[ObjC] Parsing helper and tests around unknown fields.

Make a new internal api for collecting up the unknown group fields
that will be used in a future change.

Add testing for the new api and for unknown field parsing of groups in
general.

PiperOrigin-RevId: 654875605

objectivec/GPBCodedInputStream.m

@@ -267,6 +267,60 @@ NSData *GPBCodedInputStreamReadRetainedBytesNoCopy(GPBCodedInputStreamState *sta
   return result;
 }
 
+static void SkipToEndGroupInternal(GPBCodedInputStreamState *state, uint32_t endGroupTag) {
+  CheckRecursionLimit(state);
+  ++state->recursionDepth;
+  while (YES) {
+    uint32_t tag = GPBCodedInputStreamReadTag(state);
+    if (tag == endGroupTag || tag == 0) {
+      GPBCodedInputStreamCheckLastTagWas(state, endGroupTag);  // Will fail for end of input.
+      --state->recursionDepth;
+      return;
+    }
+    switch (GPBWireFormatGetTagWireType(tag)) {
+      case GPBWireFormatVarint:
+        (void)ReadRawVarint64(state);
+        break;
+      case GPBWireFormatFixed64:
+        SkipRawData(state, sizeof(uint64_t));
+        break;
+      case GPBWireFormatLengthDelimited: {
+        uint64_t size = ReadRawVarint64(state);
+        CheckFieldSize(size);
+        size_t size2 = (size_t)size;  // Cast safe on 32bit because of CheckFieldSize() above.
+        SkipRawData(state, size2);
+        break;
+      }
+      case GPBWireFormatStartGroup:
+        SkipToEndGroupInternal(state, GPBWireFormatMakeTag(GPBWireFormatGetTagFieldNumber(tag),
+                                                           GPBWireFormatEndGroup));
+        break;
+      case GPBWireFormatEndGroup:
+        GPBRaiseStreamError(GPBCodedInputStreamErrorInvalidTag, @"Unmatched end group");
+        break;
+      case GPBWireFormatFixed32:
+        SkipRawData(state, sizeof(uint32_t));
+        break;
+    }
+  }
+}
+
+// This doesn't include the start group, but it collects all bytes until the end group including
+// the end group tag.
+NSData *GPBCodedInputStreamReadRetainedBytesToEndGroupNoCopy(GPBCodedInputStreamState *state,
+                                                             int32_t fieldNumber) {
+  // Better have just read the start of the group.
+  GPBCodedInputStreamCheckLastTagWas(state,
+                                     GPBWireFormatMakeTag(fieldNumber, GPBWireFormatStartGroup));
+  const uint8_t *start = state->bytes + state->bufferPos;
+  SkipToEndGroupInternal(state, GPBWireFormatMakeTag(fieldNumber, GPBWireFormatEndGroup));
+  // This will be after the end group tag.
+  const uint8_t *end = state->bytes + state->bufferPos;
+  return [[NSData alloc] initWithBytesNoCopy:(void *)start
+                                      length:(NSUInteger)(end - start)
+                                freeWhenDone:NO];
+}
+
 size_t GPBCodedInputStreamPushLimit(GPBCodedInputStreamState *state, size_t byteLimit) {
   byteLimit += state->bufferPos;
   size_t oldLimit = state->currentLimit;

objectivec/GPBCodedInputStream_PackagePrivate.h

@@ -76,6 +76,9 @@ NSData *GPBCodedInputStreamReadRetainedBytes(GPBCodedInputStreamState *state)
     __attribute((ns_returns_retained));
 NSData *GPBCodedInputStreamReadRetainedBytesNoCopy(GPBCodedInputStreamState *state)
     __attribute((ns_returns_retained));
+NSData *GPBCodedInputStreamReadRetainedBytesToEndGroupNoCopy(GPBCodedInputStreamState *state,
+                                                             int32_t fieldNumber)
+    __attribute((ns_returns_retained));
 
 size_t GPBCodedInputStreamPushLimit(GPBCodedInputStreamState *state, size_t byteLimit);
 void GPBCodedInputStreamPopLimit(GPBCodedInputStreamState *state, size_t oldLimit);

objectivec/Tests/GPBCodedInputStreamTests.m

@@ -6,12 +6,14 @@
 // https://developers.google.com/open-source/licenses/bsd
 
 #import <Foundation/Foundation.h>
-#import "GPBTestUtilities.h"
 
