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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.
Follow up:
proto file: prototest.proto
| option java_package = "prototest"; | |
| message User { | |
| required string nickname = 1; | |
| required string emailaddress = 2; | |
| } |
Java program: test.java
| import prototest.*; | |
| import com.google.protobuf.CodedInputStream; | |
| import java.io.*; | |
| /** | |
| * class test | |
| * Class to test protobuffer | |
| * @author Ian Lewis <IanLewis@member.fsf.org | |
| */ | |
| 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"); | |
| } | |
| } | |
| | |
| } |
Python program: test.py
| 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> |
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