How to Log Response Body in Gin Middleware?

Logging Response Body in Gin Middleware

In Gin, logging the response body in a middleware requires intercepting and storing the response before it is written. Here's how to achieve this:

Create a custom writer that intercepts Write() calls and stores the body:

import bytes

class bodyLogWriter(gin.ResponseWriter):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.body = bytes.Buffer()

    def Write(self, data):
        self.body.write(data)
        return super().Write(data)

Implement a middleware function that uses the custom writer to intercept the response:

from functools import wraps

def gin_body_log_middleware(func):
    @wraps(func)
    def inner(context, *args, **kwargs):
        context.writer = bodyLogWriter(context.writer)
        wrapped_func(context, *args, **kwargs)
        
        status_code = context.writer.status_code
        if status_code >= 400:
            # Access the logged response body
            print("Response body:", context.writer.body.getvalue().decode())

    return inner

Register the middleware in your Gin router:

router.Use(gin_body_log_middleware)

This middleware intercepts all responses and logs the body for requests with a status code of 400 or higher. For static file requests, a more sophisticated wrapper that wraps the Gin engine is necessary.

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