Add black version header to blackd responses (#1046)

README.md

@@ -893,6 +893,9 @@ Apart from the above, `blackd` can produce the following response codes:
  - `HTTP 500`: If there was any kind of error while trying to format the input.
 	The response body contains a textual representation of the error.
 
+The response headers include a `X-Black-Version` header containing the version
+of *Black*.
+
 ## Version control integration
 
 Use [pre-commit](https://pre-commit.com/). Once you [have it
@@ -1051,6 +1054,8 @@ More details can be found in [CONTRIBUTING](CONTRIBUTING.md).
 * *Black* is now able to format Python code that uses positional-only
   arguments (`/` as described in PEP-570) (#946)
 
+* `blackd` now returns the version of *Black* in the response headers (#1013)
+
 
 ### 19.3b0
 

blackd.py

@@ -10,23 +10,29 @@
 import black
 import click
 
+from _version import version as __version__
+
 # This is used internally by tests to shut down the server prematurely
 _stop_signal = asyncio.Event()
 
-VERSION_HEADER = "X-Protocol-Version"
+# Request headers
+PROTOCOL_VERSION_HEADER = "X-Protocol-Version"
 LINE_LENGTH_HEADER = "X-Line-Length"
 PYTHON_VARIANT_HEADER = "X-Python-Variant"
 SKIP_STRING_NORMALIZATION_HEADER = "X-Skip-String-Normalization"
 FAST_OR_SAFE_HEADER = "X-Fast-Or-Safe"
 
 BLACK_HEADERS = [
-    VERSION_HEADER,
+    PROTOCOL_VERSION_HEADER,
     LINE_LENGTH_HEADER,
     PYTHON_VARIANT_HEADER,
     SKIP_STRING_NORMALIZATION_HEADER,
     FAST_OR_SAFE_HEADER,
 ]
 
+# Response headers
+BLACK_VERSION_HEADER = "X-Black-Version"
+
 
 class InvalidVariantHeader(Exception):
     pass
@@ -65,8 +71,9 @@ def make_app() -> web.Application:
 
 
 async def handle(request: web.Request, executor: Executor) -> web.Response:
+    headers = {BLACK_VERSION_HEADER: __version__}
     try:
-        if request.headers.get(VERSION_HEADER, "1") != "1":
+        if request.headers.get(PROTOCOL_VERSION_HEADER, "1") != "1":
             return web.Response(
                 status=501, text="This server only supports protocol version 1"
             )
@@ -110,15 +117,18 @@ async def handle(request: web.Request, executor: Executor) -> web.Response:
             executor, partial(black.format_file_contents, req_str, fast=fast, mode=mode)
         )
         return web.Response(
-            content_type=request.content_type, charset=charset, text=formatted_str
+            content_type=request.content_type,
+            charset=charset,
+            headers=headers,
+            text=formatted_str,
         )
     except black.NothingChanged:
-        return web.Response(status=204)
+        return web.Response(status=204, headers=headers)
     except black.InvalidInput as e:
-        return web.Response(status=400, text=str(e))
+        return web.Response(status=400, headers=headers, text=str(e))
     except Exception as e:
         logging.exception("Exception during handling a request")
-        return web.Response(status=500, text=str(e))
+        return web.Response(status=500, headers=headers, text=str(e))
 
 
 def parse_python_variant_header(value: str) -> Tuple[bool, Set[black.TargetVersion]]:

tests/test_black.py

@@ -1569,7 +1569,7 @@ async def test_blackd_request_syntax_error(self) -> None:
     @unittest_run_loop
     async def test_blackd_unsupported_version(self) -> None:
         response = await self.client.post(
-            "/", data=b"what", headers={blackd.VERSION_HEADER: "2"}
+            "/", data=b"what", headers={blackd.PROTOCOL_VERSION_HEADER: "2"}
         )
         self.assertEqual(response.status, 501)
 
@@ -1578,7 +1578,7 @@ async def test_blackd_unsupported_version(self) -> None:
     @unittest_run_loop
     async def test_blackd_supported_version(self) -> None:
         response = await self.client.post(
-            "/", data=b"what", headers={blackd.VERSION_HEADER: "1"}
+            "/", data=b"what", headers={blackd.PROTOCOL_VERSION_HEADER: "1"}
         )
         self.assertEqual(response.status, 200)
 
@@ -1669,6 +1669,13 @@ async def test_blackd_invalid_line_length(self) -> None:
         )
         self.assertEqual(response.status, 400)
 
+    @skip_if_exception("ClientOSError")
+    @unittest.skipUnless(has_blackd_deps, "blackd's dependencies are not installed")
+    @unittest_run_loop
+    async def test_blackd_response_black_version_header(self) -> None:
+        response = await self.client.post("/")
+        self.assertIsNotNone(response.headers.get(blackd.BLACK_VERSION_HEADER))
+
 
 if __name__ == "__main__":
     unittest.main(module="test_black")