 #import "GPBCodedInputStream.h"
+#import "GPBCodedInputStream_PackagePrivate.h"
 #import "GPBCodedOutputStream.h"
+#import "GPBTestUtilities.h"
 #import "GPBUnknownFieldSet_PackagePrivate.h"
 #import "GPBUtilities_PackagePrivate.h"
+#import "GPBWireFormat.h"
 #import "objectivec/Tests/Unittest.pbobjc.h"
 
 @interface CodedInputStreamTests : GPBTestCase
@@ -444,4 +446,102 @@
   }
 }
 
+- (void)assertReadByteToEndGroupFails:(NSData*)data {
+  GPBCodedInputStream* input = [GPBCodedInputStream streamWithData:data];
+  uint32_t tag = [input readTag];
+  XCTAssertThrows(GPBCodedInputStreamReadRetainedBytesToEndGroupNoCopy(
+      &input->state_, GPBWireFormatGetTagFieldNumber(tag)));
+}
+
+- (void)assertReadByteToEndGroup:(NSData*)data value:(NSData*)value {
+  GPBCodedInputStream* input = [GPBCodedInputStream streamWithData:data];
+  uint32_t tag = [input readTag];
+  NSData* readValue = GPBCodedInputStreamReadRetainedBytesToEndGroupNoCopy(
+      &input->state_, GPBWireFormatGetTagFieldNumber(tag));
+  XCTAssertNotNil(readValue);
+  XCTAssertEqualObjects(readValue, value);
+  [readValue release];
+}
+
+static NSData* DataForGroupsOfDepth(NSUInteger depth) {
+  NSMutableData* data = [NSMutableData dataWithCapacity:0];
+
+  uint32_t byte = 35;  // 35 = 0b100011 -> field 4/start group
+  for (NSUInteger i = 0; i < depth; ++i) {
+    [data appendBytes:&byte length:1];
+  }
+
+  byte = 8;  // 8 = 0b1000, -> field 1/varint
+  [data appendBytes:&byte length:1];
+  byte = 1;  // 1 -> varint value of 1
+  [data appendBytes:&byte length:1];
+
+  byte = 36;  // 36 = 0b100100 -> field 4/end group
+  for (NSUInteger i = 0; i < depth; ++i) {
+    [data appendBytes:&byte length:1];
+  }
+  return data;
+}
+
+- (void)testBytesToEndGroup {
+  // 35 = 0b100011 -> field 4/start group
+  // 36 = 0b100100 -> field 4/end group
+  // 43 = 0b101011 -> field 5/end group
+  // 44 = 0b101100 -> field 5/end group
+  // 8 = 0b1000, 1 -> field 1/varint, value of 1
+  // 21 = 0b10101, 0x78, 0x56, 0x34, 0x12 -> field 2/fixed32, value of 0x12345678
+  // 25 = 0b11001, 0xf0, 0xde, 0xbc, 0x9a, 0x78, 0x56, 0x34, 0x12 -> field 3/fixed64,
+  //                                                                 value of 0x123456789abcdef0LL
+  // 50 = 0b110010, 0x0 -> field 6/length delimited, length 0
+  // 50 = 0b110010, 0x1, 42 -> field 6/length delimited, length 1, byte 42
+  // 0 -> field 0 which is invalid/varint
+  // 15 = 0b1111 -> field 1, wire type 7 which is invalid
+
+  [self assertReadByteToEndGroup:bytes(35, 36) value:bytes(36)];              // empty group
+  [self assertReadByteToEndGroup:bytes(35, 8, 1, 36) value:bytes(8, 1, 36)];  // varint
