Resume an Interrupted FTP Transfer

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Demonstrates the RestartNext and PartialTransfer properties, which request that the next transfer resume from existing content and report whether a download was incomplete.

Note: The local paths are relative to the application's current working directory. Absolute paths may also be used. Supply the paths appropriate to your own environment.

Background: For a large transfer over a flaky link, restarting from zero after a drop is wasteful. Setting RestartNext makes the next download continue from the current local file size (and the next upload from the remote size); the flag is consumed by that one transfer and then reset. Afterward PartialTransfer tells you whether the download got only part of the file — the signal to set RestartNext again and resume once more.

Chilkat C Downloads

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#include <C_CkFtp2.h>

void ChilkatSample(void)
    {
    BOOL success;
    HCkFtp2 ftp;

    success = FALSE;

    ftp = CkFtp2_Create();

    CkFtp2_putHostname(ftp,"ftp.example.com");
    CkFtp2_putUsername(ftp,"myFtpLogin");

    //  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.
    CkFtp2_putPassword(ftp,"myPassword");

    success = CkFtp2_Connect(ftp);
    if (success == FALSE) {
        printf("%s\n",CkFtp2_lastErrorText(ftp));
        CkFtp2_Dispose(ftp);
        return;
    }

    //  RestartNext requests that the NEXT transfer resume from existing content rather than starting
    //  over.  It is consumed by that transfer and then automatically reset.
    CkFtp2_putRestartNext(ftp,TRUE);

    //  Resume a partially-downloaded file.  Because RestartNext is set, the download continues from
    //  the current local file size.
    success = CkFtp2_GetFile(ftp,"public_html/bigfile.zip","qa_output/bigfile.zip");
    if (success == FALSE) {
        printf("%s\n",CkFtp2_lastErrorText(ftp));
        CkFtp2_Dispose(ftp);
        return;
    }

    //  PartialTransfer indicates whether the most recent download received some, but not all, of the
    //  remote file -- distinguishing a mid-transfer failure from other outcomes.
    if (CkFtp2_getPartialTransfer(ftp)) {
        printf("Only part of the file was received; another resume may be needed.\n");
    }
    else {
        printf("The file was fully received.\n");
    }

    success = CkFtp2_Disconnect(ftp);
    if (success == FALSE) {
        printf("%s\n",CkFtp2_lastErrorText(ftp));
        CkFtp2_Dispose(ftp);
        return;
    }



    CkFtp2_Dispose(ftp);

    }