Add ModifyRequestHeaderPlugin (#1420)

* Add `ModifyRequestHeaderPlugin`

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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* Add to README

* Fix lint issues shown by `Python3.11.8`

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: abhinavsingh

README.md

@@ -59,6 +59,7 @@
     - [Proxy Pool Plugin](#proxypoolplugin)
     - [Filter By Client IP Plugin](#filterbyclientipplugin)
     - [Modify Chunk Response Plugin](#modifychunkresponseplugin)
+    - [Modify Request Header Plugin](#modifyrequestheaderplugin)
     - [Cloudflare DNS Resolver Plugin](#cloudflarednsresolverplugin)
     - [Custom DNS Resolver Plugin](#customdnsresolverplugin)
     - [Custom Network Interface](#customnetworkinterface)
@@ -932,6 +933,31 @@ plugin
 
 Modify `ModifyChunkResponsePlugin` to your taste. Example, instead of sending hard-coded chunks, parse and modify the original `JSON` chunks received from the upstream server.
 
+### ModifyRequestHeaderPlugin
+
+This plugin demonstrate how to modify outgoing HTTPS request headers under TLS interception mode.
+
+Start `proxy.py` as:
+
+```console
+❯ proxy \
+    --plugins proxy.plugin.ModifyRequestHeaderPlugin \
+    ... [TLS interception flags] ...
+```
+
+Verify using `curl -x localhost:8899 --cacert ca-cert.pem https://httpbin.org/get`:
+
+```console
+{
+  "args": {},
+  "headers": {
+    ... [redacted] ...,
+    "X-Proxy-Py-Version": "2.4.4rc6.dev15+gf533c711"
+  },
+  ... [redacted] ...
+}
+```
+
 ### CloudflareDnsResolverPlugin
 
 This plugin uses `Cloudflare` hosted `DNS-over-HTTPS` [API](https://developers.cloudflare.com/1.1.1.1/encrypted-dns/dns-over-https/make-api-requests/dns-json) (json).

proxy/http/server/web.py

@@ -217,7 +217,7 @@ def on_client_data(self, raw: memoryview) -> None:
                 self.pipeline_request = None
 
     def on_response_chunk(self, chunk: List[memoryview]) -> List[memoryview]:
-        self._response_size += sum([len(c) for c in chunk])
+        self._response_size += sum(len(c) for c in chunk)
         return chunk
 
     def on_client_connection_close(self) -> None:

proxy/plugin/__init__.py

@@ -32,6 +32,7 @@
 from .filter_by_client_ip import FilterByClientIpPlugin
 from .filter_by_url_regex import FilterByURLRegexPlugin
 from .modify_chunk_response import ModifyChunkResponsePlugin
+from .modify_request_header import ModifyRequestHeaderPlugin
 from .redirect_to_custom_server import RedirectToCustomServerPlugin
 
 
@@ -53,4 +54,5 @@
     'CustomDnsResolverPlugin',
     'CloudflareDnsResolverPlugin',
     'ProgramNamePlugin',
+    'ModifyRequestHeaderPlugin',
 ]

proxy/plugin/modify_request_header.py

@@ -0,0 +1,40 @@
+# -*- coding: utf-8 -*-
+"""
+    proxy.py
+    ~~~~~~~~
+    ⚡⚡⚡ Fast, Lightweight, Pluggable, TLS interception capable proxy server focused on
+    Network monitoring, controls & Application development, testing, debugging.
+
+    :copyright: (c) 2013-present by Abhinav Singh and contributors.
+    :license: BSD, see LICENSE for more details.
+"""
+from typing import Optional
+
+from ..http.proxy import HttpProxyBasePlugin
+from ..http.parser import HttpParser
+from ..common.utils import bytes_
+from ..common.version import __version__
+
+
+class ModifyRequestHeaderPlugin(HttpProxyBasePlugin):
+    """Modify request header before sending to upstream server."""
+
+    # def before_upstream_connection(self, request: HttpParser) -> Optional[HttpParser]:
+    #     """NOTE: Use this for HTTP only request headers modification."""
+    #     request.add_header(
+    #         b"x-proxy-py-version",
+    #         bytes_(__version__),
+    #     )
+    #     return request
+
+    def handle_client_request(self, request: HttpParser) -> Optional[HttpParser]:
+        """NOTE: This is for HTTPS request headers modification when under TLS interception.
+
+        For HTTPS requests, modification of request under TLS interception WILL NOT WORK
+        through before_upstream_connection.
+        """
+        request.add_header(
+            b'x-proxy-py-version',
+            bytes_(__version__),
+        )
+        return request