problem: doesn't increment error metrics for HTTP call with invalid JSON

rel: #150

src/main/kotlin/io/emeraldpay/dshackle/proxy/HttpHandler.kt

@@ -41,7 +41,7 @@ class HttpHandler(
     writeRpcJson: WriteRpcJson,
     nativeCall: NativeCall,
     private val accessHandler: AccessHandlerHttp.HandlerFactory,
-    requestMetrics: ProxyServer.RequestMetricsFactory,
+    private val requestMetrics: ProxyServer.RequestMetricsFactory,
 ) : BaseHandler(writeRpcJson, nativeCall, requestMetrics) {
 
     companion object {
@@ -70,6 +70,13 @@ class HttpHandler(
     ): Flux<ByteBuf> {
         return request
             .map(readRpcJson)
+            .doOnError {
+                log.debug("Failed to process request JSON with: ${it.javaClass} ${it.message}")
+                // most of the metrics are handled inside the execute method, including most of the errors.
+                // but if we have an invalid JSON it stops here, and we cannot handle it in the main onErrorResume
+                // because it's going to be a duplicate call for other errors
+                requestMetrics.get(chain, "invalid_method").errorMetric.increment()
+            }
             .flatMapMany { call ->
                 execute(chain, call, handler)
             }

src/test/groovy/io/emeraldpay/dshackle/proxy/HttpHandlerSpec.groovy

@@ -23,6 +23,8 @@ import io.emeraldpay.dshackle.rpc.NativeCall
 import io.emeraldpay.dshackle.upstream.rpcclient.JsonRpcResponse
 import io.emeraldpay.etherjar.rpc.RpcException
 import io.emeraldpay.grpc.Chain
+import io.micrometer.core.instrument.Counter
+import io.micrometer.core.instrument.step.StepCounter
 import reactor.core.publisher.Flux
 import reactor.core.publisher.Mono
 import reactor.test.StepVerifier
@@ -72,10 +74,19 @@ class HttpHandlerSpec extends Specification {
         ReadRpcJson read = Mock(ReadRpcJson) {
             1 * apply(_) >> { throw new RpcException(-32123, "test", new JsonRpcResponse.NumberId(4)) }
         }
+        Counter errorMetric = Mock(Counter) {
+            1 * increment()
+        }
+        ProxyServer.RequestMetricsFactory metrics = Mock(ProxyServer.RequestMetricsFactory) {
+            1 * get(Chain.ETHEREUM, "invalid_method") >> Mock(ProxyServer.RequestMetrics) {
+                1 * it.errorMetric >> errorMetric
+            }
+        }
 
         def handler = new HttpHandler(
                 read, new WriteRpcJson(),
-                Stub(NativeCall), Stub(AccessHandlerHttp.HandlerFactory), Stub(ProxyServer.RequestMetricsFactory)
+                Stub(NativeCall), Stub(AccessHandlerHttp.HandlerFactory),
+                metrics
         )
         when: