Set user agent on requests to builder (sigp#4199)

## Issue Addressed

Closes sigp#4185

## Proposed Changes

- Set user agent to `Lighthouse/vX.Y.Z-<commit hash>` by default
- Allow tweaking user agent via `--builder-user-agent "agent"`

beacon_node/builder_client/Cargo.toml

@@ -10,3 +10,4 @@ sensitive_url = { path = "../../common/sensitive_url" }
 eth2 = { path = "../../common/eth2" }
 serde = { version = "1.0.116", features = ["derive"] }
 serde_json = "1.0.58"
+lighthouse_version = { path = "../../common/lighthouse_version" }

beacon_node/builder_client/src/lib.rs

@@ -17,6 +17,9 @@ pub const DEFAULT_TIMEOUT_MILLIS: u64 = 15000;
 /// This timeout is in accordance with v0.2.0 of the [builder specs](https://github.com/flashbots/mev-boost/pull/20).
 pub const DEFAULT_GET_HEADER_TIMEOUT_MILLIS: u64 = 1000;
 
+/// Default user agent for HTTP requests.
+pub const DEFAULT_USER_AGENT: &str = lighthouse_version::VERSION;
+
 #[derive(Clone)]
 pub struct Timeouts {
     get_header: Duration,
@@ -41,23 +44,23 @@ pub struct BuilderHttpClient {
     client: reqwest::Client,
     server: SensitiveUrl,
     timeouts: Timeouts,
+    user_agent: String,
 }
 
 impl BuilderHttpClient {
-    pub fn new(server: SensitiveUrl) -> Result<Self, Error> {
+    pub fn new(server: SensitiveUrl, user_agent: Option<String>) -> Result<Self, Error> {
+        let user_agent = user_agent.unwrap_or(DEFAULT_USER_AGENT.to_string());
+        let client = reqwest::Client::builder().user_agent(&user_agent).build()?;
         Ok(Self {
-            client: reqwest::Client::new(),
+            client,
             server,
             timeouts: Timeouts::default(),
+            user_agent,
         })
     }
 
-    pub fn new_with_timeouts(server: SensitiveUrl, timeouts: Timeouts) -> Result<Self, Error> {
-        Ok(Self {
-            client: reqwest::Client::new(),
-            server,
-            timeouts,
-        })
+    pub fn get_user_agent(&self) -> &str {
+        &self.user_agent
     }
 
     async fn get_with_timeout<T: DeserializeOwned, U: IntoUrl>(

beacon_node/execution_layer/src/lib.rs

@@ -230,6 +230,8 @@ pub struct Config {
     pub execution_endpoints: Vec<SensitiveUrl>,
     /// Endpoint urls for services providing the builder api.
     pub builder_url: Option<SensitiveUrl>,
+    /// User agent to send with requests to the builder API.
+    pub builder_user_agent: Option<String>,
     /// JWT secrets for the above endpoints running the engine api.
     pub secret_files: Vec<PathBuf>,
     /// The default fee recipient to use on the beacon node if none if provided from
@@ -260,6 +262,7 @@ impl<T: EthSpec> ExecutionLayer<T> {
         let Config {
             execution_endpoints: urls,
             builder_url,
+            builder_user_agent,
             secret_files,
             suggested_fee_recipient,
             jwt_id,
@@ -320,12 +323,17 @@ impl<T: EthSpec> ExecutionLayer<T> {
 
         let builder = builder_url
             .map(|url| {
-                let builder_client = BuilderHttpClient::new(url.clone()).map_err(Error::Builder);
-                info!(log,
+                let builder_client = BuilderHttpClient::new(url.clone(), builder_user_agent)
+                    .map_err(Error::Builder)?;
+
+                info!(
+                    log,
                     "Connected to external block builder";
                     "builder_url" => ?url,
-                    "builder_profit_threshold" => builder_profit_threshold);
-                builder_client
+                    "builder_profit_threshold" => builder_profit_threshold,
+                    "local_user_agent" => builder_client.get_user_agent(),
+                );
+                Ok::<_, Error>(builder_client)
             })
             .transpose()?;
 

beacon_node/src/cli.rs

@@ -1000,6 +1000,15 @@ pub fn cli_app<'a, 'b>() -> App<'a, 'b> {
                 .default_value("0")
                 .takes_value(true)
         )
+        .arg(
+            Arg::with_name("builder-user-agent")
+                .long("builder-user-agent")
+                .value_name("STRING")
+                .help("The HTTP user agent to send alongside requests to the builder URL. The \
+                       default is Lighthouse's version string.")
+                .requires("builder")
+                .takes_value(true)
+        )
         .arg(
             Arg::with_name("count-unrealized")
                 .long("count-unrealized")

beacon_node/src/config.rs

@@ -329,6 +329,9 @@ pub fn get_config<E: EthSpec>(
             let payload_builder =
                 parse_only_one_value(endpoint, SensitiveUrl::parse, "--builder", log)?;
             el_config.builder_url = Some(payload_builder);
+
+            el_config.builder_user_agent =
+                clap_utils::parse_optional(cli_args, "builder-user-agent")?;
         }
 
         // Set config values from parse values.

lighthouse/tests/beacon_node.rs

@@ -716,6 +716,40 @@ fn builder_fallback_flags() {
     );
 }
 
+#[test]
+fn builder_user_agent() {
+    run_payload_builder_flag_test_with_config(
+        "builder",
+        "http://meow.cats",
+        None,
+        None,
+        |config| {
+            assert_eq!(
+                config.execution_layer.as_ref().unwrap().builder_user_agent,
+                None
+            );
+        },
+    );
+    run_payload_builder_flag_test_with_config(
+        "builder",
+        "http://meow.cats",
+        Some("builder-user-agent"),
+        Some("anon"),
+        |config| {
+            assert_eq!(
+                config
+                    .execution_layer
+                    .as_ref()
+                    .unwrap()
+                    .builder_user_agent
+                    .as_ref()
+                    .unwrap(),
+                "anon"
+            );
+        },
+    );
+}
+
 fn run_jwt_optional_flags_test(jwt_flag: &str, jwt_id_flag: &str, jwt_version_flag: &str) {
     use sensitive_url::SensitiveUrl;