File Transfer internal network

You can use File.Copy even across domains (workgroups). You only need to have the needed credentials (username & password). As I know there is no direct implementation needed in .NET only, in the API.

I found this code for you:

public class NetworkConnection : IDisposable
{
    string _networkName;

    public NetworkConnection(string networkName, 
        NetworkCredential credentials)
    {
        _networkName = networkName;

        var netResource = new NetResource()
        {
            Scope = ResourceScope.GlobalNetwork,
            ResourceType = ResourceType.Disk,
            DisplayType = ResourceDisplaytype.Share,
            RemoteName = networkName
        };

        var result = WNetAddConnection2(
            netResource, 
            credentials.Password,
            credentials.UserName,
            0);

        if (result != 0)
        {
            throw new Win32Exception(result, "Error connecting to remote share");
        }   
    }

    ~NetworkConnection()
    {
        Dispose(false);
    }

    public void Dispose()
    {
        Dispose(true);
        GC.SuppressFinalize(this);
    }

    protected virtual void Dispose(bool disposing)
    {
        WNetCancelConnection2(_networkName, 0, true);
    }

    [DllImport("mpr.dll")]
    private static extern int WNetAddConnection2(NetResource netResource, 
        string password, string username, int flags);

    [DllImport("mpr.dll")]
    private static extern int WNetCancelConnection2(string name, int flags,
        bool force);
}

[StructLayout(LayoutKind.Sequential)]
public class NetResource
{
    public ResourceScope Scope;
    public ResourceType ResourceType;
    public ResourceDisplaytype DisplayType;
    public int Usage;
    public string LocalName;
    public string RemoteName;
    public string Comment;
    public string Provider;
}

public enum ResourceScope : int
{
    Connected = 1,
    GlobalNetwork,
    Remembered,
    Recent,
    Context
};

public enum ResourceType : int
{
    Any = 0,
    Disk = 1,
    Print = 2,
    Reserved = 8,
}

public enum ResourceDisplaytype : int
{
    Generic = 0x0,
    Domain = 0x01,
    Server = 0x02,
    Share = 0x03,
    File = 0x04,
    Group = 0x05,
    Network = 0x06,
    Root = 0x07,
    Shareadmin = 0x08,
    Directory = 0x09,
    Tree = 0x0a,
    Ndscontainer = 0x0b
}

It can be used to impersonate somebody during the file transfer. As you can see, you even can impersonate two different accounts.

using (new NetworkConnection(@"\\server\read", readCredentials))
using (new NetworkConnection(@"\\server2\write", writeCredentials)) {
   File.Copy(@"\\server\read\file", @"\\server2\write\file");
}

Of course, you can use admin shares, no need for real shares, but you need admin account for that. You could store the different credentials in your application setting (encrypted, if needed), or you could add a common username-password pair on all affected machines.

By the way, you can even use wmi to copy files (as psexec does), but it seems to me more complicated.

Sorry, was out of the country for a while, used Filestream with a BinaryWriter in the end, displaying a progress in a new window, thanks for your help.