Protocol Buffers

A few days ago Protocol Buffers was released by Google as an open source project. Protocol Buffers is a way to generate code for objects that can be serialized to and de-serialized from the protocol buffers binary format. An implementation of the protocol buffers compiler which reads a "proto" and can output Java, Python, and C++ code. Because the format is a binary format and the compiler can output in several languages, this would allow for fast message passing between applications that may or may not be implemented in the same language.

I went ahead and created two simple Java and Python applications that test protocol buffers by simply creating a simple User object, prompting the user for a nickname and e-mail and then serializing the result. I also added a command to de-serialize the output and show the contents of the reconstituted object.

Here I ran the Java program to write the protocol buffers data to a file and then I run the python program to read it.

ian@laptop:~/src/protocol-buffers-test$ make javawrite
mkdir -p java
protoc --java_out=java/ prototest.proto
javac -classpath "java/:protobuf-java-2.0.0beta.jar" java/test.java java/prototest/Prototest.java
java -cp ".:java/:protobuf-java-2.0.0beta.jar" test write test.out
Nickname: Ian <- this is input
Email: test@test.com <- this is input
土 7月 12 19:09:28
ian@laptop:~/src/protocol-buffers-test$ make javaread
java -cp ".:java/:protobuf-java-2.0.0beta.jar" test read test.out
User
Nickname: Ian <- this is output
Email: test@test.com <- this is output
土 7月 12 19:09:33
ian@laptop:~/src/protocol-buffers-test$

Code available here. Code listing follows.

proto file: prototest.proto

option java_package = "prototest";

message User {
  required string nickname = 1;
  required string emailaddress = 2;
}

Java program: test.java

</table></div>

Python program: test.py

	import prototest.*;
	import com.google.protobuf.CodedInputStream;
	import java.io.*;
	/** </td></tr>
	* class test
	* Class to test protobuffer
	* @author Ian Lewis <IanLewis@member.fsf.org
	*/</span>
	public class test {

	public static void main(String[] args) {
	if (args.length < 1) {
	System.err.println("Need a command");
	} else if (args.length < 2) {
	System.err.println("Need a file name");
	} else if (args[0].equals("write")) {
	try {
	Prototest.User.Builder userbuilder = Prototest.User.newBuilder();

	BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
	String nickname = new String();
	String email = new String();
	while (nickname.length() == 0) {
	System.out.print("Nickname: ");
	nickname = in.readLine();
	if (nickname.length() == 0) {
	System.err.println("Nickname is empty!");
	}
	}
	while (email.length() == 0) {
	System.out.print("Email: ");
	email = in.readLine();
	if (email.length() == 0) {
	System.err.println("Email is empty!");
	}
	}

	userbuilder.setEmailaddress(email);
	userbuilder.setNickname(nickname);

	FileOutputStream out = new FileOutputStream(new File(args[1]));
	userbuilder.build().writeTo(out);
	out.close();
	} catch (IOException ioe) {
	System.err.println(ioe.getMessage());
	}
	} else if (args[0].equals("read")) {
	try {
	FileInputStream filein = new FileInputStream(new File(args[1]));
	CodedInputStream in = CodedInputStream.newInstance(filein);
	Prototest.User user = Prototest.User.parseFrom(in);
	System.out.println("User");
	System.out.println("Nickname: "+user.getNickname());
	System.out.println("Email: "+user.getEmailaddress());
	filein.close();
	} catch (IOException ioe) {
	System.err.println(ioe.getMessage());
	}
	} else {
	System.err.println("Unknown command");
	}
	}

	}

	import sys
	import prototest_pb2

	def PromptForUser(person):
	user.nickname = raw_input("Nickname: ")
	user.emailaddress = raw_input("Email: ")

	def PrintUsage():
	print "Usage:", sys.argv[0], "[read/write] file"
	sys.exit(-1)

	if len(sys.argv) != 3 or (sys.argv[1] != "read" and sys.argv[1] != "write"):
	PrintUsage()

	user = prototest_pb2.User()

	# Read
	if (sys.argv[1] == "read"):
	try:
	f = open(sys.argv[2], "rb")
	user.ParseFromString(f.read())
	f.close()

	print "User"
	print "Nickname: %s" % user.nickname
	print "Email: %s" % user.emailaddress
	except IOError:
	print sys.argv[1] + ": Could not open file."
	sys.exit(-1)
	elif (sys.argv[1] == "write"):
	PromptForUser(user)
	# Write
	f = open(sys.argv[2], "wb")
	f.write(user.SerializeToString())
	f.close()
	else:
	PrintUsage()
	</code></pre>

	option java_package = "prototest";

	message User {
	required string nickname = 1;
	required string emailaddress = 2;
	}

Ian Lewis

Protocol Buffers