+  [self assertReadByteToEndGroup:bytes(35, 21, 0x78, 0x56, 0x34, 0x12, 36)    // fixed32
+                           value:bytes(21, 0x78, 0x56, 0x34, 0x12, 36)];
+  [self assertReadByteToEndGroup:bytes(35, 25, 0xf0, 0xde, 0xbc, 0x9a, 0x78, 0x56, 0x34, 0x12,
+                                       36)  // fixed64
+                           value:bytes(25, 0xf0, 0xde, 0xbc, 0x9a, 0x78, 0x56, 0x34, 0x12, 36)];
+  [self assertReadByteToEndGroup:bytes(35, 50, 0, 36)
+                           value:bytes(50, 0, 36)];  // length delimited, length 0
+  [self assertReadByteToEndGroup:bytes(35, 50, 1, 42, 36)
+                           value:bytes(50, 1, 42, 36)];  // length delimited, length 1, byte 42
+  [self assertReadByteToEndGroup:bytes(35, 43, 44, 36) value:bytes(43, 44, 36)];  // Sub group
+  [self assertReadByteToEndGroup:bytes(35, 8, 1, 43, 8, 1, 44,
+                                       36)  // varint and sub group with varint
+                           value:bytes(8, 1, 43, 8, 1, 44, 36)];
+
+  [self assertReadByteToEndGroupFails:bytes(35, 0, 36)];                 // Invalid field number
+  [self assertReadByteToEndGroupFails:bytes(35, 15, 36)];                // Invalid wire type
+  [self assertReadByteToEndGroupFails:bytes(35, 21, 0x78, 0x56, 0x34)];  // truncated fixed32
+  [self assertReadByteToEndGroupFails:bytes(35, 25, 0xf0, 0xde, 0xbc, 0x9a, 0x78, 0x56,
+                                            0x34)];  // truncated fixed64
+
+  // Mising end group
+  [self assertReadByteToEndGroupFails:bytes(35)];
+  [self assertReadByteToEndGroupFails:bytes(35, 8, 1)];
+  [self assertReadByteToEndGroupFails:bytes(35, 43)];
+  [self assertReadByteToEndGroupFails:bytes(35, 43, 8, 1)];
+
+  // Wrong end group
+  [self assertReadByteToEndGroupFails:bytes(35, 44)];
+  [self assertReadByteToEndGroupFails:bytes(35, 8, 1, 44)];
+  [self assertReadByteToEndGroupFails:bytes(35, 43, 36)];
+  [self assertReadByteToEndGroupFails:bytes(35, 43, 8, 1, 36)];
+  [self assertReadByteToEndGroupFails:bytes(35, 43, 44, 44)];
+  [self assertReadByteToEndGroupFails:bytes(35, 43, 8, 1, 44, 44)];
+
+  // This is the same limit as within GPBCodedInputStream.
+  const NSUInteger kDefaultRecursionLimit = 100;
+  // That depth parses.
+  NSData* testData = DataForGroupsOfDepth(kDefaultRecursionLimit);
+  [self assertReadByteToEndGroup:testData
+                           value:[testData subdataWithRange:NSMakeRange(1, testData.length - 1)]];
+  // One more level deep fails.
+  testData = DataForGroupsOfDepth(kDefaultRecursionLimit + 1);
+  [self assertReadByteToEndGroupFails:testData];
+}
+
 @end

