diff --git a/okhttp-protocols/src/main/java/com/squareup/okhttp/internal/ByteString.java b/okhttp-protocols/src/main/java/com/squareup/okhttp/internal/ByteString.java
new file mode 100644
index 000000000..6e3d3fea1
--- /dev/null
+++ b/okhttp-protocols/src/main/java/com/squareup/okhttp/internal/ByteString.java
@@ -0,0 +1,141 @@
+/*
+ * Copyright 2014 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 com.squareup.okhttp.internal;
+
+import java.io.EOFException;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+import java.util.Arrays;
+
+/**
+ * An immutable sequence of bytes.
+ *
+ * <p><strong>Full disclosure:</strong> this class provides untrusted input and
+ * output streams with raw access to the underlying byte array. A hostile
+ * stream implementation could keep a reference to the mutable byte string,
+ * violating the immutable guarantee of this class. For this reason a byte
+ * string's immutability guarantee cannot be relied upon for security in applets
+ * and other environments that run both trusted and untrusted code in the same
+ * process.
+ */
+public final class ByteString {
+  private final byte[] data;
+  private transient int hashCode; // Lazily computed; 0 if unknown.
+  private transient String utf8; // Lazily computed.
+
+  /**
+   * A singleton empty {@code ByteString}.
+   */
+  public static final ByteString EMPTY = new ByteString(Util.EMPTY_BYTE_ARRAY);
+
+  /**
+   * Returns a new byte string containing the bytes of {@code data}, or
+   * {@link #EMPTY} if {@code data} is an empty array.
+   */
+  public static ByteString of(byte... data) {
+    return new ByteString(data.clone());
+  }
+
+  /**
+   * Returns a new byte string containing the bytes of {@code data}
+   * from {@code offset} to {@code offset + count - 1}, inclusive, or
+   * {@link #EMPTY} if {@code count} is zero.
+   */
+  public static ByteString of(byte[] data, int offset, int count) {
+    byte[] bytes = new byte[count];
+    System.arraycopy(data, offset, bytes, 0, count);
+    return new ByteString(bytes);
+  }
+
+  /**
+   * Returns a new byte string containing the {@code UTF-8} bytes of {@code s},
+   * or {@link #EMPTY} if {@code s} is zero length.
+   */
+  public static ByteString encodeUtf8(String s) {
+    return new ByteString(s.getBytes(Util.UTF_8));
+  }
+
+  /** Constructs a new {@code String} by decoding the bytes as UTF-8. */
+  public String utf8() {
+    String result = utf8;
+    // We don't care if we double-allocate in racy code.
+    return result != null ? result : (utf8 = new String(data, Util.UTF_8));
+  }
+
+  /**
+   * Returns true when {@code s} is not null and its {@code UTF-8} encoded
+   * bytes are equivalent to the bytes wrapped by this byte string.
+   */
+  public boolean utf8Equals(String s) {
+    if (s == null) return false;
+    // TODO: avoid allocation
+    return utf8().equals(s);
+  }
+
+  /**
+   * Reads {@code count} bytes from {@code in} and returns the result.
+   *
+   * @throws EOFException if {@code in} has fewer than {@code count} bytes to
+   * read.
+   */
+  public static ByteString read(InputStream in, int count) throws IOException {
+    byte[] result = new byte[count];
+    for (int c = 0; c < count; ) {
+      int read = in.read(result, c, count - c);
+      if (read == -1) throw new EOFException("Expected " + count + "; received " + c);
+      c += read;
+    }
+    return new ByteString(result);
+  }
+
+  private ByteString(byte[] data) {
+    this.data = data; // Trusted internal constructor doesn't clone data.
+  }
+
+  /**
+   * Returns the number of bytes in this ByteString.
+   */
+  public int size() {
+    return data.length;
+  }
+
+  /**
+   * Returns a byte array containing a copy of the bytes in this {@code ByteString}.
