Lua

Get the Number of Bytes Buffered on an SSH Channel

Demonstrates the Chilkat Ssh.GetReceivedNumBytes method, which returns how many bytes are currently available in a channel's normal receive buffer. The only argument is the channel number. It returns -1 when the channel number is invalid or its retained resources have been released.

Background: This is a non-consuming look at how much is waiting, useful for deciding whether to retrieve now or keep reading, and for reporting progress on a large transfer. It counts only the normal receive buffer — bytes in the separate stderr buffer are excluded when StderrToStdout is false. Note that data received earlier can remain available even after a disconnect, so a positive count does not imply the connection is still up.

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Lua

local chilkat = require("chilkat")

-- Demonstrates the Ssh.GetReceivedNumBytes method, which returns the number of bytes currently
-- available in a channel's normal receive buffer.  The only argument is the channel number.
-- It returns -1 for an invalid channel or one whose resources have been released.

local ssh = chilkat.Ssh.new()

local sshPort = 22
local success = ssh:connect("ssh.example.com", sshPort)
if not success then
    print(ssh.last_error_text)
    return
end

-- 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.
local password = "mySshPassword"

success = ssh:authenticate_pw("mySshLogin", password)
if not success then
    print(ssh.last_error_text)
    return
end

local channelNum = ssh:open_session_channel()
if channelNum < 0 then
    print(ssh.last_error_text)
    return
end

success = ssh:send_req_exec(channelNum, "ls -l /tmp")
if not success then
    print(ssh.last_error_text)
    return
end

-- IMPORTANT: Set a read timeout.  ReadTimeoutMs defaults to 0, which means no limit -- without
-- it, this call waits forever if the server never sends channel close.
ssh.read_timeout_ms = 15000

success = ssh:channel_receive_to_close(channelNum)
if not success then
    print(ssh.last_error_text)
    return
end

-- Find out how much is waiting before retrieving it.
local numBytes = ssh:get_received_num_bytes(channelNum)
if numBytes < 0 then
    print("Invalid channel, or its resources were already released.")
    return
end

print("Bytes available: " .. numBytes)

local output = ssh:get_received_text(channelNum, "utf-8")
if not ssh.last_method_success then
    print(ssh.last_error_text)
    return
end

print(output)

ssh:disconnect()