SegmentBuilder.currentSize() and capacity()

src/capnp/InputStreamMessageReader.java

@@ -27,6 +27,7 @@ public class InputStreamMessageReader {
     static ByteBuffer makeByteBuffer(byte[] bytes) {
         ByteBuffer result = ByteBuffer.wrap(bytes);
         result.order(ByteOrder.LITTLE_ENDIAN);
+        result.mark();
         return result;
     }
 
@@ -66,12 +67,14 @@ public class InputStreamMessageReader {
 
         segmentSlices[0] = ByteBuffer.wrap(allSegments, 0, segment0Size * 8);
         segmentSlices[0].order(ByteOrder.LITTLE_ENDIAN);
+        segmentSlices[0].mark();
 
         int offset = segment0Size;
 
         for (int ii = 1; ii < segmentCount; ++ii) {
             segmentSlices[ii] = ByteBuffer.wrap(allSegments, offset * 8, moreSizes.get(ii - 1) * 8);
             segmentSlices[ii].order(ByteOrder.LITTLE_ENDIAN);
+            segmentSlices[ii].mark();
             offset += moreSizes.get(ii - 1);
         }
 

src/capnp/SegmentBuilder.java

@@ -3,18 +3,32 @@ package org.capnproto;
 import java.nio.ByteBuffer;
 
 public class SegmentBuilder extends SegmentReader {
-    public int pos = 0;
+    public int pos = 0; // in words
+
+    public static final int FAILED_ALLOCATION = -1;
 
     public SegmentBuilder(ByteBuffer buf) {
         super(buf);
     }
 
+    // the total number of words the buffer can hold
+    private final int capacity() {
+        this.buffer.reset();
+        return (this.buffer.limit() - this.buffer.position()) / 8;
+    }
+
+    // return how many words have already been allocated
     private final int currentSize() {
-        throw new Error("unimplemented");
+        return this.pos;
     }
 
     public final int allocate(int amount) {
-        throw new Error("unimplemented");
-        //        if (amount > ... this.currentSize()
+        if (amount > this.capacity() - this.currentSize()) {
+            return FAILED_ALLOCATION; // no space left;
+        } else {
+            int result = this.pos;
+            this.pos += amount;
+            return result;
+        }
     }
 }

src/capnp/WireHelpers.java

@@ -6,7 +6,18 @@ final class WireHelpers {
                                SegmentBuilder segment,
                                int amount,
                                byte kind) {
+
+        // TODO check for nullness, amount == 0 case.
+
+        int allocation = segment.allocate(amount);
+        if (allocation == SegmentBuilder.FAILED_ALLOCATION) {
+            //# Need to allocate in a new segment. We'll need to
+            //# allocate an extra pointer worth of space to act as
+            //# the landing pad for a far pointer.
             throw new Error("unimplemented");
+        } else {
+            throw new Error("unimplemented");
+        }
     }
 
     public static ListBuilder initListPointer(int refOffset,