How to copy a file in C/C++ with libssh and sftp

Question

I'm posting here because I need help with some code relating with libssh.

I read all the official documentation here but still I don't understand the things i need to do if someone can en light me I would be pleased.

Actually I want to copy a file from a client to a remote server but I don't understand how to do it with the library libssh and the function sftp in libssh.

The situation is that: The ssh session is open and the sftp session is open too, I can create a file and write in it from the client to the server with the integrated function of lib ssh.

I did not find an easy way to copy a file from the client to the server with a simple function like sftp_transfer(sourceFile(like c:\my document\hello world.txt),RemoteFile(/home/user/hello world.txt),right(read and write)) ?

With what I have understood from the tutorial it is first creating a file in the remote location (server) then it is opening this file with this line of code :

file = sftp_open(sftp, "/home/helloworld.txt",access_type,1);

After that the file is created on the server , and then it is writing into this created file with a buffer:

const char *helloworld = "Hello, World!\n";
int length = strlen(helloworld);
nwritten = sftp_write(file, helloworld, length);

My question is now if I have a file for example a .doc file and I want to transfer/upload that file from c:\mydocument\document.doc to remote the remote server /home/user/document.doc how can I do it with this method ?

How can I put this file into the sftp_write() function to send it like the helloworld in the sample function ?

I may be not good enough in programming to understand, but I really tried to understand it and i'm stuck with it.

Thanks in advance for your help

See below a sample of the code I used to test:

// Set variable for the communication
      char buffer[256];
      unsigned int nbytes;

        //create a file to send by SFTP
        int access_type = O_WRONLY | O_CREAT | O_TRUNC;
        const char *helloworld = "Hello, World!\n";
        int length = strlen(helloworld);

        //Open a SFTP session
        sftp = sftp_new(my_ssh_session);
        if (sftp == NULL)
        {
            fprintf(stderr, "Error allocating SFTP session: %s\n",
            ssh_get_error(my_ssh_session));
            return SSH_ERROR;
        }
        // Initialize the SFTP session
        rc = sftp_init(sftp);
        if (rc != SSH_OK)
        {
            fprintf(stderr, "Error initializing SFTP session: %s.\n",
            sftp_get_error(sftp));
            sftp_free(sftp);
            return rc;
         }

        //Open the file into the remote side
        file = sftp_open(sftp, "/home/helloworld.txt",access_type,1);
        if (file == NULL)
        {
            fprintf(stderr, "Can't open file for writing: %s\n",ssh_get_error(my_ssh_session));
            return SSH_ERROR;
        }

        //Write the file created with what's into the buffer
        nwritten = sftp_write(file, helloworld, length);
        if (nwritten != length)
        {
            fprintf(stderr, "Can't write data to file: %s\n",
            ssh_get_error(my_ssh_session));
            sftp_close(file);
            return SSH_ERROR;
        }

` 

Answer 1

Open the file in the usual way (using C++'s fstream or C's stdio.h), read its contents to a buffer, and pass the buffer to sftp_write.

Something like this:

ifstream fin("file.doc", ios::binary);
if (fin) {
  fin.seekg(0, ios::end);
  ios::pos_type bufsize = fin.tellg(); // get file size in bytes
  fin.seekg(0); // rewind to beginning of file

  char* buf = new char[bufsize];
  fin.read(buf, bufsize); // read file contents into buffer

  sftp_write(file, buf, bufsize); // write to remote file
}

Note that this is a very simple implementation. You should probably open the remote file in append mode, then write the data in chunks instead of sending single huge blob of data.

Answer 2

The following example uses ifstream in a loop, to void loading a whole file into a memory (what the accepted answer does):

ifstream fin("C:\\myfile.zip", ios::binary);

while (fin)
{
    #define MAX_XFER_BUF_SIZE 10240
    char buffer[MAX_XFER_BUF_SIZE];
    fin.read(buffer, sizeof(buffer));
    if (fin.gcount() > 0)
    {
        ssize_t nwritten = sftp_write(NULL, buffer, fin.gcount());
        if (nwritten != fin.gcount())
        {
            fprintf(stderr, "Can't write data to file: %s\n", ssh_get_error(ssh_session));
            sftp_close(file);
            return 1;
        }
    }
}

Answer 3

I used followed the example here.

sftp_read_sync uses an infinite loop to read a file from a server into /path/to/profile from server path /etc/profile.