Module flattrs 

Flat attribute storage for message headers.

This module provides Flattrs, a type optimized for message passing scenarios where headers are often forwarded without inspection. It uses a single contiguous buffer with inline entry lengths for efficient zero-copy passthrough.

Wire Format

┌─────────────┬──────────────────────────────────────────────────┐
│ num_entries │ entries...                                       │
│ (u16)       │ (key_hash: u64, len: u32, value: [u8])...          │
└─────────────┴──────────────────────────────────────────────────┘

Each entry is self-describing with its length inline, allowing linear scan without a separate index section.

• Key IDs are FNV-1a hashes of key names (stable, computed at compile time)
• Uses linear search (optimal for typical small header counts of 2-5 entries)

Design Benefits

• Zero-copy passthrough: Forward the entire buffer without parsing
• Zero-copy serialization: Uses Part for zero-copy through multipart codec
• Simple implementation: No mode switching, just a single buffer
• Compact wire format: u64 key IDs instead of string names

Example

use hyperactor_config::flattrs::Flattrs;
use hyperactor_config::attrs::declare_attrs;

declare_attrs! {
    pub attr TIMESTAMP: u64;
    pub attr REQUEST_ID: String;
}

let mut headers = Flattrs::new();
headers.set(TIMESTAMP, 1234567890u64);
headers.set(REQUEST_ID, "req-123".to_string());

// Lazy deserialization on access
let ts: Option<u64> = headers.get(TIMESTAMP);

Structs

Flattrs

Flat attribute storage for message headers.