Erlang mtproto proxy
====================

This part of code was extracted from [@socksy_bot](https://t.me/socksy_bot).

Features
--------

* Promoted channels. See `tag` option.
* "secure" randomized-packet-size protocol (34-symbol secrets starting with 'dd')
  to prevent detection by DPI
* Fake-TLS protocol ('ee'/base64 secrets) - another protocol to prevent DPI detection
* Secure-only mode (only allow connections with 'dd' or fake-TLS).
  See `allowed_protocols` option.
* Connection limit policies - limit number of connections by IP / tls-domain / port; IP / tls-domain
  blacklists / whitelists
* Multiple ports with unique secret and promo tag for each port
* Very high performance - can handle tens of thousands connections! Scales to all CPU cores.
  1Gbps, 90k connections on 4-core/8Gb RAM cloud server.
* Supports multiplexing (Many connections Client -> Proxy are wrapped to small amount of
  connections Proxy -> Telegram Server) - lower pings and better OS network utilization
* Protection from [replay attacks](https://habr.com/ru/post/452144/) used to detect proxies in some countries
* Automatic telegram configuration reload (no need for restarts once per day)
* IPv6 for client connections
* Most of the configuration options can be updated without service restart
* Small codebase compared to official one, code is covered by automated tests
* A lots of metrics could be exported (optional)

How to install - one-line interactive installer
-----------------------------------------------

This command will run [interactive script](https://gist.github.com/seriyps/dc00ad91bfd8a2058f30845cd0daed83)
that will install and configure proxy for your Ubuntu / Debian / CentOS server.
It will ask if you want to change default port/secret/ad-tag/protocols:

```bash
curl -L -o mtp_install.sh https://git.io/fj5ru && bash mtp_install.sh
```

You can also just provide port/secret/ad-tag/protocols/tls-domain as command line arguments:

```bash
curl -L -o mtp_install.sh https://git.io/fj5ru && bash mtp_install.sh -p 443 -s d0d6e111bada5511fcce9584deadbeef -t dcbe8f1493fa4cd9ab300891c0b5b326 -a dd -a tls -d s3.amazonaws.com
```

It does the same as described in [How to start OS-install - detailed](#how-to-start-os-install---detailed), but
generates config-file for you automatically.

How to start - docker
---------------------

### To run with default settings

```bash
docker run -d --network=host seriyps/mtproto-proxy
```

### To run on single port with custom port, secret and ad-tag

```bash
docker run -d --network=host seriyps/mtproto-proxy -p 443 -s d0d6e111bada5511fcce9584deadbeef -t dcbe8f1493fa4cd9ab300891c0b5b326
```

or via environment variables

```bash
docker run -d --network=host -e MTP_PORT=443 -e MTP_SECRET=d0d6e111bada5511fcce9584deadbeef -e MTP_TAG=dcbe8f1493fa4cd9ab300891c0b5b326 seriyps/mtproto-proxy
```

Where

* `-p 443` / `MTP_PORT=…` proxy port
* `-s d0d6e111bada5511fcce9584deadbeef` / `MTP_SECRET=…` proxy secret (don't append `dd`! it should be 32 chars long!)
* `-t dcbe8f1493fa4cd9ab300891c0b5b326` / `MTP_TAG=…` ad-tag that you get from [@MTProxybot](https://t.me/MTProxybot)
* `-a dd` / `MTP_DD_ONLY=t` only allow "secure" connections (dd-secrets)
* `-a tls` / `MTP_TLS_ONLY=t` only allow "fake-TLS" connections (base64 secrets)

It's ok to provide both `-a dd -a tls` to allow both protocols. If no `-a` option provided, all protocols will be allowed.

