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2026-07-29 01:00:10 -05:00
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#!/usr/bin/env python3
"""
Minimal MCP server that writes notification + response in a single write() with no flush.
This reproduces the buffering bug where read_message() can strand the response.
"""
import json
import sys
import os
TOOLS = [
{
"name": "echo",
"description": "Echo back the input message",
"inputSchema": {
"type": "object",
"properties": {
"message": {"type": "string"}
},
"required": ["message"]
}
}
]
def handle_initialize(params, req_id):
return {
"jsonrpc": "2.0",
"id": req_id,
"result": {
"protocolVersion": "2024-11-05",
"capabilities": {"tools": {}},
"serverInfo": {"name": "burst-test", "version": "1.0"}
}
}
def handle_tools_list(params, req_id):
return {
"jsonrpc": "2.0",
"id": req_id,
"result": {"tools": TOOLS}
}
def handle_tools_call(params, req_id):
tool_name = params.get("name")
arguments = params.get("arguments", {})
if tool_name == "echo":
message = arguments.get("message", "")
notif = {
"jsonrpc": "2.0",
"method": "notifications/progress",
"params": {"progress": 50, "total": 100}
}
response = {
"jsonrpc": "2.0",
"id": req_id,
"result": {
"content": [{"type": "text", "text": f"echo: {message}"}]
}
}
# Single os.write() call: both lines land in one pipe packet atomically.
# This is the key difference from mcp_malformed_server.py which flushes between writes.
data = (json.dumps(notif) + "\n" + json.dumps(response) + "\n").encode("utf-8")
os.write(sys.stdout.fileno(), data)
return None # already written
else:
response = {
"jsonrpc": "2.0",
"id": req_id,
"error": {"code": -32602, "message": f"Unknown tool: {tool_name}"}
}
return response
HANDLERS = {
"initialize": handle_initialize,
"tools/list": handle_tools_list,
"tools/call": handle_tools_call,
}
def main():
# Use line-buffered text mode for regular responses, but the burst write
# uses os.write() directly to guarantee a single kernel write().
sys.stdout = os.fdopen(sys.stdout.fileno(), "w", buffering=1)
sys.stderr = os.fdopen(sys.stderr.fileno(), "w", buffering=1)
for line in sys.stdin:
line = line.strip()
if not line:
continue
try:
request = json.loads(line)
except json.JSONDecodeError:
continue
method = request.get("method")
req_id = request.get("id")
params = request.get("params", {})
# JSON-RPC 2.0: a message without an id is a notification and must not receive a response
if req_id is None:
continue
handler = HANDLERS.get(method)
if handler:
response = handler(params, req_id)
if response is not None:
sys.stdout.write(json.dumps(response) + "\n")
sys.stdout.flush()
else:
response = {
"jsonrpc": "2.0",
"id": req_id,
"error": {"code": -32601, "message": f"Method not found: {method}"}
}
sys.stdout.write(json.dumps(response) + "\n")
sys.stdout.flush()
if __name__ == "__main__":
main()
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#!/usr/bin/env python3
"""
MCP server that crashes after receiving a specific tool call.
"""
import json
import sys
import os
def handle_initialize(params, req_id):
return {
"jsonrpc": "2.0",
"id": req_id,
"result": {
"protocolVersion": "2024-11-05",
"capabilities": {"tools": {}},
"serverInfo": {"name": "crash-test", "version": "1.0"}
}
}
def handle_tools_list(params, req_id):
return {
"jsonrpc": "2.0",
"id": req_id,
"result": {
"tools": [
{
"name": "echo",
"description": "Echo back the input message",
"inputSchema": {
"type": "object",
"properties": {
"message": {"type": "string"}
}
}
},
{
"name": "crash",
"description": "Crash the server",
"inputSchema": {
"type": "object",
"properties": {}
}
}
]
}
}
def handle_tools_call(params, req_id):
tool_name = params.get("name")
arguments = params.get("arguments", {})
if tool_name == "echo":
message = arguments.get("message", "")
return {
"jsonrpc": "2.0",
"id": req_id,
"result": {
"content": [{"type": "text", "text": f"echo: {message}"}]
}
}
elif tool_name == "crash":
# Send a partial response then exit
sys.stdout.write(json.dumps({"jsonrpc": "2.0", "id": req_id, "result": {"content": [{"type": "text", "text": "crashing..."}]}}) + "\n")
sys.stdout.flush()
os._exit(1)
else:
return {
"jsonrpc": "2.0",
"id": req_id,
"error": {"code": -32602, "message": f"Unknown tool: {tool_name}"}
}
HANDLERS = {
"initialize": handle_initialize,
"tools/list": handle_tools_list,
"tools/call": handle_tools_call,
}
def main():
sys.stdout = os.fdopen(sys.stdout.fileno(), "w", buffering=1)
sys.stderr = os.fdopen(sys.stderr.fileno(), "w", buffering=1)
for line in sys.stdin:
line = line.strip()
if not line:
continue
try:
request = json.loads(line)
except json.JSONDecodeError:
continue
method = request.get("method")
req_id = request.get("id")
params = request.get("params", {})
# JSON-RPC 2.0: a message without an id is a notification and must not receive a response
if req_id is None:
continue
handler = HANDLERS.get(method)
if handler:
response = handler(params, req_id)
else:
response = {
"jsonrpc": "2.0",
"id": req_id,
"error": {"code": -32601, "message": f"Method not found: {method}"}
}
sys.stdout.write(json.dumps(response) + "\n")
sys.stdout.flush()
if __name__ == "__main__":
main()
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#!/usr/bin/env python3
"""
Minimal MCP server for testing.
