Isolating header values without regular expressions

  Last updated April 24, 2018

Fastly supports the ability to extract header subfield values without regular expressions in a human-readable way.

"Headers subfields" refer to headers with a body syntax style similar to value1=123value123; testValue=asdf_true; loggedInTest=true; or max-age=0, surrogate-control=3600 These headers include Cookie, Set-Cookie, Cache-Control, or a custom header. Fastly allows you to isolate these key values with the following syntax:


In cases where a Set-Cookie response from origin is value1=123value123; testValue=asdf_true; loggedInTest=true;, the code for isolating the loggedInTest value would be:


This logic can be used in uploaded custom VCL, as well as throughout the web interface. For example, using VCL this logic would execute based on the value of staff_user within req.http.Cookie.

# in vcl_recv
if (req.http.Cookie:staff_user ~ "true") {
  # some logic goes here

For example, to isolate the value of ab_test_value from Cookie to the header req.http.AB-Test-Value, create a custom header with the following settings:

the header window showing a custom header without regular expressions

Fill out the Create a header fields as follows:

This will send the AB-Test-Value header in every inbound request.

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