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perf(http1): improve parsing of sequentially partial messages
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If request headers are received in incremental partial chunks, hyper
would restart parsing each time. This is because the HTTP/1 parser is
stateless, since the most common case is a full message and stateless
parses faster.

However, if continuing to receive more partial chunks of the request,
each subsequent full parse is slower and slower. Since partial parses is
less common, we can store a little bit of state to improve performance
in general.

Now, if a partial request is received, hyper will check for the end of
the message quickly, and if not found, simply save the length to allow
the next partial chunk to start its search from there. Only once the end
is found will a fill parse happen.

Reported-by: Datong Sun <[email protected]>
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seanmonstar committed Oct 15, 2024
1 parent 739d5e6 commit 97b595e
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Showing 2 changed files with 60 additions and 1 deletion.
10 changes: 9 additions & 1 deletion src/proto/h1/io.rs
Original file line number Diff line number Diff line change
Expand Up @@ -40,6 +40,7 @@ const MAX_BUF_LIST_BUFFERS: usize = 16;
pub(crate) struct Buffered<T, B> {
flush_pipeline: bool,
io: T,
partial_len: Option<usize>,
read_blocked: bool,
read_buf: BytesMut,
read_buf_strategy: ReadStrategy,
Expand Down Expand Up @@ -73,6 +74,7 @@ where
Buffered {
flush_pipeline: false,
io,
partial_len: None,
read_blocked: false,
read_buf: BytesMut::with_capacity(0),
read_buf_strategy: ReadStrategy::default(),
Expand Down Expand Up @@ -184,6 +186,7 @@ where
loop {
match super::role::parse_headers::<S>(
&mut self.read_buf,
self.partial_len,
ParseContext {
cached_headers: parse_ctx.cached_headers,
req_method: parse_ctx.req_method,
Expand Down Expand Up @@ -220,11 +223,13 @@ where
.reset(Instant::now() + Duration::from_secs(30 * 24 * 60 * 60));
}
}
self.partial_len = None;
return Poll::Ready(Ok(msg));
}
None => {
let max = self.read_buf_strategy.max();
if self.read_buf.len() >= max {
let curr_len = self.read_buf.len();
if curr_len >= max {
debug!("max_buf_size ({}) reached, closing", max);
return Poll::Ready(Err(crate::Error::new_too_large()));
}
Expand All @@ -242,6 +247,9 @@ where
}
}
}
if curr_len > 0 {
self.partial_len = Some(curr_len);
}
}
}
if ready!(self.poll_read_from_io(cx)).map_err(crate::Error::new_io)? == 0 {
Expand Down
51 changes: 51 additions & 0 deletions src/proto/h1/role.rs
Original file line number Diff line number Diff line change
Expand Up @@ -62,6 +62,7 @@ macro_rules! maybe_panic {

pub(super) fn parse_headers<T>(
bytes: &mut BytesMut,
prev_len: Option<usize>,
ctx: ParseContext<'_>,
) -> ParseResult<T::Incoming>
where
Expand Down Expand Up @@ -97,9 +98,37 @@ where
let span = trace_span!("parse_headers");
let _s = span.enter();

if let Some(prev_len) = prev_len {
if !is_complete_fast(bytes, prev_len) {
return Ok(None);
}
}

T::parse(bytes, ctx)
}

/// A fast scan for the end of a message.
/// Used when there was a partial read, to skip full parsing on a
/// a slow connection.
fn is_complete_fast(bytes: &[u8], prev_len: usize) -> bool {
let start = if prev_len < 3 { 0 } else { prev_len - 3 };
let bytes = &bytes[start..];

for (i, b) in bytes.iter().copied().enumerate() {
if b == b'\r' {
if bytes[i + 1..].chunks(3).next() == Some(&b"\n\r\n"[..]) {
return true;
}
} else if b == b'\n' {
if bytes.get(i + 1) == Some(&b'\n') {
return true;
}
}
}

false
}

pub(super) fn encode_headers<T>(
enc: Encode<'_, T::Outgoing>,
dst: &mut Vec<u8>,
Expand Down Expand Up @@ -2635,6 +2664,28 @@ mod tests {
assert_eq!(parsed.head.headers["server"], "hello\tworld");
}

#[test]
fn test_is_complete_fast() {
let s = b"GET / HTTP/1.1\r\na: b\r\n\r\n";
for n in 0..s.len() {
assert!(is_complete_fast(s, n), "{:?}; {}", s, n);
}
let s = b"GET / HTTP/1.1\na: b\n\n";
for n in 0..s.len() {
assert!(is_complete_fast(s, n));
}

// Not
let s = b"GET / HTTP/1.1\r\na: b\r\n\r";
for n in 0..s.len() {
assert!(!is_complete_fast(s, n));
}
let s = b"GET / HTTP/1.1\na: b\n";
for n in 0..s.len() {
assert!(!is_complete_fast(s, n));
}
}

#[test]
fn test_write_headers_orig_case_empty_value() {
let mut headers = HeaderMap::new();
Expand Down

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