### To run with custom config-file

1. Get the code `git clone https://github.com/seriyps/mtproto_proxy.git && cd mtproto_proxy/`
2. Copy config templates `cp config/{vm.args.example,prod-vm.args}; cp config/{sys.config.example,prod-sys.config}`
3. Edit configs. See [Settings](#settings).
4. Build `docker build -t mtproto-proxy-erl .`
5. Start `docker run -d --network=host mtproto-proxy-erl`

Installation via docker can work well for small setups (10-20k connections), but
for more heavily-loaded setups it's recommended to install proxy directly into
your server's OS (see below).

How to start OS-install - quick
-----------------------------------

You need at least Erlang version 20! Recommended OS is Ubuntu 18.04.

```bash
sudo apt install erlang-nox erlang-dev build-essential
git clone https://github.com/seriyps/mtproto_proxy.git
cd mtproto_proxy/
cp config/vm.args.example config/prod-vm.args
cp config/sys.config.example config/prod-sys.config
# configure your port, secret, ad_tag. See [Settings](#settings) below.
nano config/prod-sys.config
make && sudo make install
sudo systemctl enable mtproto-proxy
sudo systemctl start mtproto-proxy
```

How to start OS-install - detailed
--------------------------------------


### Install deps

Ubuntu 18.xx / Ubuntu 19.xx / Debian 10:

```bash
sudo apt install erlang-nox erlang-dev  make sed diffutils tar
```

CentOS 7

```bash
# Enable "epel" and "Erlang solutions" repositories
sudo yum install wget \
             https://dl.fedoraproject.org/pub/epel/epel-release-latest-7.noarch.rpm \
             https://packages.erlang-solutions.com/erlang-solutions-1.0-1.noarch.rpm
# Install Erlang
sudo yum install erlang-compiler erlang-erts erlang-kernel erlang-stdlib erlang-syntax_tools \
     erlang-crypto erlang-inets erlang-sasl erlang-ssl
```

You need Erlang version 20 or higher! If your version is older, please, check
[Erlang solutions esl-erlang package](https://www.erlang-solutions.com/resources/download.html)
or use [kerl](https://github.com/kerl/kerl).

### Get the code:

```bash
git clone https://github.com/seriyps/mtproto_proxy.git
cd mtproto_proxy/
```

### Create config file

see [Settings](#settings).

### Build and install

```bash
make && sudo make install
```

This will:
* install proxy into `/opt/mtp_proxy`
* create a system user
* install systemd service
* create a directory for logs in `/var/log/mtproto-proxy`
* Configure ulimit of max open files and `CAP_NET_BIND_SERVICE` by systemd

### Try to start in foreground mode

This step is optional, but it can be usefull to test if everything works as expected

```bash
./start.sh
```

try to run `./start.sh -h` to learn some useful options.

### Start in background and enable start on system start-up

```bash
sudo systemctl enable mtproto-proxy
sudo systemctl start mtproto-proxy
```

Done! Proxy is up and ready to serve now!

### Stop / uninstall

Stop:

```bash
sudo systemctl stop mtproto-proxy
```

Uninstall:

```bash
sudo systemctl stop mtproto-proxy
sudo systemctl disable mtproto-proxy
sudo make uninstall
```

Logs can be found at

```
/var/log/mtproto-proxy/application.log
```

Settings
--------

All available documented configuration options could be found
in [src/mtproto_proxy.app.src](src/mtproto_proxy.app.src). Do not edit this file!

To change configuration, edit `config/prod-sys.config`:

Comments in this file start with `%%`.
Default port is 1443 and default secret is `d0d6e111bada5511fcce9584deadbeef`.

Secret key and proxy URLs will be printed on start.

The easiest way to update config right now is to edit `config/prod-sys.config`
and then re-install proxy by

```bash
sudo make uninstall && make && sudo make install
```

There are other ways as well. It's even possible to update configuration options
without service restart / without downtime, but it's a bit trickier.

