消息编解码Nanopb - protocol buffers

Google Protocol Buffer 有各种版本的代码包，Python C/C++、JAVA、C、OBJ-C、.NET等，嵌入式设备中使用的protobuf版本，我们选择的是nanoprobuf。

1）Google Protocol Buffer 的使用和原理

https://www.ibm.com/developerworks/cn/linux/l-cn-gpb/index.html

2）Nanopb - protocol buffers with small code size

http://jpa.kapsi.fi/nanopb/

To use the nanopb library, you need to do two things:

1. Compile your .proto files for nanopb, using protoc.
2. Include pb_encode.c, pb_decode.c and pb_common.c in your project.

The easiest way to get started is to study the project in "examples/simple". It contains a Makefile, which should work directly under most Linux systems. However, for any other kind of build system, see the manual steps in README.txt in that folder.

simple.c

message SimpleMessage {

    required int32 lucky_number = ;

}

#include <stdio.h>
#include <pb_encode.h>
#include <pb_decode.h>
#include "simple.pb.h"

int main()
{
    /* This is the buffer where we will store our message. */
    uint8_t buffer[];
    size_t message_length;
    bool status;

    /* Encode our message */
    {
        /* Allocate space on the stack to store the message data.
         *
         * Nanopb generates simple struct definitions for all the messages.
         * - check out the contents of simple.pb.h!
         * It is a good idea to always initialize your structures
         * so that you do not have garbage data from RAM in there.
         */
        SimpleMessage message = SimpleMessage_init_zero;

        /* Create a stream that will write to our buffer. */
        pb_ostream_t stream = pb_ostream_from_buffer(buffer, sizeof(buffer));

        /* Fill in the lucky number */
        message.lucky_number = ;

        /* Now we are ready to encode the message! */
        status = pb_encode(&stream, SimpleMessage_fields, &message);
        message_length = stream.bytes_written;

        /* Then just check for any errors.. */
        if (!status)
        {
            printf("Encoding failed: %s\n", PB_GET_ERROR(&stream));
            return ;
        }
    }

    /* Now we could transmit the message over network, store it in a file or
     * wrap it to a pigeon's leg.
     */

    /* But because we are lazy, we will just decode it immediately. */

    {
        /* Allocate space for the decoded message. */
        SimpleMessage message = SimpleMessage_init_zero;

        /* Create a stream that reads from the buffer. */
        pb_istream_t stream = pb_istream_from_buffer(buffer, message_length);

        /* Now we are ready to decode the message. */
        status = pb_decode(&stream, SimpleMessage_fields, &message);

        /* Check for errors... */
        if (!status)
        {
            printf("Decoding failed: %s\n", PB_GET_ERROR(&stream));
            return ;
        }

        /* Print the data contained in the message. */
        printf("Your lucky number was %d!\n", message.lucky_number);
    }

    return ;
}

https://github.com/nanopb/nanopb

https://github.com/protocolbuffers/protobuf