diff --git a/objectivec/GPBCodedInputStream.m b/objectivec/GPBCodedInputStream.m
new file mode 100644
index 0000000..79d31fc
--- /dev/null
+++ b/objectivec/GPBCodedInputStream.m
@@ -0,0 +1,801 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#import "GPBCodedInputStream_PackagePrivate.h"
+
+#import "GPBDictionary_PackagePrivate.h"
+#import "GPBMessage_PackagePrivate.h"
+#import "GPBUnknownFieldSet_PackagePrivate.h"
+#import "GPBUtilities_PackagePrivate.h"
+#import "GPBWireFormat.h"
+
+static const NSUInteger kDefaultRecursionLimit = 64;
+
+static inline void CheckSize(GPBCodedInputStreamState *state, size_t size) {
+  size_t newSize = state->bufferPos + size;
+  if (newSize > state->bufferSize) {
+    [NSException raise:NSParseErrorException format:@""];
+  }
+  if (newSize > state->currentLimit) {
+    // Fast forward to end of currentLimit;
+    state->bufferPos = state->currentLimit;
+    [NSException raise:NSParseErrorException format:@""];
+  }
+}
+
+static inline int8_t ReadRawByte(GPBCodedInputStreamState *state) {
+  CheckSize(state, sizeof(int8_t));
+  return ((int8_t *)state->bytes)[state->bufferPos++];
+}
+
+static inline int32_t ReadRawLittleEndian32(GPBCodedInputStreamState *state) {
+  CheckSize(state, sizeof(int32_t));
+  int32_t value = OSReadLittleInt32(state->bytes, state->bufferPos);
+  state->bufferPos += sizeof(int32_t);
+  return value;
+}
+
+static inline int64_t ReadRawLittleEndian64(GPBCodedInputStreamState *state) {
+  CheckSize(state, sizeof(int64_t));
+  int64_t value = OSReadLittleInt64(state->bytes, state->bufferPos);
+  state->bufferPos += sizeof(int64_t);
+  return value;
+}
+
+static inline int32_t ReadRawVarint32(GPBCodedInputStreamState *state) {
+  int8_t tmp = ReadRawByte(state);
+  if (tmp >= 0) {
+    return tmp;
+  }
+  int32_t result = tmp & 0x7f;
+  if ((tmp = ReadRawByte(state)) >= 0) {
+    result |= tmp << 7;
+  } else {
+    result |= (tmp & 0x7f) << 7;
+    if ((tmp = ReadRawByte(state)) >= 0) {
+      result |= tmp << 14;
+    } else {
+      result |= (tmp & 0x7f) << 14;
+      if ((tmp = ReadRawByte(state)) >= 0) {
+        result |= tmp << 21;
+      } else {
+        result |= (tmp & 0x7f) << 21;
+        result |= (tmp = ReadRawByte(state)) << 28;
+        if (tmp < 0) {
+          // Discard upper 32 bits.
+          for (int i = 0; i < 5; i++) {
+            if (ReadRawByte(state) >= 0) {
+              return result;
+            }
+          }
+          [NSException raise:NSParseErrorException
+                      format:@"Unable to read varint32"];
+        }
+      }
+    }
+  }
+  return result;
+}
+
+static inline int64_t ReadRawVarint64(GPBCodedInputStreamState *state) {
+  int32_t shift = 0;
+  int64_t result = 0;
+  while (shift < 64) {
+    int8_t b = ReadRawByte(state);
+    result |= (int64_t)(b & 0x7F) << shift;
+    if ((b & 0x80) == 0) {
+      return result;
+    }
+    shift += 7;
+  }
+  [NSException raise:NSParseErrorException format:@"Unable to read varint64"];
+  return 0;
+}
+
+static inline void SkipRawData(GPBCodedInputStreamState *state, size_t size) {
+  CheckSize(state, size);
+  state->bufferPos += size;
+}
+
+double GPBCodedInputStreamReadDouble(GPBCodedInputStreamState *state) {
+  int64_t value = ReadRawLittleEndian64(state);
+  return GPBConvertInt64ToDouble(value);
