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enhancement(sources): pre-size HTTP request body buffer from Content-Length #25747

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enhancement(sources): pre-size HTTP request body buffer from Content-Length #25747

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enhancement(sources): pre-size HTTP request body buffer from Content-…
armleth Jul 3, 2026
2c6c5af
chore: drop changelog fragment (using no-changelog label)
armleth Jul 3, 2026
428db8b
chore: drop verbose comment
armleth Jul 3, 2026
3e16af7
fix(sources): cap HTTP body buffer preallocation at 8 MiB
armleth Jul 6, 2026
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31 changes: 23 additions & 8 deletions src/sources/util/http/encoding.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -60,13 +60,12 @@ pub(crate) fn limited_body(max_body_size: usize) -> BoxedFilter<(Bytes,)> {
max_body_size,
)))
} else {
Ok(())
Ok(declared)
}
})
.untuple_one()
.and(warp::body::stream())
.and_then(move |body| async move {
collect_body_with_limit(body, max_body_size)
.and_then(move |declared: Option<u64>, body| async move {
collect_body_with_limit(body, max_body_size, declared)
.await
.map_err(warp::reject::custom)
})
Expand Down Expand Up @@ -178,19 +177,35 @@ fn decompress_snappy(
Ok(decoded.into())
}

/// Cap on the initial buffer allocation when pre-sizing from a `Content-Length` header.
/// Prevents stalling clients from reserving large amounts of memory before sending any bytes.
#[cfg(any(
feature = "sources-utils-http-prelude",
feature = "sources-opentelemetry",
test
))]
async fn collect_body_with_limit<S, B>(body: S, max_body_size: usize) -> Result<Bytes, ErrorMessage>
const MAX_INITIAL_BODY_CAPACITY: usize = 8 * 1024 * 1024; // 8 MiB

@thomasqueirozb thomasqueirozb Jul 6, 2026

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edge case: if VECTOR_MAX_DECOMPRESSED_SIZE_BYTES/--max-decompressed-size-bytes is set to a value < 8MiB we should honor it by not allocating more than 32 + max_size + max_size / 6 (this is snappy's worst-case scenario, which is larger than gzip, zstd and zlib's worst-case scenarios)


#[cfg(any(
feature = "sources-utils-http-prelude",
feature = "sources-opentelemetry",
test
))]
async fn collect_body_with_limit<S, B>(
body: S,
max_body_size: usize,
declared_len: Option<u64>,
) -> Result<Bytes, ErrorMessage>
where
S: futures_util::Stream<Item = Result<B, warp::Error>>,
B: Buf,
{
futures_util::pin_mut!(body);

let mut bytes = BytesMut::new();
let capacity = declared_len
.and_then(|len| usize::try_from(len).ok())
.map_or(0, |len| len.min(max_body_size).min(MAX_INITIAL_BODY_CAPACITY));
let mut bytes = BytesMut::with_capacity(capacity);
Comment on lines +205 to +208

@chatgpt-codex-connector chatgpt-codex-connector Bot Jul 3, 2026

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P2 Badge Avoid allocating the full declared body before reads

When an unauthenticated HTTP client sends a Content-Length near the configured limit (100 MiB by default via max_decompressed_size_bytes()) and then stalls or disconnects, this allocates that entire buffer before any body bytes are received. I checked the HTTP source call sites in src/sources/util/http/prelude.rs and src/sources/opentelemetry/http.rs; both use this helper for incoming requests, so many concurrent header-only/slow requests can now reserve large amounts of memory where the previous streaming collector only grew after chunks arrived. Consider capping the initial preallocation to a smaller threshold or growing after the first chunk instead of trusting the header up to the full body limit.

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@armleth armleth Jul 3, 2026

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Good point. IMO, it's acceptable given the performance regression that the alternative causes.
What do you guys think about this?

@bruceg bruceg Jul 3, 2026

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I'd agree with its suggestion to cap the initial capacity at some suitably large but smaller-than-100MiB number. That would minimize still reallocations, just not eliminate them.

@armleth armleth Jul 6, 2026

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Done. I set 8 MB somewhat arbitrarily some Vector constants are around these values: Kinesis Firehose: 4 MiB, syslog recv buffer: 4 MiB, Windows event log: 10 MiB), does that seem reasonable?

while let Some(chunk) = body.next().await {
let chunk = chunk.map_err(|error| {
ErrorMessage::new(
Expand Down Expand Up @@ -368,7 +383,7 @@ mod tests {
Ok::<_, warp::Error>(Bytes::from_static(b" world")),
]);

let collected = collect_body_with_limit(body, 11).await.unwrap();
let collected = collect_body_with_limit(body, 11, Some(11)).await.unwrap();
assert_eq!(collected, Bytes::from_static(b"hello world"));
}

Expand All @@ -379,7 +394,7 @@ mod tests {
Ok::<_, warp::Error>(Bytes::from_static(b" world")),
]);

let err = collect_body_with_limit(body, 5)
let err = collect_body_with_limit(body, 5, None)
.await
.expect_err("should reject");
assert_eq!(err.status_code(), StatusCode::PAYLOAD_TOO_LARGE);
Expand Down
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