2.1.34 cs-User-Agent
The purpose of this field is to specify information regarding the client application that is sending the logging message.
The cs-User-Agent field SHOULD be set to the same value that Windows Internet Explorer specifies on the User-Agent HTTP protocol header. The field MAY be set differently as long as it adheres to the ABNF syntax as shown in the following code example.
If a logging message is forwarded by a proxy, the cs-User-Agent field MUST begin with the string "_via_". The original value specified by the client (which can be another proxy) on the cs-User-Agent field SHOULD be discarded. The proxy SHOULD include a product token on the cs-User-Agent field that specifies the brand and version of the proxy.
The syntax of the cs-User-Agent field is defined as follows.
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cs-User-Agent= [ "_via_HTTP/1.0_" ] 1*( product; [RFC2616] section 3.8 | comment ); [RFC2616] section 2.2
Example 1: media player embedded in Internet Explorer 6 on Windows XP operating system Service Pack 2 (SP2):
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Mozilla/4.0_(compatible;_MSIE_6.0;_Windows_NT_5.1;_SV1)
Example 2: application based on Windows Media Format 9 Series SDK:
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Application/2.3 (WMFSDK/9.0.1234)
Example 3: proxy:
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_via_HTTP/1.0_WMCacheProxy/9.00.00.1234