Header Mutation Rules¶

config.common.mutation_rules.v3.HeaderMutationRules¶

[config.common.mutation_rules.v3.HeaderMutationRules proto]

The HeaderMutationRules structure specifies what headers may be manipulated by a processing filter. This set of rules makes it possible to control which modifications a filter may make.

By default, an external processing server may add, modify, or remove any header except for an “Envoy internal” header (which is typically denoted by an x-envoy prefix) or specific headers that may affect further filter processing:

host
:authority
:scheme
:method

Every attempt to add, change, append, or remove a header will be tested against the rules here. Disallowed header mutations will be ignored unless disallow_is_error is set to true.

Attempts to remove headers are further constrained – regardless of the settings, system-defined headers (that start with “:”) and the “host” header may never be removed.

In addition, a counter will be incremented whenever a mutation is rejected. In the ext_proc filter, that counter is named “rejected_header_mutations”.

{
  "allow_all_routing": "{...}",
  "allow_envoy": "{...}",
  "disallow_system": "{...}",
  "disallow_all": "{...}",
  "allow_expression": "{...}",
  "disallow_expression": "{...}",
  "disallow_is_error": "{...}"
}

allow_all_routing: (BoolValue) By default, certain headers that could affect processing of subsequent filters or request routing cannot be modified. These headers are “host”, “:authority”, “:scheme”, and “:method”. Setting this parameter to true allows these headers to be modified as well.

allow_envoy: (BoolValue) If true, allow modification of envoy internal headers. By default, these start with “x-envoy” but this may be overridden in the Bootstrap configuration using the header_prefix field. Default is false.

disallow_system: (BoolValue) If true, prevent modification of any system header, defined as a header that starts with a “:” character, regardless of any other settings. A processing server may still override the “:status” of an HTTP response using an ImmediateResponse message. Default is false.

disallow_all: (BoolValue) If true, prevent modifications of all header values, regardless of any other settings. A processing server may still override the “:status” of an HTTP response using an ImmediateResponse message. Default is false.

allow_expression: (type.matcher.v3.RegexMatcher) If set, specifically allow any header that matches this regular expression. This overrides all other settings except for disallow_expression.

disallow_expression: (type.matcher.v3.RegexMatcher) If set, specifically disallow any header that matches this regular expression regardless of any other settings.

disallow_is_error: (BoolValue) If true, and if the rules in this list cause a header mutation to be disallowed, then the filter using this configuration will terminate the request with a 500 error. In addition, regardless of the setting of this parameter, any attempt to set, add, or modify a disallowed header will cause the “rejected_header_mutations” counter to be incremented. Default is false.