+}
+
+float GPBCodedInputStreamReadFloat(GPBCodedInputStreamState *state) {
+  int32_t value = ReadRawLittleEndian32(state);
+  return GPBConvertInt32ToFloat(value);
+}
+
+uint64_t GPBCodedInputStreamReadUInt64(GPBCodedInputStreamState *state) {
+  uint64_t value = ReadRawVarint64(state);
+  return value;
+}
+
+uint32_t GPBCodedInputStreamReadUInt32(GPBCodedInputStreamState *state) {
+  uint32_t value = ReadRawVarint32(state);
+  return value;
+}
+
+int64_t GPBCodedInputStreamReadInt64(GPBCodedInputStreamState *state) {
+  int64_t value = ReadRawVarint64(state);
+  return value;
+}
+
+int32_t GPBCodedInputStreamReadInt32(GPBCodedInputStreamState *state) {
+  int32_t value = ReadRawVarint32(state);
+  return value;
+}
+
+uint64_t GPBCodedInputStreamReadFixed64(GPBCodedInputStreamState *state) {
+  uint64_t value = ReadRawLittleEndian64(state);
+  return value;
+}
+
+uint32_t GPBCodedInputStreamReadFixed32(GPBCodedInputStreamState *state) {
+  uint32_t value = ReadRawLittleEndian32(state);
+  return value;
+}
+
+int32_t GPBCodedInputStreamReadEnum(GPBCodedInputStreamState *state) {
+  int32_t value = ReadRawVarint32(state);
+  return value;
+}
+
+int32_t GPBCodedInputStreamReadSFixed32(GPBCodedInputStreamState *state) {
+  int32_t value = ReadRawLittleEndian32(state);
+  return value;
+}
+
+int64_t GPBCodedInputStreamReadSFixed64(GPBCodedInputStreamState *state) {
+  int64_t value = ReadRawLittleEndian64(state);
+  return value;
+}
+
+int32_t GPBCodedInputStreamReadSInt32(GPBCodedInputStreamState *state) {
+  int32_t value = GPBDecodeZigZag32(ReadRawVarint32(state));
+  return value;
+}
+
+int64_t GPBCodedInputStreamReadSInt64(GPBCodedInputStreamState *state) {
+  int64_t value = GPBDecodeZigZag64(ReadRawVarint64(state));
+  return value;
+}
+
+BOOL GPBCodedInputStreamReadBool(GPBCodedInputStreamState *state) {
+  return ReadRawVarint32(state) != 0;
+}
+
+int32_t GPBCodedInputStreamReadTag(GPBCodedInputStreamState *state) {
+  if (GPBCodedInputStreamIsAtEnd(state)) {
+    state->lastTag = 0;
+    return 0;
+  }
+
+  state->lastTag = ReadRawVarint32(state);
+  if (state->lastTag == 0) {
+    // If we actually read zero, that's not a valid tag.
+    [NSException raise:NSParseErrorException
+                format:@"Invalid last tag %d", state->lastTag];
+  }
+  return state->lastTag;
+}
+
+NSString *GPBCodedInputStreamReadRetainedString(
+    GPBCodedInputStreamState *state) {
+  int32_t size = ReadRawVarint32(state);
+  NSString *result;
+  if (size == 0) {
+    result = @"";
+  } else {
+    CheckSize(state, size);
+    result = GPBCreateGPBStringWithUTF8(&state->bytes[state->bufferPos], size);
+    state->bufferPos += size;
+  }
+  return result;
+}
+
+NSData *GPBCodedInputStreamReadRetainedData(GPBCodedInputStreamState *state) {
+  int32_t size = ReadRawVarint32(state);
+  if (size < 0) return nil;
+  CheckSize(state, size);
+  NSData *result = [[NSData alloc] initWithBytes:state->bytes + state->bufferPos
+                                          length:size];
+  state->bufferPos += size;
+  return result;
+}
+
+NSData *GPBCodedInputStreamReadRetainedDataNoCopy(
+    GPBCodedInputStreamState *state) {
+  int32_t size = ReadRawVarint32(state);
+  if (size < 0) return nil;
+  CheckSize(state, size);
+  // Cast is safe because freeWhenDone is NO.
