trillium_http/

http_config.rs

use fieldwork::Fieldwork;

/// # Performance and security parameters for trillium-http.
///
/// Trillium's http implementation is built with sensible defaults, but applications differ in usage
/// and this escape hatch allows an application to be tuned. It is best to tune these parameters in
/// context of realistic benchmarks for your application.
///
/// Long term, trillium may export several standard defaults for different constraints and
/// application types. In the distant future, these may turn into initial values and trillium will
/// tune itself based on values seen at runtime.
///
/// ## HTTP version dispatch
///
/// trillium accepts HTTP/1.x, HTTP/2, and HTTP/3 connections on the same listener without
/// any per-version configuration. The version a given connection speaks is decided at accept
/// time based on ALPN (for TLS listeners with ALPN), or by peeking the first 24 bytes for
/// the HTTP/2 client preface (for cleartext listeners and TLS listeners where ALPN was
/// absent or returned an unrecognized value):
///
/// | Listener | ALPN result | First bytes | Protocol |
/// |---|---|---|---|
/// | TCP + TLS | `h2` | — | HTTP/2 |
/// | TCP + TLS | `http/1.1` | — | HTTP/1.1 |
/// | TCP + TLS | absent / other | match HTTP/2 preface | HTTP/2 (TLS prior-knowledge) |
/// | TCP + TLS | absent / other | anything else | HTTP/1.1 |
/// | TCP, cleartext | — | match HTTP/2 preface | HTTP/2 prior-knowledge (h2c) |
/// | TCP, cleartext | — | anything else | HTTP/1.x |
/// | QUIC (via `trillium-quinn`) | — | — | HTTP/3 |
///
/// h2c via the HTTP/1.1 `Upgrade` mechanism (RFC 7540 §3.2, removed in RFC 9113) is not
/// supported. The `h2_*` fields on this struct tune the HTTP/2 advertised settings + recv
/// windows; the `h3_*` fields tune HTTP/3. None of them affect HTTP/1.x.
///
/// ```
/// # use trillium_http::HttpConfig;
/// // Accept body bytes eagerly (65535-byte initial window) instead of the default 100-
/// // continue-like lazy window. Good for "always accept uploads" workloads.
/// let config = HttpConfig::default().with_h2_initial_stream_window_size(65_535);
/// assert_eq!(config.h2_initial_stream_window_size(), 65_535);
/// ```
#[derive(Clone, Copy, Debug, Fieldwork)]
#[fieldwork(get, get_mut, set, with, without)]
// `HttpConfig` is a user-facing tuning struct with documented per-field setters; the natural
// shape is one field per knob. Bundling bools into an enum or bitflags would make the getter/
// setter surface worse for callers.
#[allow(clippy::struct_excessive_bools)]
pub struct HttpConfig {
    /// The maximum length allowed before the http body begins for a given request.
    ///
    /// **Default**: `8kb` in bytes
    ///
    /// **Unit**: Byte count
    pub(crate) head_max_len: usize,

    /// The maximum length of a received body
    ///
    /// This limit applies regardless of whether the body is read all at once or streamed
    /// incrementally, and regardless of transfer encoding (chunked or fixed-length). The correct
    /// value will be application dependent.
    ///
    /// **Default**: `10mb` in bytes
    ///
    /// **Unit**: Byte count
    pub(crate) received_body_max_len: u64,

    #[cfg(not(feature = "parse"))]
    #[field = false] // this one is private for now
    pub(crate) max_headers: usize,

    /// The initial buffer allocated for the response.
    ///
    /// Ideally this would be exactly the length of the combined response headers and body, if the
    /// body is short. If the value is shorter than the headers plus the body, multiple transport
    /// writes will be performed, and if the value is longer, unnecessary memory will be allocated
    /// for each conn. Although a tcp packet can be up to 64kb, it is probably better to use a
    /// value less than 1.5kb.
    ///
    /// **Default**: `512`
    ///
    /// **Unit**: byte count
    pub(crate) response_buffer_len: usize,

    /// Maximum size the response buffer may grow to absorb backpressure.
    ///
    /// When the transport cannot accept data as fast as the response body is produced, the buffer
    /// absorbs the remainder up to this limit. Once the limit is reached, writes apply
    /// backpressure to the body source. This prevents a slow client from causing unbounded memory
    /// growth.
    ///
    /// **Default**: `2mb` in bytes
    ///
    /// **Unit**: byte count
    pub(crate) response_buffer_max_len: usize,

