Read an SSH Channel with a Byte Threshold

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Demonstrates the Chilkat Ssh.ChannelReadAndPoll2 method, which works like ChannelReadAndPoll but also returns once newly processed data brings the total buffered data to or above a byte threshold. The arguments are the channel number, the poll timeout, and the threshold.

The integer return value is -1 on error, -2 if nothing arrived before the timeout, 0 if EOF or channel close was processed, or — when greater than 0 — the total bytes currently buffered for the channel (not the bytes newly received by this call).

import sys
import chilkat2

success = False

# Demonstrates the Ssh.ChannelReadAndPoll2 method, which works like ChannelReadAndPoll but also
# returns once the total buffered data reaches or exceeds a byte threshold.  The 1st argument is
# the channel number, the 2nd is the poll timeout, and the 3rd is the byte threshold.

ssh = chilkat2.Ssh()

sshPort = 22
success = ssh.Connect("ssh.example.com",sshPort)
if (success == False):
    print(ssh.LastErrorText)
    sys.exit()

# 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.
password = "mySshPassword"

success = ssh.AuthenticatePw("mySshLogin",password)
if (success == False):
    print(ssh.LastErrorText)
    sys.exit()

channelNum = ssh.OpenSessionChannel()
if (channelNum < 0):
    print(ssh.LastErrorText)
    sys.exit()

# Start a shell WITHOUT requesting a PTY.  Without a PTY the shell sees it is connected to a
# raw data pipe and enters non-interactive mode: it suppresses the command prompt, does not
# echo typed commands back, and skips interactive login scripts.  The output is therefore
# clean and easily parseable -- but because no prompt is ever sent, code must not wait for
# one.  Instead, have each command print a predictable marker, or wait for EOF / channel close.
success = ssh.SendReqShell(channelNum)
if (success == False):
    print(ssh.LastErrorText)
    sys.exit()

success = ssh.ChannelSendString(channelNum,"cat /var/log/syslog\n","utf-8")
if (success == False):
    print(ssh.LastErrorText)
    sys.exit()

# Return when output goes quiet for 500ms, or once about 64KB has been buffered.  The
# threshold is not a hard buffer limit -- a whole SSH packet may push the total above it.
pollTimeoutMs = 500
maxNumBytes = 65536
# The return value is: -1 on error, -2 if nothing arrived before the timeout, 0 if EOF or
# channel close was processed, or the total number of buffered bytes when greater than 0.
result = ssh.ChannelReadAndPoll2(channelNum,pollTimeoutMs,maxNumBytes)
if (result == -1):
    print(ssh.LastErrorText)
    sys.exit()

if (result == -2):
    print("No channel data arrived before the timeout.")

if (result == 0):
    print("EOF or channel close was processed.  Buffered data may still remain.")

if (result > 0):
    print("Total bytes buffered: " + str(result))

output = ssh.GetReceivedText(channelNum,"utf-8")
if (ssh.LastMethodSuccess == False):
    print(ssh.LastErrorText)
    sys.exit()

print(output)

ssh.Disconnect()