objectivec/Tests/GPBUnknownFieldSetTest.m

@@ -6,6 +6,7 @@
 // https://developers.google.com/open-source/licenses/bsd
 
 #import "GPBTestUtilities.h"
+#import "GPBUnknownFieldSet.h"
 
 #import "GPBUnknownFieldSet_PackagePrivate.h"
 #import "GPBUnknownField_PackagePrivate.h"
@@ -376,6 +377,180 @@
   XCTAssertEqual(0x7FFFFFFFFFFFFFFFULL, [field2.varintList valueAtIndex:0]);
 }
 
+static NSData* DataForGroupsOfDepth(NSUInteger depth) {
+  NSMutableData* data = [NSMutableData dataWithCapacity:0];
+
+  uint32_t byte = 35;  // 35 = 0b100011 -> field 4/start group
+  for (NSUInteger i = 0; i < depth; ++i) {
+    [data appendBytes:&byte length:1];
+  }
+
+  byte = 8;  // 8 = 0b1000, -> field 1/varint
+  [data appendBytes:&byte length:1];
+  byte = 1;  // 1 -> varint value of 1
+  [data appendBytes:&byte length:1];
+
+  byte = 36;  // 36 = 0b100100 -> field 4/end group
+  for (NSUInteger i = 0; i < depth; ++i) {
+    [data appendBytes:&byte length:1];
+  }
+  return data;
+}
+
+- (void)testParsingNestingGroupData {
+  // 35 = 0b100011 -> field 4/start group
+  // 36 = 0b100100 -> field 4/end group
+  // 43 = 0b101011 -> field 5/end group
+  // 44 = 0b101100 -> field 5/end group
+  // 8 = 0b1000, 1 -> field 1/varint, value of 1
+  // 21 = 0b10101, 0x78, 0x56, 0x34, 0x12 -> field 2/fixed32, value of 0x12345678
+  // 25 = 0b11001, 0xf0, 0xde, 0xbc, 0x9a, 0x78, 0x56, 0x34, 0x12 -> field 3/fixed64,
+  //                                                                 value of 0x123456789abcdef0LL
+  // 50 = 0b110010, 0x0 -> field 6/length delimited, length 0
+  // 50 = 0b110010, 0x1, 42 -> field 6/length delimited, length 1, byte 42
+  // 0 -> field 0 which is invalid/varint
+  // 15 = 0b1111 -> field 1, wire type 7 which is invalid
+
+  TestEmptyMessage* m = [TestEmptyMessage parseFromData:DataFromBytes(35, 36)
+                                                  error:NULL];  // empty group
+  XCTAssertEqual(m.unknownFields.countOfFields, (NSUInteger)1);
+  GPBUnknownField* field = [m.unknownFields getField:4];
+  XCTAssertEqual(field.groupList.count, (NSUInteger)1);
+  GPBUnknownFieldSet* group = field.groupList[0];
+  XCTAssertEqual(group.countOfFields, (NSUInteger)0);
+
+  m = [TestEmptyMessage parseFromData:DataFromBytes(35, 8, 1, 36) error:NULL];  // varint
+  XCTAssertEqual(m.unknownFields.countOfFields, (NSUInteger)1);
+  field = [m.unknownFields getField:4];
+  XCTAssertEqual(field.groupList.count, (NSUInteger)1);
+  group = field.groupList[0];
+  field = [group getField:1];
+  XCTAssertEqual(field.varintList.count, (NSUInteger)1);
+  XCTAssertEqual([field.varintList valueAtIndex:0], 1);
+
+  m = [TestEmptyMessage parseFromData:DataFromBytes(35, 21, 0x78, 0x56, 0x34, 0x12, 36)
+                                error:NULL];  // fixed32
+  XCTAssertEqual(m.unknownFields.countOfFields, (NSUInteger)1);
+  field = [m.unknownFields getField:4];
+  XCTAssertEqual(field.groupList.count, (NSUInteger)1);
+  group = field.groupList[0];
+  field = [group getField:2];
+  XCTAssertEqual(field.fixed32List.count, (NSUInteger)1);
