# Linux Fax Stack Setup (HylaFax & SIP)

Linux Fax Stack using Hylafax and t38modem.

***THIS GUIDE IS WIP***

This guide was created using information from the opalvoip wiki (http://wiki.opalvoip.org/index.php?n=Main.HomePage)

## Software stack

### ptlib
(legacy) library for doing a little bit of everything.

### Opal
Voice codec used by e.g. mumble.

### t38modem
Emulates a serial modem from SIP connection

### HylaFax
Enterprise grade software, managing physical and emulated modems.

Has some problems: https://github.com/lexbailey/compilerfax/blob/main/hylafax_is_broken

## Operating Systems
Unfortunately this software stack uses a lot of legacy software. Because of this, this guide was only tested on specific software versions

### Debian 12 Bookworm
For Debian 12, we'll only install dependencies which are hard requirements.
For this guide we'll use ptlib 2.18.6 and opal 3.18.6.

#### Installing Requirements
First we'll need some packages
```bash
apt-get install build-essential git wget pkg-config libssl-dev libsrtp2-dev libspandsp-dev -y
```
#### Download sourcecode
Versions:
- libpt (2.18.6) https://sourceforge.net/projects/opalvoip/files/v3.18 Cygni/Stable 6/
- opal (3.18.6) https://sourceforge.net/projects/opalvoip/files/v3.18 Cygni/Stable 6/
- t38mdem (4.6.2) https://github.com/hehol/t38modem/releases/tag/4.6.2

#### ptlib
```bash
./configure
make
make install
```

#### opal
```bash
./configure
make -j5
make runtest
make install
```

#### t38modem
If you are getting an 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` after the `CPPFLAGS` in the Makefile to disable this error

```bash
git clone https://github.com/hehol/t38modem
cd t38modem
make
```

If running the t38modem executable, you should run these commands
```bash
cp /usr/local/lib/libpt.so.2.18.6 /lib
cp /usr/local/lib/libopal.so.3.18.6 /lib
```

To install t38modem run
```bash
cp ./t38modem /usr/local/bin
```

### Ubuntu 20.04 LTS
Was tested on Ubuntu 20.04 LTS VM (VirtualBox, LXC?)

You can relies heavily on http://wiki.opalvoip.org/index.php?n=Main.HomePage

Versions:
- libpt (2.18.6) https://sourceforge.net/projects/opalvoip/files/v3.18 Cygni/Stable 6/
- opal (3.18.6) https://sourceforge.net/projects/opalvoip/files/v3.18 Cygni/Stable 6/
- t38mdem (4.6.2) https://github.com/hehol/t38modem/releases/tag/4.6.2

Follow http://wiki.opalvoip.org/index.php?n=Main.BuildingPTLibUnix and http://wiki.opalvoip.org/index.php?n=Main.HomePage **but**
- Don't use `libavformat-dev` -> Compile error in Opal
- Configure script needs `pkg-config` to be installed to find ptlib install
- On SourceForge downloads `.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 pkg-config
```

- 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
  - https://github.com/T38Modem/t38modem could also be used, but seems to be 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` after 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

<hr/>

## Configuring t38modem
### 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/

First we'll create the configuration directory under `/etc` using `sudo mkdir -p /etc/t38modem/bin/`.

Then create a file named `/etc/t38modem/bin/run` using the following content.
It will be the script to manage the current status of t38modem.

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

export LD_LIBRARY_PATH=/usr/local/lib
export PTLIBPLUGINDIR=/usr/local/lib/ptlib-2.18.6:/usr/local/lib/opal-3.18.6 # Adjust lib versions!

if [ -z "${1}" ]; then
	>&2 echo "Config file path not set! Aborting..."
	exit 1
fi

. "${1}"

command="t38modem --ptty +/dev/ttyT38-${T38MODEM_PTTY_ID} --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 --stun ${T38MODEM_STUN_SERVER} --route t38:.*=sip:<dn>@${T38MODEM_SIP_SERVER} --route sip:.*=t38:<dn>"

if [ "$T38MODEM_DISABLE_T38" = true ]; then
	command="${command} --disable-t38-mode --audio"
fi

exec $command
```

And then we'll have to make it executable like this.

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

#### Quick script overview
- Using this script, it is possible to start t38modem with a config file as an argument 
- `-t` enables debugging
  - More `t`'s is deeper debugging (e.g. `-tttt`)
- 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/XX`

### Create the configuration file
Create a file using the following contents at `/etc/t38modem/config/XX`.

```bash
# /etc/t38modem/config
T38MODEM_PTTY_ID="XX" # /dev/ttyT38-XX
T38MODEM_SIP_USERNAME="USERNAME"
T38MODEM_SIP_PASSWORD="PASSWORD"
T38MODEM_SIP_SERVER="voip.example.com"
T38MODEM_STUN_SERVER="stun.example.com:1234"
T38MODEM_DISABLE_T38=false # enable if your SIP server prefers G.711
```

You should give only root access to the config.

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

### Testing your setup
- You can now communicate with your modem `/dev/ttyT38-XX`, 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: `atd[NUMBER]`, replace '[NUMBER]' using the number, you want to call
    - 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!
  - Do not try to used `ATO` to switch to a data connection, t38modem will return `ERROR`.
  Thats hardcoded in `pmodeme.cxx` in `void ModemEngineBody::HandleCmdRest(PString &resp)`.
  Dont let that hodld you back.

### systemd service
If you want to run a fax server, you can create a systemd service template to let your emulated fax modem start automatically on system boot.
To do this you have to copy paste the following into `/etc/systemd/system/t38modem@.service`.

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

[Service]
Type=simple
Restart=always
ExecStart=/etc/t38modem/bin/run /etc/t38modem/config/%i

[Install]
WantedBy=multi-user.target
```
Enable and start the service for your config file (`/etc/t38modem/config/XX`) using the following commands:

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

<hr/>

## Install HylaFax
These instructions were tested using Hylafax version 6
- `sudo apt install hylafax-server`
  - Set Postfix Configuration to **Local only** in dpkg-reconfigure menu
## Configure HylaFax
- Run `sudo faxsetup`
  - Add new modem
  - Enter correct modem port (`ttyT38-XX`)
  - Enter dialing configuration (see Dial Rules for Eventphone EPVPN)
  - 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 protocol errors, just let HylaFax do its thing.
    Fax over SIP is not stable at all in my experience
  - If your call is cleared because it `Could not find common media capabilities` t38modem may not have been able to load PTLib or Opal. Check your library paths!


### 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
```

### Dial Rules for Eventphone EPVPN
If you want to use Eventhone EPVPN, you can apply the following dial settings onto your modems.
You can find the config at `/etc/hylafax/config.ttyT38-1`.
In this case `ttyT38-1` is the modem block device.
```
# /etc/hylafax/config.ttyXX
CountryCode:	1
AreaCode:		999
```

## FaxDispatch

- https://legacy.hylafax.org/content/Advanced_Permissions_with_6.0

# TODO
- **TODO: Test on Debian / RockPi / RaspberryPi**
- **TODO: Test on Eventphone Infra**
- **TODO: Package t38modem with service files and config**