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sdrangel/modemm17/ax25_frame.h
2022-07-20 09:57:59 +02:00

264 lines
6.4 KiB
C++

// Copyright 2012-2021 Rob Riggs <rob@mobilinkd.com>
// All rights reserved.
#pragma once
#include <algorithm>
#include <cassert>
#include <cctype>
#include <cstdint>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <sstream>
#include <stdexcept>
#include <string>
#include <vector>
namespace modemm17 {
struct ax25_frame
{
using repeaters_type = std::vector<std::string>;
using pid_type = uint8_t;
enum frame_type {UNDEFINED, INFORMATION, SUPERVISORY, UNNUMBERED};
private:
static const std::string::size_type DEST_ADDRESS_POS = 0;
static const std::string::size_type SRC_ADDRESS_POS = 7;
static const std::string::size_type LAST_ADDRESS_POS = 13;
static const std::string::size_type FIRST_REPEATER_POS = 14;
static const std::string::size_type ADDRESS_LENGTH = 7;
std::string destination_;
std::string source_;
repeaters_type repeaters_;
frame_type type_;
uint8_t raw_type_;
std::string info_;
uint16_t fcs_;
uint16_t crc_;
pid_type pid_;
static std::string removeAddressExtensionBit(const std::string& address)
{
std::string result = address;
for (size_t i = 0; i != result.size(); i++)
{
result[i] = (uint8_t(result[i]) >> 1);
}
return result;
}
static int getSSID(const std::string& address)
{
assert(address.size() == ADDRESS_LENGTH);
return (address[6] & 0x0F);
}
static std::string appendSSID(const std::string& address, int ssid)
{
std::string result = address;
if (ssid)
{
result += '-';
result += std::to_string(ssid);
}
return result;
}
static bool fixup_address(std::string& address)
{
assert(address.size() == ADDRESS_LENGTH);
bool result = (address[ADDRESS_LENGTH - 1] & 1) == 0;
address = removeAddressExtensionBit(address);
const int ssid = getSSID(address);
// Remove trailing spaces and SSID.
size_t pos = address.find_first_of(' ');
if (pos == std::string::npos) pos = 6;
address.erase(pos);
address = appendSSID(address, ssid);
return result;
}
static frame_type parse_type(const std::string& frame, size_t pos)
{
uint8_t c(frame[pos]);
switch (c & 0x03)
{
case 0:
return INFORMATION;
case 1:
return SUPERVISORY;
case 2:
return INFORMATION;
default:
return UNNUMBERED;
}
}
static std::string parse_info(const std::string& frame, size_t pos)
{
std::ostringstream output;
for (int i = pos; i < ((int) frame.size()) - 2; i++)
{
char c = frame[i];
if (std::isprint(c))
{
output << c;
}
else
{
output << "0x" << std::setw(2)
<< std::setbase(16) << int(uint8_t(c)) << ' ';
}
}
return output.str();
}
static uint16_t parse_fcs(const std::string& frame)
{
size_t checksum_pos = frame.size() - 2;
uint16_t tmp =
((uint8_t(frame[checksum_pos + 1]) << 8) |
uint8_t(frame[checksum_pos]));
uint16_t checksum = 0;
for (size_t i = 1; i != 0x10000; i <<= 1)
{
checksum <<= 1;
checksum |= ((tmp & i) ? 1 : 0);
}
return checksum;
}
static std::string parse_destination(const std::string& frame)
{
assert(frame.size() > DEST_ADDRESS_POS + ADDRESS_LENGTH);
return frame.substr(DEST_ADDRESS_POS, ADDRESS_LENGTH);
}
static std::string parse_source(const std::string& frame)
{
assert(frame.size() > SRC_ADDRESS_POS + ADDRESS_LENGTH);
return frame.substr(SRC_ADDRESS_POS, ADDRESS_LENGTH);
}
static repeaters_type parse_repeaters(const std::string& frame)
{
repeaters_type result;
std::string::size_type index = FIRST_REPEATER_POS;
bool more = (index + ADDRESS_LENGTH) < frame.length();
while (more)
{
std::string repeater = frame.substr(index, ADDRESS_LENGTH);
index += ADDRESS_LENGTH;
more = fixup_address(repeater) && ((index + ADDRESS_LENGTH) < frame.length());
result.push_back(repeater);
}
return result;
}
void parse(const std::string& frame)
{
if (frame.length() < 17) return;
fcs_ = parse_fcs(frame);
destination_ = parse_destination(frame);
fixup_address(destination_);
source_ = parse_source(frame);
bool have_repeaters = fixup_address(source_);
if (have_repeaters)
{
repeaters_ = parse_repeaters(frame);
}
size_t index = ADDRESS_LENGTH * (repeaters_.size() + 2);
if (frame.length() < index + 5) return;
type_ = parse_type(frame, index);
raw_type_ = uint8_t(frame[index++]);
if (type_ == UNNUMBERED) pid_ = uint8_t(frame[index++]);
info_.assign(frame.begin() + index, frame.end() - 2);
}
public:
ax25_frame(const std::string& frame) :
destination_(),
source_(),
repeaters_(),
type_(UNDEFINED),
info_(),
fcs_(-1),
crc_(0),
pid_()
{
parse(frame);
}
std::string destination() const { return destination_; }
std::string source() const { return source_; }
repeaters_type repeaters() const { return repeaters_; }
frame_type type() const { return type_; }
std::string info() const { return info_; }
uint16_t fcs() const { return fcs_; }
uint16_t crc() const { return crc_; }
pid_type pid() const { return pid_; }
};
void write(std::ostream& os, const ax25_frame& frame)
{
typedef typename ax25_frame::repeaters_type repeaters_type;
os << "Dest: " << frame.destination() << std::endl
<< "Source: " << frame.source() << std::endl;
repeaters_type repeaters = frame.repeaters();
if (!repeaters.empty())
{
os << "Via: ";
std::copy(
repeaters.begin(), repeaters.end(),
std::ostream_iterator<std::string>(os, " "));
os << std::endl;
}
if (frame.pid())
{
os << "PID: " << std::setbase(16) << int(frame.pid()) << std::endl;
}
os << "Info: " << std::endl << frame.info() << std::endl;
}
} // modemm17