diff --git a/okhttp-tests/src/test/java/okhttp3/internal/io/PipeTest.java b/okhttp-tests/src/test/java/okhttp3/internal/io/PipeTest.java
new file mode 100644
index 000000000..35bfbe40d
--- /dev/null
+++ b/okhttp-tests/src/test/java/okhttp3/internal/io/PipeTest.java
@@ -0,0 +1,403 @@
+/*
+ * Copyright (C) 2016 Square, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package okhttp3.internal.io;
+
+import java.io.IOException;
+import java.io.InterruptedIOException;
+import java.util.Random;
+import java.util.concurrent.Callable;
+import java.util.concurrent.Executors;
+import java.util.concurrent.Future;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.TimeUnit;
+import okio.Buffer;
+import okio.ByteString;
+import okio.HashingSink;
+import okio.Source;
+import org.junit.After;
+import org.junit.Test;
+
+import static junit.framework.TestCase.fail;
+import static org.junit.Assert.assertEquals;
+
+public final class PipeTest {
+  final ScheduledExecutorService executorService = Executors.newScheduledThreadPool(2);
+
+  @After public void tearDown() throws Exception {
+    executorService.shutdown();
+  }
+
+  @Test public void test() throws Exception {
+    Pipe pipe = new Pipe(6);
+    pipe.sink.write(new Buffer().writeUtf8("abc"), 3L);
+
+    Source source = pipe.source;
+    Buffer readBuffer = new Buffer();
+    assertEquals(3L, source.read(readBuffer, 6L));
+    assertEquals("abc", readBuffer.readUtf8());
+
+    pipe.sink.close();
+    assertEquals(-1L, source.read(readBuffer, 6L));
+
+    source.close();
+  }
+
+  /**
+   * A producer writes the first 16 MiB of bytes generated by {@code new Random(0)} to a sink, and a
+   * consumer consumes them. Both compute hashes of their data to confirm that they're as expected.
+   */
+  @Test public void largeDataset() throws Exception {
+    final Pipe pipe = new Pipe(1000L); // An awkward size to force producer/consumer exchange.
+    final long totalBytes = 16L * 1024L * 1024L;
+    ByteString expectedHash = ByteString.decodeHex("7c3b224bea749086babe079360cf29f98d88262d");
+
+    // Write data to the sink.
+    Future<ByteString> sinkHash = executorService.submit(new Callable<ByteString>() {
+      @Override public ByteString call() throws Exception {
+        HashingSink hashingSink = HashingSink.sha1(pipe.sink);
+        Random random = new Random(0);
+        byte[] data = new byte[8192];
+
+        Buffer buffer = new Buffer();
+        for (long i = 0L; i < totalBytes; i += data.length) {
+          random.nextBytes(data);
+          buffer.write(data);
+          hashingSink.write(buffer, buffer.size());
+        }
+
+        hashingSink.close();
+        return hashingSink.hash();
+      }
+    });
+
+    // Read data from the source.
+    Future<ByteString> sourceHash = executorService.submit(new Callable<ByteString>() {
+      @Override public ByteString call() throws Exception {
+        Buffer blackhole = new Buffer();
+        HashingSink hashingSink = HashingSink.sha1(blackhole);
+
+        Buffer buffer = new Buffer();
+        while (pipe.source.read(buffer, Long.MAX_VALUE) != -1) {
+          hashingSink.write(buffer, buffer.size());
+          blackhole.clear();
+        }
+
+        pipe.source.close();
+        return hashingSink.hash();
+      }
+    });
+
+    assertEquals(expectedHash, sinkHash.get());
+    assertEquals(expectedHash, sourceHash.get());
+  }
+
+  @Test public void sinkTimeout() throws Exception {
+    Pipe pipe = new Pipe(3);
+    pipe.sink.timeout().timeout(250, TimeUnit.MILLISECONDS);
+    pipe.sink.write(new Buffer().writeUtf8("abc"), 3L);
+    double start = now();
+    try {
+      pipe.sink.write(new Buffer().writeUtf8("def"), 3L);
+      fail();
+    } catch (InterruptedIOException expected) {
+      assertEquals("timeout", expected.getMessage());
+    }
+    assertElapsed(250.0, start);
+
+    Buffer readBuffer = new Buffer();
+    assertEquals(3L, pipe.source.read(readBuffer, 6L));
+    assertEquals("abc", readBuffer.readUtf8());
+  }
+
+  @Test public void sourceTimeout() throws Exception {
+    Pipe pipe = new Pipe(3L);
+    pipe.source.timeout().timeout(250, TimeUnit.MILLISECONDS);
+    double start = now();
+    Buffer readBuffer = new Buffer();
+    try {
+      pipe.source.read(readBuffer, 6L);
+      fail();
+    } catch (InterruptedIOException expected) {
+      assertEquals("timeout", expected.getMessage());
+    }
+    assertElapsed(250.0, start);
+    assertEquals(0, readBuffer.size());
+  }
+
+  /**
+   * The writer is writing 12 bytes as fast as it can to a 3 byte buffer. The reader alternates
+   * sleeping 250 ms, then reading 3 bytes. That should make for an approximate timeline like this:
+   *
+   * 0: writer writes 'abc', blocks 0: reader sleeps until 250 250: reader reads 'abc', sleeps until
+   * 500 250: writer writes 'def', blocks 500: reader reads 'def', sleeps until 750 500: writer
+   * writes 'ghi', blocks 750: reader reads 'ghi', sleeps until 1000 750: writer writes 'jkl',
+   * returns 1000: reader reads 'jkl', returns
+   *
+   * Because the writer is writing to a buffer, it finishes before the reader does.
