The following predicates are exported from this file while their implementation is defined in imported modules or non-module files loaded by this module.
- reply_html_page(:Head, :Body) is det
- reply_html_page(+Style, :Head, :Body) is det
- Provide the complete reply as required by http_wrapper.pl for a page
constructed from Head and Body. The HTTP
Content-type
is
provided by html_current_option/1.
- See also
- - reply_html_partial/1 to avoid adding a
DOCTYPE
, and
required outer HTML elements such as <html>
.
- html_meta(+Heads) is det
- This directive can be used to declare that an HTML rendering
rule takes HTML content as argument. It has two effects. It
emits the appropriate meta_predicate/1 and instructs the
built-in editor (PceEmacs) to provide proper colouring for the
arguments. The arguments in Head are the same as for
meta_predicate or can be constant
html
. For example:
:- html_meta
page(html,html,?,?).
- http_handler(+Path, :Closure, +Options) is det
- Register Closure as a handler for HTTP requests. Path is either an
absolute path such as
'/home.html'
or a term Alias(Relative).
Where Alias is associated with a concrete path using http:location/3
and resolved using http_absolute_location/3. Relative can be a
single atom or a term `Segment1/Segment2/...`, where each element is
either an atom or a variable. If a segment is a variable it matches
any segment and the binding may be passed to the closure. If the
last segment is a variable it may match multiple segments. This
allows registering REST paths, for example:
:- http_handler(root(user/User), user(Method, User),
[ method(Method),
methods([get,post,put])
]).
user(get, User, Request) :-
...
user(post, User, Request) :-
...
If an HTTP request arrives at the server that matches Path, Closure
is called as below, where Request is the parsed HTTP request.
call(Closure, Request)
Options is a list containing the following options:
- authentication(+Type)
- Demand authentication. Authentication methods are pluggable. The
library http_authenticate.pl provides a plugin for user/password
based
Basic
HTTP authentication.
- chunked
- Use
Transfer-encoding: chunked
if the client allows for it.
- condition(:Goal)
- If present, the handler is ignored if Goal does not succeed.
- content_type(+Term)
- Specifies the content-type of the reply. This value is currently
not used by this library. It enhances the reflexive capabilities
of this library through http_current_handler/3.
- id(+Atom)
- Identifier of the handler. The default identifier is the
predicate name. Used by http_location_by_id/2 and
http_link_to_id/3.
- hide_children(+Bool)
- If
true
on a prefix-handler (see prefix), possible children
are masked. This can be used to (temporary) overrule part of the
tree.
- method(+Method)
- Declare that the handler processes Method. This is equivalent to
methods([Method])
. Using method(*)
allows for all methods.
- methods(+ListOfMethods)
- Declare that the handler processes all of the given methods. If
this option appears multiple times, the methods are combined.
- prefix
- Call Pred on any location that is a specialisation of Path. If
multiple handlers match, the one with the longest path is used.
Options defined with a prefix handler are the default options
for paths that start with this prefix. Note that the handler
acts as a fallback handler for the tree below it:
:- http_handler(/, http_404([index('index.html')]),
[spawn(my_pool),prefix]).
- priority(+Integer)
- If two handlers handle the same path, the one with the highest
priority is used. If equal, the last registered is used. Please
be aware that the order of clauses in multifile predicates can
change due to reloading files. The default priority is 0 (zero).
- spawn(+SpawnOptions)
- Run the handler in a separate thread. If SpawnOptions is an
atom, it is interpreted as a thread pool name (see
create_thread_pool/3). Otherwise the options are passed to
http_spawn/2 and from there to thread_create/3. These options
are typically used to set the stack limits.
- time_limit(+Spec)
- One of
infinite
, default
or a positive number (seconds). If
default
, the value from the setting http:time_limit
is
taken. The default of this setting is 300 (5 minutes). See
setting/2.
Note that http_handler/3 is normally invoked as a directive and
processed using term-expansion. Using term-expansion ensures proper
update through make/0 when the specification is modified.
- Errors
- -
existence_error(http_location, Location)
- -
permission_error(http_method, Method, Location)
- See also
- - http_reply_file/3 and http_redirect/3 are generic
handlers to serve files and achieve redirects.
- http_delete_handler(+Spec) is det
- Delete handler for Spec. Typically, this should only be used for
handlers that are registered dynamically. Spec is one of:
- id(Id)
- Delete a handler with the given id. The default id is the
handler-predicate-name.
- path(Path)
- Delete handler that serves the given path.
- http_dispatch(Request) is det
- Dispatch a Request using http_handler/3 registrations. It performs
the following steps:
- Find a matching handler based on the
path
member of Request.
If multiple handlers match due to the prefix
option or
variables in path segments (see http_handler/3), the longest
specification is used. If multiple specifications of equal
length match the one with the highest priority is used.
