Docs/Transforms/Response & trailer transforms

Response & trailer transforms

All response headers and trailers are copied from the proxied response to the outgoing client

Response and Response Trailers

All response headers and trailers are copied from the proxied response to the outgoing client response by default. Response and response trailer transforms may specify if they should be applied only for successful responses or for all responses.

In code these are implemented as derivations of the abstract classes ResponseTransform and ResponseTrailersTransform.

ResponseHeadersCopy

Sets whether destination response headers are copied to the client

Key Value Default Expand table ResponseHeadersCopy true/false true Required yes

Config:

JSON { "ResponseHeadersCopy": "false" }

Code:

C# routeConfig = routeConfig.WithTransformCopyResponseHeaders(copy: false);

C# transformBuilderContext.CopyResponseHeaders = false;

This sets if all proxy response headers are copied to the client response. This setting is enabled by default and can be disabled by configuring the transform with a false value. Transforms that reference specific headers will still be run if this is disabled.

ResponseHeader

Adds or replaces response headers

Key Value Default Expand table ResponseHeader The header name (none) Required Set/Append The header value (none) yes When Success/Always/Failure Success yes no

Config:

JSON   {
       "ResponseHeader": "HeaderName",
       "Append": "value",
       "When": "Success"
   }
Code:

C#   routeConfig = routeConfig.WithTransformResponseHeader(headerName: "HeaderName",
   value: "value", append: true, ResponseCondition.Success);
    C#
   transformBuilderContext.AddResponseHeader(headerName: "HeaderName", value:
   "value", append: true, always: ResponseCondition.Success);
Example:
   HeaderName: value
This sets or appends the value for the named response header. Set replaces any existing
header. Append adds an additional header with the given value. Note: setting "" as a header
value is not recommended and can cause an undefined behavior.
When specifies if the response header should be included for all, successful, or failure
responses. Any response with a status code less than 400 is considered a success.

ResponseHeaderRemove

Removes response headers

Key Value Default Required ResponseHeaderRemove The header name (none) yes When Success/Always/Failure Success no

Config:

JSON{
   "ResponseHeaderRemove": "HeaderName",
   "When": "Success"
}
Code:

C#   routeConfig = routeConfig.WithTransformResponseHeaderRemove(headerName:
   "HeaderName", ResponseCondition.Success);
    C#
   transformBuilderContext.AddResponseHeaderRemove(headerName: "HeaderName",
   ResponseCondition.Success);
Example:
HeaderName: value
AnotherHeader: another-value
This removes the named response header.
When specifies if the response header should be removed for all, successful, or failure
responses. Any response with a status code less than 400 is considered a success.

ResponseHeadersAllowed

Key Value Required ResponseHeadersAllowed A semicolon separated list of allowed header names. yes

Config:

JSON   {
       "ResponseHeadersAllowed": "Header1;header2"
   }
Code:

C#   routeConfig = routeConfig.WithTransformResponseHeadersAllowed("Header1",
   "header2");

C#   transformBuilderContext.AddResponseHeadersAllowed("Header1", "header2");
YARP copies most response headers from the proxy response by default (see
ResponseHeadersCopy). Some security models only allow specific headers to be proxied. This
transform disables ResponseHeadersCopy and only copies the given headers. Other transforms
that modify or append to existing headers may be affected if not included in the allow list.
Note that there are some headers YARP does not copy by default since they are connection
specific or otherwise security sensitive (e.g. Connection , Alt-Svc ). Putting those header names
in the allow list will bypass that restriction but is strongly discouraged as it may negatively
affect the functionality of the proxy or cause security vulnerabilities.
Example:
Header1: value1
Header2: value2
AnotherHeader: AnotherValue
Only header1 and header2 are copied from the proxy response.

ResponseTrailersCopy

Sets whether destination trailing response headers are copied to the client

Key Value Default Expand table ResponseTrailersCopy true/false true Required yes

Config:

JSON { "ResponseTrailersCopy": "false" }

Code:

C# routeConfig = routeConfig.WithTransformCopyResponseTrailers(copy: false);

C# transformBuilderContext.CopyResponseTrailers = false;

This sets if all proxy response trailers are copied to the client response. This setting is enabled by default and can be disabled by configuring the transform with a false value. Transforms that reference specific headers will still be run if this is disabled.