fix(fetch): send empty form and multipart bodies (#3239)

Author: pavelfeldman

playwright/_impl/_fetch.py

@@ -427,7 +427,7 @@ async def _inner_fetch(
                     raise Error(str(e)) from None
             else:
                 raise Error(f"Unsupported 'data' type: {type(data)}")
-        elif form:
+        elif form is not None:
             if isinstance(form, FormData):
                 form_data = []
                 for fd_name, fd_value in form._fields:
@@ -437,8 +437,8 @@ async def _inner_fetch(
                         )
                     form_data.append(NameValue(name=fd_name, value=str(fd_value)))
             else:
-                form_data = object_to_array(form)
-        elif multipart:
+                form_data = object_to_array(form) or []
+        elif multipart is not None:
             multipart_data = []
             if isinstance(multipart, FormData):
                 for fd_name, fd_value in multipart._fields:

tests/async/test_fetch_browser_context.py

@@ -365,6 +365,31 @@ async def test_should_support_multipart_form_data(
     assert request.args[b"file"][0] == file["buffer"]
 
 
+async def test_should_send_empty_form(context: BrowserContext, server: Server) -> None:
+    [request, _] = await asyncio.gather(
+        server.wait_for_request("/empty.html"),
+        context.request.post(server.EMPTY_PAGE, form={}),
+    )
+    assert request.getHeader("Content-Type") == "application/x-www-form-urlencoded"
+    assert request.getHeader("Content-Length") == "0"
+
+
+async def test_should_send_empty_multipart(
+    context: BrowserContext, server: Server
+) -> None:
+    # The test server rejects an empty multipart body in POST requests before handling them.
+    [request, _] = await asyncio.gather(
+        server.wait_for_request("/empty.html"),
+        context.request.put(server.EMPTY_PAGE, multipart={}),
+    )
+    assert cast(str, request.getHeader("Content-Type")).startswith(
+        "multipart/form-data; "
+    )
+    assert must(request.getHeader("Content-Length")) == str(
+        len(must(request.post_body))
+    )
+
+
 async def test_should_support_form_data_with_repeated_keys(
     context: BrowserContext, server: Server
 ) -> None:

tests/sync/test_fetch_browser_context.py

@@ -288,6 +288,28 @@ def test_should_support_multipart_form_data(
     assert server_req.value.args[b"file"][0] == file["buffer"]
 
 
+def test_should_send_empty_form(context: BrowserContext, server: Server) -> None:
+    with server.expect_request("/empty.html") as server_req:
+        context.request.post(server.EMPTY_PAGE, form={})
+    assert (
+        server_req.value.getHeader("Content-Type")
+        == "application/x-www-form-urlencoded"
+    )
+    assert server_req.value.getHeader("Content-Length") == "0"
+
+
+def test_should_send_empty_multipart(context: BrowserContext, server: Server) -> None:
+    # The test server rejects an empty multipart body in POST requests before handling them.
+    with server.expect_request("/empty.html") as server_req:
+        context.request.put(server.EMPTY_PAGE, multipart={})
+    content_type = server_req.value.getHeader("Content-Type")
+    assert content_type
+    assert content_type.startswith("multipart/form-data; ")
+    assert server_req.value.getHeader("Content-Length") == str(
+        len(must(server_req.value.post_body))
+    )
+
+
 def test_should_support_form_data_with_repeated_keys(
     context: BrowserContext, server: Server
 ) -> None: