# Linux Fax Stack Setup (HylaFax & SIP)

- ***This guide is WIP***
- Ubuntu 20.04 LTS VM (VirtualBox, LXC?)
- **TODO: Test on Debian / RockPi / RaspberryPi**
- **TODO: Test on Eventphone Infra** 

<hr/>

## Setup t38modem

- **TODO: Package t38modem with service files and config** 

## Opal

- http://wiki.opalvoip.org/index.php?n=Main.HomePage
- Don't use `libavformat-dev` -> Compile error in Opal
- https://sourceforge.net/projects/opalvoip/files/
- Version 3.18.6
- **TODO: Test out other versions**
- `.tar.bz2` files for *nix

### Build PTLib

- Version 2.18.6
- Dependency of Opal, bundled with Opal source code (SourceForge)
- http://wiki.opalvoip.org/index.php?n=Main.BuildingPTLibUnix
- **TODO: Remove dependencies, most of them are optional**

```bash
sudo apt install \
	g++ git make autoconf libpcap-dev libexpat1-dev libssl-dev libsasl2-dev libldap2-dev \
	unixodbc-dev liblua5.3-dev libv8-dev libncurses-dev libsdl2-dev \
	libgstreamer1.0-dev libgstreamer-plugins-base1.0-dev
```

- PTLib will be installed in the `/usr/local` tree -> set `PKG_CONFIG_PATH` to be findable (compile time)
- Set `LD_LIBRARY_PATH` to find PTLib at compile and run time
- Set `PTLIBPLUGINDIR` (compile and run time)
- (To compile as static library: `./configure --disable-shared`)

```bash
export PKG_CONFIG_PATH=/usr/local/lib/pkgconfig # compile time
export LD_LIBRARY_PATH=/usr/local/lib # compile and run time
export PTLIBPLUGINDIR=/usr/local/lib/ptlib-x.y.z # compile and run time
 
cd ptlib-x.y.z/
./configure
make
sudo make install
```

### Build Opal

- Version 3.18.6
- http://wiki.opalvoip.org/index.php?n=Main.BuildingOpalUnix
- Dont use `libavcodec-dev` -> Compile error
- **TODO: Remove dependencies, most of them are optional**

```bash
sudo apt install \
	libsrtp2-dev libgsm1-dev libspeex-dev libopus-dev libx264-dev \
	libvpx-dev libtheora-dev libspandsp-dev dahdi
```

- (To compile as static library: `./configure --disable-shared`)

```bash
export PKG_CONFIG_PATH=/usr/local/lib/pkgconfig # compile time
export LD_LIBRARY_PATH=/usr/local/lib # compile and run time
export PTLIBPLUGINDIR=/usr/local/lib/ptlib-x.y.z:/usr/local/lib/opal-a.b.c # compile and run time

cd opal-a.b.c/
./configure
make
sudo make install
```

## t38modem

- https://github.com/hehol/t38modem, Version 4.6.2
  - Could also use https://github.com/T38Modem/t38modem, not as maintained
- If you are getting error about `-1` not being able to be casted to a `long unsigned int` due to `-Wnarrowing` inside `dle.cxx`, you can add `-Wno-narrowing` to the `CPPFLAGS` in the Makefile to disable this error

```bash
cd t38modem-x.y.z/
make
sudo cp ./t38modem /usr/local/bin
```

- t38modem can only find Opal if `LD_LIBRARY_PATH` and `PTLIBPLUGINDIR` are environment variables to the program

