Isolating header values without regular expressions

  Last updated September 24, 2020

Fastly supports the ability to extract header subfield values without regular expressions in a human-readable way. "Headers subfields" are headers with a body syntax style similar to value1=123value123; testValue=asdf_true; staff_user=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:

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req.http.Header-Name:key-name

For example, if a Cookie request from a client was value1=123value123; testValue=asdf_true; staff_user=true;, you could isolate the staff_user value using this logic:

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set req.http.Staff-User = req.http.Cookie:staff_user;

The same can be accomplished by using the subfield function:

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set req.http.Staff-User = subfield(req.http.Cookie, "staff_user", ";");

You can add this logic using VCL Snippets or using a custom header.

Using VCL Snippets

To execute this logic based on the value of staff_user within req.http.Cookie using a VCL Snippet, you would:

  1. Log in to the Fastly web interface.
  2. From the All services page, select the appropriate service. You can use the search box to search by ID, name, or domain.
  3. Click the Edit configuration button and then select the option to clone the active version. The Domains page appears.
  4. Click the VCL Snippets link. The VCL Snippets page appears.
  5. Click Create Snippet. The Create a VCL snippet page appears.

    vcl snippet window

  6. In the Name field, type an appropriate name (e.g., Staff User Cookie).
  7. From the Type controls, select within subroutine.
  8. From the Select subroutine menu, select recv (vcl_recv).
  9. In the VCL field, add the following condition:

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    # in vcl_recv
    if (req.http.Cookie:staff_user ~ "true") {
      # some logic goes here
      return(pass);
    }
    
  10. Click Create to create the snippet.
  11. Click the Activate button to deploy your configuration changes.

Using a custom header

You can isolate the value of staff_user from Cookie to the header req.http.staff_user by creating 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 staff_user header in every inbound request.

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