[ObjC] Ensure `-[GPBMessage writeToOutputStream:]` still throws exception on flush failure

This restores the behavior of `-[GPBMessage writeToOutputStream:]` throwing an
exception if the underlying `GPBCodedOutputStream` failed to flush.

`GPBDictionary` and `GPBUnknownFieldSet` could also have theoretically thrown
exceptions from just about any method (although not for disk I/O reasons), so
this also restores that functionality by explicitly flushing before deallocating
the `GPBCodedOutputStream`.

PiperOrigin-RevId: 580207004

objectivec/GPBDictionary.m

@@ -1044,6 +1044,7 @@ void GPBDictionaryReadEntry(id mapDictionary, GPBCodedInputStream *stream,
 //%  GPBCodedOutputStream *outputStream = [[GPBCodedOutputStream alloc] initWithData:data];
 //%  WriteDict##KEY_NAME##Field(outputStream, key->value##KEY_NAME, kMapKeyFieldNumber, keyDataType);
 //%  WriteDictEnumField(outputStream, value, kMapValueFieldNumber, GPBDataTypeEnum);
+//%  [outputStream flush];
 //%  [outputStream release];
 //%  return data;
 //%}
@@ -2788,6 +2789,7 @@ void GPBDictionaryReadEntry(id mapDictionary, GPBCodedInputStream *stream,
   GPBCodedOutputStream *outputStream = [[GPBCodedOutputStream alloc] initWithData:data];
   WriteDictUInt32Field(outputStream, key->valueUInt32, kMapKeyFieldNumber, keyDataType);
   WriteDictEnumField(outputStream, value, kMapValueFieldNumber, GPBDataTypeEnum);
+  [outputStream flush];
   [outputStream release];
   return data;
 }
@@ -4518,6 +4520,7 @@ void GPBDictionaryReadEntry(id mapDictionary, GPBCodedInputStream *stream,
   GPBCodedOutputStream *outputStream = [[GPBCodedOutputStream alloc] initWithData:data];
   WriteDictInt32Field(outputStream, key->valueInt32, kMapKeyFieldNumber, keyDataType);
   WriteDictEnumField(outputStream, value, kMapValueFieldNumber, GPBDataTypeEnum);
+  [outputStream flush];
   [outputStream release];
   return data;
 }
@@ -6248,6 +6251,7 @@ void GPBDictionaryReadEntry(id mapDictionary, GPBCodedInputStream *stream,
   GPBCodedOutputStream *outputStream = [[GPBCodedOutputStream alloc] initWithData:data];
   WriteDictUInt64Field(outputStream, key->valueUInt64, kMapKeyFieldNumber, keyDataType);
   WriteDictEnumField(outputStream, value, kMapValueFieldNumber, GPBDataTypeEnum);
+  [outputStream flush];
   [outputStream release];
   return data;
 }
@@ -7978,6 +7982,7 @@ void GPBDictionaryReadEntry(id mapDictionary, GPBCodedInputStream *stream,
   GPBCodedOutputStream *outputStream = [[GPBCodedOutputStream alloc] initWithData:data];
   WriteDictInt64Field(outputStream, key->valueInt64, kMapKeyFieldNumber, keyDataType);
   WriteDictEnumField(outputStream, value, kMapValueFieldNumber, GPBDataTypeEnum);
+  [outputStream flush];
   [outputStream release];
   return data;
 }
@@ -9768,6 +9773,7 @@ void GPBDictionaryReadEntry(id mapDictionary, GPBCodedInputStream *stream,
   GPBCodedOutputStream *outputStream = [[GPBCodedOutputStream alloc] initWithData:data];
   WriteDictStringField(outputStream, key->valueString, kMapKeyFieldNumber, keyDataType);
   WriteDictEnumField(outputStream, value, kMapValueFieldNumber, GPBDataTypeEnum);
+  [outputStream flush];
   [outputStream release];
   return data;
 }
@@ -11741,6 +11747,7 @@ void GPBDictionaryReadEntry(id mapDictionary, GPBCodedInputStream *stream,
   GPBCodedOutputStream *outputStream = [[GPBCodedOutputStream alloc] initWithData:data];
   WriteDictBoolField(outputStream, key->valueBool, kMapKeyFieldNumber, keyDataType);
   WriteDictEnumField(outputStream, value, kMapValueFieldNumber, GPBDataTypeEnum);
+  [outputStream flush];
   [outputStream release];
   return data;
 }

objectivec/GPBMessage.m

@@ -1343,6 +1343,7 @@ static GPBUnknownFieldSet *GetOrMakeUnknownFields(GPBMessage *self) {
   GPBCodedOutputStream *stream = [[GPBCodedOutputStream alloc] initWithData:data];
   @try {
     [self writeToCodedOutputStream:stream];
+    [stream flush];
   } @catch (NSException *exception) {
     // This really shouldn't happen. Normally, this could mean there was a bug in the library and it
     // failed to match between computing the size and writing out the bytes. However, the more
@@ -1393,6 +1394,7 @@ static GPBUnknownFieldSet *GetOrMakeUnknownFields(GPBMessage *self) {
   GPBCodedOutputStream *stream = [[GPBCodedOutputStream alloc] initWithOutputStream:output];
   @try {
     [self writeToCodedOutputStream:stream];
+    [stream flush];
     size_t bytesWritten = [stream bytesWritten];
     if (bytesWritten > kMaximumMessageSize) {
       [NSException raise:GPBMessageExceptionMessageTooLarge
@@ -1436,6 +1438,7 @@ static GPBUnknownFieldSet *GetOrMakeUnknownFields(GPBMessage *self) {
   GPBCodedOutputStream *codedOutput = [[GPBCodedOutputStream alloc] initWithOutputStream:output];
   @try {
     [self writeDelimitedToCodedOutputStream:codedOutput];
+    [codedOutput flush];
   } @finally {
     [codedOutput release];
   }

objectivec/GPBUnknownFieldSet.m

@@ -207,6 +207,7 @@ static void GPBUnknownFieldSetSerializedSizeAsMessageSet(__unused const void *ke
   NSMutableData *data = [NSMutableData dataWithLength:self.serializedSize];
   GPBCodedOutputStream *output = [[GPBCodedOutputStream alloc] initWithData:data];
   [self writeToCodedOutputStream:output];
+  [output flush];
   [output release];
   return data;
 }

objectivec/Tests/GPBMessageTests.m

@@ -2225,4 +2225,17 @@
   XCTAssertNil(shouldGetAPrefixMessage);
 }
 
+- (void)testWriteToFullOutputStreamShouldThrow {
+  uint8_t buffer[1] = {0};
+
+  // Output stream which can write precisely 1 byte of data before it's full.
+  NSOutputStream *output = [[[NSOutputStream alloc] initToBuffer:buffer
+                                                        capacity:sizeof(buffer)] autorelease];
+
+  TestAllTypes *message = [TestAllTypes message];
+  [message setOptionalInt32:1];
+  XCTAssertThrowsSpecificNamed([message writeToOutputStream:output], NSException,
+                               GPBCodedOutputStreamException_WriteFailed);
+}
+
 @end