Show error spans like in dproxy (#144)

src/main/kotlin/io/emeraldpay/dshackle/rpc/NativeCall.kt

@@ -126,17 +126,22 @@ open class NativeCall(
     }
 
     private fun completeSpan(callResult: CallResult, requestCount: Int) {
+        val span = tracer.currentSpan()
+        if (callResult.isError()) {
+            errorSpan(span, callResult.error?.message ?: "Internal error")
+        }
         if (requestCount > 1) {
-            val span = tracer.currentSpan()
-            if (callResult.isError()) {
-                span?.error(
-                    RuntimeException(callResult.error?.message ?: "Internal error")
-                )
-            }
             span?.end()
         }
     }
 
+    private fun errorSpan(span: Span?, message: String) {
+        span?.apply {
+            tag("error", "true")
+            tag("status.message", message)
+        }
+    }
+
     private fun createTracingReactorContext(
         ctx: Context,
         requestCount: Int,
@@ -222,10 +227,11 @@ open class NativeCall(
             log.error("Lost context for a native call", it)
             0
         }
-        tracer.currentSpan()?.error(it)
+        val message = it?.message ?: "Internal error"
+        errorSpan(tracer.currentSpan(), message)
         return BlockchainOuterClass.NativeCallReplyItem.newBuilder()
             .setSucceed(false)
-            .setErrorMessage(it?.message ?: "Internal error")
+            .setErrorMessage(message)
             .setErrorCode(500)
             .setId(id)
             .build()