Closes #1580 Gives warning when explicit proxy configured in transparent mode (#1996)

1 files changed, 11 insertions, 4 deletions

diff --git a/mitmproxy/proxy/protocol/http.py b/mitmproxy/proxy/protocol/http.py
index b70afe33..da9a8781 100644
--- a/mitmproxy/proxy/protocol/http.py
+++ b/mitmproxy/proxy/protocol/http.py
@@ -131,7 +131,7 @@ class HTTPMode(enum.Enum):
 # At this point, we see only a subset of the proxy modes
 MODE_REQUEST_FORMS = {
     HTTPMode.regular: ("authority", "absolute"),
-    HTTPMode.transparent: ("relative"),
+    HTTPMode.transparent: ("relative",),
     HTTPMode.upstream: ("authority", "absolute"),
 }
 
@@ -143,9 +143,16 @@ def validate_request_form(mode, request):
         )
     allowed_request_forms = MODE_REQUEST_FORMS[mode]
     if request.first_line_format not in allowed_request_forms:
-        err_message = "Invalid HTTP request form (expected: %s, got: %s)" % (
-            " or ".join(allowed_request_forms), request.first_line_format
-        )
+        if mode == HTTPMode.transparent:
+            err_message = (
+                "Mitmproxy received an {} request even though it is not running in regular mode. "
+                "This usually indicates a misconfiguration, please see "
+                "http://docs.mitmproxy.org/en/stable/modes.html for details."
+            ).format("HTTP CONNECT" if request.first_line_format == "authority" else "absolute-form")
+        else:
+            err_message = "Invalid HTTP request form (expected: %s, got: %s)" % (
+                " or ".join(allowed_request_forms), request.first_line_format
+            )
         raise exceptions.HttpException(err_message)