Resume an Interrupted SFTP Download

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Demonstrates the Chilkat SFtp.ResumeDownloadFileByName method, which resumes an interrupted download. The first argument is the remote file path and the second is the local file path. Chilkat uses the existing local file size as the remote starting offset.

Note: This example uses relative local paths, which are resolved against the application's current working directory. Absolute local paths may also be used. Supply the paths appropriate to your own environment.

Background: The download counterpart to resuming an upload: it compares the local file size against the remote and fetches only what is missing — a full download if the local file is absent or empty, the remaining bytes appended if it is shorter, and nothing if it is already complete. As with resumed uploads, the check is size-based and assumes the partial file is a correct prefix of the remote file.

Chilkat C Downloads

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#include <C_CkSFtp.h>

void ChilkatSample(void)
    {
    BOOL success;
    HCkSFtp sftp;
    int port;
    const char *password;

    success = FALSE;

    //  Demonstrates the SFtp.ResumeDownloadFileByName method, which resumes an interrupted download.
    //  The 1st argument is the remote file path and the 2nd is the local file path.

    sftp = CkSFtp_Create();

    //  Connect, authenticate, and initialize the SFTP subsystem.
    port = 22;
    success = CkSFtp_Connect(sftp,"sftp.example.com",port);
    if (success == FALSE) {
        printf("%s\n",CkSFtp_lastErrorText(sftp));
        CkSFtp_Dispose(sftp);
        return;
    }

    //  Normally you would not hard-code the password in source.  You should instead obtain it
    //  from an interactive prompt, environment variable, or a secrets vault.
    password = "mySshPassword";

    success = CkSFtp_AuthenticatePw(sftp,"mySshLogin",password);
    if (success == FALSE) {
        printf("%s\n",CkSFtp_lastErrorText(sftp));
        CkSFtp_Dispose(sftp);
        return;
    }

    success = CkSFtp_InitializeSftp(sftp);
    if (success == FALSE) {
        printf("%s\n",CkSFtp_lastErrorText(sftp));
        CkSFtp_Dispose(sftp);
        return;
    }

    //  Resume downloading the remote file.  Chilkat uses the existing local file size as the remote
    //  starting offset, so only the remaining bytes are appended.  If the local file is missing or
    //  empty, a normal full download is performed.
    success = CkSFtp_ResumeDownloadFileByName(sftp,"subdir/largefile.zip","qa_output/largefile.zip");
    if (success == FALSE) {
        printf("%s\n",CkSFtp_lastErrorText(sftp));
        CkSFtp_Dispose(sftp);
        return;
    }

    printf("Download resumed and completed.\n");

    CkSFtp_Disconnect(sftp);


    CkSFtp_Dispose(sftp);

    }