+   */
+  @Test public void sinkBlocksOnSlowReader() throws Exception {
+    final Pipe pipe = new Pipe(3L);
+    executorService.execute(new Runnable() {
+      @Override public void run() {
+        try {
+          Buffer buffer = new Buffer();
+          Thread.sleep(250L);
+          assertEquals(3, pipe.source.read(buffer, Long.MAX_VALUE));
+          assertEquals("abc", buffer.readUtf8());
+          Thread.sleep(250L);
+          assertEquals(3, pipe.source.read(buffer, Long.MAX_VALUE));
+          assertEquals("def", buffer.readUtf8());
+          Thread.sleep(250L);
+          assertEquals(3, pipe.source.read(buffer, Long.MAX_VALUE));
+          assertEquals("ghi", buffer.readUtf8());
+          Thread.sleep(250L);
+          assertEquals(3, pipe.source.read(buffer, Long.MAX_VALUE));
+          assertEquals("jkl", buffer.readUtf8());
+        } catch (IOException | InterruptedException e) {
+          throw new AssertionError();
+        }
+      }
+    });
+
+    double start = now();
+    pipe.sink.write(new Buffer().writeUtf8("abcdefghijkl"), 12);
+    assertElapsed(750.0, start);
+  }
+
+  @Test public void sinkWriteFailsByClosedReader() throws Exception {
+    final Pipe pipe = new Pipe(3L);
+    executorService.schedule(new Runnable() {
+      @Override public void run() {
+        try {
+          pipe.source.close();
+        } catch (IOException e) {
+          throw new AssertionError();
+        }
+      }
+    }, 250, TimeUnit.MILLISECONDS);
+
+    double start = now();
+    try {
+      pipe.sink.write(new Buffer().writeUtf8("abcdef"), 6);
+      fail();
+    } catch (IOException expected) {
+      assertEquals("source is closed", expected.getMessage());
+      assertElapsed(250.0, start);
+    }
+  }
+
+  @Test public void sinkFlushWaitsForReaderToReadEverything() throws Exception {
+    final Buffer readBuffer = new Buffer();
+    final Pipe pipe = new Pipe(100L);
+    executorService.execute(new Runnable() {
+      @Override public void run() {
+        try {
+          Thread.sleep(250);
+          pipe.source.read(readBuffer, 3);
+          Thread.sleep(250);
+          pipe.source.read(readBuffer, 3);
+        } catch (InterruptedException | IOException e) {
+          throw new AssertionError(e);
+        }
+      }
+    });
+
+    double start = now();
+    pipe.sink.write(new Buffer().writeUtf8("abcdef"), 6);
+    pipe.sink.flush();
+    assertElapsed(500.0, start);
+    assertEquals("abcdef", readBuffer.readUtf8());
+  }
+
+  @Test public void sinkFlushFailsIfReaderIsClosedBeforeAllDataIsRead() throws Exception {
+    final Pipe pipe = new Pipe(100L);
+    executorService.execute(new Runnable() {
+      @Override public void run() {
+        try {
+          Thread.sleep(250);
+          pipe.source.read(new Buffer(), 3);
+          Thread.sleep(250);
+          pipe.source.close();
+        } catch (InterruptedException | IOException e) {
+          throw new AssertionError(e);
+        }
+      }
+    });
+
+    double start = now();
+    pipe.sink.write(new Buffer().writeUtf8("abcdef"), 6);
+    try {
+      pipe.sink.flush();
+      fail();
+    } catch (IOException expected) {
+      assertEquals("source is closed", expected.getMessage());
+      assertElapsed(500.0, start);
+    }
+  }
+
+  @Test public void sinkCloseFailsIfReaderIsClosedBeforeAllDataIsRead() throws Exception {
+    final Pipe pipe = new Pipe(100L);
+    executorService.execute(new Runnable() {
+      @Override public void run() {
+        try {
+          Thread.sleep(250);
+          pipe.source.read(new Buffer(), 3);
