feat: Support SYNC_SPANNER_EMULATOR_HOST (#1061)

Closes #915

src/db/spanner/manager/deadpool.rs

@@ -25,6 +25,7 @@ pub struct SpannerSessionManager {
     test_transactions: bool,
     max_lifespan: Option<u32>,
     max_idle: Option<u32>,
+    emulator_host: Option<String>,
 }
 
 impl fmt::Debug for SpannerSessionManager {
@@ -56,6 +57,7 @@ impl SpannerSessionManager {
             test_transactions,
             max_lifespan: settings.database_pool_connection_lifespan,
             max_idle: settings.database_pool_connection_max_idle,
+            emulator_host: settings.spanner_emulator_host.clone(),
         })
     }
 }
@@ -68,6 +70,7 @@ impl Manager<SpannerSession, DbError> for SpannerSessionManager {
             self.metrics.clone(),
             &self.database_name,
             self.test_transactions,
+            self.emulator_host.clone(),
         )
         .await?;
         Ok(session)

src/db/spanner/manager/session.rs

@@ -37,18 +37,26 @@ pub async fn create_spanner_session(
     mut metrics: Metrics,
     database_name: &str,
     use_test_transactions: bool,
+    emulator_host: Option<String>,
 ) -> Result<SpannerSession, DbError> {
     // XXX: issue732: Could google_default_credentials (or
     // ChannelBuilder::secure_connect) block?!
     let chan = block(move || -> Result<grpcio::Channel, grpcio::Error> {
         metrics.start_timer("storage.pool.grpc_auth", None);
-        // Requires
-        // GOOGLE_APPLICATION_CREDENTIALS=/path/to/service-account.json
-        let creds = ChannelCredentials::google_default_credentials()?;
-        Ok(ChannelBuilder::new(env)
-            .max_send_message_len(100 << 20)
-            .max_receive_message_len(100 << 20)
-            .secure_connect(SPANNER_ADDRESS, creds))
+        if let Some(spanner_emulator_address) = emulator_host {
+            Ok(ChannelBuilder::new(env)
+                .max_send_message_len(100 << 20)
+                .max_receive_message_len(100 << 20)
+                .connect(&spanner_emulator_address))
+        } else {
+            // Requires
+            // GOOGLE_APPLICATION_CREDENTIALS=/path/to/service-account.json
+            let creds = ChannelCredentials::google_default_credentials()?;
+            Ok(ChannelBuilder::new(env)
+                .max_send_message_len(100 << 20)
+                .max_receive_message_len(100 << 20)
+                .secure_connect(SPANNER_ADDRESS, creds))
+        }
     })
     .await
     .map_err(|e| match e {

src/settings.rs

@@ -80,6 +80,8 @@ pub struct Settings {
 
     pub enable_quota: bool,
     pub enforce_quota: bool,
+
+    pub spanner_emulator_host: Option<String>,
 }
 
 impl Default for Settings {
@@ -109,6 +111,7 @@ impl Default for Settings {
             human_logs: false,
             enable_quota: false,
             enforce_quota: false,
+            spanner_emulator_host: None,
         }
     }
 }