Fix Multipart content view parsing (#6653)

#### Description

On get_message_content_view, the content type wasn't including the
boundary, and was only setting the MIME type. This made the multipart
content view unusable, as the boundary was required on parsing. To fix
the issue, we assign the full content type instead.

This wasn't triggered by any previous tests because they would test
against the multipart parser directly, and not the generic parser.

#### Checklist

 - [X] I have updated tests where applicable.
 - [x] I have added an entry to the CHANGELOG.

---------

Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>

CHANGELOG.md

@@ -7,7 +7,8 @@
 
 ## Unreleased: mitmproxy next
 
-
+* Fix multipart form content view being unusable.
+  ([#6653](https://github.com/mitmproxy/mitmproxy/pull/6653), @DaniElectra)
 
 ## 07 March 2024: mitmproxy 10.2.4
 

mitmproxy/contentviews/multipart.py

@@ -1,3 +1,4 @@
+from .. import http
 from . import base
 from mitmproxy.coretypes import multidict
 from mitmproxy.net.http import multipart
@@ -11,7 +12,17 @@ class ViewMultipart(base.View):
         yield [("highlight", "Form data:\n")]
         yield from base.format_dict(multidict.MultiDict(v))
 
-    def __call__(self, data: bytes, content_type: str | None = None, **metadata):
+    def __call__(
+        self,
+        data: bytes,
+        content_type: str | None = None,
+        http_message: http.Message | None = None,
+        **metadata,
+    ):
+        # The content_type doesn't have the boundary, so we get it from the header again
+        headers = getattr(http_message, "headers", None)
+        if headers:
+            content_type = headers.get("content-type")
         if content_type is None:
             return
         v = multipart.decode_multipart(content_type, data)

test/mitmproxy/contentviews/test_api.py

@@ -81,6 +81,18 @@ def test_get_message_content_view():
     desc, lines, err = contentviews.get_message_content_view("raw", r, f)
     assert desc == "[cannot decode] Raw"
 
+    del r.headers["content-encoding"]
+    r.headers["content-type"] = "multipart/form-data; boundary=AaB03x"
+    r.content = b"""
+--AaB03x
+Content-Disposition: form-data; name="submit-name"
+
+Larry
+--AaB03x
+        """.strip()
+    desc, lines, err = contentviews.get_message_content_view("multipart form", r, f)
+    assert desc == "Multipart form"
+
     r.content = None
     desc, lines, err = contentviews.get_message_content_view("raw", r, f)
     assert list(lines) == [[("error", "content missing")]]

test/mitmproxy/contentviews/test_multipart.py

@@ -1,5 +1,6 @@
 from . import full_eval
 from mitmproxy.contentviews import multipart
+from mitmproxy.test import tutils
 
 
 def test_view_multipart():
@@ -13,6 +14,14 @@ Larry
         """.strip()
     assert view(v, content_type="multipart/form-data; boundary=AaB03x")
 
+    req = tutils.treq()
+    req.headers["content-type"] = "multipart/form-data; boundary=AaB03x"
+    req.content = v
+
+    assert view(
+        v, content_type="multipart/form-data; boundary=AaB03x", http_message=req
+    )
+
     assert not view(v)
 
     assert not view(v, content_type="multipart/form-data")