- Check that the handler matches the
method
member of the
Request or throw permission_error(http_method, Method, Location)
- Expand the request using expansion hooks registered by
http_request_expansion/3. This may add fields to the request,
such the authenticated user, parsed parameters, etc. The
hooks may also throw exceptions, notably using http_redirect/3
or by throwing
http_reply(Term, ExtraHeader, Context)
exceptions.
- Extract possible fields from the Request using e.g.
method(Method)
as one of the options.
- Call the registered closure, optionally spawning the
request to a new thread or enforcing a time limit.
- http_request_expansion(:Goal, +Rank:number)
- Register Goal for expanding the HTTP request handler. Goal is called
as below. If Goal fail the request is passed to the next expansion
unmodified.
call(Goal, Request0, Request, Options)
If multiple goals are registered they expand the request in a
pipeline starting with the expansion hook with the lowest rank.
Besides rewriting the request, for example by validating the user
identity based on HTTP authentication or cookies and adding this to
the request, the hook may raise HTTP exceptions to indicate a bad
request, permission error, etc. See http_status_reply/4.
Initially, auth_expansion/3 is registered with rank 100
to deal
with the older http:authenticate/3 hook.
- http_current_handler(+Location, :Closure) is semidet
- http_current_handler(-Location, :Closure) is nondet
- True if Location is handled by Closure.
- http_current_handler(+Location, :Closure, -Options) is semidet
- http_current_handler(?Location, :Closure, ?Options) is nondet
- Resolve the current handler and options to execute it.
- http_location_by_id(+ID, -Location) is det
- True when Location represents the HTTP path to which the handler
with identifier ID is bound. Handler identifiers are deduced from
the http_handler/3 declaration as follows:
- Explicit id
-
If a term
id(ID)
appears in the option list of the handler, ID
it is used and takes preference over using the predicate.
- Using the handler predicate
-
ID matches a handler if the predicate name matches ID. The
ID may have a module qualification, e.g.,
Module:Pred
If the handler is declared with a pattern, e.g., root(user/User)
,
the location to access a particular user may be accessed using
e.g., user('Bob')
. The number of arguments to the compound term must
match the number of variables in the path pattern.
A plain atom ID can be used to find a handler with a pattern. The
returned location is the path up to the first variable, e.g.,
/user/
in the example above.
User code is adviced to use http_link_to_id/3 which can also add
query parameters to the URL. This predicate is a helper for
http_link_to_id/3.
- Errors
- -
existence_error(http_handler_id, Id)
.
- See also
- - http_link_to_id/3 and the library(http/html_write) construct
location_by_id(ID)
or its abbreviation #(ID)
- http_link_to_id(+HandleID, +Parameters, -HREF)
- HREF is a link on the local server to a handler with given ID,
passing the given Parameters. This predicate is typically used
to formulate a HREF that resolves to a handler implementing a
particular predicate. The code below provides a typical example.
The predicate user_details/1 returns a page with details about a
user from a given id. This predicate is registered as a handler.
The DCG user_link//1 renders a link to a user, displaying the
name and calling user_details/1 when clicked. Note that the
location (
root(user_details)
) is irrelevant in this equation and
HTTP locations can thus be moved freely without breaking this
code fragment.
:- http_handler(root(user_details), user_details, []).
user_details(Request) :-
http_parameters(Request,
[ user_id(ID)
]),
...
user_link(ID) -->
{ user_name(ID, Name),
http_link_to_id(user_details, [id(ID)], HREF)
},
html(a([class(user), href(HREF)], Name)).
- Arguments:
-
HandleID | - is either an atom, possibly module qualified
predicate or a compound term if the hander is defined using
a pattern. See http_handler/3 and http_location_by_id/2. |
Parameters | - is one of
|
- See also
- - http_location_by_id/2 and http_handler/3 for defining and
specifying handler IDs.
- http_reload_with_parameters(+Request, +Parameters, -HREF) is det
- Create a request on the current handler with replaced search
parameters.
- http_reply_file(+FileSpec, +Options, +Request) is det
- Options is a list of
- cache(+Boolean)
- If
true
(default), handle If-modified-since and send
modification time.
- mime_type(+Type)
- Overrule mime-type guessing from the filename as
provided by file_mime_type/2.
- static_gzip(+Boolean)
- If
true
(default false
) and, in addition to the plain
file, there is a .gz
file that is not older than the
plain file and the client acceps gzip
encoding, send
the compressed file with Transfer-encoding: gzip
.
- cached_gzip(+Boolean)
- If
true
(default false
) the system maintains cached
gzipped files in a directory accessible using the file
search path http_gzip_cache
and serves these similar
to the static_gzip(true)
option. If the gzip file
does not exist or is older than the input the file is
recreated.
