Feature Variables Reference

• Rewrite Cache Key (cache_key_rewrite)
• Cache Key (cache_key). Feature variable supported is limited to the Expressions option (include_expressions).
• Add Response Headers (add_response_headers)
• Set Request Headers (set_request_headers)
• Set Response Headers (set_response_headers)
• URL Redirect (url_redirect)
• URL Rewrite (url_rewrite)

Definitions #

• Client Device
• Client Geography
• Client Network
• General
• mTLS
• Request
• Response

Client Device #

Client Geography #

Client Network #

General #

mTLS #

Request #

Response #

Usage #

• Feature Variable: Use this syntax to get the entire value corresponding to the specified feature variable.
  Example: %{host}
• Feature Variable with a Delimiter: Use this syntax to transform the value corresponding to the specified feature variable.
  Example: The following example converts the value associated with the %{host} variable to lower-case.
  %{host,}
• Feature Variable with a Delimiter and an Expression: Use regular expressions to replace, delete, or manipulate a feature variable’s value.
  Example: %{host/=^www\.([^\.]+)\.([^\.:]+)/cdn.$2.$3:80}

Delimiter Quick Reference #

• Transform the value associated with the variable.
  Example: Convert the entire value to lower-case.
• Delete the value associated with the variable.
• Manipulate the value associated with the variable.
  Example: Use regular expressions to change the value associated with the feature variable.

Exceptions #

• Escaping % Symbol: The percentage symbol can be escaped through the use of a backslash.
  Example: The following sample value will be treated as a literal value and not as a feature variable: \%{host}
• Unknown Variables: An empty string is always returned for unknown variables.
  Example: %{unknownvariable}
• Invalid Characters or Syntax: Variables that contain invalid characters or syntax are treated as literal values.
  Example #1: The following value contains an invalid character (i.e., -): %{resp_user-agent} Example #2: The following value contains a double set of curly braces: %{{host}} Example #3: The following value is missing a closing curly brace: %{host
• Missing Variable Name: A NULL value is always returned when a variable is not specified.
  Example: %{}
• Trailing Characters: Characters that trail a variable are treated as literal values.
  Example: The following sample value contains a trailing curly brace that will be treated as a literal value: %{host}}

Setting Default Header Values #

• Missing/unset
• Set to NULL.

• Set a header to a default value when the header is missing or its value is set to NULL.
  Syntax: %{<FEATURE VARIABLE>:=<DEFAULT VALUE>}
  Example: The following value sets the Referer header to unspecified when it is either missing or set to NULL. No action will take place if it has been set.
  %{http_referer:=unspecified}
• Set a header to a default value when it is missing.
  Syntax: %{<FEATURE VARIABLE>=<DEFAULT VALUE>}
  Example: The following value sets the Referer header to unspecified when it is missing. No action will take place if it has been set.
  %{http_referer=unspecified}
• Set the header to a default value when it does not meet any of the following conditions:
  • Missing header.
  • Set to NULL.
  Syntax: %{<FEATURE VARIABLE>:+<DEFAULT VALUE>}
  Example: The following value sets the Referer header to unspecified when a value has been assigned to it. No action will take place if it has been set.
  %{http_referer:+unspecified}

Manipulating Variables #

• Expanding substrings
• Removing patterns

Substring Expansion #

• The value assigned to the <OFFSET> term determines the starting character of the substring.
  • Positive: The starting character of the substring is calculated from the first character in the string.
  • Zero: The starting character of the substring is the first character in the string.
  • Negative: The starting character of the substring is calculated from the last character in the string.
• The length of the substring is determined by the <LENGTH> term.
  • Omitted: Omitting the <LENGTH> term allows the substring to include all characters between the starting character and the end of the string.
  • Positive: Determines the length of the substring from the starting character to the right.
  • Negative: Determines the length of the substring from the starting character to the left.

Pattern Removal #

• Remove text when the specified pattern is found at the beginning of a variable’s value.
  %{<VARIABLE>#<PATTERN>}
• Remove text when the specified pattern is found at the end of a variable’s value.
  %{<VARIABLE>%<PATTERN>}

Find And Replace #

• Find and replace first occurrence of the specified pattern.
  Syntax: %{<VARIABLE>/<FIND>/<REPLACE>}
• Find and replace all occurrences of the specified pattern.
  Syntax: %{<VARIABLE>//<FIND>/<REPLACE>}
• Convert the entire value to upper-case.
  Syntax: %{<VARIABLE>^}
• Convert the first occurrence of the specified pattern to upper-case.
  Syntax: %{<VARIABLE>^<FIND>}
• Convert the entire value to lower-case.
  Syntax: %{<VARIABLE>,}
• Convert the first occurrence of the specified pattern to lower-case.
  Syntax: %{<VARIABLE>,<FIND>}

• Expand text that matches the specified pattern by specifying a dollar sign followed by a whole integer (e.g., $1).
• Multiple patterns may be specified. The order in which the pattern is specified determines the integer that will be assigned to it.
  In the following example, the first pattern matches www or www followed by a single digit, the second pattern matches the second-level domain, and the third pattern matches the top-level domain.
  %{host/=^(www\d?)\.([^\.]+)\.([^\.:]+)/cdn.$2.$3:80}
• The rewritten value can consist of any combination of text and these placeholders.
  In the above example, the hostname will be rewritten according to this pattern: cdn.$2.$3:80 (e.g., cdn.mydomain.com:80).
• The case of a pattern placeholder (e.g., $1) can be modified through the following flags:
  • U: Upper-case the expanded value.
    Sample syntax: %{host/=^(www\d?)\.([^\.]+)\.([^\.:]+)/cdn.$U2.$3:80}
  • L: Lower-case the expanded value.
    Sample syntax: %{host/=^(www\d?)\.([^\.]+)\.([^\.:]+)/cdn.$L2.$3:80}
• An operator must be specified before the pattern. The specified operator determines the pattern capturing behavior:
  • = indicates that all occurrences of the specified pattern must be captured and rewritten. ^ indicates that only text that starts with the specified pattern will be captured. $ indicates that only text that ends with the specified pattern will be capture.
• Omitting the /<REWRITE> value will result in the deletion of the text that matches the pattern.