Updated StdioServer to use binary streams for stdin/stdout and added subprocess-based test for framed JSON-RPC communication

Author: m-messer

lf_toolkit/io/stdio_server.py

@@ -16,8 +16,8 @@ class StdioClient(StreamIO):
 
     def __init__(self):
         self.stream = StapledByteStream(
-            FileWriteStream(sys.stdout),
-            FileReadStream(sys.stdin),
+            FileWriteStream(sys.stdout.buffer),
+            FileReadStream(sys.stdin.buffer),
         )
 
     async def read(self, size: int) -> bytes:
@@ -43,5 +43,6 @@ def wrap_io(self, client: StreamIO) -> StreamIO:
         return PrefixStreamIO(client)
 
     async def run(self):
+        print("StdioServer started", file=sys.stderr, flush=True)
         self._client = StdioClient()
         await self._handle_client(self._client)

tests/io/stream_io_test.py

@@ -1,3 +1,6 @@
+import subprocess
+import sys
+
 import pytest
 import anyio
 
@@ -203,3 +206,32 @@ async def test_exact_read_of_partial_chunks(self, stream):
         result = await prefix_io.read(4096)
         assert result == payload
         assert len(result) == 100
+
+
+class TestStdioServerSubprocess:
+
+    def test_binary_pipe_roundtrip(self):
+        """
+        Spawn the StdioServer as a subprocess and pipe a framed JSON-RPC
+        request to its stdin (as raw bytes). Confirms sys.stdin.buffer /
+        sys.stdout.buffer is used — text-mode streams would break this.
+        """
+        msg = b'{"jsonrpc":"2.0","id":1,"method":"eval","params":{}}'
+        frame = f"Content-Length: {len(msg)}\r\n\r\n".encode() + msg
+
+        proc = subprocess.Popen(
+            [sys.executable, "-c",
+             "import anyio; from lf_toolkit.io.stdio_server import StdioServer; "
+             "anyio.run(StdioServer().run)"],
+            stdin=subprocess.PIPE,
+            stdout=subprocess.PIPE,
+            stderr=subprocess.PIPE,
+        )
+
+        stdout, stderr = proc.communicate(input=frame, timeout=5)
+
+        # Must receive a framed response
+        assert b"Content-Length:" in stdout, (
+            f"No framed response received.\nstderr: {stderr.decode()}"
+        )
+        assert b"jsonrpc" in stdout