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PacoX
77 lines
2.7 KiB
Markdown
77 lines
2.7 KiB
Markdown
# Routing Paths
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This page covers how MeshCore Open represents, selects, validates, and stores routing paths in the UI and data layer.
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## Path Routing
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MeshCore supports variable-length multi-byte routing paths so the app can scale from small meshes to very large node sets.
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### Hash Width and Multi-Byte Paths
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The device capability determines the hash width (number of bytes per hop):
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| Width | Max Unique Nodes | Typical Use |
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|-------|-----------------|-------------|
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| 1 byte | 256 | Single-byte node IDs |
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| 2 bytes | 65,536 | Medium meshes |
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| 3 bytes | 16.7M | Large networks |
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### Device Capability Detection
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On device connection, the app reads the firmware capability to set `pathHashByteWidth`:
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```dart
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// Read from device info response (offset 81)
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final modeRaw = firmwareBytes.length >= 82
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? (firmwareBytes[81] & 0xFF)
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: 0;
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final mode = modeRaw.clamp(0, 2);
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_pathHashByteWidth = mode + 1; // 1, 2, or 3 bytes per hop
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```
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The current implementation intentionally clamps to modes `0..2`, so the supported hop width is `1..3` bytes. Do not document 4-byte hops unless the connector implementation is widened first.
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### Path Data Structure
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Paths in messages and storage consist of:
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- **`pathLength`**: Hop count reported in the radio header (may differ from decoded path)
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- **`pathBytes`**: Raw bytes of the path, grouped by `pathHashByteWidth`
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- **Example**: With `pathHashByteWidth=2`, a 3-hop path needs 6 bytes:
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- `pathBytes = [0xA1, 0xA2, 0xB1, 0xB2, 0xC1, 0xC2]`
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- Hops: `[0xA1A2]`, `[0xB1B2]`, `[0xC1C2]`
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### Hop Count Calculation
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Convert path byte length to hop count:
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```dart
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int hopCount = (byteCount + hashByteWidth - 1) ~/ hashByteWidth;
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```
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Use this consistently when displaying hop counts in UI to avoid mismatch between metadata (`pathLength`) and observed paths (`pathBytes`).
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### Path Usage in Different Message Types
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- **Direct messages**: Extract path from decrypted payload to trace sender route.
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- **Channel messages**: Decrypt hop-by-hop routing chain from payload; header includes `pathLength` metadata.
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- **Contact storage**: Path length in byte 32, raw path bytes in bytes 33-96, grouped by detected `pathHashByteWidth`.
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### UI Hop Count Display
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⚠️ **Important**: In screens like "Channel Message Path", prefer the actual decoded `pathBytes` hop count over `pathLength` metadata:
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```dart
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// Preferred: use actual observed path length
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final effectiveHopCount = (pathBytes.length + width - 1) ~/ width;
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// Avoid: using radio metadata directly
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// pathLength can diverge from decoded bytes and cause UI mismatches
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```
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Example scenario:
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- Radio header reports `pathLength: 32`
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- Decoded path bytes: `[0xAB, 0xCD]` (2 bytes = 1 hop with width=2)
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- **Display**: "1 hop" (from pathBytes), NOT "32 hops" (from pathLength)
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