+          Thread.sleep(250);
+          pipe.source.close();
+        } catch (InterruptedException | IOException e) {
+          throw new AssertionError(e);
+        }
+      }
+    });
+
+    double start = now();
+    pipe.sink.write(new Buffer().writeUtf8("abcdef"), 6);
+    try {
+      pipe.sink.close();
+      fail();
+    } catch (IOException expected) {
+      assertEquals("source is closed", expected.getMessage());
+      assertElapsed(500.0, start);
+    }
+
+    try {
+      pipe.sink.flush();
+      fail();
+    } catch (IllegalStateException expected) {
+      assertEquals("closed", expected.getMessage());
+    }
+  }
+
+  @Test public void sinkClose() throws Exception {
+    Pipe pipe = new Pipe(100L);
+    pipe.sink.close();
+    try {
+      pipe.sink.write(new Buffer().writeUtf8("abc"), 3);
+      fail();
+    } catch (IllegalStateException expected) {
+      assertEquals("closed", expected.getMessage());
+    }
+    try {
+      pipe.sink.flush();
+      fail();
+    } catch (IllegalStateException expected) {
+      assertEquals("closed", expected.getMessage());
+    }
+  }
+
+  @Test public void sinkMultipleClose() throws Exception {
+    Pipe pipe = new Pipe(100L);
+    pipe.sink.close();
+    pipe.sink.close();
+  }
+
+  @Test public void sourceClose() throws Exception {
+    Pipe pipe = new Pipe(100L);
+    pipe.source.close();
+    try {
+      pipe.source.read(new Buffer(), 3);
+      fail();
+    } catch (IllegalStateException expected) {
+      assertEquals("closed", expected.getMessage());
+    }
+  }
+
+  @Test public void sourceMultipleClose() throws Exception {
+    Pipe pipe = new Pipe(100L);
+    pipe.source.close();
+    pipe.source.close();
+  }
+
+  @Test public void sourceReadUnblockedByClosedSink() throws Exception {
+    final Pipe pipe = new Pipe(3L);
+    executorService.schedule(new Runnable() {
+      @Override public void run() {
+        try {
+          pipe.sink.close();
+        } catch (IOException e) {
+          throw new AssertionError();
+        }
+      }
+    }, 250, TimeUnit.MILLISECONDS);
+
+    double start = now();
+    Buffer readBuffer = new Buffer();
+    assertEquals(-1, pipe.source.read(readBuffer, Long.MAX_VALUE));
+    assertEquals(0, readBuffer.size());
+    assertElapsed(250.0, start);
+  }
+
+  /**
+   * The writer has 12 bytes to write. It alternates sleeping 250 ms, then writing 3 bytes. The
+   * reader is reading as fast as it can. That should make for an approximate timeline like this:
+   *
+   * 0: writer sleeps until 250 0: reader blocks 250: writer writes 'abc', sleeps until 500 250:
+   * reader reads 'abc' 500: writer writes 'def', sleeps until 750 500: reader reads 'def' 750:
+   * writer writes 'ghi', sleeps until 1000 750: reader reads 'ghi' 1000: writer writes 'jkl',
+   * returns 1000: reader reads 'jkl', returns
+   */
+  @Test public void sourceBlocksOnSlowWriter() throws Exception {
+    final Pipe pipe = new Pipe(100L);
+    executorService.execute(new Runnable() {
+      @Override public void run() {
+        try {
+          Thread.sleep(250L);
+          pipe.sink.write(new Buffer().writeUtf8("abc"), 3);
+          Thread.sleep(250L);
+          pipe.sink.write(new Buffer().writeUtf8("def"), 3);
+          Thread.sleep(250L);
+          pipe.sink.write(new Buffer().writeUtf8("ghi"), 3);
+          Thread.sleep(250L);
+          pipe.sink.write(new Buffer().writeUtf8("jkl"), 3);
+        } catch (IOException | InterruptedException e) {
+          throw new AssertionError();
+        }
+      }
+    });
+
+    double start = now();
