trillium_http/http_config.rs
1use fieldwork::Fieldwork;
2
3/// # Performance and security parameters for trillium-http.
4///
5/// Trillium's http implementation is built with sensible defaults, but applications differ in usage
6/// and this escape hatch allows an application to be tuned. It is best to tune these parameters in
7/// context of realistic benchmarks for your application.
8#[derive(Clone, Copy, Debug, Fieldwork)]
9#[fieldwork(get, get_mut, set, with, without)]
10// `HttpConfig` is a user-facing tuning struct with documented per-field setters; the natural
11// shape is one field per knob. Bundling bools into an enum or bitflags would make the getter/
12// setter surface worse for callers.
13#[allow(clippy::struct_excessive_bools)]
14pub struct HttpConfig {
15 /// The maximum length allowed before the http body begins for a given request.
16 ///
17 /// **Default**: `8kb` in bytes
18 ///
19 /// **Unit**: Byte count
20 pub(crate) head_max_len: usize,
21
22 /// The maximum length of a received body
23 ///
24 /// This limit applies regardless of whether the body is read all at once or streamed
25 /// incrementally, and regardless of transfer encoding (chunked or fixed-length). The correct
26 /// value will be application dependent.
27 ///
28 /// **Default**: `10mb` in bytes
29 ///
30 /// **Unit**: Byte count
31 pub(crate) received_body_max_len: u64,
32
33 /// The initial capacity of the buffer that serializes the response head and batches body
34 /// writes.
35 ///
36 /// The response head and as much of the body as fits are coalesced into a single transport
37 /// write, so a response up to a few KiB is sent in one write regardless of this value. It
38 /// matters only for large response bodies, where a larger buffer batches more bytes per write
39 /// and so reduces the number of write syscalls on a bulk transfer — at the cost of that much
40 /// initial memory per connection. On the common path the buffer flushes when full rather than
41 /// growing; `response_buffer_max_len` bounds only the separate backpressure-absorption path.
42 ///
43 /// **Default**: `512`
44 ///
45 /// **Unit**: byte count
46 pub(crate) response_buffer_len: usize,
47
48 /// Maximum size the response buffer may grow to absorb backpressure.
49 ///
50 /// When the transport cannot accept data as fast as the response body is produced, the buffer
51 /// absorbs the remainder up to this limit. Once the limit is reached, writes apply
52 /// backpressure to the body source. This prevents a slow client from causing unbounded memory
53 /// growth.
54 ///
55 /// **Default**: `2mb` in bytes
56 ///
57 /// **Unit**: byte count
58 pub(crate) response_buffer_max_len: usize,
59
60 /// The initial buffer allocated for the request headers.
61 ///
62 /// Ideally this is the length of the request headers. It will grow nonlinearly until
63 /// `head_max_len` or the end of the headers are reached, whichever happens first.
64 ///
65 /// **Default**: `1024`
66 ///
67 /// **Unit**: byte count
68 pub(crate) request_buffer_initial_len: usize,
69
70 /// The expected number of response headers, used to size the response header map on conn
71 /// creation.
72 ///
73 /// The map grows on insertion beyond this. The value is split evenly across two internal
74 /// stores, so prefer to overestimate — an undersized map reallocates as it fills.
75 ///
76 /// **Default**: `32`
77 ///
78 /// **Unit**: Header count
79 pub(crate) response_header_initial_capacity: usize,
80
81 /// The expected number of request headers, used to size the request header map while parsing.
82 ///
83 /// The map grows on insertion beyond this. The value is split evenly across two internal
84 /// stores, so prefer to overestimate — an undersized map reallocates as it fills, which is the
85 /// dominant cost of building the header map for header-heavy requests.
86 ///
87 /// **Default**: `32`
88 ///
89 /// **Unit**: Header count
90 pub(crate) request_header_initial_capacity: usize,
91
92 /// Cooperative task-yielding knob.
93 ///
94 /// Decreasing this number will improve tail latencies at a slight cost to total throughput for
95 /// fast clients. This will have more of an impact on servers that spend a lot of time in IO
96 /// compared to app handlers.
