Adding a router class to handle messages that expect responses.

mojo/bindings/java/src/org/chromium/mojo/bindings/MessageHeader.java

Index: mojo/bindings/java/src/org/chromium/mojo/bindings/MessageHeader.java
diff --git a/mojo/bindings/java/src/org/chromium/mojo/bindings/MessageHeader.java b/mojo/bindings/java/src/org/chromium/mojo/bindings/MessageHeader.java
new file mode 100644
index 0000000000000000000000000000000000000000..7f5ee9502f012071333b7416b93a081d281ba875
--- /dev/null
+++ b/mojo/bindings/java/src/org/chromium/mojo/bindings/MessageHeader.java
@@ -0,0 +1,204 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.mojo.bindings;
+
+import org.chromium.mojo.bindings.Struct.DataHeader;
+
+import java.nio.ByteBuffer;
+
+/**
+ * Header information for a message.
+ */
+public class MessageHeader {
+
+    private static final int SIMPLE_MESSAGE_SIZE = 16;
+    private static final int SIMPLE_MESSAGE_NUM_FIELDS = 2;
+    private static final DataHeader SIMPLE_MESSAGE_STRUCT_INFO =
+            new DataHeader(SIMPLE_MESSAGE_SIZE, SIMPLE_MESSAGE_NUM_FIELDS);
+
+    private static final int MESSAGE_WITH_REQUEST_ID_SIZE = 24;
+    private static final int MESSAGE_WITH_REQUEST_ID_NUM_FIELDS = 3;
+    private static final DataHeader MESSAGE_WITH_REQUEST_ID_STRUCT_INFO =
+            new DataHeader(MESSAGE_WITH_REQUEST_ID_SIZE, MESSAGE_WITH_REQUEST_ID_NUM_FIELDS);
+
+    private static final int TYPE_OFFSET = 8;
+    private static final int FLAGS_OFFSET = 12;
+    private static final int REQUEST_ID_OFFSET = 16;
+
+    /**
+     * Flag for a header of a message that expected a response.
+     */
+    public static final int MESSAGE_EXPECTS_RESPONSE_FLAG = 1 << 0;
+
+    /**
+     * Flag for a header of a message that is a response.
+     */
+    public static final int MESSAGE_IS_RESPONSE_FLAG = 1 << 1;
+
+    private final DataHeader mDataHeader;
+    private final int mType;
+    private final int mFlags;
+    private long mRequestId;
+
+    /**
+     * Constructor for the header of a message which does not have a response.
+     */
+    public MessageHeader(int type, int flags) {
+        assert !mustHaveRequestId(flags);
+        mDataHeader = SIMPLE_MESSAGE_STRUCT_INFO;
+        mType = type;
+        mFlags = flags;
+        mRequestId = 0;
+    }
+
+    /**
+     * Constructor for the header of a message which have a response or being itself a response.
+     */
+    public MessageHeader(int type, int flags, long requestId) {
+        assert mustHaveRequestId(flags);
+        mDataHeader = MESSAGE_WITH_REQUEST_ID_STRUCT_INFO;
+        mType = type;
+        mFlags = flags;
+        mRequestId = requestId;
+    }
+
+    /**
+     * Constructor, parsing the header from a message. Should only be used by {@link Message}
+     * itself.
+     */
+    MessageHeader(Message message) {
+        Decoder decoder = new Decoder(message);
+        mDataHeader = decoder.readDataHeader();
+        validateDataHeader(mDataHeader);
+        mType = decoder.readInt(TYPE_OFFSET);
+        mFlags = decoder.readInt(FLAGS_OFFSET);
+        if (mustHaveRequestId(mFlags)) {
+            if (mDataHeader.size < MESSAGE_WITH_REQUEST_ID_SIZE) {
+                throw new DeserializationException("Incorrect message size, expecting at least "
+                        + MESSAGE_WITH_REQUEST_ID_SIZE
+                        + " for a message with a request identifier, but got: " + mDataHeader.size);
+
+            }
+            mRequestId = decoder.readLong(REQUEST_ID_OFFSET);
+        } else {
+            mRequestId = 0;
+        }
+    }
+
+    public int getSize() {
+        return mDataHeader.size;
+    }
+
+    /**
+     * Returns the type of the message.
