Notice this facility is subject to change!

"regsub" is short for regular expression substitution and it is probably
easiest to explain with some examples:

	sub vcl_recv {
		set req.url = regsub(req.url, "#.*", "");
	}

This will replace the requests URL with the output of the regsub() function

regsub() takes three arguments: the string to be examined, a regular
expression and a replacement string.

In this case, everything after the first '#' is removed (replaced
with nothing).

The replacement string recognizes the following magic sequences:
	&	- insert everything matched by the regexp
	$0	- ditto.
	$1	- replace with the first submatch of the regexp
	$2	- replace with the second submatch of the regexp
	...
	$9	- replace with the ninth submatch of the regexp

(The $0..$9 syntax was chosen over the \0...\9 syntax in order to avoid
a nightmare of escape characters in the VCL source code.  Arguments and
suggestions are welcome).

A more advanced example:

	set bereq.http.ClientIP = regsub(client.ip, "(.*):(.*)", "$2 $1");

The client.ip variable expands to IP:port number, for instance
	127.0.0.1:54662

The regular expression "(.*):(.*)" results in the the following matches:
	& + $0		"127.0.0.1:54662"
	$1		"127.0.0.1"
	$2		"54662"

So the replacement string "$2 $1" results in "54662 127.0.0.1"

And the completed header which is sent to the backend will look like:

	"ClientIP: 54662 127.0.0.1"

An even more advanced example would be:

    set bereq.http.magic = "Client IP = " regsub(client.ip, ":", " port = ");

Where we also exploint the string concatenation ability of the "set" statement.

The result string is built in the request workspace, so you may need
to increase the workspace size if you do a lot of regsub()'s.

Currently there is no decent error handling for running out of workspace.


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	set bereq.http.HeyYou = client.ip " asked for  " req.url;



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Give vcc_StringVal() a return value to say if it did anything so we can
emit better error messages when confused.



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(which are numeric, they'll follow shortly)

Unify the shmemlog tag used for failure to rewrite something, the Rx/Tx/Obj
distinction is not helpful enough to warrant the complexity of it.






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	sub vcl_deliver {
		set resp.http.phk = "Beastie" "Rules";
	}

Would result in a new header line:

	phk: BeastieRules

Notice that strings are concatenated directly, you add spaces, commas etc
where you want them.

Other variables which have STRING format (or which can be converted to
STRING format) can also be used:

	sub vcl_deliver {
		set resp.http.phk = "Server is: " resp.http.server ;
	}

Could result in:

	phk: Server is: Apache/1.3.x LaHonda (Unix)




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	sub vcl_deliver {
		remove resp.http.etag ;
		remove resp.http.server ;
	}



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default VCL



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the VCL methods vcl_miss and vcl_pass.



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wires, rather than when they get manipulated in memory.


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There should be no functional change as a result of this.



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of timestamps and clock_gettime() throughout Varnish needs reviewing (as
per IRC discussion with phk)


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current time, the latter returns the number of seconds since an object
was last requested.  The exact semantics of both are slightly fluid at
the moment, and will be revisited at a later date.


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script.


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processing pending messages before we exit.

Note that VSL_Dispatch() will read in log data as fast as it can, so when
working from a log file, varnishreplay will usually read in the entire file
into memory within the first few seconds.


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(See architect notes on wiki for reasoning)


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