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The ISAPI extension

By Christian Aberger, Robert van Engelen, and Chris Moutsos.

# Overview

SOAP/XML and REST Web services can be easily created and deployed as gSOAP standalone services or installed as (Fast)CGI applications. In addition, the `mod_gsoap` Internet Server Application Programming Interface (ISAPI) extension offers the ability to run gSOAP services directly inside the Microsoft Internet Information Server (IIS). This is achieved through an ISAPI extension DLL. The ISAPI extension supports the deployment of multiple gSOAP services that can run together with the usual services on IIS. This approach offers a production-quality Web services deployment scenario.

The `mod_gsoap` ISAPI extension is designed to keep things simple so that existing gSOAP services can be recompiled for IIS deployment without modification of the source code. The `mod_gsoap.dll` DLL (dynamic link library) implements the ISAPI extension that uses the query string of the request URL to determine which gSOAP back-end service to run. It will select the appropriate service DLL to load the service dynamically, if not already present. Therefore, to add more services, simply create new DLLs for these services. IIS need not be restarted to deploy them.

# Installation

To build and install the `mod_gsoap.dll` ISAPI extension for gSOAP:

In `gsoap\mod_gsoap\gsoap_win\isapi\`, there are two directories called `vs2006` and `vs2010`. Choose the appropriate directory and installation instructions based on your version of Visual Studio.

Visual Studio 2010 Service Pack 1 (version 10.0.40219.1) or later (IDE):

- Using Visual Studio 2010 SP1 or later, open `all4iis.sln` that can be found in `gsoap\mod_gsoap\gsoap_win\isapi\vs2010\` in the gSOAP package.
- Go to View|Other Windows|Property Manager. Select any of the projects, select the Release build dropdown, then double-click on PropertySheet.
- Under the Common Properties dropdown, choose VC++ Directories and select Executable Directories. Add the full path to the `gsoap\bin\win32` directory in the unpacked gSOAP package that contains the `soapcpp2.exe` tool.
- Under the C/C++ dropdown, choose General and select Additional Include Directories. Add the `gsoap\` directory that contains `stdsoap2.h`. Press OK.
- Click Build|Build Solution to build the ISAPI extension for gSOAP (`mod_gsoap.dll`) and the samples, or right-click on the isapi project in the Solution Explorer and click Build to build only the ISAPI extension for gSOAP.
- Install and use the `mod_gsoap.dll` ISAPI extension as described below.

Visual Studio 2010 Service Pack 1 (version 10.0.40219.1) or later (Developer Command Prompt for VS):

- In the `gsoap\mod_gsoap\gsoap_win\isapi\vs2010\` directory, open the file named `PropertySheet.props`. Make sure that the full path to the `gsoap\bin\win32` directory that contains the `soapcpp2.exe` tool is in the ExecutablePath option, for example `<ExecutablePath>C:\gsoap-2.8\gsoap\bin\win32;</ExecutablePath>`.
- Also make sure that the `gsoap\` directory that contains `stdsoap2.h` is in the IncludePath option, for example `<IncludePath>C:\gsoap-2.8\gsoap;</IncludePath>`.
- Open the Developer Command Prompt for VS and navigate to the `gsoap\mod_gsoap\gsoap_win\isapi\vs2010\` directory.
- Run the command `nmake` to build the ISAPI extension for gSOAP (`mod_gsoap.dll`) and the samples. Alternatively, run `nmake` in the `gsoap\mod_gsoap\gsoap_win\isapi\vs2010\gsoap` directory to build only the ISAPI extension for gSOAP.

Visual Studio C++ 6.0:

- Open Visual Studio C++ 6.0 (or later).
- Go to Tools|Options and activate the Directories Panel.
- Select Include Files from the dropdown and add your project directory that contains `stdsoap2.h`.
- Select Executable Path and add the full path to the `gsoap\bin\win32` directory in the unpacked gSOAP package that contains the `soapcpp2.exe` tool.
- Open `all4iis.dsw` that can be found in `gsoap\mod_gsoap\gsoap_win\isapi\vs2006` in the gSOAP package.
- Activate the all4iis project and build all.
- Install and use the `mod_gsoap.dll` ISAPI extension as described below.

# Deploying services with ISAPI

After building `mod_gsoap.dll` we are ready to deploy gSOAP services with the ISAPI extension.

The gSOAP package contains a calculator example to demonstrate the ISAPI extension. You will find this example in the gSOAP package under `gsoap\mod_gsoap\gsoap_win\isapi\vs20##\samples\calc`. We will use this example to walk you through the creation and deployment of an ISAPI service, so make sure to build it (see Intallation section).

