packruler / rewrite-body

Traefik Plugin to allow regex replacement of HTTP GET response body

Rewrite Body

This is a fork of Traefik's plugin-rewritebody that is aimed at extending support to handle gzip content. This was initially aimed at extending the support for utilizing theme.park's themes but can likely be used for a range of other uses.

Changes From Original Traefik Plugin

The primary change is to add support for gzip content. This brought another potential issue to mind, what about really large content? This was handled as well.

Process For Handling Body Content

Body Content Requirements

• The header must have Content-Type that includes text. For example:
  • text/html
  • text/json
• The header must have Content-Encoding header that is supported by this plugin
  • The original plugin supported Content-Encoding of identity or empty
  • This plugin adds support for gzip and zlib encoding

Processing Paths

• If the either of the previous conditions failes the body is passed on as is and no further processing from this plugin occurs.

• If the Content-Encoding is empty or identity it is handled in mostly the same manner as the original plugin.

• If the Content-Encoding is gzip the following process happens:

  • The body content is decompressed by Go-lang's gzip library
  • The resulting content is run through the regex process created by the original plugin
  • The processed content is then compressed with the same library and returned

Configuration

Static

pilot:
  token: "xxxx"

experimental:
    plugins:
        rewrite-body:
            moduleName: "github.com/packruler/rewrite-body"
            version: "v1.1.0"

Dynamic

To configure the Rewrite Body plugin you should create a middleware in your dynamic configuration as explained here. The following example creates and uses the rewritebody middleware plugin to replace all foo occurences by bar in the HTTP response body.

If you want to apply some limits on the response body, you can chain this middleware plugin with the Buffering middleware from Traefik.

http:
  routers:
    my-router:
      rule: "Host(`localhost`)"
      middlewares: 
        - "rewrite-foo"
      service: "my-service"

  middlewares:
    rewrite-foo:
      plugin:
        rewrite-body:
          # Keep Last-Modified header returned by the HTTP service.
          # By default, the Last-Modified header is removed.
          lastModified: true

          # Rewrites all "foo" occurences by "bar"
          rewrites:
            - regex: "foo"
              replacement: "bar"

          # logLevel is optional, defaults to Info level.
          # Available logLevels: (Trace: -2, Debug: -1, Info: 0, Warning: 1, Error: 2)
          logLevel: 0

          # monitoring is optional, defaults to below configuration
          # monitoring configuration limits the HTTP queries that are checked for regex replacement.
          monitoring:
            # methods is a string list. Options are standard HTTP Methods. Entries MUST be ALL CAPS
            # For a list of options: https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods
            methods:
              - GET
            # types is a string list. Options are HTTP Content Types. Entries should match standard formatting
            # For a list of options: https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/MIME_types
            # Wildcards(*) are not supported!
            types:
              - text/html
  services:
    my-service:
      loadBalancer:
        servers:
          - url: "http://127.0.0.1"

Example theme.park

Dynamic

http:
  routers:
    sonarr-router:
      rule: "Host(`sonarr.example.com`)"
      middlewares: 
        - sonarr-theme
      service: sonarr-service

  middlewares:
    sonarr-theme:
      plugin:
        rewrite-body:
          rewrites:
            - regex: </head>
              replacement: <link rel="stylesheet" type="text/css" href="https://theme-park.dev/css/base/sonarr/{{ env "THEME" }}.css"></head>

  services:
    sonarr-service:
      servers:
        - url: http://localhost:8989

You can set an environment variable THEME to the name of a theme for easier consistency across apps.