allow empty string for SOLANA_METRICS_CONFIG sanity checking

metrics/src/metrics.rs

@@ -34,6 +34,8 @@ pub enum MetricsError {
     ConfigIncomplete,
     #[error("SOLANA_METRICS_CONFIG database mismatch: {0}")]
     DbMismatch(String),
+    #[error("SOLANA_METRICS_CONFIG is empty")]
+    ConfigEmptyString,
 }
 
 impl From<MetricsError> for String {
@@ -80,10 +82,12 @@ impl InfluxDbMetricsWriter {
     }
 
     fn build_write_url() -> Result<String, MetricsError> {
-        let config = get_metrics_config().map_err(|err| {
-            info!("metrics disabled: {}", err);
-            err
-        })?;
+        let config = get_metrics_config()
+            .map_err(|err| {
+                info!("metrics disabled: {}", err);
+                err
+            })?
+            .ok_or(MetricsError::ConfigEmptyString)?;
 
         info!(
             "metrics configuration: host={} db={} username={}",
@@ -402,10 +406,14 @@ impl MetricsConfig {
     }
 }
 
-fn get_metrics_config() -> Result<MetricsConfig, MetricsError> {
+fn get_metrics_config() -> Result<Option<MetricsConfig>, MetricsError> {
     let mut config = MetricsConfig::default();
     let config_var = env::var("SOLANA_METRICS_CONFIG")?;
 
+    if config_var.is_empty() {
+        return Ok(None);
+    }
+
     for pair in config_var.split(',') {
         let nv: Vec<_> = pair.split('=').collect();
         if nv.len() != 2 {
@@ -425,13 +433,13 @@ fn get_metrics_config() -> Result<MetricsConfig, MetricsError> {
         return Err(MetricsError::ConfigIncomplete);
     }
 
-    Ok(config)
+    Ok(Some(config))
 }
 
 pub fn metrics_config_sanity_check(cluster_type: ClusterType) -> Result<(), MetricsError> {
     let config = match get_metrics_config() {
-        Ok(config) => config,
-        Err(MetricsError::VarError(std::env::VarError::NotPresent)) => return Ok(()),
+        Ok(Some(config)) => config,
+        Ok(None) | Err(MetricsError::VarError(std::env::VarError::NotPresent)) => return Ok(()),
         Err(e) => return Err(e),
     };
     match &config.db[..] {
@@ -446,7 +454,7 @@ pub fn metrics_config_sanity_check(cluster_type: ClusterType) -> Result<(), Metr
 }
 
 pub fn query(q: &str) -> Result<String, MetricsError> {
-    let config = get_metrics_config()?;
+    let config = get_metrics_config()?.ok_or(MetricsError::ConfigEmptyString)?;
     let query_url = format!(
         "{}/query?u={}&p={}&q={}",
         &config.host, &config.username, &config.password, &q