wsgi: properly pass through requests headers

Author: posborne

examples/bottle-app.py

@@ -27,6 +27,7 @@ def info():
         "vcpu_time_ms": vcpu_time,
         "request_method": request.environ.get("REQUEST_METHOD"),
         "path_info": request.environ.get("PATH_INFO"),
+        "request_headers": dict(request.headers),
     }
 
 

examples/flask-app.py

@@ -28,6 +28,7 @@ def info():
         "request_method": request.environ.get("REQUEST_METHOD"),
         "path_info": request.environ.get("PATH_INFO"),
         "python_version": sys.version,
+        "request_headers": dict(request.headers),
     }
 
 

fastly_compute/wsgi.py

@@ -86,6 +86,49 @@ def start_response(
         "HTTP_HOST": url.netloc or "localhost",
     }
 
+    # Add incoming HTTP headers to environ (WSGI spec requires HTTP_ prefix)
+    # Use cursor-based iteration to read all header names
+    cursor = 0
+    while True:
+        header_names_str, next_cursor = req.get_header_names(
+            max_len=8192, cursor=cursor
+        )
+        if not header_names_str:
+            break
+
+        # Header names are NUL-separated
+        header_names_split = (
+            header_names_str.rstrip("\0").split("\0") if header_names_str else []
+        )
+
+        for header_name in header_names_split:
+            if not header_name:
+                continue
+
+            # Get the header value
+            header_value_bytes = req.get_header_value(header_name, max_len=8192)
+            if header_value_bytes is None:
+                continue
+
+            # See https://peps.python.org/pep-3333/ - ISO-8859-1 encoding
+            # should be used for bytes values across this boundary.
+            header_value_str = header_value_bytes.decode("iso-8859-1")
+
+            # Special handling for Content-Type and Content-Length (no HTTP_ prefix)
+            if header_name.lower() == "content-type":
+                environ["CONTENT_TYPE"] = header_value_str
+            elif header_name.lower() == "content-length":
+                environ["CONTENT_LENGTH"] = header_value_str
+            else:
+                # Convert to WSGI format: HTTP_ prefix, uppercase, hyphens to underscores
+                wsgi_key = "HTTP_" + header_name.upper().replace("-", "_")
+                environ[wsgi_key] = header_value_str
+
+        # If there are more headers, continue with next cursor
+        if next_cursor is None:
+            break
+        cursor = next_cursor
+
     try:
         # Call the WSGI app and collect response body chunks
         for body_chunk in app(environ, start_response):

tests/test_app.py

@@ -57,6 +57,8 @@ def test_custom_headers(self):
         headers = {"X-Custom-Header": "test-value"}
         response = self.get("/info", headers=headers)
         assert response.status_code == 200
+        data = response.json()
+        assert data["request_headers"]["X-Custom-Header"] == "test-value"
 
     def test_error_endpoint_handling(self):
         """Test that the error endpoint returns 500 and triggers viceroy output display."""

tests/test_flask_example.py

@@ -17,7 +17,7 @@ def test_hello_endpoint(self):
 
     def test_info_endpoint(self):
         """Test the info endpoint returns expected JSON with WIT data."""
-        response = self.get("/info")
+        response = self.get("/info", headers={"Test-Header": "test-value"})
 
         assert response.status_code == 200
         assert response.headers.get("content-type", "").startswith("application/json")
@@ -32,6 +32,7 @@ def test_info_endpoint(self):
         # Check WIT API data
         assert "vcpu_time_ms" in data
         assert isinstance(data["vcpu_time_ms"], int)
+        assert data["request_headers"]["Test-Header"] == "test-value"
 
     def test_error_endpoint_handling(self):
         """Test that the error endpoint returns 500."""