97 ///
98 /// **Default**: `16`
99 ///
100 /// **Unit**: the number of consecutive `Poll::Ready` async writes to perform before yielding
101 /// the task back to the runtime.
102 pub(crate) copy_loops_per_yield: usize,
103
104 /// The initial buffer capacity allocated when reading a chunked http body to bytes or string.
105 ///
106 /// Ideally this would be the size of the http body, which is highly application dependent. As
107 /// with other initial buffer lengths, further allocation will be performed until the necessary
108 /// length is achieved. A smaller number will result in more vec resizing, and a larger number
109 /// will result in unnecessary allocation.
110 ///
111 /// **Default**: `128`
112 ///
113 /// **Unit**: byte count
114 pub(crate) received_body_initial_len: usize,
115
116 /// Maximum size to pre-allocate based on content-length for buffering a complete request body
117 ///
118 /// When we receive a fixed-length (not chunked-encoding) body that is smaller than this size,
119 /// we can allocate a buffer with exactly the right size before we receive the body. However,
120 /// if this is unbounded, malicious clients can issue headers with large content-length and
121 /// then keep the connection open without sending any bytes, allowing them to allocate
122 /// memory faster than their bandwidth usage. This does not limit the ability to receive
123 /// fixed-length bodies larger than this, but the memory allocation will grow as with
124 /// chunked bodies. Note that this has no impact on chunked bodies. If this is set higher
125 /// than the `received_body_max_len`, this parameter has no effect. This parameter only
126 /// impacts [`ReceivedBody::read_string`](crate::ReceivedBody::read_string) and
127 /// [`ReceivedBody::read_bytes`](crate::ReceivedBody::read_bytes).
128 ///
129 /// **Default**: `1mb` in bytes
130 ///
131 /// **Unit**: Byte count
132 pub(crate) received_body_max_preallocate: usize,
133
134 /// The maximum cumulative size of a header block the peer may send.
135 ///
136 /// Advertised in SETTINGS as `SETTINGS_MAX_HEADER_LIST_SIZE` on HTTP/2 (RFC 9113) and
137 /// `SETTINGS_MAX_FIELD_SECTION_SIZE` on HTTP/3 (RFC 9114). Guards against pathological
138 /// header lists inflating memory per stream during HPACK/QPACK decode.
139 ///
140 /// On HTTP/2 this also bounds the cumulative compressed bytes of a header block
141 /// accumulated across HEADERS + CONTINUATION frames: a block exceeding this limit closes
142 /// the connection with `ENHANCE_YOUR_CALM`, mitigating the CONTINUATION-flood `DoS`
143 /// (CVE-2024-27316 class). Otherwise the peer is expected to self-police.
144 ///
145 /// **Default**: `32 KiB` in bytes
146 ///
147 /// **Unit**: byte count
148 pub(crate) max_header_list_size: u64,
149
150 /// Maximum capacity of the dynamic header-compression table.
151 ///
152 /// Advertised to peers as `SETTINGS_HEADER_TABLE_SIZE` (HPACK / RFC 7541) and
153 /// `SETTINGS_QPACK_MAX_TABLE_CAPACITY` (QPACK / RFC 9204). Bounds both the decoder's
154 /// inbound table and our encoder's outbound table; set to `0` to disable dynamic-table
155 /// compression entirely (encoder reduces to static-or-literal).
156 ///
157 /// **Default**: `4 KiB` in bytes
158 ///
159 /// **Unit**: Byte count
160 pub(crate) dynamic_table_capacity: usize,
161
162 /// Maximum number of HTTP/3 request streams that may be blocked waiting for dynamic table
163 /// updates.
164 ///
165 /// Advertised to peers as `SETTINGS_QPACK_BLOCKED_STREAMS`. A value of `0` prevents peers
166 /// from sending header blocks that reference table entries not yet seen by this decoder.
167 ///
168 /// **Default**: 100
169 ///
170 /// **Unit**: Stream count
171 pub(crate) h3_blocked_streams: usize,
172
173 /// Per-connection ring size for the header encoder's recently-seen-pair predictor.
