Markus Fritsche
70103792df
- Pump loop after fork: parent streams stdin to child through pipe - netstring: enforce .isdigit() on length field - netstring: require exact consumption (no trailing data) - argv split: use .split space not .split - Non-ASCII command: fail loudly - Child exec failure: os._exit(1) 17/17 pytest green
129 lines
3.7 KiB
Python
Executable File
129 lines
3.7 KiB
Python
Executable File
#!/usr/bin/env python3
|
|
"""sic wire protocol v2 daemon — read one frame, exec command, forward stdin."""
|
|
import os
|
|
import struct
|
|
import sys
|
|
|
|
|
|
def read_exactly(fd: int, n: int) -> bytes:
|
|
"""Read exactly n bytes from fd, or raise EOFError."""
|
|
buf = bytearray()
|
|
while len(buf) < n:
|
|
chunk = os.read(fd, n - len(buf))
|
|
if not chunk:
|
|
raise EOFError(f"expected {n} bytes, got {len(buf)}")
|
|
buf.extend(chunk)
|
|
return bytes(buf)
|
|
|
|
|
|
def parse_netstring(data: bytes) -> tuple[bytes, bytes]:
|
|
"""Parse a DJB netstring from data. Returns (content, rest)."""
|
|
colon = data.find(b":")
|
|
if colon < 0:
|
|
raise ValueError("netstring missing colon")
|
|
# Enforce non-canonical lengths: must be all digits
|
|
if not data[:colon].isdigit():
|
|
raise ValueError("netstring length not all digits")
|
|
ns_len = int(data[:colon])
|
|
# Need at least colon+1 + ns_len + 1 for trailing comma
|
|
if len(data) < colon + 1 + ns_len + 1:
|
|
raise ValueError("netstring truncated")
|
|
content = data[colon + 1 : colon + 1 + ns_len]
|
|
if data[colon + 1 + ns_len : colon + 1 + ns_len + 1] != b",":
|
|
raise ValueError("netstring missing trailing comma")
|
|
# Require exact consumption: no rest after the comma
|
|
rest = data[colon + 1 + ns_len + 1 :]
|
|
if rest:
|
|
raise ValueError("netstring has trailing data after comma")
|
|
return content, rest
|
|
|
|
|
|
def main() -> None:
|
|
# Read 5-byte preamble: magic + len32
|
|
try:
|
|
preamble = read_exactly(sys.stdin.fileno(), 5)
|
|
except EOFError:
|
|
sys.stderr.write("sicd: EOF reading preamble\n")
|
|
sys.exit(1)
|
|
|
|
if preamble[0:1] != b"\x00":
|
|
sys.stderr.write("sicd: missing magic byte 0x00\n")
|
|
sys.exit(1)
|
|
|
|
ns_len = struct.unpack(">I", preamble[1:5])[0]
|
|
|
|
# Read the netstring
|
|
try:
|
|
ns_data = read_exactly(sys.stdin.fileno(), ns_len)
|
|
except EOFError:
|
|
sys.stderr.write("sicd: EOF reading netstring body\n")
|
|
sys.exit(1)
|
|
|
|
try:
|
|
content, _ = parse_netstring(ns_data)
|
|
except ValueError as e:
|
|
sys.stderr.write(f"sicd: {e}\n")
|
|
sys.exit(1)
|
|
|
|
# Split at first NUL
|
|
nul_pos = content.find(b"\x00")
|
|
if nul_pos < 0:
|
|
sys.stderr.write("sicd: missing NUL separator between command and payload\n")
|
|
sys.exit(1)
|
|
|
|
command_bytes = content[:nul_pos]
|
|
payload = content[nul_pos + 1 :]
|
|
|
|
# Decode command, validate ASCII
|
|
try:
|
|
command_str = command_bytes.decode("ascii")
|
|
except UnicodeDecodeError:
|
|
sys.stderr.write("sicd: command contains non-ASCII bytes\n")
|
|
sys.exit(1)
|
|
|
|
# Split on ASCII space only (not .split())
|
|
argv = command_str.split(" ")
|
|
|
|
# Create pipe for child's stdin
|
|
r_fd, w_fd = os.pipe()
|
|
|
|
pid = os.fork()
|
|
if pid == 0:
|
|
# Child
|
|
os.close(w_fd)
|
|
os.dup2(r_fd, sys.stdin.fileno())
|
|
os.close(r_fd)
|
|
try:
|
|
os.execvp(argv[0], argv)
|
|
except FileNotFoundError:
|
|
sys.stderr.write(f"sicd: command not found: {argv[0]}\n")
|
|
os._exit(1)
|
|
except Exception as e:
|
|
sys.stderr.write(f"sicd: exec failed: {e}\n")
|
|
os._exit(1)
|
|
else:
|
|
# Parent
|
|
os.close(r_fd)
|
|
# Write payload first
|
|
os.write(w_fd, payload)
|
|
# Then pump remaining stdin to child
|
|
try:
|
|
while True:
|
|
chunk = os.read(sys.stdin.fileno(), 65536)
|
|
if not chunk:
|
|
break
|
|
os.write(w_fd, chunk)
|
|
except OSError:
|
|
pass
|
|
os.close(w_fd)
|
|
# Wait for child
|
|
_, status = os.waitpid(pid, 0)
|
|
if os.WIFEXITED(status):
|
|
sys.exit(os.WEXITSTATUS(status))
|
|
else:
|
|
sys.exit(1)
|
|
|
|
|
|
if __name__ == "__main__":
|
|
main()
|