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About SSI Support

The HTTP server that comes with lwIP has been extended to support rudimentary Server Side Include (SSI) facility. To enable the SSI support in the lwIP-HTTP server, you need to define the macro INCLUDE_HTTPD_SSI in the lwipopts.h header file. You must also provide your SSI callback function and register it by calling the http_set_ssi_handler() function. The HTTP server will then scan each file with extension .shtml, .shtm or .ssi for the SSI tags of the form <!--#tag--> and will replace on-the-fly every recognized SSI tag with the string composed by your SSI callback function. See the HTML source code for this web page (ssi_demo.shtm) and the SSI callback function definition in lwipmgr.c.

While designing your own SSI tags, remember that the tag names are limited to 8 characters and the length of the replacement strings cannot exceed 192 characters. You can re-define these limits by changing the macros MAX_TAG_NAME_LEN and MAX_TAG_INSERT_LEN, respectively, in the http.h header file.

Please refer to the Quantum Leaps Application Note: "QP and lwIP TCP/IP Stack" for more information. The Application Note is included in the QP-lwIP example code download.

SSI Example

The following table contains SSI tags embedded in the HTML of this web page. Client browsers never see these tags, as the lwIP-HTTP server replaces them on-the-fly while serving this page. These particular SSI tags cause the target to generate various lwIP link statistics. Please click the Refresh button on your browser to cause re-loading of this page and updating the statistics:

NOTE: the webpage loads much slower than the others, because it contains 12 SSI tags, and each tag is sent is a separate TCP/IP packet.