CODEWITHSUNDEEP
javaconstructorbyteprotocol-buffers
Nikolay Kuznetsov
Nikolay Kuznetsov

Reputation: 9579

java protobuf how to create ByteString from int

I would like to use google protobuf in my project.

The point is that I have to set first byte of very message because of underlying code which rejects or accepts the message based on the first byte and it does not know about protobuf.

So this page says https://developers.google.com/protocol-buffers/docs/proto#scalar that I have to use bytes field that corresponds to ByteString in Java.

bytes May contain any arbitrary sequence of bytes. string ByteString

But I do not know how to create ByteString from int value. I have tried this way:

ByteBuffer eventTypeBuffer = ByteBuffer.allocate(1);
eventTypeBuffer.put(0x1c);
ByteString eventType = ByteString.copyFrom(eventTypeBuffer);
System.out.println(eventType.size() + " " + eventTypeBuffer.array().length);

Header.Builder mh = Header.newBuilder();
mh.setEventType(eventType);

Does not work properly and println gives 0 1

Upvotes: 3

Views: 15288

Answers (3)

nes1983
nes1983

Reputation: 15756

Using Guava:

ByteString byteStringFromInt(int in) {
  return ByteString.copyFrom(Ints.toByteArray(in));
}

Upvotes: 0

Konstantin Alexandrov
Konstantin Alexandrov

Reputation: 91

ByteBuffer eventTypeBuffer = ByteBuffer.allocate(1);
eventTypeBuffer.put(0x1c);
eventTypeBuffer.flip();
ByteString eventType = ByteString.copyFrom(eventTypeBuffer);
System.out.println(eventType.size() + " " + eventTypeBuffer.array().length);

Header.Builder mh = Header.newBuilder();
mh.setEventType(eventType);

Upvotes: 4

FirstName LastName
FirstName LastName

Reputation: 1911

Consider protobuf message to be a 'black-box' string of bytes. Get the protobuf message out after reading the first byte and then handle the protobuf part.

Create a byte buffer

Byte[] buf = new Byte[100]; //length as per your application

Then give the first byte as per your application (which rejects or accepts messages depending upon the first byte). The rest of the bytes you can fill with the protobuf message.

Upvotes: 3

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