+  XCTAssertEqual([field.fixed32List valueAtIndex:0], 0x12345678);
+
+  m = [TestEmptyMessage
+      parseFromData:DataFromBytes(35, 25, 0xf0, 0xde, 0xbc, 0x9a, 0x78, 0x56, 0x34, 0x12,
+                                  36)
+              error:NULL];  // fixed64
+  XCTAssertEqual(m.unknownFields.countOfFields, (NSUInteger)1);
+  field = [m.unknownFields getField:4];
+  XCTAssertEqual(field.groupList.count, (NSUInteger)1);
+  group = field.groupList[0];
+  field = [group getField:3];
+  XCTAssertEqual(field.fixed64List.count, (NSUInteger)1);
+  XCTAssertEqual([field.fixed64List valueAtIndex:0], 0x123456789abcdef0LL);
+
+  m = [TestEmptyMessage parseFromData:DataFromBytes(35, 50, 0, 36)
+                                error:NULL];  // length delimited, length 0
+  XCTAssertEqual(m.unknownFields.countOfFields, (NSUInteger)1);
+  field = [m.unknownFields getField:4];
+  XCTAssertEqual(field.groupList.count, (NSUInteger)1);
+  group = field.groupList[0];
+  field = [group getField:6];
+  XCTAssertEqual(field.lengthDelimitedList.count, (NSUInteger)1);
+  XCTAssertEqualObjects(field.lengthDelimitedList[0], [NSData data]);
+
+  m = [TestEmptyMessage parseFromData:DataFromBytes(35, 50, 1, 42, 36)
+                                error:NULL];  // length delimited, length 1, byte 42
+  XCTAssertEqual(m.unknownFields.countOfFields, (NSUInteger)1);
+  field = [m.unknownFields getField:4];
+  XCTAssertEqual(field.groupList.count, (NSUInteger)1);
+  group = field.groupList[0];
+  field = [group getField:6];
+  XCTAssertEqual(field.lengthDelimitedList.count, (NSUInteger)1);
+  XCTAssertEqualObjects(field.lengthDelimitedList[0], DataFromBytes(42));
+
+  m = [TestEmptyMessage parseFromData:DataFromBytes(35, 43, 44, 36) error:NULL];  // Sub group
+  field = [m.unknownFields getField:4];
+  XCTAssertEqual(field.groupList.count, (NSUInteger)1);
+  group = field.groupList[0];
+  XCTAssertEqual(group.countOfFields, (NSUInteger)1);
+  field = [group getField:5];
+  XCTAssertEqual(field.groupList.count, (NSUInteger)1);
+  group = field.groupList[0];
+  XCTAssertEqual(group.countOfFields, (NSUInteger)0);
+
+  m = [TestEmptyMessage parseFromData:DataFromBytes(35, 8, 1, 43, 8, 2, 44, 36)
+                                error:NULL];  // varint and sub group with varint
+  XCTAssertEqual(m.unknownFields.countOfFields, (NSUInteger)1);
+  field = [m.unknownFields getField:4];
+  XCTAssertEqual(field.groupList.count, (NSUInteger)1);
+  group = field.groupList[0];
+  XCTAssertEqual(group.countOfFields, (NSUInteger)2);
+  field = [group getField:1];
+  XCTAssertEqual(field.varintList.count, (NSUInteger)1);
+  XCTAssertEqual([field.varintList valueAtIndex:0], 1);
+  field = [group getField:5];
+  XCTAssertEqual(field.groupList.count, (NSUInteger)1);
+  group = field.groupList[0];
+  field = [group getField:1];
+  XCTAssertEqual(field.varintList.count, (NSUInteger)1);
+  XCTAssertEqual([field.varintList valueAtIndex:0], 2);
+
+  XCTAssertNil([TestEmptyMessage parseFromData:DataFromBytes(35, 0, 36)
+                                         error:NULL]);  // Invalid field number