+  NSData *result = [[NSData alloc]
+      initWithBytesNoCopy:(void *)(state->bytes + state->bufferPos)
+                   length:size
+             freeWhenDone:NO];
+  state->bufferPos += size;
+  return result;
+}
+
+size_t GPBCodedInputStreamPushLimit(GPBCodedInputStreamState *state,
+                                    size_t byteLimit) {
+  byteLimit += state->bufferPos;
+  size_t oldLimit = state->currentLimit;
+  if (byteLimit > oldLimit) {
+    [NSException raise:NSInvalidArgumentException
+                format:@"byteLimit > oldLimit: %tu > %tu", byteLimit, oldLimit];
+  }
+  state->currentLimit = byteLimit;
+  return oldLimit;
+}
+
+void GPBCodedInputStreamPopLimit(GPBCodedInputStreamState *state,
+                                 size_t oldLimit) {
+  state->currentLimit = oldLimit;
+}
+
+size_t GPBCodedInputStreamBytesUntilLimit(GPBCodedInputStreamState *state) {
+  if (state->currentLimit == SIZE_T_MAX) {
+    return state->currentLimit;
+  }
+
+  return state->currentLimit - state->bufferPos;
+}
+
+BOOL GPBCodedInputStreamIsAtEnd(GPBCodedInputStreamState *state) {
+  return (state->bufferPos == state->bufferSize) ||
+         (state->bufferPos == state->currentLimit);
+}
+
+void GPBCodedInputStreamCheckLastTagWas(GPBCodedInputStreamState *state,
+                                        int32_t value) {
+  if (state->lastTag != value) {
+    [NSException raise:NSParseErrorException
+                format:@"Last tag: %d should be %d", state->lastTag, value];
+  }
+}
+
+@implementation GPBCodedInputStream
+
++ (instancetype)streamWithData:(NSData *)data {
+  return [[[self alloc] initWithData:data] autorelease];
+}
+
+- (instancetype)initWithData:(NSData *)data {
+  if ((self = [super init])) {
+#ifdef DEBUG
+    NSCAssert([self class] == [GPBCodedInputStream class],
+              @"Subclassing of GPBCodedInputStream is not allowed.");
+#endif
+    buffer_ = [data retain];
+    state_.bytes = (const uint8_t *)[data bytes];
+    state_.bufferSize = [data length];
+    state_.currentLimit = NSUIntegerMax;
+  }
+  return self;
+}
+
+- (void)dealloc {
+  [buffer_ release];
+  [super dealloc];
+}
+
+- (int32_t)readTag {
+  return GPBCodedInputStreamReadTag(&state_);
+}
+
+- (void)checkLastTagWas:(int32_t)value {
+  GPBCodedInputStreamCheckLastTagWas(&state_, value);
+}
+
+- (BOOL)skipField:(int32_t)tag {
+  switch (GPBWireFormatGetTagWireType(tag)) {
+    case GPBWireFormatVarint:
+      GPBCodedInputStreamReadInt32(&state_);
+      return YES;
+    case GPBWireFormatFixed64:
+      SkipRawData(&state_, sizeof(int64_t));
+      return YES;
+    case GPBWireFormatLengthDelimited:
+      SkipRawData(&state_, ReadRawVarint32(&state_));
+      return YES;
+    case GPBWireFormatStartGroup:
+      [self skipMessage];
+      GPBCodedInputStreamCheckLastTagWas(
+          &state_, GPBWireFormatMakeTag(GPBWireFormatGetTagFieldNumber(tag),
+                                        GPBWireFormatEndGroup));
+      return YES;
+    case GPBWireFormatEndGroup:
+      return NO;
+    case GPBWireFormatFixed32:
+      SkipRawData(&state_, sizeof(int32_t));
+      return YES;
+  }
+  [NSException raise:NSParseErrorException format:@"Invalid tag %d", tag];
+  return NO;
+}
+
+- (void)skipMessage {
+  while (YES) {
+    int32_t tag = GPBCodedInputStreamReadTag(&state_);
+    if (tag == 0 || ![self skipField:tag]) {
+      return;
+    }
+  }
+}
+
+- (double)readDouble {
+  return GPBCodedInputStreamReadDouble(&state_);
+}
+
+- (float)readFloat {
+  return GPBCodedInputStreamReadFloat(&state_);
+}
+
+- (uint64_t)readUInt64 {
+  return GPBCodedInputStreamReadUInt64(&state_);
+}
+
+- (int64_t)readInt64 {
+  return GPBCodedInputStreamReadInt64(&state_);
+}
+
+- (int32_t)readInt32 {
+  return GPBCodedInputStreamReadInt32(&state_);
+}
+
+- (uint64_t)readFixed64 {
+  return GPBCodedInputStreamReadFixed64(&state_);