Implements JSON-RPC 2.0 over stdio (line-delimited JSON).
"""
import json
import sys
import os
# Ensure we use python3 from the current environment
if sys.platform == "win32":
# On Windows, we need to use the same python interpreter
pass
TOOLS = [
{
"name": "echo",
"description": "Echo back the input message",
"inputSchema": {
"type": "object",
"properties": {
"message": {"type": "string", "description": "Message to echo"}
},
"required": ["message"]
}
},
{
"name": "add",
"description": "Add two numbers",
"inputSchema": {
"type": "object",
"properties": {
"a": {"type": "number"},
"b": {"type": "number"}
},
"required": ["a", "b"]
}
},
{
"name": "fail_once",
"description": "Fails on first call, succeeds on subsequent calls",
"inputSchema": {
"type": "object",
"properties": {}
}
}
]
_state = {"fail_once_called": False}
def handle_initialize(params, req_id):
return {
"jsonrpc": "2.0",
"id": req_id,
"result": {
"protocolVersion": "2024-11-05",
"capabilities": {"tools": {}},
"serverInfo": {"name": "echo-test", "version": "1.0"}
}
}
def handle_tools_list(params, req_id):
return {
"jsonrpc": "2.0",
"id": req_id,
"result": {"tools": TOOLS}
}
def handle_tools_call(params, req_id):
tool_name = params.get("name")
arguments = params.get("arguments", {})
if tool_name == "echo":
message = arguments.get("message", "")
return {
"jsonrpc": "2.0",
"id": req_id,
"result": {
"content": [{"type": "text", "text": f"echo: {message}"}]
}
}
elif tool_name == "add":
a = arguments.get("a", 0)
b = arguments.get("b", 0)
return {
"jsonrpc": "2.0",
"id": req_id,
"result": {
"content": [{"type": "text", "text": str(a + b)}]
}
}
elif tool_name == "fail_once":
if not _state["fail_once_called"]:
_state["fail_once_called"] = True
return {
"jsonrpc": "2.0",
"id": req_id,
"error": {"code": -32000, "message": "transient error"}
}
return {
"jsonrpc": "2.0",
"id": req_id,
"result": {
"content": [{"type": "text", "text": "ok"}]
}
}
else:
return {
"jsonrpc": "2.0",
"id": req_id,
"error": {"code": -32602, "message": f"Unknown tool: {tool_name}"}
}
def handle_ping(params, req_id):
return {
"jsonrpc": "2.0",
"id": req_id,
"result": {}
}
HANDLERS = {
"initialize": handle_initialize,
"tools/list": handle_tools_list,
"tools/call": handle_tools_call,
"ping": handle_ping,
}
def main():
# Use unbuffered output
sys.stdout = os.fdopen(sys.stdout.fileno(), "w", buffering=1)
sys.stderr = os.fdopen(sys.stderr.fileno(), "w", buffering=1)
for line in sys.stdin:
line = line.strip()
if not line:
continue
try:
request = json.loads(line)
except json.JSONDecodeError:
continue
method = request.get("method")
req_id = request.get("id")
params = request.get("params", {})
# JSON-RPC 2.0: a message without an id is a notification and must not receive a response
if req_id is None:
continue
handler = HANDLERS.get(method)
if handler:
response = handler(params, req_id)
else:
response = {
"jsonrpc": "2.0",
"id": req_id,
"error": {"code": -32601, "message": f"Method not found: {method}"}
}
sys.stdout.write(json.dumps(response) + "\n")
sys.stdout.flush()
if __name__ == "__main__":
main()
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#!/usr/bin/env python3
"""
MCP server (NDJSON JSON-RPC over stdio) that spawns a long-lived grandchild which inherits
this process's stdin/stdout/stderr and keeps them open.