+   */
+  public byte[] toByteArray() {
+    return data.clone();
+  }
+
+  /** Writes the contents of this byte string to {@code out}. */
+  public void write(OutputStream out) throws IOException {
+    out.write(data);
+  }
+
+  /** Writes a subsequence of this byte string to {@code out}. */
+  public void write(OutputStream out, int offset, int count) throws IOException {
+    out.write(data, offset, count);
+  }
+
+  @Override public boolean equals(Object o) {
+    return o == this || o instanceof ByteString && Arrays.equals(((ByteString) o).data, data);
+  }
+
+  @Override public int hashCode() {
+    int result = hashCode;
+    return result != 0 ? result : (hashCode = Arrays.hashCode(data));
+  }
+}
diff --git a/okhttp-protocols/src/test/java/com/squareup/okhttp/internal/ByteStringTest.java b/okhttp-protocols/src/test/java/com/squareup/okhttp/internal/ByteStringTest.java
new file mode 100644
index 000000000..ab142f0a1
--- /dev/null
+++ b/okhttp-protocols/src/test/java/com/squareup/okhttp/internal/ByteStringTest.java
@@ -0,0 +1,78 @@
+/*
+ * Copyright 2014 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 com.squareup.okhttp.internal;
+
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.InputStream;
+import java.util.Arrays;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+public class ByteStringTest {
+
+  @Test public void equals() throws Exception {
+    ByteString byteString = ByteString.of((byte) 0x0, (byte) 0x1, (byte) 0x2);
+    assertTrue(byteString.equals(byteString));
+    assertTrue(byteString.equals(ByteString.of((byte) 0x0, (byte) 0x1, (byte) 0x2)));
+    assertTrue(ByteString.of().equals(ByteString.EMPTY));
+    assertTrue(ByteString.EMPTY.equals(ByteString.of()));
+    assertFalse(byteString.equals(new Object()));
+    assertFalse(byteString.equals(ByteString.of((byte) 0x0, (byte) 0x2, (byte) 0x1)));
+  }
+
+  private final String bronzeHorseman = "На берегу пустынных волн";
+
+  @Test public void utf8() throws Exception {
+    ByteString byteString = ByteString.encodeUtf8(bronzeHorseman);
+    assertByteArraysEquals(byteString.toByteArray(), bronzeHorseman.getBytes("UTF-8"));
+    assertTrue(byteString.equals(ByteString.of(bronzeHorseman.getBytes("UTF-8"))));
+    assertTrue(byteString.utf8Equals(bronzeHorseman));
+    assertEquals(byteString.utf8(), bronzeHorseman);
+  }
+
+  @Test public void testHashCode() throws Exception {
+    ByteString byteString = ByteString.of((byte) 0x1, (byte) 0x2);
+    assertEquals(byteString.hashCode(), byteString.hashCode());
+    assertEquals(byteString.hashCode(), ByteString.of((byte) 0x1, (byte) 0x2).hashCode());
+  }
+
+  @Test public void read() throws Exception {
+    InputStream in = new ByteArrayInputStream("abc".getBytes("UTF-8"));
+    assertEquals(ByteString.of((byte) 0x61, (byte) 0x62), ByteString.read(in, 2));
+    assertEquals(ByteString.of((byte) 0x63), ByteString.read(in, 1));
+    assertEquals(ByteString.of(), ByteString.read(in, 0));
+  }
+
+  @Test public void write() throws Exception {
+    ByteArrayOutputStream out = new ByteArrayOutputStream();
+    ByteString.of((byte) 0x61, (byte) 0x62, (byte) 0x63).write(out);
+    assertByteArraysEquals(new byte[] { 0x61, 0x62, 0x63 }, out.toByteArray());
+  }
+
+  @Test public void writeWithOffset() throws Exception {
+    ByteArrayOutputStream out = new ByteArrayOutputStream();
+    ByteString.of((byte) 0x61, (byte) 0x62, (byte) 0x63).write(out, 1, 2);
+    assertByteArraysEquals(new byte[] { 0x62, 0x63 }, out.toByteArray());
+  }
+
+  private static void assertByteArraysEquals(byte[] a, byte[] b) {
+    assertEquals(Arrays.toString(a), Arrays.toString(b));
+  }
+}