    /// The initial buffer allocated for the request headers.
    ///
    /// Ideally this is the length of the request headers. It will grow nonlinearly until
    /// `max_head_len` or the end of the headers are reached, whichever happens first.
    ///
    /// **Default**: `128`
    ///
    /// **Unit**: byte count
    pub(crate) request_buffer_initial_len: usize,

    /// The number of response headers to allocate space for on conn creation.
    ///
    /// Headers will grow on insertion when they reach this size.
    ///
    /// **Default**: `16`
    ///
    /// **Unit**: Header count
    pub(crate) response_header_initial_capacity: usize,

    /// A sort of cooperative task yielding knob.
    ///
    /// Decreasing this number will improve tail latencies at a slight cost to total throughput for
    /// fast clients. This will have more of an impact on servers that spend a lot of time in IO
    /// compared to app handlers.
    ///
    /// **Default**: `16`
    ///
    /// **Unit**: the number of consecutive `Poll::Ready` async writes to perform before yielding
    /// the task back to the runtime.
    pub(crate) copy_loops_per_yield: usize,

    /// The initial buffer capacity allocated when reading a chunked http body to bytes or string.
    ///
    /// Ideally this would be the size of the http body, which is highly application dependent. As
    /// with other initial buffer lengths, further allocation will be performed until the necessary
    /// length is achieved. A smaller number will result in more vec resizing, and a larger number
    /// will result in unnecessary allocation.
    ///
    /// **Default**: `128`
    ///
    /// **Unit**: byte count
    pub(crate) received_body_initial_len: usize,

    /// Maximum size to pre-allocate based on content-length for buffering a complete request body
    ///
    /// When we receive a fixed-length (not chunked-encoding) body that is smaller than this size,
    /// we can allocate a buffer with exactly the right size before we receive the body.  However,
    /// if this is unbounded, malicious clients can issue headers with large content-length and
    /// then keep the connection open without sending any bytes, allowing them to allocate
    /// memory faster than their bandwidth usage. This does not limit the ability to receive
    /// fixed-length bodies larger than this, but the memory allocation will grow as with
    /// chunked bodies. Note that this has no impact on chunked bodies. If this is set higher
    /// than the `received_body_max_len`, this parameter has no effect. This parameter only
    /// impacts [`ReceivedBody::read_string`](crate::ReceivedBody::read_string) and
    /// [`ReceivedBody::read_bytes`](crate::ReceivedBody::read_bytes).
    ///
    /// **Default**: `1mb` in bytes
    ///
    /// **Unit**: Byte count
    pub(crate) received_body_max_preallocate: usize,

    /// The maximum cumulative size of a header block the peer may send.
    ///
    /// Advertised in SETTINGS as `SETTINGS_MAX_HEADER_LIST_SIZE` on HTTP/2 (RFC 9113 §6.5.2)
    /// and `SETTINGS_MAX_FIELD_SECTION_SIZE` on HTTP/3 (RFC 9114 §7.2.4.1). Guards against
    /// pathological header lists inflating memory per stream during HPACK/QPACK decode.
    /// Currently advertised only — the peer is expected to self-police.
    ///
    /// **Default**: `32 KiB`
    ///
    /// **Unit**: byte count
    pub(crate) max_header_list_size: u64,

    /// Maximum capacity of the dynamic header-compression table.
    ///
    /// Advertised to peers as `SETTINGS_HEADER_TABLE_SIZE` (HPACK / RFC 7541 §6.5.2) and
    /// `SETTINGS_QPACK_MAX_TABLE_CAPACITY` (QPACK / RFC 9204 §5). Bounds both the decoder's
    /// inbound table and our encoder's outbound table; set to `0` to disable dynamic-table
    /// compression entirely (encoder reduces to static-or-literal).
    ///
    /// **Default**: 4096 bytes
    ///
    /// **Unit**: Byte count
    pub(crate) dynamic_table_capacity: usize,

    /// Maximum number of HTTP/3 request streams that may be blocked waiting for dynamic table
    /// updates.
    ///
    /// Advertised to peers as `SETTINGS_QPACK_BLOCKED_STREAMS`. A value of `0` prevents peers
    /// from sending header blocks that reference table entries not yet seen by this decoder.
    ///
    /// **Default**: 100
    ///
    /// **Unit**: Stream count
    pub(crate) h3_blocked_streams: usize,

