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Fix stdio, protocol, and format-handling bugs blocking Windows + Anthropic clients #37

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Fix stdio, protocol, and format-handling bugs blocking Windows + Anthropic clients #37

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53d3ed1
fix: reconfigure stdio to UTF-8 + LF at startup (#36)
kdjkdjkdj Apr 19, 2026
15997ab
fix: handle missing HOME/USERPROFILE in get_safe_working_directories …
kdjkdjkdj Apr 19, 2026
d4bd710
fix: do not reply to JSON-RPC notifications (#36)
kdjkdjkdj Apr 19, 2026
a55a0ec
fix: drop anyOf from convert_file inputSchema (#36)
kdjkdjkdj Apr 19, 2026
e1094c6
fix: dispatch format-specific validation on exact MIME type (#36)
kdjkdjkdj Apr 19, 2026
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83 changes: 59 additions & 24 deletions markitdown_mcp/server.py
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Original file line number Diff line number Diff line change
Expand Up @@ -29,6 +29,14 @@
logging.basicConfig(level=logging.INFO)
logger = logging.getLogger("markitdown-mcp")

# Exact MIME types for format-specific security validation. A substring check
# like `"xml" in mime_type` incorrectly matches Office OpenXML formats (docx,
# xlsx, pptx — whose MIME contains "openxmlformats") and routes them through
# the XML sanitizer, corrupting the binary payload.
_XML_MIME_TYPES = {"text/xml", "application/xml"}
_JSON_MIME_TYPES = {"application/json", "text/json"}
_CSV_MIME_TYPES = {"text/csv", "application/csv"}


class SecurityError(Exception):
"""Raised when a security violation is detected."""
Expand Down Expand Up @@ -281,12 +289,13 @@ def validate_file_content_security(file_path: str) -> str:
mime_type, _ = mimetypes.guess_type(file_path)
file_ext = Path(file_path).suffix.lower()

# Apply format-specific validation
if (mime_type and "xml" in mime_type) or file_ext in [".xml", ".xhtml"]:
# Apply format-specific validation. Use exact MIME-type matching to
# avoid false positives (e.g. docx MIME contains "xml" as substring).
if (mime_type in _XML_MIME_TYPES) or file_ext in [".xml", ".xhtml"]:
return validate_xml_security(file_path)
if (mime_type and "json" in mime_type) or file_ext == ".json":
if (mime_type in _JSON_MIME_TYPES) or file_ext == ".json":
return validate_json_security(file_path)
if (mime_type and "csv" in mime_type) or file_ext == ".csv":
if (mime_type in _CSV_MIME_TYPES) or file_ext == ".csv":
return validate_csv_security(file_path)

# General file size check
Expand Down Expand Up @@ -640,13 +649,22 @@ def get_safe_working_directories() -> list[str]:
# Add current working directory
safe_dirs.append(str(Path.cwd()))

# Add home directory subdirectories (but not root directories)
home = Path.home()
safe_subdirs = ["Documents", "Downloads", "Desktop", "tmp"]
for subdir in safe_subdirs:
potential_dir = home / subdir
if potential_dir.exists():
safe_dirs.append(str(potential_dir))
# Home directory subdirectories. Path.home() raises RuntimeError if neither
# HOME nor USERPROFILE is set, which can happen when MCP clients spawn the
# server with an empty environment. Fall back gracefully rather than
# crashing the server at init.
try:
home = Path.home()
except RuntimeError:
logger.warning("Could not determine user home; skipping home subdirs")
home = None

if home is not None:
safe_subdirs = ["Documents", "Downloads", "Desktop", "tmp"]
for subdir in safe_subdirs:
potential_dir = home / subdir
if potential_dir.exists():
safe_dirs.append(str(potential_dir))

# Add temp directories
temp_dir = Path(tempfile.gettempdir())
Expand All @@ -664,7 +682,8 @@ def get_safe_working_directories() -> list[str]:
class MCPRequest:
"""Represents an incoming MCP protocol request."""

id: str
# JSON-RPC 2.0: id may be str, int, or absent (notification → None here).
id: str | int | None
method: str
params: dict[str, Any]

Expand All @@ -673,7 +692,7 @@ class MCPRequest:
class MCPResponse:
"""Represents an MCP protocol response."""

id: str
id: str | int | None
result: dict[str, Any] | None = None
error: dict[str, Any] | None = None

Expand Down Expand Up @@ -758,7 +777,11 @@ def get_tools(self) -> list[dict[str, Any]]:
return [
{
"name": "convert_file",
"description": "Convert a file to Markdown using MarkItDown",
"description": (
"Convert a file to Markdown using MarkItDown. "
"Provide either 'file_path' OR both 'file_content' (base64) "
"and 'filename'."
),
"inputSchema": {
"type": "object",
"properties": {
Expand All @@ -777,10 +800,6 @@ def get_tools(self) -> list[dict[str, Any]]:
"description": "Original filename when using file_content",
},
},
"anyOf": [
{"required": ["file_path"]},
{"required": ["file_content", "filename"]},
],
},
},
{
Expand Down Expand Up @@ -828,7 +847,11 @@ async def handle_request(self, request: MCPRequest) -> MCPResponse:
"tools": [
{
"name": "convert_file",
"description": "Convert a file to Markdown using MarkItDown",
"description": (
"Convert a file to Markdown using MarkItDown. "
"Provide either 'file_path' OR both "
"'file_content' (base64) and 'filename'."
),
"inputSchema": {
"type": "object",
"properties": {
Expand All @@ -849,10 +872,6 @@ async def handle_request(self, request: MCPRequest) -> MCPResponse:
"file_content",
},
},
"anyOf": [
{"required": ["file_path"]},
{"required": ["file_content", "filename"]},
],
},
},
{
Expand Down Expand Up @@ -1259,14 +1278,22 @@ async def run(self) -> None:

try:
message = json.loads(line.strip())

# JSON-RPC 2.0 §4.1: messages without "id" are notifications;
# the server MUST NOT reply to them.
is_notification = "id" not in message

request = MCPRequest(
id=message.get("id", "unknown"),
id=message.get("id"),
method=message["method"],
params=message.get("params", {}),
)

response = await self.handle_request(request)

if is_notification:
continue

# Send response
response_dict: dict[str, Any] = {"jsonrpc": "2.0", "id": response.id}
if response.result is not None:
Expand All @@ -1289,6 +1316,14 @@ async def run(self) -> None:

def main() -> None:
"""Main entry point for console script."""
# Force UTF-8 + LF on stdio. Python's text-mode defaults on Windows are
# cp1252 for stdin/stdout and CRLF translation on stdout, both of which
# break the MCP protocol: clients send UTF-8 JSON-RPC framed by LF, so
# cp1252 stdin corrupts non-ASCII input (e.g. path names with umlauts)
# and CRLF stdout corrupts the line-delimited framing. No-op on platforms
# that already default to UTF-8/LF.
sys.stdout.reconfigure(encoding="utf-8", newline="\n")
sys.stdin.reconfigure(encoding="utf-8")

async def run_server() -> None:
"""Run the MCP server asynchronously."""
Expand Down
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