update error msg (#1134)

docs/07.Reference/7.02.Filters.md

@@ -246,6 +246,36 @@ filters:
     name: proxy
 ```
 
+The following example demonstrates a forward proxy setup. Requests directed to 'example.com' will be forwarded, while all other requests will be denied. It's important to note that when operating a forward proxy, the paths attribute in the `HTTPServer` rule should be left empty. This is because, for HTTPS requests, the client initiates a `CONNECT` request which does not include a path.
+
+```yaml
+kind: HTTPServer
+name: httpserver
+port: 8088
+keepAlive: true
+https: false
+rules:
+  - host: 'example.com'
+    paths:
+      - backend: pipeline-forward
+
+---
+
+name: pipeline-forward
+kind: Pipeline
+
+filters:
+- name: forward-proxy
+  kind: SimpleHTTPProxy
+  serverMaxBodySize: -1
+```
+
+To test this forward proxy configuration, use the following command:
+
+```bash
+https_proxy=http://127.0.0.1:8088 http_proxy=http://127.0.0.1:8088 curl https://example.com
+```
+
 ### Configuration
 | Name | Type | Description | Required |
 | ---- | ---- | ----------- | -------- |

pkg/filters/proxies/httpproxy/pool.go

@@ -512,7 +512,7 @@ func (sp *ServerPool) buildResponse(spCtx *serverPoolContext) (err error) {
 		maxBodySize = sp.proxy.spec.ServerMaxBodySize
 	}
 	if err = resp.FetchPayload(maxBodySize); err != nil {
-		logger.Errorf("%s: failed to fetch response payload: %v", sp.Name, err)
+		logger.Errorf("%s: failed to fetch response payload: %v, please consider to set serverMaxBodySize of Proxy to -1.", sp.Name, err)
 		body.Close()
 		return err
 	}

pkg/filters/proxies/httpproxy/simplehttpproxy.go

@@ -282,7 +282,7 @@ func (shp *SimpleHTTPProxy) Handle(ctx *context.Context) (result string) {
 
 	maxBodySize := shp.spec.ServerMaxBodySize
 	if err = httpResp.FetchPayload(maxBodySize); err != nil {
-		logger.Errorf("%s: failed to fetch response payload: %v", shp.Name(), err)
+		logger.Errorf("%s: failed to fetch response payload: %v, please consider to set serverMaxBodySize of SimpleHTTPProxy to -1.", shp.Name(), err)
 		return resultServerError
 	}