    /// Per-connection ring size for the header encoder's recently-seen-pair predictor.
    ///
    /// Applies to both HPACK (HTTP/2) and QPACK (HTTP/3). The predictor lets the encoder
    /// defer dynamic-table inserts until a `(name, value)` pair has been seen at least
    /// once on the connection — first sighting emits a literal, subsequent sightings
    /// within the ring's retention window invest in an insert so future sections can
    /// index it. A larger ring catches repetitions across more intervening header lines
    /// (good for header-heavy reverse proxies); a smaller ring forgets faster (fine for
    /// tiny APIs). A cross-connection observer short-circuits this for already-known-hot
    /// pairs.
    ///
    /// The predictor is consulted once per emitted header line via a u32 hash compare;
    /// cost grows linearly with `size` but is dominated by the per-line hash, so
    /// oversizing here is cheap.
    ///
    /// **Default**: 64
    ///
    /// **Unit**: Pair count
    pub(crate) recent_pairs_size: usize,

    /// Initial HTTP/2 stream flow-control window advertised to peers as
    /// `SETTINGS_INITIAL_WINDOW_SIZE`.
    ///
    /// Controls how many request-body bytes the peer may send on a newly-opened stream before
    /// waiting for a `WINDOW_UPDATE`. The default of `0` implements a lazy / 100-continue-like
    /// pattern: the peer cannot send any body bytes until the handler calls `read` on the
    /// request body, at which point the driver emits a `WINDOW_UPDATE` topping the window up
    /// to [`h2_max_stream_recv_window_size`][Self::h2_max_stream_recv_window_size]. A handler
    /// that returns an error from its header-level checks never pays the bandwidth cost of
    /// reading the body.
    ///
    /// Set to `65_535` (the RFC 9113 baseline) to match nginx / Apache / hyper behavior — body
    /// bytes arrive eagerly at the cost of 1 RTT less latency on the first DATA frame and the
    /// possible waste of up to this many bytes on requests the handler rejects.
    ///
    /// Must not exceed `2^31 - 1`.
    ///
    /// **Default**: `0` (lazy-WU)
    ///
    /// **Unit**: byte count
    pub(crate) h2_initial_stream_window_size: u32,

    /// Per-stream recv window target — how high the driver keeps the peer's stream window
    /// topped up as the handler consumes request-body bytes.
    ///
    /// After the handler signals intent to read (first `poll_read` on the request body), the
    /// driver emits `WINDOW_UPDATE` frames to keep the effective peer window near this target.
    /// Also serves as the hard per-stream buffer cap — a peer that sends past this amount of
    /// unconsumed DATA on a single stream earns a connection-level `FLOW_CONTROL_ERROR`.
    ///
    /// **Default**: `1 MiB`
    ///
    /// **Unit**: byte count
    pub(crate) h2_max_stream_recv_window_size: u32,

    /// Connection-level recv window target — how high the driver keeps the peer's
    /// connection-level window topped up as handlers consume bytes.
    ///
    /// Raised via an initial `WINDOW_UPDATE(stream_id=0)` right after SETTINGS (RFC 9113
    /// §6.9.2 forbids SETTINGS from altering the connection window), then refilled on
    /// consumption. Bounds total concurrent in-flight request-body bytes across all streams on
    /// a single HTTP/2 connection. Leaving at the RFC baseline of `65_535` would cap bulk
    /// uploads at ~5 Mbit/s × RTT.
    ///
    /// **Default**: `2 MiB`
    ///
    /// **Unit**: byte count
    pub(crate) h2_initial_connection_window_size: u32,

    /// HTTP/2 `SETTINGS_MAX_CONCURRENT_STREAMS` — the maximum number of concurrent
    /// peer-initiated streams the server will accept.
    ///
    /// Peer-opened streams beyond this count get `RST_STREAM(RefusedStream)` per RFC 9113
    /// §5.1.2. A value in the 100–250 range is the post-Rapid-Reset (CVE-2023-44487)
    /// consensus; lower values cap parallelism, higher values need per-connection reset-rate
    /// limiting to avoid `DoS` exposure.
    ///
    /// **Default**: `100`
    ///
    /// **Unit**: stream count
    pub(crate) h2_max_concurrent_streams: u32,

