JavaScript

Check Whether the Last SFTP Read Failed

Demonstrates the Chilkat SFtp.LastReadFailed method, which returns whether the most recent read for a handle failed. The only argument is the handle. A normal end-of-file is not a failure.

Background: A chunked read loop needs to tell three outcomes apart: more data, a clean end-of-file, and an actual error such as a dropped connection or a revoked handle. LastReadFailed isolates the error case — it is false on a normal EOF read (which succeeds with zero bytes) and true for an empty, malformed, or already-closed handle — so the loop can stop cleanly on EOF but bail out with an error message on a genuine failure.

Note

This example is intended for running within a Chilkat.Js embedded JavaScript engine. All Chilkat JavaScript examples require Chilkat v11.4.0 or greater.

JavaScript

var success = false;

//  Demonstrates the SFtp.LastReadFailed method, which returns whether the most recent read for a
//  handle failed.  The only argument is the handle.  A normal end-of-file is NOT a failure.

var sftp = new CkSFtp();

//  Connect, authenticate, and initialize the SFTP subsystem.
var port = 22;
success = sftp.Connect("sftp.example.com",port);
if (success == false) {
    console.log(sftp.LastErrorText);
    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.
var password = "mySshPassword";

success = sftp.AuthenticatePw("mySshLogin",password);
if (success == false) {
    console.log(sftp.LastErrorText);
    return;
}

success = sftp.InitializeSftp();
if (success == false) {
    console.log(sftp.LastErrorText);
    return;
}

var handle = sftp.OpenFile("subdir/data.txt","readOnly","openExisting");
if (sftp.LastMethodSuccess == false) {
    console.log(sftp.LastErrorText);
    return;
}

var reading = true;
var chunkSize = 4096;
var bd = new CkBinData();
while (reading) {
    success = sftp.ReadFileBd(handle,chunkSize,bd);

    //  Distinguish an actual read failure from a normal EOF.  On EOF the read succeeds, returns
    //  zero bytes, and LastReadFailed is false.
    if (sftp.LastReadFailed(handle)) {
        console.log("Read failed: " + sftp.LastErrorText);
        return;
    }

    reading = !sftp.Eof(handle);
}

success = sftp.CloseHandle(handle);
if (success == false) {
    console.log(sftp.LastErrorText);
    return;
}

console.log("Read " + bd.NumBytes + " bytes with no read failures.");

sftp.Disconnect();