201 lines
7.3 KiB
Python
Executable File
201 lines
7.3 KiB
Python
Executable File
#!/usr/bin/env python3
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"""Send one CoAP request over UDP and show both datagrams byte by byte.
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./coap-inspect.py get "/hello?name=Imran"
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./coap-inspect.py post /hello Imran
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./coap-inspect.py get /health
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No CoAP library: the packet is built and decoded right here, so every byte on
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screen is accounted for. COAP_HOST / COAP_PORT retarget it (127.0.0.1:5683).
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"""
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import os
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import random
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import socket
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import sys
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import time
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TYPES = {0: "CON confirmable", 1: "NON non-confirmable", 2: "ACK acknowledgement", 3: "RST reset"}
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METHODS = {"get": 1, "post": 2, "put": 3, "delete": 4}
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CODES = {
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"0.00": "Empty", "0.01": "GET", "0.02": "POST", "0.03": "PUT", "0.04": "DELETE",
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"2.01": "Created", "2.02": "Deleted", "2.03": "Valid", "2.04": "Changed", "2.05": "Content",
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"4.00": "Bad Request", "4.04": "Not Found", "4.05": "Method Not Allowed",
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"5.00": "Internal Server Error",
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}
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OPTIONS = {3: "Uri-Host", 7: "Uri-Port", 11: "Uri-Path", 12: "Content-Format", 15: "Uri-Query", 17: "Accept"}
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FORMATS = {0: "text/plain", 50: "application/json"}
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TTY = sys.stdout.isatty()
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def bold(text):
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return f"\033[1m{text}\033[0m" if TTY else text
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def encode_option(delta, value):
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"""One option: a byte of 4-bit delta + 4-bit length, then any extended bytes, then the value."""
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def nibble(n):
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if n < 13:
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return n, b""
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if n < 269:
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return 13, bytes([n - 13])
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return 14, (n - 269).to_bytes(2, "big")
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d, d_ext = nibble(delta)
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l, l_ext = nibble(len(value))
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return bytes([(d << 4) | l]) + d_ext + l_ext + value
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def build_request(method, path, query, payload):
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token = os.urandom(4)
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header = bytes([(1 << 6) | (0 << 4) | len(token), METHODS[method]]) # ver 1, CON, TKL, code
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header += random.randrange(1 << 16).to_bytes(2, "big") + token # message id, token
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# Options must be in ascending number order; each stores the gap from the previous one.
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options = [(11, s.encode()) for s in path.split("/") if s]
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options += [(15, q.encode()) for q in query.split("&") if q]
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body, last = b"", 0
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for number, value in options:
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body += encode_option(number - last, value)
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last = number
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if payload:
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body += b"\xff" + payload
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return header + body
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def decode(pkt):
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"""Return (rows, meta). Each row is (start, end, field, meaning) over pkt[start:end]."""
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if len(pkt) < 4:
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raise ValueError(f"{len(pkt)} bytes is shorter than the 4-byte CoAP header")
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rows = []
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b0 = pkt[0]
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ver, typ, tkl = b0 >> 6, (b0 >> 4) & 0b11, b0 & 0b1111
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rows.append((0, 1, "ver|type|tkl",
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f"{ver:02b} {typ:02b} {tkl:04b} -> version {ver}, {TYPES[typ]}, token {tkl} bytes"))
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cls, detail = pkt[1] >> 5, pkt[1] & 0b11111
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code = f"{cls}.{detail:02d}"
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rows.append((1, 2, "code", f"{cls:03b} {detail:05b} -> {code} {CODES.get(code, '')}"))
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mid = int.from_bytes(pkt[2:4], "big")
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rows.append((2, 4, "message id", f"{mid} (0x{mid:04x})"))
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token = pkt[4:4 + tkl]
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if tkl:
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rows.append((4, 4 + tkl, "token", f"0x{token.hex()}"))
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i, number = 4 + tkl, 0
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while i < len(pkt):
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if pkt[i] == 0xFF:
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body = pkt[i + 1:]
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rows.append((i, i + 1, "payload marker", "0xff -> the rest is the body"))
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rows.append((i + 1, len(pkt), "payload",
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f"{len(body)} bytes: {body.decode('utf-8', 'replace')}"))
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break
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start = i
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delta, length = pkt[i] >> 4, pkt[i] & 0b1111
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i += 1
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extended = []
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for which, n in (("delta", delta), ("length", length)):
