Java: Implements union generation.

mojo/public/java/bindings/src/org/chromium/mojo/bindings/Decoder.java

Index: mojo/public/java/bindings/src/org/chromium/mojo/bindings/Decoder.java
diff --git a/mojo/public/java/bindings/src/org/chromium/mojo/bindings/Decoder.java b/mojo/public/java/bindings/src/org/chromium/mojo/bindings/Decoder.java
index 81cbc9871e756207cc046272f375ce74183c2d7d..91ba791473da873abd923a924eff88b3bb3ad53a 100644
--- a/mojo/public/java/bindings/src/org/chromium/mojo/bindings/Decoder.java
+++ b/mojo/public/java/bindings/src/org/chromium/mojo/bindings/Decoder.java
@@ -5,7 +5,6 @@
 package org.chromium.mojo.bindings;
 
 import org.chromium.mojo.bindings.Interface.Proxy;
-import org.chromium.mojo.bindings.Struct.DataHeader;
 import org.chromium.mojo.system.DataPipe;
 import org.chromium.mojo.system.Handle;
 import org.chromium.mojo.system.InvalidHandle;
@@ -114,11 +113,42 @@ public class Decoder {
     }
 
     /**
-     * Deserializes a {@link DataHeader} at the given offset.
+     * Deserializes a {@link DataHeader} at the current position.
      */
     public DataHeader readDataHeader() {
+        DataHeader result = readDataHeaderAtOffset(0);
+        // Claim the remaining memory.
+        mValidator.claimMemory(mBaseOffset + DataHeader.HEADER_SIZE, mBaseOffset + result.size);
+        return result;
+    }
+
+    /**
+     * Deserializes a {@link DataHeader} for an union at the given offset.
+     */
+    public DataHeader readDataHeaderForUnion(int offset) {
+        DataHeader result = readDataHeaderAtOffset(offset);
+        if (result.size == 0) {
+            if (result.elementsOrVersion != 0) {

[azani, 2015/05/19 21:13:23]

The design doc doesn't specify an error when the tag is not equal to 0 for a
null union. Do you think that is an oversight? I think that we should enforce
the same rules for the tag and the data field. Either both have to be 0 for null
unions or neither has to be.

[qsr, 2015/05/20 09:22:36]

That's not correct though. 0 is a valid value for a non-null union, as this will
be the tag value.

But I indeed think that we should have 0 for the tag when the union is null.

+                throw new DeserializationException(
+                        "Unexpected tag for a null union. Expecting 0, found: "
+                        + result.elementsOrVersion);
+            }
+        } else if (result.size != BindingsHelper.UNION_SIZE) {
+            throw new DeserializationException(
+                    "Unexpected size of an union. The size must be 0 for a null union, and 16 for "

[azani, 2015/05/19 21:13:23]

nit: "or 16 for..."

[qsr, 2015/05/20 09:22:36]

Done.

+                    + "a non-null union.");
+        }
+        mValidator.claimMemory(mBaseOffset + offset + DataHeader.HEADER_SIZE,
+                mBaseOffset + offset + BindingsHelper.UNION_SIZE);
+        return result;
+    }
+
+    /**
+     * Deserializes a {@link DataHeader} at the given offset.
+     */
+    private DataHeader readDataHeaderAtOffset(int offset) {
         // Claim the memory for the header.
-        mValidator.claimMemory(mBaseOffset, mBaseOffset + DataHeader.HEADER_SIZE);
+        mValidator.claimMemory(mBaseOffset + offset, mBaseOffset + offset + DataHeader.HEADER_SIZE);
         int size = readInt(DataHeader.SIZE_OFFSET);
         int elementsOrVersion = readInt(DataHeader.ELEMENTS_OR_VERSION_OFFSET);
         if (size < 0) {
@@ -130,10 +160,7 @@ public class Decoder {
                     "Negative elements or version. Unsigned integers are not valid for java.");
         }
 
-        // Claim the remaining memory.
-        mValidator.claimMemory(mBaseOffset + DataHeader.HEADER_SIZE, mBaseOffset + size);
-        DataHeader res = new DataHeader(size, elementsOrVersion);
-        return res;
+        return new DataHeader(size, elementsOrVersion);
     }
 
     public DataHeader readAndValidateDataHeader(DataHeader[] versionArray) {
@@ -163,10 +190,18 @@ public class Decoder {
 
     /**
      * Deserializes a {@link DataHeader} at the given offset and checks if it is correct for an
-     * array where element have the given size.
+     * array where elements are pointers.
      */
     public DataHeader readDataHeaderForPointerArray(int expectedLength) {
-        return readDataHeaderForArray(8, expectedLength);
+        return readDataHeaderForArray(BindingsHelper.POINTER_SIZE, expectedLength);
+    }
+
+    /**
+     * Deserializes a {@link DataHeader} at the given offset and checks if it is correct for an
+     * array where elements are unions.
+     */
+    public DataHeader readDataHeaderForUnionArray(int expectedLength) {
+        return readDataHeaderForArray(BindingsHelper.UNION_SIZE, expectedLength);
     }
 
     /**