feat: add x-timeout-ms header support (#363)

Author: jclapis

crates/common/src/pbs/constants.rs

@@ -16,6 +16,7 @@ pub const RELOAD_PATH: &str = "/reload";
 pub const HEADER_VERSION_KEY: &str = "X-CommitBoost-Version";
 pub const HEADER_VERSION_VALUE: &str = COMMIT_BOOST_VERSION;
 pub const HEADER_START_TIME_UNIX_MS: &str = "Date-Milliseconds";
+pub const HEADER_TIMEOUT_MS: &str = "X-Timeout-Ms";
 
 pub const BUILDER_EVENTS_PATH: &str = "/builder_events";
 pub const DEFAULT_PBS_JWT_KEY: &str = "DEFAULT_PBS";

crates/pbs/src/mev_boost/get_header.rs

@@ -14,7 +14,7 @@ use cb_common::{
     pbs::{
         error::{PbsError, ValidationError},
         GetHeaderParams, GetHeaderResponse, RelayClient, VersionedResponse, EMPTY_TX_ROOT_HASH,
-        HEADER_START_TIME_UNIX_MS,
+        HEADER_START_TIME_UNIX_MS, HEADER_TIMEOUT_MS,
     },
     signature::verify_signed_message,
     types::{BlsPublicKey, BlsSignature, Chain},
@@ -81,6 +81,19 @@ pub async fn get_header<S: BuilderApiState>(
         return Ok(None);
     }
 
+    // Use the minimum of the time left and the user provided timeout header
+    let max_timeout_ms = req_headers
+        .get(HEADER_TIMEOUT_MS)
+        .map(|header| match header.to_str().ok().and_then(|v| v.parse::<u64>().ok()) {
+            None | Some(0) => {
+                // Header can't be stringified, or parsed, or it's set to 0
+                warn!(?header, "invalid user-supplied timeout header, using {max_timeout_ms}ms");
+                max_timeout_ms
+            }
+            Some(user_timeout) => user_timeout.min(max_timeout_ms),
+        })
+        .unwrap_or(max_timeout_ms);
+
     // prepare headers, except for start time which is set in `send_one_get_header`
     let mut send_headers = HeaderMap::new();
     send_headers.insert(USER_AGENT, get_user_agent_with_version(&req_headers)?);
@@ -301,6 +314,10 @@ async fn send_one_get_header(
     let start_request_time = utcnow_ms();
     req_config.headers.insert(HEADER_START_TIME_UNIX_MS, HeaderValue::from(start_request_time));
 
+    // The timeout header indicating how long a relay has to respond, so they can
+    // minimize timing games without losing the bid
+    req_config.headers.insert(HEADER_TIMEOUT_MS, HeaderValue::from(req_config.timeout_ms));
+
     let start_request = Instant::now();
     let res = match relay
         .client