_json(+Request, -JSON, +Options) is det
- Extract JSON data posted to this HTTP request. Options are
passed to json_read/3. In addition, this option is processed:
- One of
term (default) to generate a classical Prolog
dict to exploit the SWI-Prolog version 7 data type
extensions. See json_read_dict/3.
domain_error(mimetype, Found) if the mimetype is
not known (see json_type/1).
domain_error(method, Method) if the request method is not
- http_read_json_dict(+Request, -Dict) is det
- http_read_json_dict(+Request, -Dict, +Options) is det
- Similar to http_read_json/2,3, but by default uses the version 7
- reply_json(+JSONTerm) is det
- reply_json(+JSONTerm, +Options) is det
- Formulate a JSON HTTP reply. See json_write/2 for details.
The processed options are listed below. Remaining options are
forwarded to json_write/3.
- The default
charset=UTF8 should not be required
because JSON is defined to be UTF-8 encoded, but some
clients insist on it.
- The default status is 200. REST API functions may use
other values from the 2XX range, such as 201 (created).
- One of
term (classical json representation) or
to use the new dict representation. If omitted and Term
is a dict,
dict is assumed. SWI-Prolog Version 7.
- reply_json_dict(+JSONTerm) is det
- reply_json_dict(+JSONTerm, +Options) is det
- As reply_json/1 and reply_json/2, but assumes the new dict based
data representation. Note that this is the default if the outer
object is a dict. This predicate is needed to serialize a list
of objects correctly and provides consistency with
http_read_json_dict/2 and friends.
- True when the accept encoding prefers JSON.
- json_status_reply(+Term, -MsgLines, -ExtraJSON) is semidet[private]
The following predicates are exported, but not or incorrectly documented.
- http_read_json_dict(Arg1, Arg2, Arg3)
- http_read_json(Arg1, Arg2, Arg3)
- reply_json_dict(Arg1, Arg2)
- reply_json(Arg1, Arg2)