Addressed 7 critical issues in the v1 fragmentation implementation identified during PR #503 review. These fixes improve protocol safety and clarify known limitations while v2 integration proceeds.

Changes

Fragment validation (fragmentation.rs)

• Added bounds check: fragment_index < total_fragments in FragmentHeader::from_bytes()
• Prevents processing of malformed fragments that could corrupt reassembly

Collision risk documentation (fragmentation.rs)

• Documented non-cryptographic message ID generation (wrapping_sum) with explicit collision scenarios
• Added inline warnings and migration path to v2's session-scoped IDs

Wire format compatibility (gatt.rs)

• Documented breaking change: 12-byte headers (u64 message_id) → 8-byte headers (u32)
• Clarified fragment_large_message() ignores its message_id parameter (changed to _message_id)
• Old/new clients cannot interoperate

Stale fragment cleanup (gatt.rs)

• Changed cleanup_stale_fragments() from clearing ALL pending to logging-only
• Prevents disruption of concurrent valid reassemblies
• Documents v1 reassembler limitation and v2 migration path

Backward compatibility (blockchain_sync/mod.rs)

• Added missing deprecated re-exports: BLE_CHUNK_SIZE, WIFI_CHUNK_SIZE
• Prevents compile failures in existing code

Reassembly logging (gatt.rs)

• Removed misleading pending_count() call after message completion (always returns 0 or unrelated count)

Example

// Fragment validation now catches malformed data
let mut invalid_bytes = [0u8; 8];
invalid_bytes[4..6].copy_from_slice(&10u16.to_le_bytes());  // total_fragments = 10
invalid_bytes[6..8].copy_from_slice(&10u16.to_le_bytes());  // fragment_index = 10 (invalid)

let result = FragmentHeader::from_bytes(&invalid_bytes);
// Now returns: Err("Invalid fragment: index 10 >= total_fragments 10")

All v1 limitations are now clearly documented with migration guidance to fragmentation_v2.

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.