174 ///
175 /// Applies to both HPACK (HTTP/2) and QPACK (HTTP/3). The predictor lets the encoder
176 /// defer dynamic-table inserts until a `(name, value)` pair has been seen at least
177 /// once on the connection — first sighting emits a literal, subsequent sightings
178 /// within the ring's retention window invest in an insert so future sections can
179 /// index it. A larger ring catches repetitions across more intervening header lines
180 /// (good for header-heavy reverse proxies); a smaller ring forgets faster (fine for
181 /// tiny APIs). A cross-connection observer short-circuits this for already-known-hot
182 /// pairs.
183 ///
184 /// The predictor is consulted once per emitted header line via a u32 hash compare;
185 /// cost grows linearly with `size` but is dominated by the per-line hash, so
186 /// oversizing here is cheap.
187 ///
188 /// **Default**: 64
189 ///
190 /// **Unit**: Pair count
191 pub(crate) recent_pairs_size: usize,
192
193 /// Initial HTTP/2 stream flow-control window advertised to peers as
194 /// `SETTINGS_INITIAL_WINDOW_SIZE` — the lower tier of the two-tier per-stream window.
195 ///
196 /// Controls how many request-body bytes the peer may send on a newly-opened stream before the
197 /// handler starts reading. Once the handler signals intent to read (first `poll_read` on the
198 /// request body), the window is promoted to `h2_max_stream_recv_window_size`; a stream whose
199 /// handler never reads the body stays at this initial.
200 ///
201 /// Must not exceed `2^31 - 1`.
202 ///
203 /// **Default**: `256 KiB`
204 ///
205 /// **Unit**: byte count
206 pub(crate) h2_initial_stream_window_size: u32,
207
208 /// Per-stream recv window target — the upper tier of the two-tier window. A stream opens at
209 /// `h2_initial_stream_window_size` and is promoted to this value once the handler signals
210 /// intent to read the request body (first `poll_read`); the driver then tops the peer's window
211 /// back up to it via `WINDOW_UPDATE` as the handler drains. Because strict flow control bounds
212 /// the recv buffer to the granted window, this is also the per-stream buffer bound — a peer
213 /// that sends past the window earns a connection-level `FLOW_CONTROL_ERROR`.
214 ///
215 /// Must be `>= h2_initial_stream_window_size`; a smaller value is clamped up to the initial
216 /// (with a one-time log warning), since the window is only ever promoted upward.
217 ///
218 /// **Default**: `1 MiB` in bytes
219 ///
220 /// **Unit**: byte count
221 pub(crate) h2_max_stream_recv_window_size: u32,
222
223 /// Connection-level recv window target — how high the driver keeps the peer's
224 /// connection-level window topped up as handlers consume bytes.
225 ///
226 /// Raised via an initial `WINDOW_UPDATE(stream_id=0)` right after SETTINGS (RFC 9113
227 /// forbids SETTINGS from altering the connection window), then refilled on consumption.
228 /// Bounds total concurrent in-flight request-body bytes across all streams on a single
229 /// HTTP/2 connection. Leaving at the RFC baseline of `65_535` would cap bulk uploads at
230 /// ~5 Mbit/s × RTT.
231 ///
232 /// **Default**: `2 MiB` in bytes
233 ///
234 /// **Unit**: byte count
235 pub(crate) h2_initial_connection_window_size: u32,
236
237 /// HTTP/2 `SETTINGS_MAX_CONCURRENT_STREAMS` — the maximum number of concurrent
238 /// peer-initiated streams the server will accept.
239 ///
240 /// Peer-opened streams beyond this count get `RST_STREAM(RefusedStream)` per RFC 9113.
241 /// A value in the 100–250 range is the post-Rapid-Reset (CVE-2023-44487) consensus;
242 /// lower values cap parallelism, higher values need per-connection reset-rate limiting
243 /// to avoid `DoS` exposure.
