Markus Fritsche
833a0432b8
Review round 3 fixes: - write_all helper: handle partial writes from signals - EPIPE on write side: catch BrokenPipeError (child dead), not all OSError - Read-side OSError: diagnose on stderr + exit 1 (not silent truncation) - parse_netstring: sanity cap 1<<24, return content only (not tuple) - 128+WTERMSIG for signal-killed children (shell convention) - 24/24 pytest green
133 lines
3.9 KiB
Python
Executable File
133 lines
3.9 KiB
Python
Executable File
#!/usr/bin/env python3
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"""sic wire protocol v2 daemon — read one frame, exec command, forward stdin."""
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import os
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import struct
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import sys
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def read_exactly(fd: int, n: int) -> bytes:
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"""Read exactly n bytes from fd, or raise EOFError."""
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buf = bytearray()
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while len(buf) < n:
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chunk = os.read(fd, n - len(buf))
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if not chunk:
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raise EOFError(f"expected {n} bytes, got {len(buf)}")
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buf.extend(chunk)
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return bytes(buf)
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def write_all(fd: int, data: bytes) -> None:
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"""Write all of data to fd, handling partial writes from signals."""
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offset = 0
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while offset < len(data):
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n = os.write(fd, data[offset:])
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offset += n
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def parse_netstring(data: bytes) -> bytes:
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"""Parse a DJB netstring from data. Returns content or raises ValueError."""
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colon = data.find(b":")
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if colon < 0:
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raise ValueError("netstring missing colon")
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if not data[:colon].isdigit():
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raise ValueError("netstring length not all digits")
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ns_len = int(data[:colon])
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if ns_len > 1 << 24:
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raise ValueError("netstring length exceeds sanity cap")
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if len(data) < colon + 1 + ns_len + 1:
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raise ValueError("netstring truncated")
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content = data[colon + 1 : colon + 1 + ns_len]
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if data[colon + 1 + ns_len : colon + 1 + ns_len + 1] != b",":
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raise ValueError("netstring missing trailing comma")
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rest = data[colon + 1 + ns_len + 1 :]
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if rest:
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raise ValueError("netstring has trailing data after comma")
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return content
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def main() -> None:
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try:
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preamble = read_exactly(sys.stdin.fileno(), 5)
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except EOFError:
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sys.stderr.write("sicd: EOF reading preamble\n")
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sys.exit(1)
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if preamble[0:1] != b"\x00":
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sys.stderr.write("sicd: missing magic byte 0x00\n")
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sys.exit(1)
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ns_len = struct.unpack(">I", preamble[1:5])[0]
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try:
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ns_data = read_exactly(sys.stdin.fileno(), ns_len)
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except EOFError:
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sys.stderr.write("sicd: EOF reading netstring body\n")
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sys.exit(1)
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try:
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content = parse_netstring(ns_data)
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except ValueError as e:
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sys.stderr.write(f"sicd: {e}\n")
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sys.exit(1)
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nul_pos = content.find(b"\x00")
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if nul_pos < 0:
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sys.stderr.write("sicd: missing NUL separator between command and payload\n")
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sys.exit(1)
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command_bytes = content[:nul_pos]
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payload = content[nul_pos + 1 :]
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try:
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command_str = command_bytes.decode("ascii")
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except UnicodeDecodeError:
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sys.stderr.write("sicd: command contains non-ASCII bytes\n")
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sys.exit(1)
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argv = command_str.split(" ")
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r_fd, w_fd = os.pipe()
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pid = os.fork()
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if pid == 0:
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os.close(w_fd)
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os.dup2(r_fd, sys.stdin.fileno())
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os.close(r_fd)
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try:
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os.execvp(argv[0], argv)
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except FileNotFoundError:
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sys.stderr.write(f"sicd: command not found: {argv[0]}\n")
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os._exit(1)
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except Exception as e:
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sys.stderr.write(f"sicd: exec failed: {e}\n")
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os._exit(1)
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else:
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os.close(r_fd)
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read_error = False
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try:
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if payload:
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write_all(w_fd, payload)
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while True:
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chunk = os.read(sys.stdin.fileno(), 65536)
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if not chunk:
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break
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write_all(w_fd, chunk)
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except BrokenPipeError:
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pass
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except OSError as e:
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sys.stderr.write(f"sicd: stdin read error: {e}\n")
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read_error = True
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os.close(w_fd)
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_, status = os.waitpid(pid, 0)
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if read_error:
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sys.exit(1)
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if os.WIFEXITED(status):
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sys.exit(os.WEXITSTATUS(status))
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elif os.WIFSIGNALED(status):
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sys.exit(128 + os.WTERMSIG(status))
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else:
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sys.exit(1)
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if __name__ == "__main__":
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main() |