JavaScript

Read Text at a 32-bit Offset from a Remote SFTP File

Demonstrates the Chilkat SFtp.ReadFileText32 method, which reads up to a number of bytes from a specific 32-bit byte offset of an open handle and decodes them to text. The arguments are the handle, the offset, the maximum number of bytes, and the charset.

Background: Reading from an explicit offset lets you fetch just the part of a file you need — a header, a record at a known position, a slice of a large log — without downloading everything before it. As with offset writes, the offset counts bytes rather than characters, so it must respect the encoded width of any multibyte content.

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.ReadFileText32 method, which reads up to a number of bytes from a
//  specific 32-bit byte offset of an open handle and decodes them to text.  The 1st argument is
//  the handle, the 2nd is the offset, the 3rd is the maximum number of bytes, and the 4th is the
//  charset.

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/record.dat","readOnly","openExisting");
if (sftp.LastMethodSuccess == false) {
    console.log(sftp.LastErrorText);
    return;
}

//  Read 5 bytes starting at byte offset 10, without first reading the bytes before it.
var offset = 10;
var numBytes = 5;
var text = sftp.ReadFileText32(handle,offset,numBytes,"utf-8");
if (sftp.LastMethodSuccess == false) {
    console.log(sftp.LastErrorText);
    return;
}

console.log(text);

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

sftp.Disconnect();