Sun RPC: transferring binary files

Question

I want to transfer binary files to remote server. I am using SUN/ONC RPC (rpcgen on Linux) for my code. I am using C. I have written code for server and client and it works for text files, but when I try to transfer binary files it says the file is corrupted after transfer. I am storing data chunks in character array or XDR strings. I think there is some problem with me storing data as a character array. Can some one please tell me what the problem is? Can some one please help me?

I am attaching my code snippetes here for reference if some one wants to have a look at what I am doing.

My IDL:

const MAXLEN = 1024;

/*
 * Type for storing path
 */
typedef string filename<MAXLEN>;

/*
 * Structure for sending request. Expects the path of the file
 * and the byte number at which to start reading the file from
 */
struct request {
    filename name;
    int start;
};

/*
 * Type that represents the structute for request
 */
typedef struct request request;

/*
 * Type for storing a chunk of the file that is being
 * sent from the server to the client in the current
 * remote procedure call
 */
typedef string filechunk<MAXLEN>;

/*
 * Response sent by the server to the client as a response
 * to remote procedure call, containing the filechunk for
 * the current call and number of bytes actually read
 */
struct chunkreceive {
    filechunk data;
    int bytes;
};

/*
 * Type that represents the structure for file's chunks
 * to be received from the server
 */
typedef struct chunkreceive chunkreceive;

/*
 * File data sent by the server from client to store
 * it on the server along with the filename and the
 * number of bytes in the data
 */
struct chunksend {
    filename name;
    filechunk data;
    int bytes;
};

/*
 * Type that represents the structure for file's chunks
 * to be sent to the server 
 */
typedef struct chunksend chunksend;

/*
 * union for returning from remote procedure call, returns
 * the proper chunkdata response if everything worked fine
 * or will return the error number if an error occured
 */
union readfile_res switch (int errno) {
    case 0:
        chunkreceive chunk;
    default:
        void;
};

/*
 * Remote procedure defined in the Interface Definition Language
 * of SUN RPC, contains PROGRAM and VERSION name definitions and
 * the remote procedure signature
 */
program FTPPROG {
    version FTPVER {
        readfile_res retrieve_file(request *) = 1;
        int send_file(chunksend *) = 2;
    } = 1;
} = 0x20000011;

My Server:

#include <rpc/rpc.h>
#include <stdio.h>
#include "ftp.h"

extern __thread int errno;

readfile_res* retrieve_file_1_svc(request *req, struct svc_req *rqstp)
{
    FILE *file;
    char data[1024];
    int bytes;
    static readfile_res res;

    file = fopen(req->name, "rb");
    if (file == NULL) {
        res.errno = errno;
        return (&res);
    }

    fseek (file, req->start, SEEK_SET);
    bytes = fread(data, 1, 1024, file);

    res.readfile_res_u.chunk.data = data;
    res.readfile_res_u.chunk.bytes = bytes;

    /*
     * Return the result
     */
    res.errno = 0;
    fclose(file);
    return (&res);
}

int* send_file_1_svc(chunksend *rec, struct svc_req *rqstp)
{
    FILE *file;
    int write_bytes;
    static int result;

    file = fopen(rec->name, "a");
    if (file == NULL) {
        result = errno;
        return &result;
    }

    write_bytes = fwrite(rec->data, 1, rec->bytes, file);
    fclose(file);

    result = 0;
    return &result;
}

My Client:

#include <rpc/rpc.h>
#include <stdio.h>
#include <string.h>
#include "ftp.h"

extern __thread int errno;

int get_file(char *host, char *name)
{
    CLIENT *clnt;
    int total_bytes = 0, write_bytes;
    readfile_res *result;
    request req;
    FILE *file;

    req.name = name;
    req.start = 0;