### Init script

- To automatically start t38modem, you need to create Systemd services, as well as start and stop scripts
- script is adapted from https://web.archive.org/web/20111231021042/https://www.foriamroot.org/hylafax-6-0-debian-or-ubuntu-t38modem-1-0-asterisk-1-6/
- `sudo mkdir -p /etc/t38modem/bin/`

```bash
#!/bin/bash
# /etc/t38modem/bin/run

export LD_LIBRARY_PATH=/usr/local/lib
export PTLIBPLUGINDIR=/usr/local/lib/ptlib-x.y.z:/usr/local/lib/opal-a.b.c # Adjust lib versions!

case "$1" in
	start)
		. /etc/t38modem/config
		# defines
		# - T38MODEM_SIP_USERNAME
		# - T38MODEM_SIP_PASSWORD
		# - T38MODEM_SIP_SERVER
		# - T38MODEM_STUN
		
		if [ -z ${T38MODEM_STUN+x} ]; then
			$STUN="--stun ${T38MODEM_STUN}"
		else
			$STUN=""
		fi

		COMMAND="t38modem -u T38modem --ptty +/dev/ttyT38-1 --sip-proxy ${T38MODEM_SIP_USERNAME}:${T38MODEM_SIP_PASSWORD}@${T38MODEM_SIP_SERVER} --sip-register ${T38MODEM_SIP_USERNAME}@${T38MODEM_SIP_SERVER},${T38MODEM_SIP_PASSWORD} --sip-listen udp\$:5060 --route t38:.*=sip:<dn>@${T38MODEM_SIP_SERVER} --route sip:.*=t38:<dn> ${STUN}"
		echo "${COMMAND}"
		exec $COMMAND > /dev/null 2>&1 &
		PID=$!
		echo "Starting t38modem with pid $PID (pidfile /run/t38modem.pid)"
		echo $PID > /run/t38modem.pid
	;;
	stop)
		if [ ! -f "/run/t38modem.pid" ]; then
			echo "t38modem is not running! (/run/t38modem.pid does not exist)"
			exit 1
		fi

		echo -n "Stopping t38modem pid: "
		PID=`cat /run/t38modem.pid`
		kill -9 $PID
		rm /run/t38modem.pid
		echo "${PID} Done"
	;;
	*)
		echo "Usage: $0 {start|stop}"
		exit 1
	;;
esac

exit 0
```

```bash
sudo chmod +x /etc/t38modem/bin/run
```

- `-t` enables debugging
  - More `t`'s is deeper debugging (e.g. `-tttt`)
- You can of course run the t38modem command without this init script
- If t38modem says it was able to create the virtual modem but `/dev/ttyT38-1` is not available, you do not have sufficient permissions
- Configuration is specified in `/etc/t38modem/config`

```bash
# /etc/t38modem/config
T38MODEM_SIP_USERNAME="USERNAME"
T38MODEM_SIP_PASSWORD="PASSWORD"
T38MODEM_SIP_SERVER="voip.example.com"
# T38MODEM_STUN="stun.example.com" # optional
```

- Give only root access to the config

```bash
sudo chown root:root /etc/t38modem/config
sudo chmod 700 /etc/t38modem/config
```

- You can now communicate with your modem `/dev/ttyT38-1` , just as if it was a real Hayes compatible modem (https://www.computerhope.com/atcom.htm)
- Test using minicom, configure it to point to our modem. Each command is initiated by a Return
  - Dial a number:
    - Get the attention of the modem: `at` -> `OK`
    - Dial: `atd0123456789`
    - If all works correctly you should be able to answer the phone and hear a single beep
  - Answer a call:
    - Get the attention of the modem: `at` -> `OK`
    - *Call the number of your modem*
    - -> `RING`
    - Answer the call: `ata` -> `CONNECT`
    - You should now hear your modem "talking" to you
- Pitfalls:
  - If you are already connected to your SIP server it may not give proper response codes. My provider returns `500 Internal Server Error`
  - Test the command before running the init script!

### systemd service

```toml
# /etc/systemd/system/t38modem.service
[Unit]
Description=t38modem
After=network-online.target
Wants=network-online.target

[Service]
Type=simple
ExecStart=/etc/t38modem/bin/run start
ExecStop=/etc/t38modem/bin/run stop
PIDFile=/run/t38modem.pid
KillMode=none
Restart=always

[Install]
WantedBy=multi-user.target
```

- Enable the service:

```bash
sudo systemctl daemon-reload
sudo systemctl enable t38modem.service
sudo systemctl start t38modem.service
```

<hr/>

## Install HylaFax

- Version 6
- `sudo apt install hylafax-server`

  - Set Postfix Configuration to **Local only** in dpkg-reconfigure menu
- Run `sudo faxsetup`

  - Add new modem
  - Enter correct modem port (`ttyT38-1`)
  - Enter dialing configuration
  - Accept default configuration for everything else
  - It should automatically detect it to be a `T38FAX` modem
- Look at `man sendfax` to send faxes
- `fgetty` (the service to receive faxes) should be enabled automatically
- Bugs:

  - If you get some error about protocol errors, just let HylaFax do its thing.
    Fax over SIP is not stable at all in my experience


<hr/>

## Cron

- Alias your fax admin account as `FaxMaster` (`/etc/aliases`)

```bash
# /etc/aliases
# [...]
# HylaFax
FaxMaster: $USER # replace with fax admin account
```

- Add standard tasks to crontab file: `crontab -e`

```bash
0       *       *       *       *       /usr/sbin/faxqclean
25      23      *       *       *       sh /usr/sbin/faxcron | mail FaxMaster
```