This reproduces the reader-teardown deadlock: killing the direct MCP child (SIGKILL, which is
all subprocess_terminate() does) does NOT close the stdout/stderr pipe write ends, because the
grandchild still holds them. A server that reads those pipes with a blocking read would then
wait forever for an EOF that never arrives, hanging teardown (both warmup shutdown at startup
and process shutdown). The polled, running-aware reader must exit regardless.
"""
import json
import os
import subprocess
import sys
# Spawn a grandchild that inherits our std handles (fds 0/1/2 = the MCP pipes) and lives well
# past any teardown in the tests. We do NOT redirect its stdio, so it keeps the pipe write ends
# open even after this process is killed.
subprocess.Popen([sys.executable, "-c", "import time; time.sleep(30)"])
TOOLS = [
{
"name": "echo",
"description": "Echo back the input message",
"inputSchema": {
"type": "object",
"properties": {"message": {"type": "string", "description": "Message to echo"}},
"required": ["message"],
},
}
]
def handle_initialize(params, req_id):
return {
"jsonrpc": "2.0",
"id": req_id,
"result": {
"protocolVersion": "2024-11-05",
"capabilities": {"tools": {}},
"serverInfo": {"name": "grandchild-test", "version": "1.0"},
},
}
def handle_tools_list(params, req_id):
return {"jsonrpc": "2.0", "id": req_id, "result": {"tools": TOOLS}}
def handle_tools_call(params, req_id):
if params.get("name") == "echo":
message = params.get("arguments", {}).get("message", "")
return {
"jsonrpc": "2.0",
"id": req_id,
"result": {"content": [{"type": "text", "text": f"echo: {message}"}]},
}
return {"jsonrpc": "2.0", "id": req_id, "error": {"code": -32602, "message": "Unknown tool"}}
HANDLERS = {
"initialize": handle_initialize,
"tools/list": handle_tools_list,
"tools/call": handle_tools_call,
}
def main():
sys.stdout = os.fdopen(sys.stdout.fileno(), "w", buffering=1)
sys.stderr = os.fdopen(sys.stderr.fileno(), "w", buffering=1)
for line in sys.stdin:
line = line.strip()
if not line:
continue
try:
request = json.loads(line)
except json.JSONDecodeError:
continue
method = request.get("method")
req_id = request.get("id")
params = request.get("params", {})
if req_id is None:
continue # notification, no response
handler = HANDLERS.get(method)
if handler:
response = handler(params, req_id)
else:
response = {"jsonrpc": "2.0", "id": req_id, "error": {"code": -32601, "message": f"Method not found: {method}"}}
sys.stdout.write(json.dumps(response) + "\n")
sys.stdout.flush()
if __name__ == "__main__":
main()
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#!/usr/bin/env python3
"""
MCP server that sends malformed responses and notifications during requests.