    /// HTTP/2 `SETTINGS_MAX_FRAME_SIZE` — the largest frame payload the server will accept.
    ///
    /// Peer frames whose payload exceeds this get `FRAME_SIZE_ERROR` per RFC 9113 §4.2. The
    /// RFC floor is `16_384`; the ceiling is `16_777_215`. Larger values amortize per-frame
    /// overhead on bulk transfers but increase the upper bound on a single read.
    ///
    /// **Default**: `16_384`
    ///
    /// **Unit**: byte count
    pub(crate) h2_max_frame_size: u32,

    /// whether [datagrams](https://www.rfc-editor.org/rfc/rfc9297.html) are enabled for HTTP/3
    ///
    /// This is a protocol-level setting and is communicated to the peer as well as enforced.
    ///
    /// **Default**: false
    pub(crate) h3_datagrams_enabled: bool,

    /// whether [webtransport](https://datatracker.ietf.org/doc/html/draft-ietf-webtrans-http3)
    /// (`draft-ietf-webtrans-http3`) is enabled for HTTP/3
    ///
    /// This is a protocol-level setting and is communicated to the peer. You do not need to
    /// manually configure this if using
    /// [`trillium-webtransport`](https://docs.rs/trillium-webtransport)
    ///
    /// **Default**: false
    pub(crate) webtransport_enabled: bool,

    /// `SETTINGS_ENABLE_CONNECT_PROTOCOL` — advertises that the server accepts extended
    /// CONNECT requests, enabling protocols layered on top of HTTP that bootstrap via a
    /// CONNECT with a `:protocol` pseudo-header. The same identifier (0x08) is used by
    /// HTTP/2 (RFC 8441 §3) and HTTP/3 (RFC 9220 §3).
    ///
    /// Use cases include WebSocket-over-h2 (RFC 8441), WebSocket-over-h3 (RFC 9220),
    /// and WebTransport (`draft-ietf-webtrans-http2` and `draft-ietf-webtrans-http3`).
    ///
    /// When set, the server's initial SETTINGS frame includes
    /// `SETTINGS_ENABLE_CONNECT_PROTOCOL = 1` (on both HTTP/2 and HTTP/3) and the runtime
    /// accepts CONNECT requests carrying a `:protocol` pseudo-header. Without it, clients
    /// won't attempt extended CONNECT, which is the correct default — handlers that don't
    /// expect extended CONNECT shouldn't see those requests.
    ///
    /// You don't need to set this manually if using a handler that requires it (e.g. an
    /// h2 websocket handler will flip it from `Handler::init`, the same way the
    /// trillium-webtransport handler flips `webtransport_enabled`).
    ///
    /// **Default**: false
    pub(crate) extended_connect_enabled: bool,

    /// whether to panic when a response header with an invalid value (containing `\r`, `\n`, or
    /// `\0`) is encountered.
    ///
    /// Invalid header values are always skipped to prevent header injection. When this is `true`,
    /// Trillium will additionally panic, surfacing the bug loudly. When `false`, the skip is only
    /// logged (to the `log` backend) at error level.
    ///
    /// **Default**: `true` when compiled with `debug_assertions` (i.e. debug builds), `false` in
    /// release builds. Override to `true` in release if you want strict production behavior, or to
    /// `false` in debug if you prefer not to panic during development.
    pub(crate) panic_on_invalid_response_headers: bool,
}

impl HttpConfig {
    /// Default Config
    pub const DEFAULT: Self = HttpConfig {
        response_buffer_len: 512,
        response_buffer_max_len: 2 * 1024 * 1024,
        request_buffer_initial_len: 128,
        head_max_len: 8 * 1024,
        #[cfg(not(feature = "parse"))]
        max_headers: 128,
        response_header_initial_capacity: 16,
        copy_loops_per_yield: 16,
        received_body_max_len: 10 * 1024 * 1024,
        received_body_initial_len: 128,
        received_body_max_preallocate: 1024 * 1024,
        max_header_list_size: 32 * 1024,
        dynamic_table_capacity: 4096,
        h3_blocked_streams: 100,
        recent_pairs_size: 64,
        h3_datagrams_enabled: false,
        h2_initial_stream_window_size: 0,
        h2_max_stream_recv_window_size: 1 << 20,
        h2_initial_connection_window_size: 2 << 20,
        h2_max_concurrent_streams: 100,
        h2_max_frame_size: 16_384,
        webtransport_enabled: false,
        extended_connect_enabled: false,
        panic_on_invalid_response_headers: cfg!(debug_assertions),
    };
}

impl Default for HttpConfig {
    fn default() -> Self {
        HttpConfig::DEFAULT
    }
}