### Change default port / secret / ad tag

To change default settings, change `mtproto_proxy` section of `prod-sys.config` as:

```erlang
 {mtproto_proxy,
  %% see src/mtproto_proxy.app.src for examples.
  [
   {ports,
    [#{name => mtp_handler1,
       listen_ip => "0.0.0.0",
       port => 1443,
       secret => <<"d0d6e111bada5511fcce9584deadbeef">>,
       tag => <<"dcbe8f1493fa4cd9ab300891c0b5b326">>}
    ]}
   ]},

 {lager,
<...>
```
(so, remove `%%`s) and replace `port` / `secret` / `tag` with yours.

### Listen on multiple ports / IPs

You can start proxy on many IP addresses or ports with different secrets/ad tags.
To do so, just add more configs to `ports` section, separated by comma, eg:

```erlang
 {mtproto_proxy,
  %% see src/mtproto_proxy.app.src for examples.
  [
   {ports,
    [#{name => mtp_handler_1,
       listen_ip => "0.0.0.0",
       port => 1443,
       secret => <<"d0d6e111bada5511fcce9584deadbeef">>,
       tag => <<"dcbe8f1493fa4cd9ab300891c0b5b326">>},
     #{name => mtp_handler_2,
       listen_ip => "0.0.0.0",
       port => 2443,
       secret => <<"100000000000000000000000000000001">>,
       tag => <<"cf8e6baff125ed5f661a761e69567711">>}
    ]}
   ]},

 {lager,
<...>
```

Each section should have unique `name`!

### Only allow connections with 'dd'-secrets

This protocol uses randomized packet sizes, so it's more difficult to detect on DPI by
packet sizes.
It might be useful in Iran, where proxies are detected by DPI.
You should disable all protocols other than `mtp_secure` by providing `allowed_protocols` option:

```erlang
  {mtproto_proxy,
   [
    {allowed_protocols, [mtp_secure]},
    {ports,
     [#{name => mtp_handler_1,
      <..>
```

### Only allow fake-TLS connections with ee/base64-secrets

Another censorship circumvention technique. MTPRoto proxy protocol pretends to be
HTTPS web traffic (technically speaking, TLSv1.3 + HTTP/2).
It's possible to only allow connections with this protocol by changing `allowed_protocols` to
be list with only `mtp_fake_tls`.

```erlang
  {mtproto_proxy,
   [
    {allowed_protocols, [mtp_fake_tls]},
    {ports,
     [#{name => mtp_handler_1,
      <..>
```

### Connection limit policies

Proxy supports flexible connection limit rules. It's possible to limit number of connections from
single IP or to single fake-TLS domain or to single port name; or any combination of them.
It also supports whitelists and blacklists: you can allow or forbid to connect from some IP or IP subnet
or with some TLS domains.

Policy is set as value of `policy` config key and the value is the list of policy structures.
If list is empty, no limits will be checked.

Following policies are supported:

* `{in_table, KEY, TABLE_NAME}` - only allow connections if KEY is present in TABLE_NAME (whitelist)
* `{not_in_table, KEY, TABLE_NAME}` - only allow connections if KEY is *not* present in TABLE_NAME (blacklist)
* `{max_connections, KEYS, NUMBER}` - EXPERIMENTAL! if there are more than NUMBER connections with
  KEYS to the proxy, new connections with those KEYS will be rejected.

Where:

- `KEY` is one of:
  - `port_name` - proxy port name
  - `client_ipv4` - client's IPv4 address; ignored on IPv6 ports!
  - `client_ipv6` - client's IPv6 address; ignored on IPv4 ports!
  - `{client_ipv4_subnet, MASK}` - client's IPv4 subnet; mask is from 8 to 32
  - `{client_ipv6_subnet, MASK}` - client's IPv6 subnet; mask is from 32 to 128
  - `tls_domain` - domain name from fake-TLS secret; ignored if connection with non-fake-TLS protocol
- `KEYS` is a list of one or more `KEY`, eg, `[port, tls_domain]`
- `TABLE_NAME` is free-form text name of special internal database table, eg, `my_table`.
  Tables will be created automatically when proxy is started; data in tables is not preserved when proxy
  is restarted!
  You can add or remove new values from table dynamically at any moment with commands like:
    - `/opt/mtp_proxy/bin/mtp_proxy eval 'mtp_policy_table:add(my_table, tls_domain, "google.com")'` to add
    - `/opt/mtp_proxy/bin/mtp_proxy eval 'mtp_policy_table:del(my_table, tls_domain, "google.com")'` to remove

