9756538f16
Organizes 11 projects for Cerbo GX/Venus OS into a single repository: - axiom-nmea: Raymarine LightHouse protocol decoder - dbus-generator-ramp: Generator current ramp controller - dbus-lightning: Blitzortung lightning monitor - dbus-meteoblue-forecast: Meteoblue weather forecast - dbus-no-foreign-land: noforeignland.com tracking - dbus-tides: Tide prediction from depth + harmonics - dbus-vrm-history: VRM cloud history proxy - dbus-windy-station: Windy.com weather upload - mfd-custom-app: MFD app deployment package - venus-html5-app: Custom Victron HTML5 app fork - watermaker: Watermaker PLC control UI Adds root README, .gitignore, project template, and per-project .gitignore files. Sensitive config files excluded via .gitignore with .example templates provided. Made-with: Cursor
95 lines
3.2 KiB
Python
95 lines
3.2 KiB
Python
#!/usr/bin/env python3
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"""
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Analyze packet structure to understand why offsets vary.
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Look for common headers and protobuf nesting patterns.
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"""
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import struct
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def read_pcap(filename):
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packets = []
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with open(filename, 'rb') as f:
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header = f.read(24)
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magic = struct.unpack('<I', header[0:4])[0]
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swapped = magic == 0xd4c3b2a1
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endian = '>' if swapped else '<'
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while True:
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pkt_header = f.read(16)
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if len(pkt_header) < 16:
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break
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ts_sec, ts_usec, incl_len, orig_len = struct.unpack(f'{endian}IIII', pkt_header)
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pkt_data = f.read(incl_len)
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if len(pkt_data) < incl_len:
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break
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if len(pkt_data) > 42 and pkt_data[12:14] == b'\x08\x00':
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ip_header_len = (pkt_data[14] & 0x0F) * 4
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payload_start = 14 + ip_header_len + 8
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if payload_start < len(pkt_data):
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packets.append(pkt_data[payload_start:])
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return packets
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packets = read_pcap("raymarine_sample_TWD_62-70_HDG_29-35.pcap")
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# Group by size
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by_size = {}
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for pkt in packets:
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pkt_len = len(pkt)
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if pkt_len not in by_size:
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by_size[pkt_len] = []
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by_size[pkt_len].append(pkt)
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print("=" * 70)
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print("PACKET HEADER ANALYSIS")
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print("=" * 70)
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for pkt_len in sorted(by_size.keys()):
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if pkt_len < 100:
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continue
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pkts = by_size[pkt_len][:3] # First 3 packets of each size
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print(f"\n{'='*70}")
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print(f"PACKET SIZE: {pkt_len} bytes ({len(by_size[pkt_len])} total)")
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print("=" * 70)
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pkt = pkts[0]
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# Show first 128 bytes as hex
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print("\nFirst 128 bytes (hex):")
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for row in range(0, min(128, pkt_len), 16):
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hex_str = ' '.join(f'{b:02x}' for b in pkt[row:row+16])
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ascii_str = ''.join(chr(b) if 32 <= b < 127 else '.' for b in pkt[row:row+16])
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print(f" 0x{row:04x}: {hex_str:<48} {ascii_str}")
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# Look for the GPS pattern (0x09 followed by lat, 0x11 followed by lon)
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gps_offset = None
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for i in range(0x20, min(pkt_len - 18, 0x60)):
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if pkt[i] == 0x09 and i + 9 < pkt_len and pkt[i + 9] == 0x11:
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lat = struct.unpack('<d', pkt[i+1:i+9])[0]
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lon = struct.unpack('<d', pkt[i+10:i+18])[0]
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if -90 <= lat <= 90 and -180 <= lon <= 180 and abs(lat) > 1:
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gps_offset = i
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print(f"\n GPS found at offset 0x{i:04x}: {lat:.6f}, {lon:.6f}")
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break
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# Look for string patterns (device name)
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for i in range(0x10, min(pkt_len - 10, 0x40)):
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if pkt[i:i+5] == b'AXIOM':
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print(f" 'AXIOM' string at offset 0x{i:04x}")
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# Show surrounding context
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end = min(i + 30, pkt_len)
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print(f" Context: {pkt[i:end]}")
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break
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# Analyze protobuf wire types at key offsets
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print(f"\n Protobuf tags at key offsets:")
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for offset in [0x0070, 0x00a0, 0x00a7, 0x00c5, 0x00fc]:
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if offset < pkt_len:
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tag = pkt[offset]
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wire_type = tag & 0x07
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field_num = tag >> 3
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wire_names = {0: 'varint', 1: 'fixed64', 2: 'length', 5: 'fixed32'}
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print(f" 0x{offset:04x}: tag=0x{tag:02x} (field {field_num}, {wire_names.get(wire_type, '?')})")
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