Are there C equivalents for the \'Delimited\' I/O functions (parseDelimitedFrom, mergeDelimitedFrom, and writeDelimitedTo) introduced in the Java API for Protocol Buffers v2.1.0? If not, h

Delimited I/O Functions for Protocol Buffers in C

Question:

The Java API for Protocol Buffers v2.1.0 introduced a set of "Delimited" I/O functions, including parseDelimitedFrom, mergeDelimitedFrom, and writeDelimitedTo. Do these functions have C equivalents? If not, how can message size prefixes be handled in C ?

Answer:

As of v3.3.0, Google has added delimited I/O functions to the C library in google/protobuf/util/delimited_message_util.h. However, there are alternative implementations that provide more optimizations and address potential pitfalls:

<code class="cpp">bool writeDelimitedTo(
    const google::protobuf::MessageLite&amp; message,
    google::protobuf::io::ZeroCopyOutputStream* rawOutput) {
  // Create a new coded stream for each message.
  google::protobuf::io::CodedOutputStream output(rawOutput);

  // Write the size.
  int size = message.ByteSize();
  output.WriteVarint32(size);

  // Optimize for messages that fit in a single buffer.
  uint8_t* buffer = output.GetDirectBufferForNBytesAndAdvance(size);
  if (buffer != NULL) {
    message.SerializeWithCachedSizesToArray(buffer);
    return true;
  }

  // Slower path for messages that span multiple buffers.
  message.SerializeWithCachedSizes(&amp;output);
  return !output.HadError();
}

bool readDelimitedFrom(
    google::protobuf::io::ZeroCopyInputStream* rawInput,
    google::protobuf::MessageLite* message) {
  // Create a new coded stream for each message.
  google::protobuf::io::CodedInputStream input(rawInput);

  // Read the size.
  uint32_t size;
  if (!input.ReadVarint32(&amp;size)) return false;

  // Limit the stream to the message size.
  google::protobuf::io::CodedInputStream::Limit limit = input.PushLimit(size);

  // Parse the message.
  if (!message->MergeFromCodedStream(&amp;input)) return false;
  if (!input.ConsumedEntireMessage()) return false;

  // Release the limit.
  input.PopLimit(limit);

  return true;
}</code>

These implementations ensure proper handling of messages with sizes exceeding 64MB, while still enforcing a 64MB limit on individual messages.

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