From 8bfca83e4820d0d9b09a4b27f99127289fea9e80 Mon Sep 17 00:00:00 2001
From: Synvoya <16019863+Synvoya@users.noreply.github.com>
Date: Sat, 11 Jul 2026 21:49:22 +1000
Subject: [PATCH] Honor multipart boundary from an explicit Content-Type header

When a multipart boundary was supplied only via a Content-Type header (no
--boundary flag), HTTPie declared that boundary in the header but wrote the
body with a different random boundary, producing an unparseable request.
Reconcile the encoder's boundary with the one declared in the header;
--boundary still takes precedence.
---
 httpie/uploads.py     |  8 ++++++++
 tests/test_uploads.py | 18 ++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/httpie/uploads.py b/httpie/uploads.py
index 4a993b3a25..7659d98f76 100644
--- a/httpie/uploads.py
+++ b/httpie/uploads.py
@@ -233,6 +233,14 @@ def get_multipart_data_and_content_type(
     content_type: str = None,
 ) -> Tuple['MultipartEncoder', str]:
     from requests_toolbelt import MultipartEncoder
+    from .utils import parse_content_type_header
+
+    if not boundary and content_type:
+        # Honor a boundary specified via an explicit `Content-Type` header
+        # (e.g. `Content-Type:multipart/form-data; boundary=xoxo`) so that the
+        # body delimiter matches the boundary declared in the header.
+        _, ct_params = parse_content_type_header(content_type)
+        boundary = ct_params.get('boundary')
 
     encoder = MultipartEncoder(
         fields=data.items(),
diff --git a/tests/test_uploads.py b/tests/test_uploads.py
index e6bb80ac70..40ba4ecf7a 100644
--- a/tests/test_uploads.py
+++ b/tests/test_uploads.py
@@ -300,6 +300,24 @@ def test_multipart_custom_content_type_boundary_preserved(self, httpbin):
         assert f'multipart/magic; boundary={boundary_in_header}' in r
         assert r.count(boundary_in_body) == 3
 
+    def test_multipart_boundary_from_content_type_without_flag(self, httpbin):
+        # A boundary specified only via an explicit Content-Type header
+        # (no --boundary) must be used for the body delimiter too.
+        boundary = 'HTTPIE_FTW'
+        r = http(
+            '--print=HB',
+            '--check-status',
+            '--multipart',
+            httpbin + '/post',
+            f'Content-Type: multipart/form-data; boundary={boundary}',
+            'AAAA=AAA',
+            'BBB=BBB',
+        )
+        assert f'multipart/form-data; boundary={boundary}' in r
+        # 1 in the header + 3 body delimiters (two parts + closing). Without the
+        # fix the body uses a random boundary and this count is 1.
+        assert r.count(boundary) == 4
+
     def test_multipart_chunked(self, httpbin_with_chunked_support):
         r = http(
             '--verbose',