- Make sure to compile all sources in C++ compilation mode with Visual Studio C++. If you migrate to a project file `.vcproj` then set `CompileAs="2"` in your `.vcproj`.
- Add a `gsoap` directory to your `wwwroot` directory, for example `C:\Inetpub\wwwroot\gsoap`.
- Open Internet Service Manager from the `Control Panel` select `Administrative` tools.
- Create in Internet Service Manager a new virtual directory called `gsoap`, see details here on how to create a virtual root and also shown in this screen shot.
- Copy `mod_gsoap.dll` (in `gsoap\mod_gsoap\gsoap_win\isapi\vs20##\gsoap\`) and `calc.dll` (in `gsoap\mod_gsoap\gsoap_win\isapi\vs20##\samples\calc`) to the newly created `gsoap` directory (for example `C:\Inetpub\wwwroot\gsoap`).
- On 64-bit machines, you may have to enable 32-bit applications to run on the application pool. Go to Application Pools and find the pool your website is using (the default is DefaultAppPool). Right-click the pool, go to Advanced Settings, and set Enable 32-Bit Applications to True. Press OK.
- Start the "World Wide Web Publishing Service".
- Enter in your browser `http://localhost/gsoap/mod_gsoap.dll`. This should give a response from the server that explains what the correct URL is. This proves that `mod_gsoap.dll` is configured correctly.
- If your browser downloads the .dll instead, you must set up a script map. In IIS, select Default Web Site, go to Handler Mappings, and click Add Script Map.... Type `gsoap\mod_gsoap.dll` as the request path. Use the full path to the `mod_gsoap.dll` in your virtual directory as the executable path. In Request Restrictions..., make sure the Access is set to Execute. Click OK and Yes.
- Enter in your browser `http://localhost/gsoap/mod_gsoap.dll?gsoap/calc`. This should give a response from the server that you should use a POST command, not a GET. This proves that `mod_gsoap` was able to load your DLL. So in principle your installation and service deployment is OK.

To test the calculator IIS service with a simple client, do the following:

- Check that the client code `calcclnt.c` of the calculator example in `gsoap\mod_gsoap\gsoap_win\isapi\vs20##\samples\calc` has the correct service endpoint URL, which must correspond to your installation: `const char server[] = "http://localhost/gsoap/mod_gsoap.dll?gsoap/calc";`
- Build the `calcclnt.exe` client, e.g. using the `calcclnt` project file.
- Open a DOS command window and go to the directory where `calcclnt.exe` was built and execute `calcclnt.exe add 3 5`.
- The response should be: `result=8`.

We recommend to test services first as standalone gSOAP services to ensure that the service logic is correct. If the service logic is correct but the service DLL does not produce a response, then please see the next section. Otherwise, read on.

A `Makefile` is included that contains commands to start and stop debugging of IIS and for cleaning the directory. The advanced user can compile everything with just one command. Be sure that `msdev.exe` (VS2006 only) and `nmake.exe` are on your PATH. Then enter the command `nmake` from a DOS command window and presto!

To develop your own service DLL in Visual Studio, select `File|New` and create a new empty Dynamic Link Library project. Copy `stdsoap2.def` from the `mod_gsoap\gsoap_win\isapi\vs20##\samples\calc` directory to your project directory and add it to the project. This will ensure that the required functions are exported and visible to `mod_gsoap`, such as `soap_serve` that invokes service operations (this function is auto-generated by `soapcpp2.exe` and defined in `soapServer.cpp`).

In addition, two C functions should be defined by your service code, namely `int mod_gsoap_init(void)` and `int mod_gsoap_terminate(void)`:

extern "C" {
int mod_gsoap_init(void) {
// TODO: add your initialization code here
return SOAP_OK;
}
int mod_gsoap_terminate(void) {
// TODO: add your termination code here
return SOAP_OK;
}

The `mod_gsoap_init` function is called by `mod_gsoap` when the DLL was successfully loaded and before processing begins. The `mod_gsoap_terminate` function is called when the DLL is unloaded. These functions should return `SOAP_OK` on success. You can use these initialization and termination hooks as you see fit.

Multiple ISAPI services can run together with all other Internet services on your machine on port 80 (or another port, as configured in IIS). The request your client must submit is a URL with a query string, such as was illustrated above with `http://127.0.0.1/gsoap/mod_gsoap.dll?gsoap/calc`.

The requested URL is evaluated by IIS and the query string (the part after the `?`) is used to dispatch the service request to the `calc.dll` service.

Note that instead of `127.0.0.1` (which is the `localhost`), clients on the network should use the full domain name of the machine.