+  XCTAssertNil([TestEmptyMessage parseFromData:DataFromBytes(35, 15, 36)
+                                         error:NULL]);  // Invalid wire type
+  XCTAssertNil([TestEmptyMessage parseFromData:DataFromBytes(35, 21, 0x78, 0x56, 0x34)
+                                         error:NULL]);  // truncated fixed32
+  XCTAssertNil([TestEmptyMessage
+      parseFromData:DataFromBytes(35, 25, 0xf0, 0xde, 0xbc, 0x9a, 0x78, 0x56,
+                                  0x34)
+              error:NULL]);  // truncated fixed64
+
+  // Mising end group
+  XCTAssertNil([TestEmptyMessage parseFromData:DataFromBytes(35) error:NULL]);
+  XCTAssertNil([TestEmptyMessage parseFromData:DataFromBytes(35, 8, 1) error:NULL]);
+  XCTAssertNil([TestEmptyMessage parseFromData:DataFromBytes(35, 43) error:NULL]);
+  XCTAssertNil([TestEmptyMessage parseFromData:DataFromBytes(35, 43, 8, 1) error:NULL]);
+
+  // Wrong end group
+  XCTAssertNil([TestEmptyMessage parseFromData:DataFromBytes(35, 44) error:NULL]);
+  XCTAssertNil([TestEmptyMessage parseFromData:DataFromBytes(35, 8, 1, 44) error:NULL]);
+  XCTAssertNil([TestEmptyMessage parseFromData:DataFromBytes(35, 43, 36) error:NULL]);
+  XCTAssertNil([TestEmptyMessage parseFromData:DataFromBytes(35, 43, 8, 1, 36) error:NULL]);
+  XCTAssertNil([TestEmptyMessage parseFromData:DataFromBytes(35, 43, 44, 44) error:NULL]);
+  XCTAssertNil([TestEmptyMessage parseFromData:DataFromBytes(35, 43, 8, 1, 44, 44) error:NULL]);
+
+  // This is the same limit as within GPBCodedInputStream.
+  const NSUInteger kDefaultRecursionLimit = 100;
+  // That depth parses.
+  NSData* testData = DataForGroupsOfDepth(kDefaultRecursionLimit);
+  m = [TestEmptyMessage parseFromData:testData error:NULL];
+  XCTAssertEqual(m.unknownFields.countOfFields, (NSUInteger)1);
+  field = [m.unknownFields getField:4];
+  for (NSUInteger i = 0; i < kDefaultRecursionLimit; ++i) {
+    XCTAssertEqual(field.varintList.count, (NSUInteger)0);
+    XCTAssertEqual(field.fixed32List.count, (NSUInteger)0);
+    XCTAssertEqual(field.fixed64List.count, (NSUInteger)0);
+    XCTAssertEqual(field.lengthDelimitedList.count, (NSUInteger)0);
+    XCTAssertEqual(field.groupList.count, (NSUInteger)1);
+    group = field.groupList[0];
+    XCTAssertEqual(group.countOfFields, (NSUInteger)1);
+    field = [group getField:(i < (kDefaultRecursionLimit - 1) ? 4 : 1)];
+  }
+  // field is of the inner most group
+  XCTAssertEqual(field.varintList.count, (NSUInteger)1);
+  XCTAssertEqual([field.varintList valueAtIndex:0], (NSUInteger)1);
+  XCTAssertEqual(field.fixed32List.count, (NSUInteger)0);
+  XCTAssertEqual(field.fixed64List.count, (NSUInteger)0);
+  XCTAssertEqual(field.lengthDelimitedList.count, (NSUInteger)0);
+  XCTAssertEqual(field.groupList.count, (NSUInteger)0);
+  // One more level deep fails.
+  testData = DataForGroupsOfDepth(kDefaultRecursionLimit + 1);
+  XCTAssertNil([TestEmptyMessage parseFromData:testData error:NULL]);
+}
+
 #pragma mark - Field tests
 // Some tests directly on fields since the dictionary in FieldSet can gate
 // testing some of these.

