Compress Response

Overview

The Compress Response policy action enables you to improve the performance of your web applications by compressing HTTP response bodies returned by your upstream service.

If an HTTP request includes an Accept-Encoding header, HTTP responses will be automatically compressed and a Content-Encoding response header will be added. If the response was already compressed by your upstream service, ngrok takes no action.

Example

Use this action config in your Traffic Policy

YAML

# snippet
---
actions:
  - type: "compress-response"
    config:
      algorithms:
        - "gzip"
        - "br"
        - "deflate"
        - "compress"

JSON

// snippet
{
  "actions": [
    {
      "type": "compress-response",
      "config": {
        "algorithms": [
          "gzip",
          "br",
          "deflate",
          "compress"
        ]
      }
    }
  ]
}

Request:

curl https://example.ngrok.app/api/v1

Result:

< HTTP/2 200
< content-encoding: gzip
< content-type: application/json; charset=utf-8

<compressed-body-here>

Behavior

Streaming Compression

When ngrok performs compression, the response body is not buffered; the response body is compressed as it is streamed through the ngrok endpoint.

Algorithm Choice

If a request specifies Accept-Encoding but no requested values are supported, ngrok takes no action and the upstream response is returned without modification.

ngrok negotiates the encoding type as defined by the RFC for Accept-Encoding. It respects q-values and chooses the Accept-Encoding supported algorithm with the highest q-value.

ngrok supports the following compression algorithms in the Accept-Encoding header by default, but this list may be restricted through policy action configuration.

Algorithm
br
compress
deflate
gzip

Response Headers

When ngrok performs compression, the following changes are made to the HTTP response header:

• The Content-Length header is removed
• A Content-Encoding header is added with the negotiated algorithm
• A Vary: Accept-Encoding header is added

Reference

Supported Directions

• Inbound
• Outbound

Configuration

Type
compress-response

Parameter		Description
algorithms	Array<string>	The compression algorithms that will be considered during encoding type negotiation. By default ngrok uses [gzip, deflate, br, compress].

Action Result Variables

The following variables are available following the invocation of this action.

Name	Type	Description
actions.ngrok.compress.already_compressed	boolean	True if the body was already encoded.
actions.ngrok.compress.negotiated_algorithm	string	The algorithm selected by the action.