- unsafe(+Boolean)
- If
false
(default), validate that FileSpec does not
contain references to parent directories. E.g.,
specifications such as www('../../etc/passwd')
are
not allowed.
- headers(+List)
- Provides additional reply-header fields, encoded as a
list of Field(Value).
If caching is not disabled, it processes the request headers
If-modified-since
and Range
.
- throws
- -
http_reply(not_modified)
- -
http_reply(file(MimeType, Path))
- http_redirect(+How, +To, +Request) is det
- Redirect to a new location. The argument order, using the
Request as last argument, allows for calling this directly from
the handler declaration:
:- http_handler(root(.),
http_redirect(moved, myapp('index.html')),
[]).
- Arguments:
-
How | - is one of moved , moved_temporary or see_other |
To | - is an atom, a aliased path as defined by
http_absolute_location/3. or a term location_by_id(Id) or its
abbreviations #(Id) or #(Id)+Parameters . If To is not absolute,
it is resolved relative to the current location. |
- http_404(+Options, +Request) is det
- Reply using an "HTTP 404 not found" page. This handler is
intended as fallback handler for prefix handlers. Options
processed are:
- index(Location)
- If there is no path-info, redirect the request to
Location using http_redirect/3.
- Errors
- -
http_reply(not_found(Path))
- http_switch_protocol(:Goal, +Options)
- Send an
"HTTP 101 Switching Protocols"
reply. After sending
the reply, the HTTP library calls call(Goal, InStream,
OutStream)
, where InStream and OutStream are the raw streams to
the HTTP client. This allows the communication to continue using
an an alternative protocol.
If Goal fails or throws an exception, the streams are closed by
the server. Otherwise Goal is responsible for closing the
streams. Note that Goal runs in the HTTP handler thread.
Typically, the handler should be registered using the spawn
option if http_handler/3 or Goal must call thread_create/3 to
allow the HTTP worker to return to the worker pool.
The streams use binary (octet) encoding and have their I/O
timeout set to the server timeout (default 60 seconds). The
predicate set_stream/2 can be used to change the encoding,
change or cancel the timeout.
This predicate interacts with the server library by throwing an
exception.
The following options are supported:
- header(+Headers)
- Backward compatible. Use
headers(+Headers)
.
- headers(+Headers)
- Additional headers send with the reply. Each header takes the
form Name(Value).
- 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.
- 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
extended datatypes.
- 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
extended datatypes.
- 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.
- 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.
- http_parameters(+Request, ?Parms) is det
- http_parameters(+Request, ?Parms, :Options) is det
- Get HTTP GET or POST form-data, applying type validation,
default values, etc. Provided options are:
- attribute_declarations(:Goal)
- Causes the declarations for an attributed named A to be
fetched using
call(Goal, A, Declarations)
.
- form_data(-Data)
- Return the data read from the GET por POST request as a
list Name = Value. All data, including name/value pairs
used for Parms, is unified with Data.
The attribute_declarations hook allows sharing the declaration
of attribute-properties between many http_parameters/3 calls. In
this form, the requested attribute takes only one argument and
the options are acquired by calling the hook. For example:
...,
http_parameters(Request,
[ sex(Sex)
],
[ attribute_declarations(http_param)
]),
...
http_param(sex, [ oneof(male, female),
description('Sex of the person')
]).
- bug
- - If both request parameters (?name=value&...) and a POST are
present the parameters are extracted from the request parameters.
Still, as it is valid to have request parameters in a POST request
this predicate should not process POST requests. We will keep the
current behaviour as the it is not common for a request to have both
request parameters and a POST data of the type
application/x-www-form-urlencoded
.
In the unlikely event this poses a problem the request may be
specified as [method(get)
|Request].
- http_parameters(+Request, ?Parms) is det
- http_parameters(+Request, ?Parms, :Options) is det
- Get HTTP GET or POST form-data, applying type validation,
default values, etc. Provided options are:
- attribute_declarations(:Goal)
- Causes the declarations for an attributed named A to be
fetched using
call(Goal, A, Declarations)
.
- form_data(-Data)
- Return the data read from the GET por POST request as a
list Name = Value. All data, including name/value pairs
used for Parms, is unified with Data.
The attribute_declarations hook allows sharing the declaration
of attribute-properties between many http_parameters/3 calls. In
this form, the requested attribute takes only one argument and
the options are acquired by calling the hook. For example:
...,
http_parameters(Request,
[ sex(Sex)
],
[ attribute_declarations(http_param)
]),
...
http_param(sex, [ oneof(male, female),
description('Sex of the person')
]).
- bug
- - If both request parameters (?name=value&...) and a POST are
present the parameters are extracted from the request parameters.