objectivec/Tests/GPBUnknownFieldsTest.m

@@ -847,4 +847,164 @@
   XCTAssertEqual(varint, 0x7FFFFFFFFFFFFFFFL);
 }
 
+static NSData* DataForGroupsOfDepth(NSUInteger depth) {
+  NSMutableData* data = [NSMutableData dataWithCapacity:0];
+
+  uint32_t byte = 35;  // 35 = 0b100011 -> field 4/start group
+  for (NSUInteger i = 0; i < depth; ++i) {
+    [data appendBytes:&byte length:1];
+  }
+
+  byte = 8;  // 8 = 0b1000, -> field 1/varint
+  [data appendBytes:&byte length:1];
+  byte = 1;  // 1 -> varint value of 1
+  [data appendBytes:&byte length:1];
+
+  byte = 36;  // 36 = 0b100100 -> field 4/end group
+  for (NSUInteger i = 0; i < depth; ++i) {
+    [data appendBytes:&byte length:1];
+  }
+  return data;
+}
+
+- (void)testParsingNestingGroupData {
+  // 35 = 0b100011 -> field 4/start group
+  // 36 = 0b100100 -> field 4/end group
+  // 43 = 0b101011 -> field 5/end group
+  // 44 = 0b101100 -> field 5/end group
+  // 8 = 0b1000, 1 -> field 1/varint, value of 1
+  // 21 = 0b10101, 0x78, 0x56, 0x34, 0x12 -> field 2/fixed32, value of 0x12345678
+  // 25 = 0b11001, 0xf0, 0xde, 0xbc, 0x9a, 0x78, 0x56, 0x34, 0x12 -> field 3/fixed64,
+  //                                                                 value of 0x123456789abcdef0LL
+  // 50 = 0b110010, 0x0 -> field 6/length delimited, length 0
+  // 50 = 0b110010, 0x1, 42 -> field 6/length delimited, length 1, byte 42
+  // 0 -> field 0 which is invalid/varint
+  // 15 = 0b1111 -> field 1, wire type 7 which is invalid
+
+  TestEmptyMessage* m = [TestEmptyMessage parseFromData:DataFromBytes(35, 36)
+                                                  error:NULL];  // empty group
+  GPBUnknownFields* ufs = [[[GPBUnknownFields alloc] initFromMessage:m] autorelease];
+  XCTAssertEqual(ufs.count, (NSUInteger)1);
+  GPBUnknownFields* group = [ufs firstGroup:4];
+  XCTAssertTrue(group.empty);
+
+  m = [TestEmptyMessage parseFromData:DataFromBytes(35, 8, 1, 36) error:NULL];  // varint
+  ufs = [[[GPBUnknownFields alloc] initFromMessage:m] autorelease];
+  XCTAssertEqual(ufs.count, (NSUInteger)1);
+  group = [ufs firstGroup:4];
+  XCTAssertEqual(group.count, (NSUInteger)1);
+  uint64_t varint = 0;
+  XCTAssertTrue([group getFirst:1 varint:&varint]);
+  XCTAssertEqual(varint, 1);
+
+  m = [TestEmptyMessage parseFromData:DataFromBytes(35, 21, 0x78, 0x56, 0x34, 0x12, 36)
+                                error:NULL];  // fixed32
+  ufs = [[[GPBUnknownFields alloc] initFromMessage:m] autorelease];
+  XCTAssertEqual(ufs.count, (NSUInteger)1);
+  group = [ufs firstGroup:4];
+  XCTAssertEqual(group.count, (NSUInteger)1);
+  uint32_t fixed32 = 0;
+  XCTAssertTrue([group getFirst:2 fixed32:&fixed32]);
+  XCTAssertEqual(fixed32, 0x12345678);
+
+  m = [TestEmptyMessage
+      parseFromData:DataFromBytes(35, 25, 0xf0, 0xde, 0xbc, 0x9a, 0x78, 0x56, 0x34, 0x12,
+                                  36)
+              error:NULL];  // fixed64
+  ufs = [[[GPBUnknownFields alloc] initFromMessage:m] autorelease];
+  XCTAssertEqual(ufs.count, (NSUInteger)1);
+  group = [ufs firstGroup:4];
+  XCTAssertEqual(group.count, (NSUInteger)1);
+  uint64_t fixed64 = 0;
+  XCTAssertTrue([group getFirst:3 fixed64:&fixed64]);
+  XCTAssertEqual(fixed64, 0x123456789abcdef0LL);
+  XCTAssertEqual(m.unknownFields.countOfFields, (NSUInteger)1);
+
+  m = [TestEmptyMessage parseFromData:DataFromBytes(35, 50, 0, 36)
+                                error:NULL];  // length delimited, length 0
+  ufs = [[[GPBUnknownFields alloc] initFromMessage:m] autorelease];
+  XCTAssertEqual(ufs.count, (NSUInteger)1);
+  group = [ufs firstGroup:4];
+  XCTAssertEqual(group.count, (NSUInteger)1);
+  NSData* lengthDelimited = [group firstLengthDelimited:6];
+  XCTAssertEqualObjects(lengthDelimited, [NSData data]);
+
+  m = [TestEmptyMessage parseFromData:DataFromBytes(35, 50, 1, 42, 36)
