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SSH Connection using libexpect in C

From: andrew cooke <andrew@...>

Date: Wed, 25 May 2011 16:30:44 -0400

The code below may not compile as it's a rough sketch based on private code,
but hopefully it's useful anyway.  It should work both with passwords and when
certificates are configured to not need them.  Note that the password handling
is not particularly secure (not an issue in my use case - we're just using ssh
as a telnet).

    char *password = NULL;
    FILE *ssh;

    if (! (ssh = exp_popen("ssh ...@...."))) goto error;

    enum {CERT_ERROR, CERT_CONFIRM, PASSWORD, DENIED};
retry:
    switch(exp_fexpectl(*ssh,
        exp_glob, "@@@@", CERT_ERROR,
        exp_glob, "Are you sure", CERT_CONFIRM,
        exp_glob, "Password", PASSWORD,
        exp_glob, "Permission denied", DENIED,
        exp_end)) {
    case CERT_ERROR:
        log("error", "Certificate error with ssh connection");
        goto error;
    case CERT_CONFIRM:
        fprintf(*ssh, "yes\n");
        goto retry;
    case PASSWORD:
        if (! password) {
            log("error", "No password");
            goto error;
        }
        fprintf(*ssh, "%s\n", password);
        goto retry;
    case DENIED:
        log("error", "Password incorrect");
        goto error;
    case EXP_TIMEOUT:
        log("debug", "Timeout on first step of ssh (not an error)");
        break;
    default:
        log("error", "Expect error");
        goto error;
    }

    enum {OK};
    log("debug", "Checking ssh connection");
    fprintf(*ssh, "echo magic");
    switch(exp_fexpectl(*ssh,
        exp_glob, "magic", OK,
        exp_end)) {
    case OK:
        log("info", "Connected via ssh");
        break;
    case EXP_TIMEOUT:
        log("error", "Unknown error connecting via ssh");
        goto error;
    default:
        log("error", "Expect error");
	goto error;
    }

Andrew

enum from 1

From: andrew cooke <andrew@...>

Date: Thu, 26 May 2011 11:06:08 -0400

To avoid conflicts with values defined in the expect package the enums above
should start at 1.  So use

    enum {CERT_ERROR=1, CERT_CONFIRM, PASSWORD, DENIED};
    enum {OK=1};

Andrew

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