+}
+
+- (uint32_t)readFixed32 {
+  return GPBCodedInputStreamReadFixed32(&state_);
+}
+
+- (BOOL)readBool {
+  return GPBCodedInputStreamReadBool(&state_);
+}
+
+- (NSString *)readString {
+  return [GPBCodedInputStreamReadRetainedString(&state_) autorelease];
+}
+
+- (void)readGroup:(int32_t)fieldNumber
+              message:(GPBMessage *)message
+    extensionRegistry:(GPBExtensionRegistry *)extensionRegistry {
+  if (state_.recursionDepth >= kDefaultRecursionLimit) {
+    [NSException raise:NSParseErrorException
+                format:@"recursionDepth(%tu) >= %tu", state_.recursionDepth,
+                       kDefaultRecursionLimit];
+  }
+  ++state_.recursionDepth;
+  [message mergeFromCodedInputStream:self extensionRegistry:extensionRegistry];
+  GPBCodedInputStreamCheckLastTagWas(
+      &state_, GPBWireFormatMakeTag(fieldNumber, GPBWireFormatEndGroup));
+  --state_.recursionDepth;
+}
+
+- (void)readUnknownGroup:(int32_t)fieldNumber
+                 message:(GPBUnknownFieldSet *)message {
+  if (state_.recursionDepth >= kDefaultRecursionLimit) {
+    [NSException raise:NSParseErrorException
+                format:@"recursionDepth(%tu) >= %tu", state_.recursionDepth,
+                       kDefaultRecursionLimit];
+  }
+  ++state_.recursionDepth;
+  [message mergeFromCodedInputStream:self];
+  GPBCodedInputStreamCheckLastTagWas(
+      &state_, GPBWireFormatMakeTag(fieldNumber, GPBWireFormatEndGroup));
+  --state_.recursionDepth;
+}
+
+- (void)readMessage:(GPBMessage *)message
+    extensionRegistry:(GPBExtensionRegistry *)extensionRegistry {
+  int32_t length = ReadRawVarint32(&state_);
+  if (state_.recursionDepth >= kDefaultRecursionLimit) {
+    [NSException raise:NSParseErrorException
+                format:@"recursionDepth(%tu) >= %tu", state_.recursionDepth,
+                       kDefaultRecursionLimit];
+  }
+  size_t oldLimit = GPBCodedInputStreamPushLimit(&state_, length);
+  ++state_.recursionDepth;
+  [message mergeFromCodedInputStream:self extensionRegistry:extensionRegistry];
+  GPBCodedInputStreamCheckLastTagWas(&state_, 0);
+  --state_.recursionDepth;
+  GPBCodedInputStreamPopLimit(&state_, oldLimit);
+}
+
+- (void)readMapEntry:(id)mapDictionary
+    extensionRegistry:(GPBExtensionRegistry *)extensionRegistry
+                field:(GPBFieldDescriptor *)field
+        parentMessage:(GPBMessage *)parentMessage {
+  int32_t length = ReadRawVarint32(&state_);
+  if (state_.recursionDepth >= kDefaultRecursionLimit) {
+    [NSException raise:NSParseErrorException
+                format:@"recursionDepth(%tu) >= %tu", state_.recursionDepth,
+                       kDefaultRecursionLimit];
+  }
+  size_t oldLimit = GPBCodedInputStreamPushLimit(&state_, length);
+  ++state_.recursionDepth;
+  GPBDictionaryReadEntry(mapDictionary, self, extensionRegistry, field,
+                         parentMessage);
+  GPBCodedInputStreamCheckLastTagWas(&state_, 0);
+  --state_.recursionDepth;
+  GPBCodedInputStreamPopLimit(&state_, oldLimit);
+}
+
+- (NSData *)readData {
+  return [GPBCodedInputStreamReadRetainedData(&state_) autorelease];
+}
+
+- (uint32_t)readUInt32 {
+  return GPBCodedInputStreamReadUInt32(&state_);
+}
+
+- (int32_t)readEnum {
+  return GPBCodedInputStreamReadEnum(&state_);
+}
+
+- (int32_t)readSFixed32 {
+  return GPBCodedInputStreamReadSFixed32(&state_);
+}
+
+- (int64_t)readSFixed64 {
+  return GPBCodedInputStreamReadSFixed64(&state_);
+}
+
+- (int32_t)readSInt32 {
+  return GPBCodedInputStreamReadSInt32(&state_);
+}
+
+- (int64_t)readSInt64 {
+  return GPBCodedInputStreamReadSInt64(&state_);
+}
+
+@end
+
+@implementation GPBString {
+ @package
+  CFStringRef string_;
+  unsigned char *utf8_;
+  NSUInteger utf8Len_;
+
+  // This lock is used to gate access to utf8_.  Once GPBStringInitStringValue()
+  // has been called, string_ will be filled in, and utf8_ will be NULL.
