Erlang 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.


The following data types are used in the functions for mod_esi:

env() =

{EnvKey()::atom(), Value::term()}

Currently supported key value pairs

{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 be no_peercert, and if TLS is not used (HTTP or connection is lost due to network failure) the value will be undefined.

{script_name, string()}

Request URI

{http_LowerCaseHTTPHeaderName, string()}

example: {http_content_type, "text/html"}


deliver(SessionID, Data) -> ok | {error, Reason}

  • SessionID = term()
  • Data = string() | io_list() | binary()
  • Reason = term()

This function is only intended to be used from functions called by the Erl Scheme interface to deliver parts of the content to the user.

Sends data from an Erl Scheme script back to the client.


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.

ESI Callback Functions


Module:Function(SessionID, Env, Input)-> _

  • SessionID = term()
  • Env = env()
  • Input = string()

Module must be found in the code path and export Function with an arity of three. An erlScriptAlias must also be set up in the configuration file for the web server.

If the HTTP request is a 'post' request and a body is sent, content_length is the length of the posted data. If 'get' is used, query_string is the data after ? in the URL.

ParsedHeader is the HTTP request as a key-value tuple list. The keys in ParsedHeader are in lower case.

SessionID is an identifier the server uses when deliver/2 is called. Do not assume anything about the datatype.

Use this callback function to generate dynamic web content dynamically. When a part of the page is generated, send the data back to the client through deliver/2. 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.

Module:Function(Env, Input)-> Response

  • Env = env()
  • Input = string()
  • Response = string()

This callback format consumes much memory, as the whole response must be generated before it is sent to the user. This function is deprecated and is only kept for backwards compatibility. For new development, use Module:Function/3.