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#include "KISS_TO_TNC2.h"
bool validateTNC2Frame(const String &tnc2FormattedFrame);
String encode_address_ax25(String tnc2Address);
String decode_address_ax25(const String &ax25Address, bool &isLast, bool isRelay);
bool validateKISSFrame(const String &kissFormattedFrame);
String decapsulateKISS(const String &frame);
/*
* https://ham.zmailer.org/oh2mqk/aprx/PROTOCOLS
After successfull login, communication carries "TNC2" format
APRS messages. Namely text encoding of AX.25 UI frames in
what became known as "TNC2 monitor style":
SOURCE>DESTIN:payload
SOURCE>DESTIN,VIA,VIA:payload
The SOURCE, DESTIN, and VIA fields are AX.25 address fields,
and have "-SSID" value annexed if the SSID is not zero.
Also in VIA-fields, if the "HAS BEEN DIGIPEATED" bit is set
(AX.25 v2 protocol feature) a star ('*') character is appended.
VIA-fields are separated by comma (',') from DESTIN, and each
other.
A double-colon (':') separates address data from payload.
The payload is passed _AS_IS_ without altering any message
content bytes, however ending at first CR or LF character
encountered in the packet.
*/
String encode_kiss(const String &tnc2FormattedFrame) {
String ax25Frame = "";
if (validateTNC2Frame(tnc2FormattedFrame)) {
String address = "";
bool dst_addres_written = false;
for (int p = 0; p <= tnc2FormattedFrame.indexOf(':'); p++) {
char currentChar = tnc2FormattedFrame.charAt(p);
if (currentChar == ':' || currentChar == '>' || currentChar == ',') {
if (!dst_addres_written && (currentChar == ',' || currentChar == ':')) {
// ax25 frame DST SRC
// tnc2 frame SRC DST
ax25Frame = encode_address_ax25(address) + ax25Frame;
dst_addres_written = true;
} else {
ax25Frame += encode_address_ax25(address);
}
address = "";
} else {
address += currentChar;
}
}
auto lastAddressChar = (uint8_t) ax25Frame.charAt(ax25Frame.length() - 1);
ax25Frame.setCharAt(ax25Frame.length() - 1, (char) (lastAddressChar | IS_LAST_ADDRESS_POSITION_MASK));
ax25Frame += (char) APRS_CONTROL_FIELD;
ax25Frame += (char) APRS_INFORMATION_FIELD;
ax25Frame += tnc2FormattedFrame.substring(tnc2FormattedFrame.indexOf(':') + 1);
}
String kissFrame = encapsulateKISS(ax25Frame, CMD_DATA);
return kissFrame;
}
String encapsulateKISS(const String &ax25Frame, uint8_t TNCCmd) {
String kissFrame = "";
kissFrame += (char) FEND; // start of frame
kissFrame += (char) (0x0f & TNCCmd); // TNC0, cmd
for (int i = 0; i < ax25Frame.length(); ++i) {
char currentChar = ax25Frame.charAt(i);
if (currentChar == (char) FEND) {
kissFrame += (char) FESC;
kissFrame += (char) TFEND;
} else if (currentChar == (char) FESC) {
kissFrame += (char) FESC;
kissFrame += (char) TFESC;
} else {
kissFrame += currentChar;
}
}
kissFrame += (char) FEND; // end of frame
return kissFrame;
}
String decapsulateKISS(const String &frame) {
String ax25Frame = "";
for (int i = 2; i < frame.length() - 1; ++i) {
char currentChar = frame.charAt(i);
if (currentChar == (char) FESC) {
char nextChar = frame.charAt(i + 1);
if (nextChar == (char) TFEND) {
ax25Frame += (char) FEND;
} else if (nextChar == (char) TFESC) {