"""
import json
import sys
import os
def handle_initialize(params, req_id):
return {
"jsonrpc": "2.0",
"id": req_id,
"result": {
"protocolVersion": "2024-11-05",
"capabilities": {"tools": {}},
"serverInfo": {"name": "malformed-test", "version": "1.0"}
}
}
def handle_tools_list(params, req_id):
return {
"jsonrpc": "2.0",
"id": req_id,
"result": {
"tools": [
{
"name": "echo",
"description": "Echo back the input message",
"inputSchema": {
"type": "object",
"properties": {
"message": {"type": "string"}
}
}
}
]
}
}
def handle_tools_call(params, req_id):
tool_name = params.get("name")
arguments = params.get("arguments", {})
if tool_name == "echo":
message = arguments.get("message", "")
# Send a notification first (no id field)
notif = {
"jsonrpc": "2.0",
"method": "notifications/progress",
"params": {"progress": 50, "total": 100}
}
sys.stdout.write(json.dumps(notif) + "\n")
sys.stdout.flush()
# Then send the actual response
return {
"jsonrpc": "2.0",
"id": req_id,
"result": {
"content": [{"type": "text", "text": f"echo: {message}"}]
}
}
else:
return {
"jsonrpc": "2.0",
"id": req_id,
"error": {"code": -32602, "message": f"Unknown tool: {tool_name}"}
}
HANDLERS = {
"initialize": handle_initialize,
"tools/list": handle_tools_list,
"tools/call": handle_tools_call,
}
def main():
sys.stdout = os.fdopen(sys.stdout.fileno(), "w", buffering=1)
sys.stderr = os.fdopen(sys.stderr.fileno(), "w", buffering=1)
for line in sys.stdin:
line = line.strip()
if not line:
continue
try:
request = json.loads(line)
except json.JSONDecodeError:
# Send malformed JSON response
sys.stdout.write("THIS IS NOT JSON\n")
sys.stdout.flush()
continue
method = request.get("method")
req_id = request.get("id")
params = request.get("params", {})
# JSON-RPC 2.0: a message without an id is a notification and must not receive a response
if req_id is None:
continue
handler = HANDLERS.get(method)
if handler:
response = handler(params, req_id)
else:
response = {
"jsonrpc": "2.0",
"id": req_id,
"error": {"code": -32601, "message": f"Method not found: {method}"}
}
sys.stdout.write(json.dumps(response) + "\n")
sys.stdout.flush()
if __name__ == "__main__":
main()
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#!/usr/bin/env python3
"""
MCP server that sleeps before responding, for timeout testing.
"""
import json
import sys
import os
import time
import argparse
TOOLS = [
{
"name": "sleep",
"description": "Sleep for a given number of seconds",
"inputSchema": {
"type": "object",
"properties": {
"seconds": {"type": "number", "description": "Seconds to sleep"}
},
"required": ["seconds"]
}
}
]
def handle_initialize(params, req_id):
return {
"jsonrpc": "2.0",
"id": req_id,
"result": {
"protocolVersion": "2024-11-05",
"capabilities": {"tools": {}},
"serverInfo": {"name": "slow-test", "version": "1.0"}
}
}
def handle_tools_list(params, req_id):
return {
"jsonrpc": "2.0",
"id": req_id,
"result": {"tools": TOOLS}
}
def handle_tools_call(params, req_id):
tool_name = params.get("name")
arguments = params.get("arguments", {})
if tool_name == "sleep":
seconds = arguments.get("seconds", 1)
time.sleep(seconds)
return {
"jsonrpc": "2.0",
"id": req_id,
"result": {
"content": [{"type": "text", "text": f"slept {seconds}s"}]
}
}
else:
return {
"jsonrpc": "2.0",
"id": req_id,
"error": {"code": -32602, "message": f"Unknown tool: {tool_name}"}
}
HANDLERS = {
"initialize": handle_initialize,
"tools/list": handle_tools_list,
"tools/call": handle_tools_call,
}
def main():
parser = argparse.ArgumentParser()
parser.add_argument("--delay", type=float, default=5.0, help="Delay in seconds for sleep tool")
args = parser.parse_args()
# Override the sleep duration
global handle_tools_call
def handle_tools_call(params, req_id):
tool_name = params.get("name")
arguments = params.get("arguments", {})
if tool_name == "sleep":
seconds = arguments.get("seconds", args.delay)
time.sleep(seconds)
return {
"jsonrpc": "2.0",
"id": req_id,
"result": {
"content": [{"type": "text", "text": f"slept {seconds}s"}]
}
}
else:
return {
"jsonrpc": "2.0",
"id": req_id,
"error": {"code": -32602, "message": f"Unknown tool: {tool_name}"}
}
sys.stdout = os.fdopen(sys.stdout.fileno(), "w", buffering=1)
sys.stderr = os.fdopen(sys.stderr.fileno(), "w", buffering=1)
for line in sys.stdin:
line = line.strip()
if not line:
continue
try:
request = json.loads(line)
except json.JSONDecodeError:
continue
method = request.get("method")
req_id = request.get("id")
params = request.get("params", {})
# JSON-RPC 2.0: a message without an id is a notification and must not receive a response
if req_id is None:
continue
handler = HANDLERS.get(method)
if handler:
response = handler(params, req_id)
else:
response = {
"jsonrpc": "2.0",
"id": req_id,
"error": {"code": -32601, "message": f"Method not found: {method}"}
}
sys.stdout.write(json.dumps(response) + "\n")
sys.stdout.flush()
if __name__ == "__main__":
main()