[OTLP] Log HTTP response body

Log the HTTP response body, if available.

Resolves #6454.

Author: martincostello

src/OpenTelemetry.Exporter.OpenTelemetryProtocol/Implementation/ExportClient/OtlpExportClient.cs

@@ -65,6 +65,29 @@ public bool Shutdown(int timeoutMilliseconds)
         return true;
     }
 
+    protected static string? TryGetResponseBody(HttpResponseMessage? httpResponse, CancellationToken cancellationToken)
+    {
+        if (httpResponse?.Content == null)
+        {
+            return null;
+        }
+
+        try
+        {
+#if NET
+            var stream = httpResponse.Content.ReadAsStream(cancellationToken);
+            using var reader = new StreamReader(stream);
+            return reader.ReadToEnd();
+#else
+            return httpResponse.Content.ReadAsStringAsync().GetAwaiter().GetResult();
+#endif
+        }
+        catch (Exception)
+        {
+            return null;
+        }
+    }
+
     protected HttpRequestMessage CreateHttpRequest(byte[] buffer, int contentLength)
     {
         var request = new HttpRequestMessage(HttpMethod.Post, this.Endpoint);

src/OpenTelemetry.Exporter.OpenTelemetryProtocol/Implementation/ExportClient/OtlpGrpcExportClient.cs

@@ -36,6 +36,8 @@ public OtlpGrpcExportClient(OtlpExporterOptions options, HttpClient httpClient,
     /// <inheritdoc/>
     public override ExportClientResponse SendExportRequest(byte[] buffer, int contentLength, DateTime deadlineUtc, CancellationToken cancellationToken = default)
     {
+        HttpResponseMessage? httpResponse = null;
+
         try
         {
             using var httpRequest = this.CreateHttpRequest(buffer, contentLength);
@@ -44,7 +46,7 @@ public override ExportClientResponse SendExportRequest(byte[] buffer, int conten
             // A missing TE header results in servers aborting the gRPC call.
             httpRequest.Headers.TryAddWithoutValidation("TE", "trailers");
 
-            using var httpResponse = this.SendHttpRequest(httpRequest, cancellationToken);
+            httpResponse = this.SendHttpRequest(httpRequest, cancellationToken);
 
             httpResponse.EnsureSuccessStatusCode();
 
@@ -121,7 +123,8 @@ public override ExportClientResponse SendExportRequest(byte[] buffer, int conten
         catch (HttpRequestException ex)
         {
             // Handle non-retryable HTTP errors.
-            OpenTelemetryProtocolExporterEventSource.Log.HttpRequestFailed(this.Endpoint, ex);
+            var response = TryGetResponseBody(httpResponse, cancellationToken);
+            OpenTelemetryProtocolExporterEventSource.Log.HttpRequestFailed(this.Endpoint, response, ex);
             return new ExportClientGrpcResponse(
                 success: false,
                 deadlineUtc: deadlineUtc,
@@ -156,6 +159,10 @@ public override ExportClientResponse SendExportRequest(byte[] buffer, int conten
             OpenTelemetryProtocolExporterEventSource.Log.FailedToReachCollector(this.Endpoint, ex);
             return DefaultExceptionExportClientGrpcResponse;
         }
+        finally
+        {
+            httpResponse?.Dispose();
+        }
     }
 
     private static bool IsTransientNetworkError(HttpRequestException ex)

src/OpenTelemetry.Exporter.OpenTelemetryProtocol/Implementation/ExportClient/OtlpHttpExportClient.cs

@@ -35,7 +35,8 @@ public override ExportClientResponse SendExportRequest(byte[] buffer, int conten
             }
             catch (HttpRequestException ex)
             {
-                OpenTelemetryProtocolExporterEventSource.Log.HttpRequestFailed(this.Endpoint, ex);
+                var response = TryGetResponseBody(httpResponse, cancellationToken);
+                OpenTelemetryProtocolExporterEventSource.Log.HttpRequestFailed(this.Endpoint, response, ex);
                 return new ExportClientHttpResponse(success: false, deadlineUtc: deadlineUtc, response: httpResponse, ex);
             }
 

src/OpenTelemetry.Exporter.OpenTelemetryProtocol/Implementation/OpenTelemetryProtocolExporterEventSource.cs

@@ -60,11 +60,11 @@ public void TransientHttpError(Uri endpoint, Exception ex)
     }
 
     [NonEvent]
-    public void HttpRequestFailed(Uri endpoint, Exception ex)
+    public void HttpRequestFailed(Uri endpoint, string? response, Exception ex)
     {
         if (Log.IsEnabled(EventLevel.Error, EventKeywords.All))
         {
-            this.HttpRequestFailed(endpoint.ToString(), ex.ToInvariantString());
+            this.HttpRequestFailed(endpoint.ToString(), response, ex.ToInvariantString());
         }
     }
 
@@ -200,10 +200,10 @@ public void TransientHttpError(string endpoint, string exceptionMessage)
         this.WriteEvent(16, endpoint, exceptionMessage);
     }
 
-    [Event(17, Message = "HTTP request to {0} failed. Exception: {1}", Level = EventLevel.Error)]
-    public void HttpRequestFailed(string endpoint, string exceptionMessage)
+    [Event(17, Message = "HTTP request to {0} failed. Response: {1}. Exception: {2}", Level = EventLevel.Error)]
+    public void HttpRequestFailed(string endpoint, string? response, string exceptionMessage)
     {
-        this.WriteEvent(17, endpoint, exceptionMessage);
+        this.WriteEvent(17, endpoint, response, exceptionMessage);
     }
 
     [Event(18, Message = "Operation unexpectedly canceled for endpoint {0}. Exception: {1}", Level = EventLevel.Warning)]