+    Buffer readBuffer = new Buffer();
+
+    assertEquals(3, pipe.source.read(readBuffer, Long.MAX_VALUE));
+    assertEquals("abc", readBuffer.readUtf8());
+    assertElapsed(250.0, start);
+
+    assertEquals(3, pipe.source.read(readBuffer, Long.MAX_VALUE));
+    assertEquals("def", readBuffer.readUtf8());
+    assertElapsed(500.0, start);
+
+    assertEquals(3, pipe.source.read(readBuffer, Long.MAX_VALUE));
+    assertEquals("ghi", readBuffer.readUtf8());
+    assertElapsed(750.0, start);
+
+    assertEquals(3, pipe.source.read(readBuffer, Long.MAX_VALUE));
+    assertEquals("jkl", readBuffer.readUtf8());
+    assertElapsed(1000.0, start);
+  }
+
+  /** Returns the nanotime in milliseconds as a double for measuring timeouts. */
+  private double now() {
+    return System.nanoTime() / 1000000.0d;
+  }
+
+  /**
+   * Fails the test unless the time from start until now is duration, accepting differences in
+   * -50..+150 milliseconds.
+   */
+  private void assertElapsed(double duration, double start) {
+    assertEquals(duration, now() - start + 50d, 100.0);
+  }
+}
diff --git a/okhttp-tests/src/test/java/okhttp3/internal/io/WaitUntilNotifiedTest.java b/okhttp-tests/src/test/java/okhttp3/internal/io/WaitUntilNotifiedTest.java
new file mode 100644
index 000000000..443b5a24e
--- /dev/null
+++ b/okhttp-tests/src/test/java/okhttp3/internal/io/WaitUntilNotifiedTest.java
@@ -0,0 +1,147 @@
+/*
+ * Copyright (C) 2016 Square, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package okhttp3.internal.io;
+
+import java.io.InterruptedIOException;
+import java.util.concurrent.Executors;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.TimeUnit;
+import okio.Timeout;
+import org.junit.After;
+import org.junit.Test;
+
+import static junit.framework.TestCase.fail;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+
+public final class WaitUntilNotifiedTest {
+  final ScheduledExecutorService executorService = Executors.newScheduledThreadPool(0);
+
+  @After public void tearDown() throws Exception {
+    executorService.shutdown();
+  }
+
+  @Test public synchronized void notified() throws Exception {
+    Timeout timeout = new Timeout();
+    timeout.timeout(5000, TimeUnit.MILLISECONDS);
+
+    double start = now();
+    executorService.schedule(new Runnable() {
+      @Override public void run() {
+        synchronized (WaitUntilNotifiedTest.this) {
+          WaitUntilNotifiedTest.this.notify();
+        }
+      }
+    }, 250, TimeUnit.MILLISECONDS);
+
+    Pipe.waitUntilNotified(this, timeout);
+    assertElapsed(250.0, start);
+  }
+
+  @Test public synchronized void timeout() throws Exception {
+    Timeout timeout = new Timeout();
+    timeout.timeout(250, TimeUnit.MILLISECONDS);
+    double start = now();
+    try {
+      Pipe.waitUntilNotified(this, timeout);
+      fail();
+    } catch (InterruptedIOException expected) {
+      assertEquals("timeout", expected.getMessage());
+    }
+    assertElapsed(250.0, start);
+  }
+
+  @Test public synchronized void deadline() throws Exception {
+    Timeout timeout = new Timeout();
+    timeout.deadline(250, TimeUnit.MILLISECONDS);
+    double start = now();
+    try {
+      Pipe.waitUntilNotified(this, timeout);
+      fail();
+    } catch (InterruptedIOException expected) {
+      assertEquals("timeout", expected.getMessage());
+    }
+    assertElapsed(250.0, start);
+  }
+
+  @Test public synchronized void deadlineBeforeTimeout() throws Exception {
+    Timeout timeout = new Timeout();
+    timeout.timeout(5000, TimeUnit.MILLISECONDS);
+    timeout.deadline(250, TimeUnit.MILLISECONDS);