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if n == 13:
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n, i = pkt[i] + 13, i + 1
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elif n == 14:
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n, i = int.from_bytes(pkt[i:i + 2], "big") + 269, i + 2
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extended.append(n)
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delta, length = extended
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number += delta
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value = pkt[i:i + length]
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i += length
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if number in (12, 17):
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n = int.from_bytes(value, "big") if value else 0
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shown = f"{n} = {FORMATS.get(n, 'unknown format')}"
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else:
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shown = f'"{value.decode("utf-8", "replace")}"'
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rows.append((start, i, OPTIONS.get(number, f"option {number}"),
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f"delta {delta} -> option {number}, {length} bytes: {shown}"))
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return rows, {"type": typ, "code": code, "mid": mid, "token": token}
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def show(title, pkt):
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print(bold(f"\n{title} ({len(pkt)} bytes)"))
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print(bold("\n hex + ascii"))
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for off in range(0, len(pkt), 16):
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chunk = pkt[off:off + 16]
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hexes = " ".join(f"{b:02x}" for b in chunk)
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text = "".join(chr(b) if 32 <= b < 127 else "." for b in chunk)
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print(f" {off:04x} {hexes:<47} |{text}|")
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print(bold("\n binary"))
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for off in range(0, len(pkt), 4):
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chunk = pkt[off:off + 4]
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bits = " ".join(f"{b:08b}" for b in chunk)
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text = "".join(chr(b) if 32 <= b < 127 else "." for b in chunk)
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print(f" {off:04x} {bits:<35} |{text}|")
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rows, meta = decode(pkt)
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print(bold("\n fields"))
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print(f" {'byte':<7} {'hex':<24} {'field':<15} meaning")
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for start, end, field, meaning in rows:
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span = f"{start}" if end - start == 1 else f"{start}-{end - 1}"
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hexes = pkt[start:end].hex(" ")
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if len(hexes) > 23:
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hexes = hexes[:20] + "..."
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print(f" {span:<7} {hexes:<24} {field:<15} {meaning}")
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return meta
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def main():
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args = sys.argv[1:]
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if not args or args[0].lower() not in METHODS:
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print(__doc__.strip())
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return 2
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method = args[0].lower()
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target = args[1] if len(args) > 1 else "/hello"
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payload = args[2].encode() if len(args) > 2 else b""
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path, _, query = target.partition("?")
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host = os.environ.get("COAP_HOST", "127.0.0.1")
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port = int(os.environ.get("COAP_PORT", "5683"))
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request = build_request(method, path, query, payload)
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sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM) # SOCK_DGRAM = UDP
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sock.settimeout(3)
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sock.connect((host, port))
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local = "%s:%d" % sock.getsockname()
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req = show(f">>> REQUEST udp {local} -> {host}:{port}", request)
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sent_at = time.perf_counter()
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sock.send(request)
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try:
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response = sock.recv(1152)
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except socket.timeout:
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print(f"\nno reply within 3s - is the CoAP server running on {host}:{port}?")
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return 1
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except ConnectionRefusedError:
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print(f"\nport unreachable - nothing is listening on udp {host}:{port}")
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return 1
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elapsed = (time.perf_counter() - sent_at) * 1000
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res = show(f"<<< RESPONSE udp {host}:{port} -> {local}", response)
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print(bold("\n exchange"))
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print(f" request {TYPES[req['type']].split()[0]} {req['code']} mid 0x{req['mid']:04x} "
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f"token 0x{req['token'].hex()} {len(request)} bytes")
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print(f" response {TYPES[res['type']].split()[0]} {res['code']} mid 0x{res['mid']:04x} "
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f"token 0x{res['token'].hex()} {len(response)} bytes after {elapsed:.2f} ms")
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same_mid = "yes" if req["mid"] == res["mid"] else "NO"
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same_token = "yes" if req["token"] == res["token"] else "NO"
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kind = " (piggybacked: the ACK carries the answer)" if res["type"] == 2 else ""
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print(f" message id matches: {same_mid} token matches: {same_token}{kind}")
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return 0
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if __name__ == "__main__":
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sys.exit(main())
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