For security reasons only DLLs stored in the same directory as `mod_gsoap.dll` can be used. If you want to do specialized initializations in your DLL then you may want to add and export a `DllMain` function, which will be called when the IIS process attaches to your DLL and before it detaches it. Do not rely on the Thread attach/detach callback: in my experience IIS does not always call `DllMain` in your DLL if these threads were already in the thread pool before your DLL was loaded. Use thread local storage instead.

# IIS Settings

This depends on the version of the Windows OS.

The gSOAP ISAPI extension uses `ReadClient`. The documentation of this function states: *"The number of bytes that the Web Server reads when receiving POST data is specified in the `HKEY_LOCAL_MACHINE\COMM\HTTPD\PostReadSize` registry key. The Web Server will read in, at most, the number of bytes specified in this registry value before calling the ISAPI extension."* This value should be changed if it is too small to handle POST requests that are larger than this value.

Furthermore, IIS enforces file upload size limits, which by default is 2MB. This is a problem for POST requests that are larger than the default. The IIS settings should be updated in `web.config`, for example to increase the allowed size of the POST request messages to 100MB:

    <configuration>
        <system.webServer>
            <security>
              <requestFiltering>
                <requestLimits maxAllowedContentLength="100000000"/>
              </requestFiltering>
            </security>
        </system.webServer>
    </configuration>

The gSOAP engine limits the size of requests to 2GB max, which can be changed by setting the value of `soap->recv_maxlength` to the max number of bytes allowed to receive. For other gSOAP settings, please see the gSOAP documentation.

# Troubleshooting

If the client receives an error from the ISAPI service, such as for example:

    SOAP FAULT: SOAP-ENV:Client
    "End of file or no input"
    Detail: http://localhost/gsoap/mod_gsoap.dll?gsoap/calc

Then we recommend the following steps:

- Make sure that `dumpbin.exe` is in your PATH (it can be found somewhere in the Visual Studio binaries).
- Open a DOS command window and go to the directory where `mod_gsoap.dll` is located (`C:\Inetpub\wwwroot\gsoap`). Execute the following command: `dumpbin /exports calc.dll`.
- The output should contain the exported symbols that are listed in the `stdsoap2.def` file. If you don't find these symbols you propably forgot to add the necessary `stdsoap2.def` exports for your project. This should include `soap_initialize`, `soap_serve`, `soap_delete`, `soap_end`, `soap_done`, `soap_register_plugin_arg`, and `soap_lookup_plugin`. See for example `stdsoap2.def` in `gsoap\mod_gsoap\gsoap_win\isapi\vs20##\samples\calc`.

If you want to debug a DLL, you must set the DLL to run in-proccess. Right-click on the `gsoap` virtual root in internet service manager and set the `Application Protection` to `Low (IIS Process)`. Remove the `Enable Session State` and buffering and `Parent Paths`. Don't forget to allow the IISAdmin and WWW Service to interact with the desktop.

To enable debugging of services and/or clients:

- Compile `calc.dll` and/or `calcclnt.exe` with the `DEBUG` option (in `Preprocessor Definitions` add `DEBUG`).
- Delete all `.log` files from the current directory, if any.
- Run the client `calcclnt.exe add 3 5` again.
- You should get three files with the extension `.log` in the current directory of the client and in the DLL directory. Please read what is there.

Note: for Debugging with Win2000 there are two `.reg` files in the `Div` directory, that switch debugging of IIS on and off (see Q273639 and related), and a start and stop command in the `Makefile` to start and stop IIS debugging. Make sure that the path to `msdev` is in the System environment variables (`PATH`) of the system account (not only of your own user account, this is not seen by IISAdmin).

# Creating the virtual root

If you have problems creating the virtual root then these instructions should help.

- Open from the control panel `Administrative Tools` and then select `Internet Services Manager` (may be located in the Option Pack submenus).
- Click with the right mouse button on `Default Web Site`, then select `New` and `Virtual Directory`.
- Click `Next` and enter as `Alias` the name you want to give to the URL, such as `soap`. Then press `Next` again and browse for the directory where your DLL that you have built in the previous step is, for example in `c:\Inetpub\wwwroot\gsoap` and press `Next`.
- In the access permissions, disable all permissions except `Execute (such as ISAPI applications or CGI)`. This must be enabled.
- Click `Next` and `Finish`.

For testing it might be best to enable the `Browse` permission and then browse to `http://localhost/gsoap`.

# License

The ISAPI extension for gSOAP is released under the gSOAP open source public license and the GPLv2.

# Further reading

What is an ISAPI Extension?

ISAPI Extensions as explained by Microsoft