diff --git a/objectivec/GPBCodedInputStream.m b/objectivec/GPBCodedInputStream.m
new file mode 100644
index 0000000..fd87783
--- /dev/null
+++ b/objectivec/GPBCodedInputStream.m
@@ -0,0 +1,490 @@
+// 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 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 int8_t ReadRawByte(GPBCodedInputStreamState *state) {
+  CheckSize(state, sizeof(int8_t));
+  return ((int8_t *)state->bytes)[state->bufferPos++];
+}
+
+static 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 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 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 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 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 = [[NSString alloc] initWithBytes:&state->bytes[state->bufferPos]
+                                      length:size
+                                    encoding:NSUTF8StringEncoding];
+    if (!result) {
+      result = @"";
+#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
+    }
+    state->bufferPos += size;
+  }
+  return result;
+}
+
+NSData *GPBCodedInputStreamReadRetainedBytes(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 *GPBCodedInputStreamReadRetainedBytesNoCopy(
+    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) {
+  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 = state_.bufferSize;
+  }
+  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 *)readBytes {
+  return [GPBCodedInputStreamReadRetainedBytes(&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