+    double start = now();
+    try {
+      Pipe.waitUntilNotified(this, timeout);
+      fail();
+    } catch (InterruptedIOException expected) {
+      assertEquals("timeout", expected.getMessage());
+    }
+    assertElapsed(250.0, start);
+  }
+
+  @Test public synchronized void timeoutBeforeDeadline() throws Exception {
+    Timeout timeout = new Timeout();
+    timeout.timeout(250, TimeUnit.MILLISECONDS);
+    timeout.deadline(5000, TimeUnit.MILLISECONDS);
+    double start = now();
+    try {
+      Pipe.waitUntilNotified(this, timeout);
+      fail();
+    } catch (InterruptedIOException expected) {
+      assertEquals("timeout", expected.getMessage());
+    }
+    assertElapsed(250.0, start);
+  }
+
+  @Test public synchronized void deadlineAlreadyReached() throws Exception {
+    Timeout timeout = new Timeout();
+    timeout.deadlineNanoTime(System.nanoTime());
+    double start = now();
+    try {
+      Pipe.waitUntilNotified(this, timeout);
+      fail();
+    } catch (InterruptedIOException expected) {
+      assertEquals("timeout", expected.getMessage());
+    }
+    assertElapsed(0.0, start);
+  }
+
+  @Test public synchronized void threadInterrupted() throws Exception {
+    Timeout timeout = new Timeout();
+    double start = now();
+    Thread.currentThread().interrupt();
+    try {
+      Pipe.waitUntilNotified(this, timeout);
+      fail();
+    } catch (InterruptedIOException expected) {
+      assertEquals("interrupted", expected.getMessage());
+      assertFalse(Thread.interrupted());
+    }
+    assertElapsed(0.0, start);
+  }
+
+  /** Returns the nanotime in milliseconds as a double for measuring timeouts. */
+  private double now() {
+    return System.nanoTime() / 1000000.0d;
+  }
+
+  /**
+   * Fails the test unless the time from start until now is duration, accepting differences in
+   * -50..+150 milliseconds.
+   */
+  private void assertElapsed(double duration, double start) {
+    assertEquals(duration, now() - start + 50d, 100.0);
+  }
+}
diff --git a/okhttp/src/main/java/okhttp3/internal/io/Pipe.java b/okhttp/src/main/java/okhttp3/internal/io/Pipe.java
new file mode 100644
index 000000000..f1c30578c
--- /dev/null
+++ b/okhttp/src/main/java/okhttp3/internal/io/Pipe.java
@@ -0,0 +1,182 @@
+/*
+ * Copyright (C) 2016 Square, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package okhttp3.internal.io;
+
+import java.io.IOException;
+import java.io.InterruptedIOException;
+import okio.Buffer;
+import okio.Sink;
+import okio.Source;
+import okio.Timeout;
+
+/**
+ * A source and a sink that are attached. The sink's output is the source's input. Typically each
+ * is accessed by its own thread: a producer thread writes data to the sink and a consumer thread
+ * reads data from the source.
+ *
+ * <p>This class uses a buffer to decouple source and sink. This buffer has a user-specified maximum
+ * size. When a producer thread outruns its consumer the buffer fills up and eventually writes to
+ * the sink will block until the consumer has caught up. Symmetrically, if a consumer outruns its
+ * producer reads block until there is data to be read. Limits on the amount of time spent waiting
+ * for the other party can be configured with {@linkplain Timeout timeouts} on the source and the
+ * sink.
+ *
+ * <p>When the sink is closed, source reads will continue to complete normally until the buffer has
+ * been exhausted. At that point reads will return -1, indicating the end of the stream. But if the
+ * source is closed first, writes to the sink will immediately fail with an {@link IOException}.
