Rewriter

3.3.0

The Rewriter can dynamically modify HTTP request and response bodies. Unlike the built-in rewriteBody/rewriteResponseBody/rewriteRequestBody rules (based on regex matching and replacement), the rewriter provides more flexible modification capabilities through external plugin services.

Using a Rewriter

The rewriter can be configured at the service level and referenced in services:

services:
- name: service-0
  addr: :8080
  handler:
    type: auto
  listener:
    type: tcp
  rewriter: rewriter-0

rewriters:
- name: rewriter-0
  plugin:
    type: grpc
    addr: 127.0.0.1:8000

Plugin Configuration

plugin.type (string, default=grpc)

plugin type: grpc or http.

plugin.addr (string, required)

plugin server address.

plugin.token (string)

credentials for server-side authentication.

plugin.tls (object)

enable TLS encryption for the plugin connection.

plugin.timeout (duration)

request timeout.

HTTP Plugin

rewriters:
- name: rewriter-0
  plugin:
    type: http
    addr: http://127.0.0.1:8000/rewrite

Request format:

{"data":"<base64 original content>","metadata":<metadata>}

Response format:

{"ok":true,"data":"<base64 modified content>"}

Node-Level Rewriter

The rewriter can also be used in each forwarder node's rewriteBody/rewriteResponseBody/rewriteRequestBody rules:

forwarder:
  nodes:
  - name: target-0
    addr: example.com:80
    http:
      rewriteResponseBody:
      - type: text/html
        match: "Hello"
        replacement: "Hola"
      rewriteRequestBody:
      - type: application/json
        rewriter: rewriter-0

When a rule has rewriter set, the body modification is delegated to the rewriter plugin, and the match/replacement fields are ignored.

When rewriter is not set, the match field can be either:

• A regex pattern (applied to the raw body bytes via regexp.ReplaceAll). The replacement value supports Go's regex replacement syntax ($1, $2, etc.).
• A json: prefix for JSON path-based field matching: json:<path>[=<value-regex>]. The field value is extracted with gjson and matched against the optional value regex. When matched, the field is replaced with replacement using sjson.

# Regex mode (existing behavior)
rewriteRequestBody:
- match: '"model"\s*:\s*"[^"]*"'
  replacement: '"model":"deepseek-v4-pro"'

# JSON path mode — match any model field and replace it
rewriteRequestBody:
- match: json:model
  replacement: deepseek-v4-pro

# JSON path mode — match only specific effort values
rewriteRequestBody:
- match: json:output_config.effort=(xhigh|max)
  replacement: low

JSON mode auto-detects application/json content type, no type field needed.

The rewriter can be combined with type (content-type filtering) to send different body types to different rewriters.

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