fix: basic_otlp example. (#438)

Without http:// prefix, tonic will throw a panic. This commit fix it by use http://localhost as default endpoint. Also set it in example explicitly.

Author: TommyCpp

examples/basic-otlp/src/main.rs

@@ -14,7 +14,9 @@ use std::error::Error;
 use std::time::Duration;
 
 fn init_tracer() -> Result<(sdktrace::Tracer, opentelemetry_otlp::Uninstall), TraceError> {
-    opentelemetry_otlp::new_pipeline().install()
+    opentelemetry_otlp::new_pipeline()
+        .with_endpoint("http://localhost:4317")
+        .install()
 }
 
 // Skip first immediate tick from tokio, not needed for async_std.
@@ -97,7 +99,7 @@ async fn main() -> Result<(), Box<dyn Error + Send + Sync + 'static>> {
         });
     });
 
-    // wait for 1 seconds so that we could see metrics being pushed via OTLP every 10 seconds.
+    // wait for 1 minutes so that we could see metrics being pushed via OTLP every 10 seconds.
     tokio::time::sleep(Duration::from_secs(60)).await;
 
     Ok(())

opentelemetry-otlp/src/span.rs

@@ -140,7 +140,7 @@ impl Default for ExporterConfig {
     #[cfg(feature = "tonic")]
     fn default() -> Self {
         ExporterConfig {
-            endpoint: format!("localhost:{}", DEFAULT_OTLP_PORT),
+            endpoint: format!("http://localhost:{}", DEFAULT_OTLP_PORT),
             protocol: Protocol::Grpc,
             #[cfg(all(feature = "tonic", feature = "tls"))]
             tls_config: None,