Fix #395, properly update the content-type header

curl_cffi/requests/session.py

@@ -163,13 +163,17 @@ def _update_url_params(url: str, *params_list: Union[Dict, List, Tuple, None]) -
     return new_url
 
 
-def _update_header_line(header_lines: List[str], key: str, value: str, force: bool = False):
+# TODO: should we move this function to headers.py?
+def _update_header_line(header_lines: List[str], key: str, value: str, replace: bool = False):
     """Update header line list by key value pair."""
+    found = False
     for idx, line in enumerate(header_lines):
-        if line.lower().startswith(key.lower() + ":") and force:
-            header_lines[idx] = f"{key}: {value}"
+        if line.lower().startswith(key.lower() + ":"):
+            found = True
+            if replace:
+                header_lines[idx] = f"{key}: {value}"
             break
-    else:  # if not break
+    if not found:
         header_lines.append(f"{key}: {value}")
 
 
@@ -449,14 +453,14 @@ def _set_curl_options(
 
         # Add content-type if missing
         if json is not None:
-            _update_header_line(header_lines, "Content-Type", "application/json", force=True)
+            _update_header_line(header_lines, "Content-Type", "application/json", replace=True)
         if isinstance(data, dict) and method != "POST":
             _update_header_line(header_lines, "Content-Type", "application/x-www-form-urlencoded")
         if isinstance(data, (str, bytes)):
             _update_header_line(header_lines, "Content-Type", "application/octet-stream")
 
         # Never send `Expect` header.
-        _update_header_line(header_lines, "Expect", "", force=True)
+        _update_header_line(header_lines, "Expect", "", replace=True)
 
         c.setopt(CurlOpt.HTTPHEADER, [h.encode() for h in header_lines])
 

tests/unittest/test_headers.py

@@ -1,4 +1,5 @@
 from curl_cffi.requests import Headers
+from curl_cffi.requests.session import _update_header_line
 
 
 def test_headers():
@@ -21,3 +22,15 @@ def test_header_output():
     headers = Headers({"X-Foo": "bar"})
     header_list = headers.multi_items()
     assert header_list[0][0] == "X-Foo"
+
+
+def test_replace_header():
+    header_lines = []
+    _update_header_line(header_lines, "content-type", "image/png")
+    assert header_lines == ["content-type: image/png"]
+    _update_header_line(header_lines, "Content-Type", "application/json")
+    assert header_lines == ["content-type: image/png"]
+    _update_header_line(header_lines, "Content-Type", "application/json", replace=True)
+    assert header_lines == ["Content-Type: application/json"]
+    _update_header_line(header_lines, "Host", "example.com", replace=True)
+    assert header_lines == ["Content-Type: application/json", "Host: example.com"]