+  OSSpinLock lock_;
+
+  BOOL hasBOM_;
+  BOOL is7BitAscii_;
+}
+
+// Returns true if the passed in bytes are 7 bit ascii.
+// This routine needs to be fast.
+static inline bool AreBytesIn7BitASCII(const uint8_t *bytes, NSUInteger len) {
+// In the loops below, it's more efficient to collect rather than do
+// conditional at every step.
+#if __LP64__
+  // Align bytes. This is especially important in case of 3 byte BOM.
+  while (len > 0 && ((size_t)bytes & 0x07)) {
+    if (*bytes++ & 0x80) return false;
+    len--;
+  }
+  while (len >= 32) {
+    uint64_t val = *(const uint64_t *)bytes;
+    uint64_t hiBits = (val & 0x8080808080808080ULL);
+    bytes += 8;
+    val = *(const uint64_t *)bytes;
+    hiBits |= (val & 0x8080808080808080ULL);
+    bytes += 8;
+    val = *(const uint64_t *)bytes;
+    hiBits |= (val & 0x8080808080808080ULL);
+    bytes += 8;
+    val = *(const uint64_t *)bytes;
+    if (hiBits | (val & 0x8080808080808080ULL)) return false;
+    bytes += 8;
+    len -= 32;
+  }
+
+  while (len >= 16) {
+    uint64_t val = *(const uint64_t *)bytes;
+    uint64_t hiBits = (val & 0x8080808080808080ULL);
+    bytes += 8;
+    val = *(const uint64_t *)bytes;
+    if (hiBits | (val & 0x8080808080808080ULL)) return false;
+    bytes += 8;
+    len -= 16;
+  }
+
+  while (len >= 8) {
+    uint64_t val = *(const uint64_t *)bytes;
+    if (val & 0x8080808080808080ULL) return false;
+    bytes += 8;
+    len -= 8;
+  }
+#else   // __LP64__
+  // Align bytes. This is especially important in case of 3 byte BOM.
+  while (len > 0 && ((size_t)bytes & 0x03)) {
+    if (*bytes++ & 0x80) return false;
+    len--;
+  }
+  while (len >= 16) {
+    uint32_t val = *(const uint32_t *)bytes;
+    uint32_t hiBits = (val & 0x80808080U);
+    bytes += 4;
+    val = *(const uint32_t *)bytes;
+    hiBits |= (val & 0x80808080U);
+    bytes += 4;
+    val = *(const uint32_t *)bytes;
+    hiBits |= (val & 0x80808080U);
+    bytes += 4;
+    val = *(const uint32_t *)bytes;
+    if (hiBits | (val & 0x80808080U)) return false;
+    bytes += 4;
+    len -= 16;
+  }
+
+  while (len >= 8) {
+    uint32_t val = *(const uint32_t *)bytes;
+    uint32_t hiBits = (val & 0x80808080U);
+    bytes += 4;
+    val = *(const uint32_t *)bytes;
+    if (hiBits | (val & 0x80808080U)) return false;
+    bytes += 4;
+    len -= 8;
+  }
+#endif  // __LP64__
+
+  while (len >= 4) {
+    uint32_t val = *(const uint32_t *)bytes;
+    if (val & 0x80808080U) return false;
+    bytes += 4;
+    len -= 4;
+  }
+
+  while (len--) {
+    if (*bytes++ & 0x80) return false;
+  }
+
+  return true;
+}
+
+static inline void GPBStringInitStringValue(GPBString *string) {
+  OSSpinLockLock(&string->lock_);
+  GPBStringInitStringValueAlreadyLocked(string);
+  OSSpinLockUnlock(&string->lock_);
+}
+
+static void GPBStringInitStringValueAlreadyLocked(GPBString *string) {
+  if (string->string_ == NULL && string->utf8_ != NULL) {
+    // Using kCFAllocatorMalloc for contentsDeallocator, as buffer in
+    // string->utf8_ is being handed off.
