Zig

Resume an Interrupted FTP Transfer

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.

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Zig

const std = @import("std");
const chilkat = @import("chilkat");

pub fn main(init: std.process.Init) !void {
    const alloc = init.arena.allocator();

    const ftp = try chilkat.Ftp2.init();
    defer ftp.deinit();

    ftp.setHostname("ftp.example.com");
    ftp.setUsername("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.
    ftp.setPassword("myPassword");

    ftp.connect() catch {
        std.debug.print("{s}\n", .{try ftp.getLastErrorText(alloc)});
        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.
    ftp.setRestartNext(true);

    // Resume a partially-downloaded file.  Because RestartNext is set, the download continues from
    // the current local file size.
    ftp.getFile("public_html/bigfile.zip", "qa_output/bigfile.zip") catch {
        std.debug.print("{s}\n", .{try ftp.getLastErrorText(alloc)});
        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 (ftp.getPartialTransfer()) {
        std.debug.print("Only part of the file was received; another resume may be needed.\n", .{});
    } else {
        std.debug.print("The file was fully received.\n", .{});
    }

    ftp.disconnect() catch {
        std.debug.print("{s}\n", .{try ftp.getLastErrorText(alloc)});
        return;
    };
}