Crate h2session 

Stateful HTTP/2 frame parser with HPACK support for passive traffic monitoring.

This crate decodes HTTP/2 frames and HPACK-compressed headers from raw byte streams, maintaining per-connection decoder state so that dynamic table entries are preserved across successive feed() calls.

Key types

• H2SessionCache — thread-safe cache of many connections keyed by an arbitrary K. Best when you have many connections and want automatic state management.
• H2ConnectionState — state for a single HTTP/2 connection. Use feed() to push data incrementally and try_pop() to retrieve completed messages.

Examples

Multi-connection cache

use h2session::{H2SessionCache, ParsedH2Message};

let cache = H2SessionCache::<u64>::new();

// Parse a buffer for connection 42
let completed = cache.parse(42, &raw_bytes).unwrap();
for (stream_id, msg) in &completed {
    if msg.is_request() {
        println!(
            "{} {}",
            msg.method.as_deref().unwrap_or("?"),
            msg.path.as_deref().unwrap_or("/")
        );
    }
}

Single-connection incremental parsing

use h2session::{H2ConnectionState, TimestampNs};

let mut state = H2ConnectionState::new();

// Feed data as it arrives
state.feed(&chunk, TimestampNs(0)).unwrap();

// Pop completed messages
while let Some((stream_id, msg)) = state.try_pop() {
    println!("stream {stream_id}: request={}", msg.is_request());
}

Feature flags

• tracing — emit tracing::warn! events for non-fatal parse issues (stale stream eviction, etc.)

Structs

H2ConnectionState

Connection-level HTTP/2 state

H2Limits

Configurable limits for HTTP/2 header decoding and stream management.

H2SessionCache

HTTP/2 session cache with generic connection keys.

HttpRequest

HTTP request parsed from any HTTP version

HttpResponse

HTTP response parsed from any HTTP version

ParseError

Parse error with optional stream context (public API)

ParsedH2Message

A fully parsed HTTP/2 message extracted from a completed stream.

StreamId

Newtype for HTTP/2 stream identifiers (RFC 7540 §5.1.1: 31-bit unsigned integer).

TimestampNs

Newtype for nanosecond-precision timestamps (monotonic clock).

Enums

ParseErrorKind

Classification of parse errors (public API)

Constants

CONNECTION_PREFACE

HTTP/2 connection preface: “PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n”

Functions

is_http2_preface

Check if buffer starts with HTTP/2 connection preface

looks_like_http2_frame

Heuristic check if buffer looks like an HTTP/2 frame header. Checks for valid frame type and reasonable length.