ax25Frame += (char) FESC;
}
i++;
} else {
ax25Frame += currentChar;
}
}
return ax25Frame;
}
/**
*
* @param inputKISSTNCFrame
* @param dataFrame
* @return Decapsulated TNC2KISS APRS data frame, or raw command data frame
*/
String decode_kiss(const String &inputKISSTNCFrame, bool &dataFrame) {
String TNC2Frame = "";
if (validateKISSFrame(inputKISSTNCFrame)) {
dataFrame = inputKISSTNCFrame.charAt(1) == CMD_DATA;
if (dataFrame){
String ax25Frame = decapsulateKISS(inputKISSTNCFrame);
bool isLast = false;
String dst_addr = decode_address_ax25(ax25Frame.substring(0, 7), isLast, false);
String src_addr = decode_address_ax25(ax25Frame.substring(7, 14), isLast, false);
TNC2Frame = src_addr + ">" + dst_addr;
int digi_info_index = 14;
while (!isLast && digi_info_index + 7 < ax25Frame.length()) {
String digi_addr = decode_address_ax25(ax25Frame.substring(digi_info_index, digi_info_index + 7), isLast, true);
TNC2Frame += ',' + digi_addr;
digi_info_index += 7;
}
TNC2Frame += ':';
TNC2Frame += ax25Frame.substring(digi_info_index + 2);
} else {
// command frame, currently ignored
TNC2Frame += inputKISSTNCFrame;
}
}
return TNC2Frame;
}
/**
* Encode adress in TNC2 monitor format to ax.25 format
* @param tnc2Address
* @return
*/
String encode_address_ax25(String tnc2Address) {
bool hasBeenDigipited = tnc2Address.indexOf('*') != -1;
if (tnc2Address.indexOf('-') == -1) {
if (hasBeenDigipited) {
// ex. TCPIP* in tnc2Address
// so we skip last char
tnc2Address = tnc2Address.substring(0, tnc2Address.length() - 1);
}
tnc2Address += "-0";
}
int separatorIndex = tnc2Address.indexOf('-');
int ssid = tnc2Address.substring(separatorIndex + 1).toInt();
// TODO: SSID should not be > 16
String kissAddress = "";
for (int i = 0; i < 6; ++i) {
char addressChar;
if (tnc2Address.length() > i && i < separatorIndex) {
addressChar = tnc2Address.charAt(i);
} else {
addressChar = ' ';
}
kissAddress += (char) (addressChar << 1);
}
kissAddress += (char) ((ssid << 1) | 0b01100000 | (hasBeenDigipited ? HAS_BEEN_DIGIPITED_MASK : 0));
return kissAddress;
}
/**
* Decode address from ax.25 format to TNC2 monitor format
* @param ax25Address
* @return
*/
String decode_address_ax25(const String &ax25Address, bool &isLast, bool isRelay) {
String TNCAddress = "";
for (int i = 0; i < 6; ++i) {
uint8_t currentCharacter = ax25Address.charAt(i);
currentCharacter >>= 1;
if (currentCharacter != ' ') {
TNCAddress += (char) currentCharacter;
}
}
auto ssid_char = (uint8_t) ax25Address.charAt(6);
bool hasBeenDigipited = ssid_char & HAS_BEEN_DIGIPITED_MASK;
isLast = ssid_char & IS_LAST_ADDRESS_POSITION_MASK;
ssid_char >>= 1;
int ssid = 0b1111 & ssid_char;
if (ssid) {
TNCAddress += '-';
TNCAddress += ssid;
}
if (isRelay && hasBeenDigipited) {
TNCAddress += '*';
}
return TNCAddress;
}
bool validateTNC2Frame(const String &tnc2FormattedFrame) {
return (tnc2FormattedFrame.indexOf(':') != -1) && (tnc2FormattedFrame.indexOf('>') != -1);
}
bool validateKISSFrame(const String &kissFormattedFrame) {
return kissFormattedFrame.charAt(0) == (char) FEND &&
kissFormattedFrame.charAt(kissFormattedFrame.length() - 1) == (char) FEND;
}