+    string->string_ = CFStringCreateWithBytesNoCopy(
+        NULL, string->utf8_, string->utf8Len_, kCFStringEncodingUTF8, false,
+        kCFAllocatorMalloc);
+    if (!string->string_) {
+#ifdef DEBUG
+      // https://developers.google.com/protocol-buffers/docs/proto#scalar
+      NSLog(@"UTF8 failure, is some field type 'string' when it should be "
+            @"'bytes'?");
+#endif
+      string->string_ = CFSTR("");
+      string->utf8Len_ = 0;
+      // On failure, we have to clean up the buffer.
+      free(string->utf8_);
+    }
+    string->utf8_ = NULL;
+  }
+}
+
+GPBString *GPBCreateGPBStringWithUTF8(const void *bytes, NSUInteger length) {
+  GPBString *result = [[GPBString alloc] initWithBytes:bytes length:length];
+  return result;
+}
+
+- (instancetype)initWithBytes:(const void *)bytes length:(NSUInteger)length {
+  self = [super init];
+  if (self) {
+    utf8_ = malloc(length);
+    memcpy(utf8_, bytes, length);
+    utf8Len_ = length;
+    lock_ = OS_SPINLOCK_INIT;
+    is7BitAscii_ = AreBytesIn7BitASCII(bytes, length);
+    if (length >= 3 && memcmp(utf8_, "\xef\xbb\xbf", 3) == 0) {
+      // We can't just remove the BOM from the string here, because in the case
+      // where we have > 1 BOM at the beginning of the string, we will remove one,
+      // and the internal NSString we create will remove the next one, and we will
+      // end up with a GPBString != NSString issue.
+      // We also just can't remove all the BOMs because then we would end up with
+      // potential cases where a GPBString and an NSString made with the same
+      // UTF8 buffer would in fact be different.
+      // We record the fact we have a BOM, and use it as necessary to simulate
+      // what NSString would return for various calls.
+      hasBOM_ = YES;
+#if DEBUG
+      // Sending BOMs across the line is just wasting bits.
+      NSLog(@"Bad data? String should not have BOM!");
+#endif  // DEBUG
+    }
+  }
+  return self;
+}
+
+- (void)dealloc {
+  if (string_ != NULL) {
+    CFRelease(string_);
+  }
+  if (utf8_ != NULL) {
+    free(utf8_);
+  }
+  [super dealloc];
+}
+
+// Required NSString overrides.
+- (NSUInteger)length {
+  if (is7BitAscii_) {
+    return utf8Len_;
+  } else {
+    GPBStringInitStringValue(self);
+    return CFStringGetLength(string_);
+  }
+}
+
+- (unichar)characterAtIndex:(NSUInteger)anIndex {
+  OSSpinLockLock(&lock_);
+  if (is7BitAscii_ && utf8_) {
+    unichar result = utf8_[anIndex];
+    OSSpinLockUnlock(&lock_);
+    return result;
+  } else {
+    GPBStringInitStringValueAlreadyLocked(self);
+    OSSpinLockUnlock(&lock_);
+    return CFStringGetCharacterAtIndex(string_, anIndex);
+  }
+}
+
+// Override a couple of methods that typically want high performance.
+
+- (id)copyWithZone:(NSZone *)zone {
+  GPBStringInitStringValue(self);
+  return [(NSString *)string_ copyWithZone:zone];
+}
+
+- (id)mutableCopyWithZone:(NSZone *)zone {
+  GPBStringInitStringValue(self);
+  return [(NSString *)string_ mutableCopyWithZone:zone];
+}
+
+- (NSUInteger)hash {
+  // Must convert to string here to make sure that the hash is always
+  // consistent no matter what state the GPBString is in.
