Using the chat class

The chat class provides a framework for running chat scripts across file descriptors.

Chat scripts are commonly used to communicate with modems and other serial devices. A chat script consists of a series of send/expect pairs. The script sends a string to the device and then waits for an expected response. Timeouts and abort strings can also be defined so the script doesn't hang indefinitely.

The chat script is specified as an XML string containing send, expect, timeout, and abort elements.

The following example defines a chat script to initialize a modem, opens a serial device, runs the script, and checks the result. The result indicates whether the script succeeded, timed out, encountered an error, or was aborted by one of the defined abort strings.

#include <rudiments/chat.h>
#include <rudiments/device.h>
#include <rudiments/stdio.h>

int main(int argc, const char **argv) {

	// define a chat script to initialize a modem
	const char	*chatscript=
		"<script>"
		"  <timeout seconds=\"5\"/>"
		"  <abort string=\"ERROR\"/>"
		"  <abort string=\"NO CARRIER\"/>"
		"  <send string=\"ATZ\\r\\n\"/>"
		"  <expect string=\"OK\"/>"
		"  <send string=\"ATQ0V1E1\\r\\n\"/>"
		"  <expect string=\"OK\"/>"
		"</script>";


	// open a serial device to chat with
	// (will fail without a real serial device)
	device	d;
	if (!d.open("/dev/ttyS0",O_RDWR|O_NOCTTY)) {
		stdoutput.write("failed to open /dev/ttyS0\n");
		stdoutput.write("(no serial device available)\n\n");
	} else {

		// create a chat instance and run the script
		chat	c;
		c.setReadAndWriteFileDescriptor(&d);

		stdoutput.write("running chat script...\n");

		char	*abortstr=NULL;
		int32_t	result=c.runScript(chatscript,&abortstr);

		if (result==RESULT_SUCCESS) {
			stdoutput.write("chat script succeeded\n");
		} else if (result==RESULT_TIMEOUT) {
			stdoutput.write("chat script timed out\n");
		} else if (result==RESULT_ERROR) {
			stdoutput.write("chat script error\n");
		} else {
			stdoutput.printf("chat script aborted: %s\n",
								abortstr);
		}

		delete[] abortstr;
		d.close();
	}


	// display the chat script
	stdoutput.write("chat script:\n");
	stdoutput.printf("%s\n",chatscript);
}