+     */
+    public int getType() {
+        return mType;
+    }
+
+    /**
+     * Returns the flags associated to the message.
+     */
+    public int getFlags() {
+        return mFlags;
+    }
+
+    /**
+     * Returns if the message has the given flag.
+     */
+    public boolean hasFlag(int flag) {
+        return (mFlags & flag) == flag;
+    }
+
+    /**
+     * Returns if the message has a request id.
+     */
+    public boolean hasRequestId() {
+        return mustHaveRequestId(mFlags);
+    }
+
+    /**
+     * Return the request id for the message. Must only be called if the message has a request id.
+     */
+    public long getRequestId() {
+        assert hasRequestId();
+        return mRequestId;
+    }
+
+    /**
+     * Encode the header.
+     */
+    public void encode(Encoder encoder) {
+        encoder.encode(mDataHeader);
+        encoder.encode(getType(), TYPE_OFFSET);
+        encoder.encode(getFlags(), FLAGS_OFFSET);
+        if (hasRequestId()) {
+            encoder.encode(getRequestId(), REQUEST_ID_OFFSET);
+        }
+    }
+
+    /**
+     * Returns true if the header has the expected flags. Only considers flags this class knows
+     * about in order to allow this class to work with future version of the header format.
+     */
+    public boolean validateHeader(int expectedFlags) {
+        int knownFlags = getFlags() & (MESSAGE_EXPECTS_RESPONSE_FLAG | MESSAGE_IS_RESPONSE_FLAG);
+        return knownFlags == expectedFlags;
+    }
+
+    /**
+     * Returns true if the header has the expected type and flags. Only consider flags this class
+     * knows about in order to allow this class to work with future version of the header format.
+     */
+    public boolean validateHeader(int expectedType, int expectedFlags) {
+        return getType() == expectedType && validateHeader(expectedFlags);
+    }
+
+    /**
+     * Set the request id on the message contained in the given buffer.
+     */
+    static void setRequestId(ByteBuffer buffer, long requestId) {
+        assert mustHaveRequestId(buffer.getInt(FLAGS_OFFSET));
+        buffer.putLong(REQUEST_ID_OFFSET, requestId);
+    }
+
+    /**
+     * Returns whether a message with the given flags must have a request Id.
+     */
+    private static boolean mustHaveRequestId(int flags) {
+        return (flags & (MESSAGE_EXPECTS_RESPONSE_FLAG | MESSAGE_IS_RESPONSE_FLAG)) != 0;
+    }
+
+    /**
+     * Validate that the given {@link DataHeader} can be the data header of a message header.
+     */
+    private static void validateDataHeader(DataHeader dataHeader) {
+        if (dataHeader.numFields < SIMPLE_MESSAGE_NUM_FIELDS) {
+            throw new DeserializationException(
+                    "Incorrect number of fields, expecting at least " + SIMPLE_MESSAGE_NUM_FIELDS
+                    + ", but got: " + dataHeader.numFields);
+        }
+        if (dataHeader.size < SIMPLE_MESSAGE_SIZE) {
+            throw new DeserializationException(
+                    "Incorrect message size, expecting at least " + SIMPLE_MESSAGE_SIZE
+                    + ", but got: " + dataHeader.size);
+        }
+        if (dataHeader.numFields == SIMPLE_MESSAGE_NUM_FIELDS
+                && dataHeader.size != SIMPLE_MESSAGE_SIZE) {
+            throw new DeserializationException(
+                    "Incorrect message size for a message with " + SIMPLE_MESSAGE_NUM_FIELDS
+                    + " fields, expecting " + SIMPLE_MESSAGE_SIZE + ", but got: "
+                    + dataHeader.size);
+        }
+        if (dataHeader.numFields == MESSAGE_WITH_REQUEST_ID_NUM_FIELDS
+                && dataHeader.size != MESSAGE_WITH_REQUEST_ID_SIZE) {
+            throw new DeserializationException(
+                    "Incorrect message size for a message with "
+                    + MESSAGE_WITH_REQUEST_ID_NUM_FIELDS + " fields, expecting "
+                    + MESSAGE_WITH_REQUEST_ID_SIZE + ", but got: " + dataHeader.size);
+        }
+    }
+
+}