244 ///
245 /// **Default**: `100`
246 ///
247 /// **Unit**: stream count
248 pub(crate) h2_max_concurrent_streams: u32,
249
250 /// HTTP/2 `SETTINGS_MAX_FRAME_SIZE` — the largest frame payload the server will accept.
251 ///
252 /// Peer frames whose payload exceeds this get `FRAME_SIZE_ERROR` per RFC 9113. The RFC
253 /// floor is `16_384`; the ceiling is `16_777_215`. Larger values amortize per-frame
254 /// overhead on bulk transfers but increase the upper bound on a single read.
255 ///
256 /// **Default**: `16 KiB` in bytes
257 ///
258 /// **Unit**: byte count
259 pub(crate) h2_max_frame_size: u32,
260
261 /// whether [datagrams](https://www.rfc-editor.org/rfc/rfc9297.html) are enabled for HTTP/3
262 ///
263 /// This is a protocol-level setting and is communicated to the peer as well as enforced.
264 ///
265 /// **Default**: false
266 pub(crate) h3_datagrams_enabled: bool,
267
268 /// whether [webtransport](https://datatracker.ietf.org/doc/html/draft-ietf-webtrans-http3)
269 /// (`draft-ietf-webtrans-http3`) is enabled for HTTP/3
270 ///
271 /// This is a protocol-level setting and is communicated to the peer. You do not need to
272 /// manually configure this if using
273 /// [`trillium-webtransport`](https://docs.rs/trillium-webtransport)
274 ///
275 /// **Default**: false
276 pub(crate) webtransport_enabled: bool,
277
278 /// `SETTINGS_ENABLE_CONNECT_PROTOCOL` — advertises that the server accepts extended
279 /// CONNECT requests, enabling protocols layered on top of HTTP that bootstrap via a
280 /// CONNECT with a `:protocol` pseudo-header.
281 ///
282 /// You likely don't need to set this directly if using a trillium handler that uses extended
283 /// connect.
284 ///
285 /// **Default**: false
286 pub(crate) extended_connect_enabled: bool,
287
288 /// whether to panic when an outbound (app-controlled) header with an invalid value (containing
289 /// `\r`, `\n`, or `\0`) is encountered.
290 ///
291 /// Invalid header values are always skipped to prevent header injection. When this is `true`,
292 /// Trillium will additionally panic, surfacing the bug loudly. When `false`, the skip is only
293 /// logged (to the `log` backend) at error level.
294 ///
295 /// **Default**: `true` when compiled with `debug_assertions` (i.e. debug builds), `false` in
296 /// release builds. Override to `true` in release if you want strict production behavior, or to
297 /// `false` in debug if you prefer not to panic during development.
298 pub(crate) panic_on_invalid_response_headers: bool,
299}
300
301const KB: u32 = 1024;
302const MB: u32 = 1024 * KB;
303
304impl HttpConfig {
305 /// Default Config
306 pub const DEFAULT: Self = HttpConfig {
307 response_buffer_len: 512,
308 response_buffer_max_len: 2 * MB as usize,
309 request_buffer_initial_len: 1024,
310 head_max_len: 8 * KB as usize,
311 response_header_initial_capacity: 32,
312 request_header_initial_capacity: 32,
313 copy_loops_per_yield: 16,
314 received_body_max_len: 10 * MB as u64,
315 received_body_initial_len: 128,
316 received_body_max_preallocate: MB as usize,
317 max_header_list_size: 32 * KB as u64,
318 dynamic_table_capacity: 4 * KB as usize,
319 h3_blocked_streams: 100,
320 recent_pairs_size: 64,
321 h3_datagrams_enabled: false,
322 h2_initial_stream_window_size: 256 * KB,
323 h2_max_stream_recv_window_size: MB,
324 h2_initial_connection_window_size: 2 * MB,
325 h2_max_concurrent_streams: 100,
326 h2_max_frame_size: 16 * KB,
327 webtransport_enabled: false,
328 extended_connect_enabled: false,
329 panic_on_invalid_response_headers: cfg!(debug_assertions),
330 };
331}
332
333impl Default for HttpConfig {
334 fn default() -> Self {
335 HttpConfig::DEFAULT
336 }
337}