Add more debug information to HTTP/2 GOAWAY frame

Motivation:

An HTTP/2 GOAWAY frame with non-zero error code sometimes gives an empty
debugData, making it hard to determine the root cause of the error.

Modifications:

- Add the following information to debugData:
  - the exact type of Http2Exception
  - the original message of Http2Exception
  - the exact type, message and stack trace of the cause of Http2Exception
- Add Exceptions.traceText() to stringify the stack trace of an
  exception
- Fix incorrect Logger level check

Result:

We will have more information when we get an error GOAWAY frame.

src/main/java/com/linecorp/armeria/common/http/AbstractHttpToHttp2ConnectionHandler.java

@@ -16,12 +16,17 @@
 
 package com.linecorp.armeria.common.http;
 
+import static io.netty.handler.codec.http2.Http2Error.INTERNAL_ERROR;
+
+import com.linecorp.armeria.common.util.Exceptions;
+
 import io.netty.channel.ChannelHandlerContext;
 import io.netty.channel.ChannelPromise;
 import io.netty.handler.codec.http2.Http2ConnectionDecoder;
 import io.netty.handler.codec.http2.Http2ConnectionEncoder;
 import io.netty.handler.codec.http2.Http2ConnectionHandler;
 import io.netty.handler.codec.http2.Http2Exception;
+import io.netty.handler.codec.http2.Http2Exception.ClosedStreamCreationException;
 import io.netty.handler.codec.http2.Http2Settings;
 import io.netty.handler.codec.http2.Http2Stream.State;
 import io.netty.handler.codec.http2.Http2StreamVisitor;
@@ -43,8 +48,10 @@ public abstract class AbstractHttpToHttp2ConnectionHandler extends HttpToHttp2Co
     private boolean closing;
     private boolean handlingConnectionError;
 
-    protected AbstractHttpToHttp2ConnectionHandler(Http2ConnectionDecoder decoder, Http2ConnectionEncoder encoder,
-                                                   Http2Settings initialSettings, boolean validateHeaders) {
+    protected AbstractHttpToHttp2ConnectionHandler(
+            Http2ConnectionDecoder decoder, Http2ConnectionEncoder encoder,
+            Http2Settings initialSettings, boolean validateHeaders) {
+
         super(decoder, encoder, initialSettings, validateHeaders);
     }
 
@@ -59,9 +66,45 @@ protected void onConnectionError(ChannelHandlerContext ctx, Throwable cause, Htt
         }
 
         handlingConnectionError = true;
+
+        // TODO(trustin): Remove this once Http2ConnectionHandler.goAway() sends better debugData.
+        //                See https://github.com/netty/netty/issues/5160
+        if (http2Ex == null) {
+            http2Ex = new Http2Exception(INTERNAL_ERROR, goAwayDebugData(null, cause), cause);
+        } else if (http2Ex instanceof ClosedStreamCreationException) {
+            final ClosedStreamCreationException e = (ClosedStreamCreationException) http2Ex;
+            http2Ex = new ClosedStreamCreationException(e.error(), goAwayDebugData(e, cause), cause);
+        } else {
+            http2Ex = new Http2Exception(
+                    http2Ex.error(), goAwayDebugData(http2Ex, cause), cause, http2Ex.shutdownHint());
+        }
+
         super.onConnectionError(ctx, cause, http2Ex);
     }
 
+    private static String goAwayDebugData(Http2Exception http2Ex, Throwable cause) {
+        final StringBuilder buf = new StringBuilder(256);
+        final String type;
+        final String message;
+
+        if (http2Ex != null) {
+            type = http2Ex.getClass().getName();
+            message = http2Ex.getMessage();
+        } else {
+            type = null;
+            message = null;
+        }
+
+        buf.append("type: ");
+        buf.append(type != null ? type : "n/a");
+        buf.append(", message: ");
+        buf.append(message != null ? message : "n/a");
+        buf.append(", cause: ");
+        buf.append(cause != null ? Exceptions.traceText(cause) : "n/a");
+
+        return buf.toString();
+    }
+
     @Override
     public void close(ChannelHandlerContext ctx, ChannelPromise promise) throws Exception {
         closing = true;

src/main/java/com/linecorp/armeria/common/http/Http2GoAwayListener.java

@@ -70,7 +70,7 @@ ch, sentOrReceived, lastStreamId, errorStr(errorCode),
                             ByteBufUtil.hexDump(debugData));
             }
         } else {
-            if (logger.isInfoEnabled()) {
+            if (logger.isDebugEnabled()) {
                 logger.debug("{} {} a GOAWAY frame: lastStreamId={}, errorCode=NO_ERROR",
                              ch, sentOrReceived, lastStreamId);
             }

src/main/java/com/linecorp/armeria/common/util/Exceptions.java

@@ -19,6 +19,8 @@
 import static java.util.Objects.requireNonNull;
 
 import java.io.IOException;
+import java.io.PrintWriter;
+import java.io.StringWriter;
 import java.nio.channels.ClosedChannelException;
 import java.util.regex.Pattern;
 
@@ -118,5 +120,17 @@ public static <T extends Throwable> T clearTrace(T exception) {
         return exception;
     }
 
+    /**
+     * Returns the stack trace of the specified {@code exception} as a {@link String}.
+     */
+    public static String traceText(Throwable exception) {
+        requireNonNull(exception, "exception");
+        final StringWriter out = new StringWriter(256);
+        final PrintWriter pout = new PrintWriter(out);
+        exception.printStackTrace(pout);
+        pout.flush();
+        return out.toString();
+    }
+
     private Exceptions() {}
 }