Auto switch telnet mode option on session basis.

ATDTnumber will use the currently defined telnet mode.
ATDT+number will use NET2 for the session and return
to the defined telnet mode when the session ends.
Similarly, ATDT=number will use NET1, and ATDT-number
will use NET0.

RetroWiFiModem/RetroWiFiModem.ino

@@ -54,6 +54,7 @@ void setup(void) {
       // no valid data in EEPROM/NVRAM, populate with defaults
       factoryDefaults(NULL);
    }
+   sessionTelnetType = settings.telnet;
 
    Serial.begin(settings.serialSpeed, getSerialConfig());
    digitalWrite(TXEN, LOW);      // enable the TX output

RetroWiFiModem/at_basic.h

@@ -144,6 +144,22 @@ char *dialNumber(char *atCmd) {
       }
    }
 
+   sessionTelnetType = settings.telnet;
+   switch( host[0] ) {
+      case '-':
+         ++host;
+			sessionTelnetType = NO_TELNET;
+         break;
+      case '=':
+         ++host;
+			sessionTelnetType = REAL_TELNET;
+         break;
+      case '+':
+         ++host;
+			sessionTelnetType = FAKE_TELNET;
+         break;
+   }
+
    yield();
    if( settings.extendedCodes ) {
       Serial.printf("DIALLING %s:%u\r\n", host, portNum);

RetroWiFiModem/globals.h

@@ -60,4 +60,5 @@
    uint8_t  passwordTries = 0;   // # of unsuccessful tries at incoming password
    uint8_t  passwordLen = 0;
    uint8_t  txBuf[TX_BUF_SIZE];  // Transmit Buffer
+   uint8_t  sessionTelnetType;
 #endif

RetroWiFiModem/support.h

@@ -51,7 +51,7 @@ void sendSerialData() {
    static unsigned long lastSerialData = 0;
    // in telnet mode, we might have to escape every single char,
    // so don't use more than half the buffer
-   size_t maxBufSize = (settings.telnet != NO_TELNET) ? TX_BUF_SIZE / 2 : TX_BUF_SIZE;
+   size_t maxBufSize = (sessionTelnetType != NO_TELNET) ? TX_BUF_SIZE / 2 : TX_BUF_SIZE;
    size_t len = Serial.available();
    if( len > maxBufSize) {
       len = maxBufSize;
@@ -83,12 +83,12 @@ void sendSerialData() {
    //
    // also in Telnet mode, escape every CR (0x0D) by inserting a NUL
    // after it into the buffer
-   if( settings.telnet != NO_TELNET ) {
+   if( sessionTelnetType != NO_TELNET ) {
       for( int i = len - 1; i >= 0; --i ) {
          if( txBuf[i] == IAC ) {
             memmove( txBuf + i + 1, txBuf + i, len - i);
             ++len;
-         } else if( txBuf[i] == CR && settings.telnet == REAL_TELNET ) {
+         } else if( txBuf[i] == CR && sessionTelnetType == REAL_TELNET ) {
             memmove( txBuf + i + 1, txBuf + i, len - 1);
             txBuf[i + 1] = NUL;
             ++len;
@@ -113,7 +113,7 @@ int receiveTcpData() {
    int rxByte = tcpClient.read();
    ++bytesIn;
 
-   if( settings.telnet != NO_TELNET && rxByte == IAC ) {
+   if( sessionTelnetType != NO_TELNET && rxByte == IAC ) {
       rxByte = tcpClient.read();
       ++bytesIn;
       if( rxByte != IAC ) { // 2 times 0xff is just an escaped real 0xff
@@ -216,7 +216,7 @@ int receiveTcpData() {
    }
    // Telnet sends <CR> as <CR><NUL>
    // We filter out that <NUL> here
-   if( lastc == CR && (char)rxByte == 0 && settings.telnet == REAL_TELNET ) {
+   if( lastc == CR && (char)rxByte == 0 && sessionTelnetType == REAL_TELNET ) {
       rxByte = -1;
    }
    lastc = (char)rxByte;
@@ -304,6 +304,9 @@ void sendResult(int resultCode) {
          }
       }
    }
+   if( resultCode == R_NO_CARRIER || resultCode == R_NO_ANSWER ) {
+      sessionTelnetType = settings.telnet;
+   }
 }
 
 //