    /*
     * Create client handle used for calling FTPPROG on
     * the server designated on the command line. Use
     * the tcp protocol when contacting the server.
     */
    clnt = clnt_create(host, FTPPROG, FTPVER, "tcp");
    if (clnt == NULL) {
        /*
         * Couldn't establish connection with server.
         * Print error message and stop.
         */
         clnt_pcreateerror(host);
         exit(1);
    }

    file = fopen(name, "wb");

    /*
     * Call the remote procedure readdir on the server
     */
    while (1) {
        req.start = total_bytes;
        result = retrieve_file_1(&req, clnt);
        if (result == NULL) {
            /*
             * An RPC error occurred while calling the server.
             * Print error message and stop.
             */
            clnt_perror(clnt, host);
            exit(1);
        }

        /*
         * Okay, we successfully called the remote procedure.
         */
        if (result->errno != 0) {
            /*
             * A remote system error occurred.
             * Print error message and stop.
             */
            errno = result->errno;
            perror(name);
            exit(1);
        }

        /*
         * Successfully got a chunk of the file.
         * Write into our local file.
         */
        write_bytes = fwrite(result->readfile_res_u.chunk.data, 1, result->readfile_res_u.chunk.bytes, file);
        total_bytes += result->readfile_res_u.chunk.bytes;
        if (result->readfile_res_u.chunk.bytes < MAXLEN) 
            break;
    }

    fclose(file);

    return 0;
}

int put_file(char *host, char *name)
{
    CLIENT *clnt;
    char data[1024];
    int total_bytes = 0, read_bytes;
    int *result;
    chunksend chunk;
    FILE *file;

    /*
     * Create client handle used for calling FTPPROG on
     * the server designated on the command line. Use
     * the tcp protocol when contacting the server.
     */
    clnt = clnt_create(host, FTPPROG, FTPVER, "tcp");
    if (clnt == NULL) {
        /*
         * Couldn't establish connection with server.
         * Print error message and stop.
         */
         clnt_pcreateerror(host);
         exit(1);
    }

    file = fopen(name, "r");

    chunk.name = name;

    /*
     * Call the remote procedure readdir on the server
     */
    while (1) {
        read_bytes = fread(data, 1, MAXLEN, file);
        total_bytes += read_bytes;

        chunk.data = data;
        chunk.bytes = read_bytes;
        result = send_file_1(&chunk, clnt);

        if (result == NULL) {
            /*
             * An RPC error occurred while calling the server.
             * Print error message and stop.
             */
            clnt_perror(clnt, host);
            exit(1);
        }

        /*
         * Okay, we successfully called the remote procedure.
         */
        if (*result != 0) {
            /*
             * A remote system error occurred.
             * Print error message and stop.
             */
            errno = *result;
            perror(name);
            exit(1);
        }

        /*
         * Successfully got a chunk of the file.
         * Write into our local file.
         */
        if (read_bytes < MAXLEN) 
            break;
    }

    fclose(file);

    return 0;
}

int read_command(char *host)
{
    char command[MAXLEN], filepath[MAXLEN];

    printf("> ");
    fflush(stdin);
    scanf("%s %s", command, filepath);

    if (strcmp(command, "get") == 0) {
        return get_file(host, filepath);
    } else if(strcmp(command, "put") == 0){
        return put_file(host, filepath);
    } else if(strcmp(command, "exit") == 0){
        exit(0);
    } else {
        return -1;
    }
}

int main(int argc, char *argv[])
{
   int result;

   if (argc != 2) {
        fprintf(stderr, "usage: %s host\n", argv[0]);
        exit(1);
   }

   while(TRUE) {
       result = read_command(argv[1]);
   }

   return 0;
}

Answer 1

Just for future reference, Madhusudan.C.S own "solution" using integers will give you all kinds of fun when using machines with different endianness. RPC should translate integers in that case, mucking up your string or binary data.

The correct solution is using the 'opaque' XDR data type. It will create a struct with a _len unsigned int for the amount of bytes, and a _var pointer which you can point to your data.