add fuzz test for receiver (#10790)

Adds a fuzz test for the 3 exposed handlers of the receiver:
`handleTraces`, `handleMetrics`, `handleLogs`. The fuzzer decides which
content type header to set an also which of the handlers to invoke.

Signed-off-by: Adam Korczynski <adam@adalogics.com>

receiver/otlpreceiver/fuzz_test.go

@@ -0,0 +1,52 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package otlpreceiver
+
+import (
+	"bytes"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"go.opentelemetry.io/collector/component/componenttest"
+	"go.opentelemetry.io/collector/receiver/otlpreceiver/internal/logs"
+	"go.opentelemetry.io/collector/receiver/otlpreceiver/internal/metrics"
+	"go.opentelemetry.io/collector/receiver/otlpreceiver/internal/trace"
+	"go.opentelemetry.io/collector/receiver/receivertest"
+)
+
+func FuzzReceiverHandlers(f *testing.F) {
+	f.Fuzz(func(_ *testing.T, data []byte, pb bool, handler int) {
+		req, err := http.NewRequest("POST", "", bytes.NewReader(data))
+		if err != nil {
+			return
+		}
+		if pb {
+			req.Header.Add("Content-Type", pbContentType)
+		} else {
+			req.Header.Add("Content-Type", jsonContentType)
+		}
+		set := receivertest.NewNopSettings()
+		set.TelemetrySettings = componenttest.NewNopTelemetrySettings()
+		set.ID = otlpReceiverID
+		cfg := createDefaultConfig().(*Config)
+		r, err := newOtlpReceiver(cfg, &set)
+		if err != nil {
+			panic(err)
+		}
+		resp := httptest.NewRecorder()
+		switch handler % 3 {
+		case 0:
+			httpTracesReceiver := trace.New(r.nextTraces, r.obsrepHTTP)
+			handleTraces(resp, req, httpTracesReceiver)
+		case 1:
+			httpMetricsReceiver := metrics.New(r.nextMetrics, r.obsrepHTTP)
+			handleMetrics(resp, req, httpMetricsReceiver)
+		case 2:
+			httpLogsReceiver := logs.New(r.nextLogs, r.obsrepHTTP)
+			handleLogs(resp, req, httpLogsReceiver)
+		}
+
+	})
+}