+                                error:NULL];  // length delimited, length 1, byte 42
+  ufs = [[[GPBUnknownFields alloc] initFromMessage:m] autorelease];
+  XCTAssertEqual(ufs.count, (NSUInteger)1);
+  group = [ufs firstGroup:4];
+  XCTAssertEqual(group.count, (NSUInteger)1);
+  lengthDelimited = [group firstLengthDelimited:6];
+  XCTAssertEqualObjects(lengthDelimited, DataFromBytes(42));
+
+  m = [TestEmptyMessage parseFromData:DataFromBytes(35, 43, 44, 36) error:NULL];  // Sub group
+  ufs = [[[GPBUnknownFields alloc] initFromMessage:m] autorelease];
+  XCTAssertEqual(ufs.count, (NSUInteger)1);
+  group = [ufs firstGroup:4];
+  XCTAssertEqual(group.count, (NSUInteger)1);
+  group = [group firstGroup:5];
+  XCTAssertTrue(group.empty);
+
+  m = [TestEmptyMessage parseFromData:DataFromBytes(35, 8, 1, 43, 8, 2, 44, 36)
+                                error:NULL];  // varint and sub group with varint
+  ufs = [[[GPBUnknownFields alloc] initFromMessage:m] autorelease];
+  XCTAssertEqual(ufs.count, (NSUInteger)1);
+  group = [ufs firstGroup:4];
+  XCTAssertEqual(group.count, (NSUInteger)2);
+  varint = 0;
+  XCTAssertTrue([group getFirst:1 varint:&varint]);
+  XCTAssertEqual(varint, 1);
+  group = [group firstGroup:5];
+  XCTAssertEqual(group.count, (NSUInteger)1);
+  XCTAssertTrue([group getFirst:1 varint:&varint]);
+  XCTAssertEqual(varint, 2);
+
+  XCTAssertNil([TestEmptyMessage parseFromData:DataFromBytes(35, 0, 36)
+                                         error:NULL]);  // Invalid field number
+  XCTAssertNil([TestEmptyMessage parseFromData:DataFromBytes(35, 15, 36)
+                                         error:NULL]);  // Invalid wire type
+  XCTAssertNil([TestEmptyMessage parseFromData:DataFromBytes(35, 21, 0x78, 0x56, 0x34)
+                                         error:NULL]);  // truncated fixed32
+  XCTAssertNil([TestEmptyMessage
+      parseFromData:DataFromBytes(35, 25, 0xf0, 0xde, 0xbc, 0x9a, 0x78, 0x56,
+                                  0x34)
+              error:NULL]);  // truncated fixed64
+
+  // Mising end group
+  XCTAssertNil([TestEmptyMessage parseFromData:DataFromBytes(35) error:NULL]);
+  XCTAssertNil([TestEmptyMessage parseFromData:DataFromBytes(35, 8, 1) error:NULL]);
+  XCTAssertNil([TestEmptyMessage parseFromData:DataFromBytes(35, 43) error:NULL]);
+  XCTAssertNil([TestEmptyMessage parseFromData:DataFromBytes(35, 43, 8, 1) error:NULL]);
+
+  // Wrong end group
+  XCTAssertNil([TestEmptyMessage parseFromData:DataFromBytes(35, 44) error:NULL]);
+  XCTAssertNil([TestEmptyMessage parseFromData:DataFromBytes(35, 8, 1, 44) error:NULL]);
+  XCTAssertNil([TestEmptyMessage parseFromData:DataFromBytes(35, 43, 36) error:NULL]);
+  XCTAssertNil([TestEmptyMessage parseFromData:DataFromBytes(35, 43, 8, 1, 36) error:NULL]);
+  XCTAssertNil([TestEmptyMessage parseFromData:DataFromBytes(35, 43, 44, 44) error:NULL]);
+  XCTAssertNil([TestEmptyMessage parseFromData:DataFromBytes(35, 43, 8, 1, 44, 44) error:NULL]);
+
+  // This is the same limit as within GPBCodedInputStream.
+  const NSUInteger kDefaultRecursionLimit = 100;
+  // That depth parses.
+  NSData* testData = DataForGroupsOfDepth(kDefaultRecursionLimit);
+  m = [TestEmptyMessage parseFromData:testData error:NULL];
+  ufs = [[[GPBUnknownFields alloc] initFromMessage:m] autorelease];
+  XCTAssertEqual(ufs.count, (NSUInteger)1);
+  group = [ufs firstGroup:4];
+  for (NSUInteger i = 1; i < kDefaultRecursionLimit; ++i) {
+    XCTAssertEqual(group.count, (NSUInteger)1);
+    group = [group firstGroup:4];
+  }
+  // group is now the inner most group.
+  XCTAssertEqual(group.count, (NSUInteger)1);
+  varint = 0;
+  XCTAssertTrue([group getFirst:1 varint:&varint]);
+  XCTAssertEqual(varint, 1);
+  // One more level deep fails.
+  testData = DataForGroupsOfDepth(kDefaultRecursionLimit + 1);
+  XCTAssertNil([TestEmptyMessage parseFromData:testData error:NULL]);
+}
+
 @end