![[Erlang Systems]](min_head.gif)
The Erlang Scripting Interface (ESI) provides a tight and
efficient interface to the execution of Erlang functions. Erlang
functions can be executed with two alternative schemes,
eval and erl. Both of these schemes can utilize
the functionality in an Erlang node efficiently.
Even though the server supports CGI-1.1 the use of the Erlang Scripting Interface (ESI) is encouraged for reasons of efficiency. CGI is resource intensive because of its design. CGI requires the server to fork a new OS process for each executable it needs to start.
An Erlang function can be written and executed as a CGI script
by using erl_call(3) in the erl_interface library, for
example. The cost is a forked OS process, as described
above. This is a waste of resources, at least when the Web
server itself is written in Erlang (as in this case).
The following config directives are described:
The erl scheme is designed to mimic plain CGI, but
without the extra overhead. An URL which calls an Erlang
erl function has the following syntax (regular
expression):
http://your.server.org/***/Mod[:/]Func(?QueryString|/PathInfo)
The module (Mod) referred to must be found in the code
path, and it must define a function (Func) with an arity
of two, i.e. Func(Env,Input). Env contains
information about the connecting client (see below), and
Input the QueryString or PathInfo as
defined in the
CGI specification.
*** above depends on how the
ErlScriptAlias config
directive has been used. Data returned from the function must
furthermore take the form as specified in the
CGI specification.
Take a look at httpd_example.erl in the
code release (UNIX: $INETS/src, Windows: %INETS\src) for
a clarifying example. Start an example server as described in
httpd:start/0 and test the
following from a browser (The server name for your example
server will differ!):
http://your.server.org:8888/cgi-bin/erl/httpd_example/get
httpd_example:get/2
and two input fields and a Submit button will promptly be
shown in the browser. Enter text into the input fields and
click on the Submit button. Something like this will promptly
be shown in the browser:
Environment:
[{query_string,"input1=blaha&input2=blaha"},
{server_software,"eddie/2.2"},
{server_name,"localhost"},
{gateway_interface,"CGI/1.1"},
{server_protocol,"HTTP/1.0"},
{server_port,8080},
{request_method,"GET"},
{remote_addr,"127.0.0.1"},
{script_name,"/cgi-bin/erl/httpd_example:get?input1=blaha&
input2=blaha"},
{http_accept_charset,"iso-8859-1,*,utf-8"},
{http_accept_language,"en"},
{http_accept,"image/gif, image/x-xbitmap, image/jpeg,
image/pjpeg, */*"},
{http_host,"localhost:8080"},
{http_user_agent,"Mozilla/4.03 [en] (X11; I;
Linux 2.0.30 i586)"},
{http_connection,"Keep-Alive"}, {http_referer,
"http://localhost:8080/cgi-bin/erl/httpd_example/get"}]
Input:
input1=blaha&input2=blaha
Parsed Input:
[{"input1","blaha"},{"input2","blaha"}]
http://your.server.org:8888/cgi-bin/erl/httpd_example:post
httpd_example:post/2. The
same thing will happen as in the example above but the HTTP POST
method will be used instead of the HTTP GET method.
http://your.server.org:8888/cgi-bin/erl/httpd_example:yahoo
httpd_example:yahoo/2
and the Yahoo! site will
promptly be shown in your browser.
 |
httpd:parse_query/1 is
used to generate the If a client closes the connection prematurely a message will
be sent to the function, that is either |
 |
The http://your.server.org/eval?httpd_example:
print(atom_to_list(apply(erlang,halt,[])))
which effectively will close down the Erlang node, that is
use the |
The eval scheme is straight-forward and does not
mimic the behavior of plain CGI. An URL which calls an Erlang
eval function has the following syntax:
http://your.server.org/***/Mod:Func(Arg1,...,ArgN)
The module (Mod) referred to must be found in the code
path, and data returned by the function (Func) is passed
back to the client. *** depends on how the EvalScriptAlias config directive
has been used. Data returned from the function must furthermore
take the form as specified in the
CGI specification.
Take a look at httpd_example.erl in the
code release (UNIX: $INETS/src, Windows: %INETS\src) for
an example. Start an example server as described in
httpd:start/0 and test the
following from a browser (The server name for your example
server will differ!):
http://your.server.org:8888/eval?httpd_example:print("Hi!")
httpd_example:print/1
and "Hi!" will promptly be shown in your browser.
Syntax: ErlScriptAlias url-path allowed-module allowed-module ...
Default: - None -
Module: mod_esi(3)
ErlScriptAlias marks all URLs matching url-path
as erl scheme scripts. A matching
URL is mapped into a specific module and function. The module
must be one of the allowed-module:s. For example:
ErlScriptAlias /cgi-bin/hit_me httpd_example md4
and a request to
http://your.server.org/cgi-bin/hit_me/httpd_example:yahoo
would refer to httpd_example:yahoo/2. Refer to the
Erl Scheme description above.
Syntax: EvalScriptAlias url-path allowed-module allowed-module ...
Default: - None -
Module: mod_esi(3)
EvalScriptAlias marks all URLs matching url-path
as eval scheme scripts. A matching
URL is mapped into a specific module and function. The module
must be one of the allowed-module:s. For example:
EvalScriptAlias /cgi-bin/hit_me_to httpd_example md5
and a request to
http://your.server.org/cgi-bin/hit_me_to/httpd_example:print("Hi!")
would refer to httpd_example:print/1. Refer to the
Eval Scheme description above.
Uses the following EWSAPI interaction data, if available:
{remote_user,RemoteUser}
Exports the following EWSAPI interaction data, if possible:
{mime_type,MimeType}
MimeType as defined in the
Mime Type Settings
section of httpd_core(3).
Uses the following EWSAPI functions: