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).

#include <C_CkSsh.h>

void ChilkatSample(void)
    {
    BOOL success;
    HCkSsh ssh;
    int sshPort;
    const char *password;
    int channelNum;
    int pollTimeoutMs;
    int maxNumBytes;
    int result;
    const char *output;

    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 = CkSsh_Create();

    sshPort = 22;
    success = CkSsh_Connect(ssh,"ssh.example.com",sshPort);
    if (success == FALSE) {
        printf("%s\n",CkSsh_lastErrorText(ssh));
        CkSsh_Dispose(ssh);
        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.
    password = "mySshPassword";

    success = CkSsh_AuthenticatePw(ssh,"mySshLogin",password);
    if (success == FALSE) {
        printf("%s\n",CkSsh_lastErrorText(ssh));
        CkSsh_Dispose(ssh);
        return;
    }

    channelNum = CkSsh_OpenSessionChannel(ssh);
    if (channelNum < 0) {
        printf("%s\n",CkSsh_lastErrorText(ssh));
        CkSsh_Dispose(ssh);
        return;
    }

    //  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 = CkSsh_SendReqShell(ssh,channelNum);
    if (success == FALSE) {
        printf("%s\n",CkSsh_lastErrorText(ssh));
        CkSsh_Dispose(ssh);
        return;
    }

    success = CkSsh_ChannelSendString(ssh,channelNum,"cat /var/log/syslog\n","utf-8");
    if (success == FALSE) {
        printf("%s\n",CkSsh_lastErrorText(ssh));
        CkSsh_Dispose(ssh);
        return;
    }

    //  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 = CkSsh_ChannelReadAndPoll2(ssh,channelNum,pollTimeoutMs,maxNumBytes);
    if (result == -1) {
        printf("%s\n",CkSsh_lastErrorText(ssh));
        CkSsh_Dispose(ssh);
        return;
    }

    if (result == -2) {
        printf("No channel data arrived before the timeout.\n");
    }

    if (result == 0) {
        printf("EOF or channel close was processed.  Buffered data may still remain.\n");
    }

    if (result > 0) {
        printf("Total bytes buffered: %d\n",result);
    }

    output = CkSsh_getReceivedText(ssh,channelNum,"utf-8");
    if (CkSsh_getLastMethodSuccess(ssh) == FALSE) {
        printf("%s\n",CkSsh_lastErrorText(ssh));
        CkSsh_Dispose(ssh);
        return;
    }

    printf("%s\n",output);

    CkSsh_Disconnect(ssh);


    CkSsh_Dispose(ssh);

    }