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Bound the metrics response body size #305

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Bound the metrics response body size #305

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31 changes: 27 additions & 4 deletions ldk-server-client/src/client.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -100,6 +100,9 @@ const MAX_GRPC_UNARY_RESPONSE_LEN: usize = 10 * 1024 * 1024;
// constrained by this limit.
const MAX_GRPC_STREAM_MESSAGE_LEN: usize = 4 * 1024 * 1024;

// Applies to the complete Prometheus metrics response body.

@Anyitechs Anyitechs Oct 7, 2026

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Should we update the docs for this as well? Prometheus exposes a body_size_limit field in the config file that users can use to limit the number of bytes acceptable in the response body per scrape. Given that this change supersedes that, I believe it's worth documenting.

@benthecarman benthecarman Oct 7, 2026

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eh, we should never hit this, this is just some added safety in the client.

const MAX_METRICS_RESPONSE_LEN: usize = 10 * 1024 * 1024;

/// Client to access a hosted instance of LDK Server via gRPC.
///
/// The client requires the server's TLS certificate to be provided for verification.
Expand Down Expand Up @@ -156,7 +159,7 @@ impl LdkServerClient {
if let (Some(u), Some(p)) = (username, password) {
builder = builder.basic_auth(u, Some(p));
}
let response = builder.send().await.map_err(|e| {
let mut response = builder.send().await.map_err(|e| {
LdkServerError::new(InternalError, format!("HTTP request failed: {}", e))
})?;
if !response.status().is_success() {
Expand All @@ -165,10 +168,30 @@ impl LdkServerClient {
format!("Metrics request failed with status {}", response.status()),
));
}
let payload = response.bytes().await.map_err(|e| {
let too_large = || {
LdkServerError::new(
InternalError,
format!(
"Metrics response exceeds maximum size of {} bytes",
MAX_METRICS_RESPONSE_LEN
),
)
};
let capacity = match response.content_length() {
Some(len) if len > MAX_METRICS_RESPONSE_LEN as u64 => return Err(too_large()),
Some(len) => len as usize,
None => 0,
};
let mut payload = Vec::with_capacity(capacity);
while let Some(chunk) = response.chunk().await.map_err(|e| {
LdkServerError::new(InternalError, format!("Failed to read response body: {}", e))
})?;
String::from_utf8(payload.to_vec()).map_err(|e| {
})? {
if payload.len() + chunk.len() > MAX_METRICS_RESPONSE_LEN {
return Err(too_large());
}
payload.extend_from_slice(&chunk);
}
String::from_utf8(payload).map_err(|e| {
LdkServerError::new(
InternalError,
format!("Failed to decode metrics response as string: {}", e),
Expand Down
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