Still, as it is valid to have request parameters in a POST request
this predicate should not process POST requests. We will keep the
current behaviour as the it is not common for a request to have both
request parameters and a POST data of the type
application/x-www-form-urlencoded
.
In the unlikely event this poses a problem the request may be
specified as [method(get)
|Request].
- http_current_request(-Request) is semidet
- Returns the HTTP request currently being processed. Fails
silently if there is no current request. This typically happens
if a goal is run outside the HTTP server context.
- http_peer(+Request, -PeerIP:atom) is semidet
- True when PeerIP is the IP address of the connection peer. If the
connection is established via a proxy or CDN we try to find the
initiating peer. Currently supports:
Fastly-client-ip
X-real-ip
X-forwarded-for
- Direct connections
- bug
- - The
X-forwarded-for
header is problematic. According to
Wikipedia, the
original client is the first, while according to
AWS
it is the last.
- http_server(:Goal, :Options) is det
- Create a server at Port that calls Goal for each parsed request.
Options provide a list of options. Defined options are
- port(?Address)
- Port to bind to. Address is either a port or a term
Host:Port. The port may be a variable, causing the system
to select a free port. See tcp_bind/2.
- unix_socket(+Path)
- Instead of binding to a TCP port, bind to a Unix Domain
Socket at Path.
- entry_page(+URI)
- Affects the message printed while the server is started.
Interpreted as a URI relative to the server root.
- tcp_socket(+Socket)
- If provided, use this socket instead of the creating one and
binding it to an address. The socket must be bound to an
address. Note that this also allows binding an HTTP server to
a Unix domain socket (
AF_UNIX
). See socket_create/2.
- workers(+Count)
- Determine the number of worker threads. Default is 5. This
is fine for small scale usage. Public servers typically need
a higher number.
- timeout(+Seconds)
- Maximum time of inactivity trying to read the request after a
connection has been opened. Default is 60 seconds. See
set_stream/1 using the timeout option.
- keep_alive_timeout(+Seconds)
- Time to keep `Keep alive' connections alive. Default is
2 seconds.
- stack_limit(+Bytes)
- Stack limit to use for the workers. The default is inherited
from the
main
thread.
If you need to control resource usage you may consider the
spawn
option of http_handler/3 and library(thread_pool).
- silent(Bool)
- If
true
(default false
), do not print an informational
message that the server was started.
A typical initialization for an HTTP server that uses
http_dispatch/1 to relay requests to predicates is:
:- use_module(library(http/thread_httpd)).
:- use_module(library(http/http_dispatch)).
start_server(Port) :-
http_server(http_dispatch, [port(Port)]).
Note that multiple servers can coexist in the same Prolog
process. A notable application of this is to have both an HTTP
and HTTPS server, where the HTTP server redirects to the HTTPS
server for handling sensitive requests.
- http_current_server(:Goal, ?Port) is nondet
- True if Goal is the goal of a server at Port.
- deprecated
- - Use
http_server_property(Port, goal(Goal))
- http_server_property(?Port, ?Property) is nondet
- True if Property is a property of the HTTP server running at
Port. Defined properties are:
- goal(:Goal)
- Goal used to start the server. This is often
http_dispatch/1.
- scheme(-Scheme)
- Scheme is one of
http
or https
.
- start_time(?Time)
- Time-stamp when the server was created.
- http_workers(?Port, -Workers) is nondet
- http_workers(+Port, +Workers:int) is det
- Query or set the number of workers for the server at this port. The
number of workers is dynamically modified. Setting it to 1 (one) can
be used to profile the worker using tprofile/1.
- See also
- - library(http/http_dyn_workers) implements dynamic management of
the worker pool depending on usage.
- http_add_worker(+Port, +Options) is det
- Add a new worker to the HTTP server for port Port. Options
overrule the default queue options. The following additional
options are processed:
- max_idle_time(+Seconds)
- The created worker will automatically terminate if there is
no new work within Seconds.
- http_current_worker(?Port, ?ThreadID) is nondet
- True if ThreadID is the identifier of a Prolog thread serving
Port. This predicate is motivated to allow for the use of
arbitrary interaction with the worker thread for development and
statistics.
- http_stop_server(+Port, +Options)
- Stop the indicated HTTP server gracefully. First stops all
workers, then stops the server.
- To be done
- - Realise non-graceful stop
- http_spawn(:Goal, +Options) is det
- Continue this connection on a new thread. A handler may call
http_spawn/2 to start a new thread that continues processing the
current request using Goal. The original thread returns to the
worker pool for processing new requests. Options are passed to
thread_create/3, except for:
- pool(+Pool)
- Interfaces to library(thread_pool), starting the thread
on the given pool.
If a pool does not exist, this predicate calls the multifile
hook create_pool/1 to create it. If this predicate succeeds
the operation is retried.
The following predicates are exported, but not or incorrectly documented.