+ */
+public final class Pipe {
+  final long maxBufferSize;
+  final Buffer buffer = new Buffer();
+  boolean sinkClosed;
+  boolean sourceClosed;
+  public final Sink sink = new PipeSink();
+  public final Source source = new PipeSource();
+
+  public Pipe(long maxBufferSize) {
+    if (maxBufferSize < 1L) {
+      throw new IllegalArgumentException("maxBufferSize < 1: " + maxBufferSize);
+    }
+    this.maxBufferSize = maxBufferSize;
+  }
+
+  final class PipeSink implements Sink {
+    final Timeout timeout = new Timeout();
+
+    @Override public void write(Buffer source, long byteCount) throws IOException {
+      synchronized (buffer) {
+        if (sinkClosed) throw new IllegalStateException("closed");
+
+        while (byteCount > 0) {
+          if (sourceClosed) throw new IOException("source is closed");
+
+          long bufferSpaceAvailable = maxBufferSize - buffer.size();
+          if (bufferSpaceAvailable == 0) {
+            waitUntilNotified(buffer, timeout); // Wait until the source drains the buffer.
+            continue;
+          }
+
+          long bytesToWrite = Math.min(bufferSpaceAvailable, byteCount);
+          buffer.write(source, bytesToWrite);
+          byteCount -= bytesToWrite;
+          buffer.notifyAll(); // Notify the source that it can resume reading.
+        }
+      }
+    }
+
+    @Override public void flush() throws IOException {
+      synchronized (buffer) {
+        if (sinkClosed) throw new IllegalStateException("closed");
+
+        while (buffer.size() > 0) {
+          if (sourceClosed) throw new IOException("source is closed");
+          waitUntilNotified(buffer, timeout);
+        }
+      }
+    }
+
+    @Override public void close() throws IOException {
+      synchronized (buffer) {
+        if (sinkClosed) return;
+        try {
+          flush();
+        } finally {
+          sinkClosed = true;
+          buffer.notifyAll(); // Notify the source that no more bytes are coming.
+        }
+      }
+    }
+
+    @Override public Timeout timeout() {
+      return timeout;
+    }
+  }
+
+  final class PipeSource implements Source {
+    final Timeout timeout = new Timeout();
+
+    @Override public long read(Buffer sink, long byteCount) throws IOException {
+      synchronized (buffer) {
+        if (sourceClosed) throw new IllegalStateException("closed");
+
+        while (buffer.size() == 0) {
+          if (sinkClosed) return -1L;
+          waitUntilNotified(buffer, timeout); // Wait until the sink fills the buffer.
+        }
+
+        long result = buffer.read(sink, byteCount);
+        buffer.notifyAll(); // Notify the sink that it can resume writing.
+        return result;
+      }
+    }
+
+    @Override public void close() throws IOException {
+      synchronized (buffer) {
+        sourceClosed = true;
+        buffer.notifyAll(); // Notify the sink that no more bytes are desired.
+      }
+    }
+
+    @Override public Timeout timeout() {
+      return timeout;
+    }
+  }
+
+  /**
+   * Waits on {@code monitor} until it is notified. Throws {@link InterruptedIOException} if either
+   * the thread is interrupted or if {@code timeout} elapses before {@code monitor} is notified. The
+   * caller must be synchronized on {@code monitor}.
+   */
+  static void waitUntilNotified(Object monitor, Timeout timeout) throws IOException {
+    try {
+      boolean hasDeadline = timeout.hasDeadline();
+      long timeoutNanos = timeout.timeoutNanos();
+
+      if (!hasDeadline && timeoutNanos == 0L) {
+        monitor.wait(); // There is no timeout: wait forever.
+        return;
+      }
+
+      // Compute how long we'll wait.
+      long waitNanos;
+      long start = System.nanoTime();
+      if (hasDeadline && timeoutNanos != 0) {
+        long deadlineNanos = timeout.deadlineNanoTime() - start;
+        waitNanos = Math.min(timeoutNanos, deadlineNanos);
+      } else if (hasDeadline) {
+        waitNanos = timeout.deadlineNanoTime() - start;
+      } else {
+        waitNanos = timeoutNanos;
+      }
+
+      // Attempt to wait that long. This will break out early if the monitor is notified.
+      long elapsedNanos = 0L;
+      if (waitNanos > 0L) {
+        long waitMillis = waitNanos / 1000000L;
+        monitor.wait(waitMillis, (int) (waitNanos - waitMillis * 1000000L));
+        elapsedNanos = System.nanoTime() - start;
+      }
+
+      // Throw if the timeout elapsed before the monitor was notified.
+      if (elapsedNanos >= waitNanos) {
+        throw new InterruptedIOException("timeout");
+      }
+    } catch (InterruptedException e) {
+      throw new InterruptedIOException("interrupted");
+    }
+  }
+}
+