Isolating header values without regular expressions

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:

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:

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

The same can be accomplished by using the subfield function:

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

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

WARNING

The subfield function as well as the : accessor cannot be used for Set-Cookie headers.

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 Home page, select the appropriate service. You can use the search box to search by ID, name, or domain. You can also go to CDN > CDN Services or Compute > Compute Services to access a list of services by type.
  3. Click Edit configuration and then select the option to clone the active version.
  4. Click VCL Snippets.

  5. Click Create Snippet.

    vcl snippet window

  6. In the Name field, enter 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:

    1# in vcl_recv
    2if (req.http.Cookie:staff_user ~ "true") {
    3 # some logic goes here
    4 return(pass);
    5}
  10. Click Create to create the snippet.

  11. Click Activate 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:

  • In the Name field, enter Staff User Header.
  • From the Type menu, select Request, and from the Action menu select Set.
  • In the Destination field, enter http.staff_user.
  • In the Source field, enter req.http.Cookie:staff_user.
  • From the Ignore if set menu, select No.
  • In the Priority field, enter 10.

This will send the staff_user header in every inbound request.

NOTE

You can use the Attach a condition link to only create this header when it's needed. See our Using Conditions docs for more information.

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