mod_esi behaviour (inets v9.4)
View SourceErlang Server Interface
This module defines the Erlang Server Interface (ESI) API. It is a more
efficient way of writing Erlang scripts for your Inets web server than writing
them as common CGI scripts.
Summary
Callbacks: ESI Callback Functions
Called by mod_esi in response to requests.
Functions
Sends data from an ESI script back to the client.
Types
-type env() :: {server_software, string()} | {server_name, string()} | {gateway_interface, string()} | {server_protocol, string()} | {server_port, integer()} | {request_method, string()} | {remote_adress, inet:ip_address()} | {peer_cert, undefined | no_peercert | public_key:der_encoded()} | {script_name, string()} | {http_LowerCaseHTTPHeaderName, string()}.
Environment data associated with a request.
Possible values
{server_software, string()}- Indicates the inets version.{server_name, string()}- The local hostname.{gateway_interface, string()}- Legacy string used in CGI, just ignore.{server_protocol, string()}- HTTP version, currently "HTTP/1.1"{server_port, integer()}- Servers port number.{request_method, "GET" | "PUT" | "DELETE" | "POST" | "PATCH"}- HTTP request method.{remote_adress, inet:ip_address()}- The clients ip address.{peer_cert, undefined | no_peercert | DER:binary()}- For TLS connections where client certificates are used this will be an ASN.1 DER-encoded X509-certificate as an Erlang binary. If client certificates are not used the value will beno_peercert, and if TLS is not used (HTTP or connection is lost due to network failure) the value will beundefined.{script_name, string()}- Request URI{http_LowerCaseHTTPHeaderName, string()}- example:{http_content_type, "text/html"}
-opaque session_id()
Identifies the requesting client.
Callbacks: ESI Callback Functions
-callback 'Function'(SessionID, Env, Input) -> {continue, State} | _ when SessionID :: session_id(), Env :: [env()], Input :: string() | ChunkedData, ChunkedData :: {first, Data :: binary()} | {continue, Data :: binary(), State :: term()} | {last, Data :: binary(), State :: term()}, State :: term().
Called by mod_esi in response to requests.
Module must be found in the code path and export Function with an arity of
three. An erl_script_alias must also be set up in the configuration file for
the web server, see the ESI properties documentation.
The Module and Function that are called depend on the URL. See the ESI
introductory documentation for more details.
mod_esi:deliver/2 shall be used to generate the response to the client, and
SessionID shall be passed as the first argument.
Chunking
This function may be called several times to chunk the response data. Notice
that the first chunk of data sent to the client must at least contain all HTTP
header fields that the response will generate. If the first chunk does not
contain the end of HTTP header, that is, "\r\n\r\n", the server assumes
that no HTTP header fields will be generated. This behaviour depends on the
httpd configuration, see below.
Parameters
SessionID: request identifier.Pass this to
mod_esi:deliver/2when generating a response.Env: environment data of the request, seeenv/0.Input: query data of a GET request or the body of a PUT or POST request.The default behavior (legacy reasons) for delivering the body, is that the whole body is gathered and converted to a string. But if the httpd config parameter
max_client_body_chunkis set, the body will be delivered as binary chunks instead. The maximum size of the chunks is eithermax_client_body_chunkor decided by the client if it uses HTTP chunked encoding to send the body.When using the chunking mechanism, this callback must return
{continue, State::term()}for all calls whereInputis{first, Data::binary()}or{continue, Data::binary(), State::term()}. WhenInputis{last, Data::binary(), State::term()}the return value will be ignored.The input
Stateis the last returnedState, in it the callback can include any data that it needs to keep track of when handling the chunks.
Note
Note that if the body is small all data may be delivered in only one chunk and
then the callback will be called with {last, Data::binary(), undefined}
without getting called with {first, Data::binary()}.
Setting a response status
To set the response status code, the special status response header can be
sent. For instance, to acknowledge creation of a resource and send an empty
JSON response body, one could pass the following:
"status: 201 Created\r\ncontent-type: application/json\r\n\r\n{}"
Functions
-spec deliver(SessionID, Data) -> ok | {error, Reason} when SessionID :: session_id(), Data :: iolist(), Reason :: bad_sessionID.
Sends data from an ESI script back to the client.
This function is only intended to be used from functions called by the ESI interface to deliver parts of the content to the user.
Note
If any HTTP header fields are added by the script, they must be in the first
call to deliver/2, and the data in the call must be a string.
Calls after the headers are complete can contain binary data to reduce copying
overhead. Do not assume anything about the data type of SessionID.
SessionID must be the value given as input to the ESI callback function that
you implemented.