How Can I Inspect and Preserve an HTTP Request Body for Reverse Proxy Handling?

Preserving Request Bodies for Reverse Proxy Handling

In some scenarios, while inspecting HTTP requests in a custom http.Handler, it may be necessary to examine the request body, but also preserve the original request for further processing, such as forwarding it to a reverse proxy handler. To achieve this, consider the following approach:

The issue arises when the request body is drained during inspection, leaving nothing for subsequent consumers like the reverse proxy. To work around this, you can read the request body into a buffer, and then create two new readers backed by this buffer:

1. Create a Buffer: Use io.ReadAll(r.Body) to read the request body into a []byte buffer. This operation drains the original request body.
2. Create Two Readers: Use io.NopCloser(bytes.NewBuffer(buf)) to create two new readers (rdr1 and rdr2) backed by the same buffer. These readers will allow you to access the body multiple times without affecting the original request.
3. Use the New Reader: Perform your inspections using rdr1.
4. Reset Request Body: Set the request body (r.Body) to rdr2 (wrapped in io.NopCloser) to reset it to its original state. This allows the reverse proxy to process the request as if the body had not been drained.

Using this approach, you can inspect the request body, perform necessary actions, and still pass the original request unmodified to the reverse proxy, avoiding errors.

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