Erlang -- WebTool User Guide

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WebTool
User's Guide
Version 0.8.9.1

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Chapters

- WebTool User Guide
  - Top of chapter
  - Introduction
  - Starting WebTool
  - Using WebTool
  - Start a web based tool
  - Stop a web based tool
  - Develop new web based tools

# 1 WebTool User Guide

### 1.1 Introduction

WebTool provides an easy and efficient way to implement web based tools with Erlang/OTP. WebTool configures and starts the webserver and the various web based tools.

All tools that shall run under WebTool must have a *.tool file in the code path or in its priv directory. When WebTool starts it searches the code path for such files. For each ebin directory in the path, the priv directory is also searched. The *.tool files contain the configuration data for each web based tool.

### 1.2 Starting WebTool

Start WebTool by calling the function webtool:start/0 or webtool:start/2. If webtool:start/0 is used the start page of WebTool is available at http://localhost:8888/ or http://127.0.0.1:8888/, and the directory containing the root directory for the webserver, is assumed to be webtool-<vsn>/priv.

Use webtool:start/2 if the default path for the root directory, port, ip-number or server name can not be used. See the Reference Manual for webtool for more information.

WebTool, with the default configuration as in start/0, can also be started with the start_webtool script which is available in the priv directory of the WebTool application. See the Reference Manual for start_webtool for further information about this script. For Windows users, the batch file start_webtool.bat can be used for the same purpose.

### 1.3 Using WebTool

Start WebTool and point the browser to the corresponding URL. At the top of the page there is a frame with a link named WebTool. Click that link and a page where it is possible to start the available tools will appear in the main frame.

### 1.4 Start a web based tool

Click on the link labeled WebTool in the topmost frame, select the checkbox for each tool to start and click on the button labeled Start. A link to each tool that WebTool succeeded to start will appear in the topmost frame.

### 1.5 Stop a web based tool

Click on the link labeled WebTool in the topmost frame. Select Stop Tools in the left frame. Select the checkbox for each tool to stop and click on the button labeled Stop.

### 1.6 Develop new web based tools

WebTool can be used as a framework when developing new web based tools.

A web based tool running under WebTool will typically consist of three parts.

- A *.tool file which defines how WebTool can find the tool's configuration data
- The Erlang code generating the web interface to the tool (HTML code)
- The tool itself.

In most cases it is a good idea to separate the code for creation of the html-pages and the code for the logic. This increases the readability of the code and the logic might be possible to reuse.

#### The *.tool file

When WebTool starts it searches the current path for *.tool files to find all available tools. The *.tool file contains a version identifier and a list of tuples which is the configuration data. The version identifier specifies the *.tool file version, i.e. not the version of webtool. Currently the only valid version is "1.2" and the only valid configuration tag is config_func. config_func specifies which function WebTool must call to get further configuration data for the tool. This means that a *.tool file generally must look like this:

       {version,"1.2"}.
       [{config_func,{Module,Function,Arguments}}].

Module is the name of the module where the callback function is defined. Function is the name of the callback function, and Arguments is the list of arguments to the callback function.

#### The configuration function

The *.tool file points out a configuration function. This function must return a list of configuration parameters (see the Reference Manual for webtool).

The web_data parameter is mandatory and it specifies the name of the tool and the link to the tool's start page. All other parameters are optional.

If the tool requires any processes to run, the start parameter specifies the function that WebTool must call in order to start the process(es).

The alias parameters are passed directly on to the webserver (INETS). The webserver has three ways to create dynamic web pages CGI, Eval Scheme and Erl Scheme. All tools running under WebTool must use Erl Scheme.

Erl Scheme tries to resemble plain CGI. The big difference is that Erl Scheme can only execute Erlang code. The code will furthermore be executed on the same instance as the webserver.

An URL which calls an Erlang function with Erl Scheme can have the following syntax:

    http://Servername:Port/ErlScriptAlias/Mod/Func<?QueryString>

An alias parameter in the configuration function can be an ErlScriptAlias as used in the above URL. The definition of an ErlScriptAlias shall be like this:

{alias,{erl_alias,Path,[Modules]}}, e.g.

{alias,{erl_alias,"/testtool",[helloworld]}}

The following URL will then cause a call to the function helloworld:helloworld/2 (if WebTool is started with default settings i.e. servername "localhost" and port 8888):

http://localhost:8888/testtool/helloworld/helloworld

Note that the module helloworld must be in the code path of the node running WebTool.

Functions that are called via the Erl Scheme must take two arguments, Environment and Input.

- Environment is a list of key/value tuples.
- Input is the part of the URL after the "?", i.e. the part of the URL containing name-value pairs. If the page was called with the URL:
  http://localhost:8888/testtool/helloworld/helloworld?input1=one&amp;input2=two
  Input will be the string "input1=one&amp;input2=two". In the module httpd in the INETS application there is a function parse_query which will parse such a string and return a list of key-value tuples.

An alias parameter in the configuration function can also be a normal path alias. This can e.g. be used to point out a directory where HTML files are stored. The following definition states that the URL http://localhost:8888/mytool_home/ really points to the directory /usr/local/otp/lib/myapp-1.0/priv:

{alias,{"/mytool_home","/usr/local/otp/lib/myapp-1.0/priv"}}

See the INETS documentation, especially the module mod_esi, for a more in depth coverage of the Erl Scheme.

#### A small example

A Hello World example that uses Erl Scheme would look like this. Note that this example does not have a process running and thus does not need a start parameter in the configuration function.

helloworld.erl:

            -module(helloworld).
            -export([config_data/0]).
            -export([helloworld/2]).

            config_data()->
                {testtool,
                 [{web_data,{"TestTool","/testtool/helloworld/helloworld"}},
                  {alias,{erl_alias,"/testtool",[helloworld]}}]}.

            helloworld(_Env,_Input)->
                [header(),html_header(),helloworld_body(),html_end()].

            header() ->
                header("text/html").

            header(MimeType) ->
                "Content-type: " ++ MimeType ++ "\r\n\r\n".

            html_header() ->
                "<HTML>
                   <HEAD>
                      <TITLE>Hello world Example </TITLE>
                   </HEAD>\n".

            helloworld_body()->
                "<BODY>Hello World</BODY>".

            html_end()->
                "</HTML>".

To use this example with WebTool a *.tool file must be created and added to a directory in the current path, e.g. the same directory as the compiled helloworld.beam.

testtool.tool:

            {version,"1.2"}.
            [{config_func, {helloworld,config_data,[]}}].

When helloworld.erl is compiled, start WebTool by calling the function webtool:start() and point your browser to http://localhost:8888/. Select WebTool in the topmost frame and start TestTool from the web page. Click on the link labeled TestTool in the topmost frame.