+  GPBStringInitStringValue(self);
+  return CFHash(string_);
+}
+
+- (BOOL)isEqual:(id)object {
+  if (self == object) {
+    return YES;
+  }
+  if ([object isKindOfClass:[NSString class]]) {
+    GPBStringInitStringValue(self);
+    return CFStringCompare(string_, (CFStringRef)object, 0) ==
+           kCFCompareEqualTo;
+  }
+  return NO;
+}
+
+- (void)getCharacters:(unichar *)buffer range:(NSRange)aRange {
+  OSSpinLockLock(&lock_);
+  if (is7BitAscii_ && utf8_) {
+    unsigned char *bytes = &(utf8_[aRange.location]);
+    for (NSUInteger i = 0; i < aRange.length; ++i) {
+      buffer[i] = bytes[i];
+    }
+    OSSpinLockUnlock(&lock_);
+  } else {
+    GPBStringInitStringValueAlreadyLocked(self);
+    OSSpinLockUnlock(&lock_);
+    CFStringGetCharacters(string_, CFRangeMake(aRange.location, aRange.length),
+                          buffer);
+  }
+}
+
+- (NSUInteger)lengthOfBytesUsingEncoding:(NSStringEncoding)encoding {
+  if ((encoding == NSUTF8StringEncoding) ||
+      (encoding == NSASCIIStringEncoding && is7BitAscii_)) {
+    return utf8Len_ - (hasBOM_ ? 3 : 0);
+  } else {
+    GPBStringInitStringValue(self);
+    return [(NSString *)string_ lengthOfBytesUsingEncoding:encoding];
+  }
+}
+
+- (BOOL)getBytes:(void *)buffer
+         maxLength:(NSUInteger)maxLength
+        usedLength:(NSUInteger *)usedLength
+          encoding:(NSStringEncoding)encoding
+           options:(NSStringEncodingConversionOptions)options
+             range:(NSRange)range
+    remainingRange:(NSRangePointer)remainingRange {
+  // [NSString getBytes:maxLength:usedLength:encoding:options:range:remainingRange]
+  // does not return reliable results if the maxLength argument is 0
+  // (Radar 16385183). Therefore we have special cased it as a slow case so
+  // that it behaves however Apple intends it to behave. It should be a rare
+  // case.
+  //
+  // [NSString getBytes:maxLength:usedLength:encoding:options:range:remainingRange]
+  // does not return reliable results if the range is outside of the strings
+  // length (Radar 16396177). Therefore we have special cased it as a slow
+  // case so that it behaves however Apple intends it to behave.  It should
+  // be a rare case.
+  //
+  // We can optimize the UTF8StringEncoding and NSASCIIStringEncoding with no
+  // options cases.
+  if ((options == 0) &&
+      (encoding == NSUTF8StringEncoding || encoding == NSASCIIStringEncoding) &&
+      (maxLength != 0) &&
+      (NSMaxRange(range) <= utf8Len_)) {
+    // Might be able to optimize it.
+    OSSpinLockLock(&lock_);
+    if (is7BitAscii_ && utf8_) {
+      NSUInteger length = range.length;
+      length = (length < maxLength) ? length : maxLength;
+      memcpy(buffer, utf8_ + range.location, length);
+      if (usedLength) {
+        *usedLength = length;
+      }
+      if (remainingRange) {
+        remainingRange->location = range.location + length;
+        remainingRange->length = range.length - length;
+      }
+      OSSpinLockUnlock(&lock_);
+      if (length > 0) {
+        return YES;
+      } else {
+        return NO;
+      }
+    } else {
+      GPBStringInitStringValueAlreadyLocked(self);
+      OSSpinLockUnlock(&lock_);
+    }
+  } else {
+    GPBStringInitStringValue(self);
+  }
+  return [(NSString *)string_ getBytes:buffer
+                             maxLength:maxLength
+                            usedLength:usedLength
+                              encoding:encoding
+                               options:options
+                                 range:range
+                        remainingRange:remainingRange];
+}
+
+@end