diff --git a/runtime/src/main/java/org/capnproto/BufferedInputStreamWrapper.java b/runtime/src/main/java/org/capnproto/BufferedInputStreamWrapper.java
new file mode 100644
index 0000000..3a5bb68
--- /dev/null
+++ b/runtime/src/main/java/org/capnproto/BufferedInputStreamWrapper.java
@@ -0,0 +1,77 @@
+package org.capnproto;
+
+import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.nio.channels.ReadableByteChannel;
+
+public final class BufferedInputStreamWrapper implements BufferedInputStream {
+
+    private final ReadableByteChannel inner;
+    private final ByteBuffer buf;
+    private int cap = 0;
+
+    public BufferedInputStreamWrapper(ReadableByteChannel chan) {
+        this.inner = chan;
+        this.buf = ByteBuffer.allocate(8192);
+    }
+
+    public final int read(ByteBuffer dst) throws IOException {
+        int numBytes = dst.remaining();
+        if (numBytes < cap - this.buf.position()) {
+            //# Serve from the current buffer.
+            ByteBuffer slice = this.buf.slice();
+            slice.limit(numBytes);
+            dst.put(slice);
+            this.buf.position(this.buf.position() + numBytes);
+            return numBytes;
+        } else {
+            //# Copy current available into destination.
+            ByteBuffer slice = this.buf.slice();
+            int fromFirstBuffer = cap - this.buf.position();
+            slice.limit(fromFirstBuffer);
+            dst.put(slice);
+
+            numBytes -= fromFirstBuffer;
+            if (numBytes <= this.buf.capacity()) {
+                //# Read the next buffer-full.
+                this.buf.rewind();
+                int n = readAtLeast(this.inner, this.buf, numBytes);
+
+                // ...
+                //ByteBuffer slice =
+                //dst.put(
+
+                this.cap = n;
+                this.buf.position(numBytes);
+                return fromFirstBuffer + numBytes;
+            } else {
+                //# Forward large read to the underlying stream.
+            }
+        }
+        throw new Error("unimplemented");
+    }
+
+    public final ByteBuffer getReadBuffer() {
+        return this.buf;
+    }
+
+    public final void close() throws IOException {
+        this.inner.close();
+    }
+
+    public final boolean isOpen() {
+        return this.inner.isOpen();
+    }
+
+    public static int readAtLeast(ReadableByteChannel reader, ByteBuffer buf, int minBytes) throws IOException {
+        int numRead = 0;
+        while (numRead < minBytes) {
+            int res = reader.read(buf);
+            if (res < 0) {
+                throw new Error("premature EOF");
+            }
+            numRead += res;
+        }
+        return numRead;
+    }
+}
diff --git a/runtime/src/main/java/org/capnproto/BufferedOutputStreamWrapper.java b/runtime/src/main/java/org/capnproto/BufferedOutputStreamWrapper.java
index 23713d1..36acdc4 100644
--- a/runtime/src/main/java/org/capnproto/BufferedOutputStreamWrapper.java
+++ b/runtime/src/main/java/org/capnproto/BufferedOutputStreamWrapper.java
@@ -6,8 +6,8 @@ import java.nio.channels.WritableByteChannel;
 
 public final class BufferedOutputStreamWrapper implements BufferedOutputStream {
 
-    public final WritableByteChannel inner;
-    public final ByteBuffer buf;
+    private final WritableByteChannel inner;
+    private final ByteBuffer buf;
 
     public BufferedOutputStreamWrapper(WritableByteChannel w) {
         this.inner = w;
diff --git a/runtime/src/main/java/org/capnproto/ByteChannelMessageReader.java b/runtime/src/main/java/org/capnproto/ByteChannelMessageReader.java
index 10eb9c3..330c3ec 100644
--- a/runtime/src/main/java/org/capnproto/ByteChannelMessageReader.java
+++ b/runtime/src/main/java/org/capnproto/ByteChannelMessageReader.java
@@ -15,7 +15,7 @@ public final class ByteChannelMessageReader {
         return result;
     }
 
-    static void fillBuffer(ByteBuffer buffer, ReadableByteChannel bc) throws IOException {
+    public static void fillBuffer(ByteBuffer buffer, ReadableByteChannel bc) throws IOException {
         while(buffer.hasRemaining()) {
             int r = bc.read(buffer);
             if (r < 0) {