Some policy recipes / examples below

#### Limit max connections to proxy port from single IP

Here we allow maximum 100 concurrent connections from single IP to proxy port:

```erlang
{mtproto_proxy,
 [
  {policy,
    [{max_connections, [port_name, client_ipv4], 100}]},
  {ports,
    <..>
```

#### Limit number of connections with single fake-TLS domain; only allow certain domains

We basically can assign each customer unique fake-TLS domain, give them unique TLS secret
and allow only 10 connections with this fake-TLS secret, so, they will not shere their credentials with
others:

```erlang
{mtproto_proxy
 [
   {policy,
     [{max_connections, [port_name, tls_domain], 15},
      {in_table, tls_domain, customer_domains}]},
   {ports,
     <..>
```

After that we can create unique fake-TLS secret for each customer using code like this:

```erlang
/opt/mtp_proxy/bin/mtp_proxy eval '
ProxySecret = mtp_handler:unhex(maps:get(secret, hd(application:get_env(mtproto_proxy, ports, [])))),
NumRecords = mtp_policy_table:table_size(customer_domains),
Rand = crypto:rand_bytes(2),
SubDomain = mtp_handler:hex(<<NumRecords:16, Rand/binary>>),
Domain = <<SubDomain/binary, ".google.com">>,
mtp_policy_table:add(customer_domains, tls_domain, Domain),
Secret = mtp_handler:hex(<<16#ee, ProxySecret/binary, Domain/binary>>),
io:format("Secret: ~s;\nDomain: ~s\n", [Secret, Domain]).'
```

### IPv6

Currently proxy only supports client connections via IPv6, but can only connect to Telegram servers
using IPv4.

To enable IPv6, you should put IPv6 address in `listen_ip` config key.
If you want proxy to accept clients on the same port with both IPv4 and IPv6, you should
have 2 `ports` sections with the same `port`, `secret` and `tag`, but with different names and
different `listen_ip` (one v4 and one v6):

```erlang
 {mtproto_proxy,
  %% see src/mtproto_proxy.app.src for examples.
  [
   {ports,
    [#{name => mtp_handler_all_ipv4,
       listen_ip => "0.0.0.0",  % IPv4 address, eg 203.0.113.1
       port => 1443,
       secret => <<"d0d6e111bada5511fcce9584deadbeef">>,
       tag => <<"dcbe8f1493fa4cd9ab300891c0b5b326">>},
     #{name => mtp_handler_all_ipv6,
       listen_ip => "::",  % IPv6 address, eg "2001:db8:85a3::8a2e:370:7334"
       port => 1443,
       secret => <<"d0d6e111bada5511fcce9584deadbeef">>,
       tag => <<"dcbe8f1493fa4cd9ab300891c0b5b326">>}
    ]}
   ]},

 {lager,
<...>
```

### Tune resource consumption

If your server have low amount of RAM, try to set

```erlang
{upstream_socket_buffer_size, 5120},
{downstream_socket_buffer_size, 51200},
{replay_check_session_storage, off},
```

this may make proxy slower, it can start to consume bit more CPU, will be vulnerable to replay attacks,
but will use less RAM.
You should also avoid `max_connections` policy because it uses RAM to track connections.

If your server have lots of RAM, you can make it faster (users will get higher uppload/download speed),
it will use less CPU and will be better protected from replay attacks, but will use more RAM:

```erlang
{max_connections, 128000},
{upstream_socket_buffer_size, 20480},
{downstream_socket_buffer_size, 512000},
{replay_check_session_storage, on},
{replay_check_session_storage_opts,
  #{max_memory_mb => 2048,
    max_age_minutes => 1440}},
```

Also, for highload setups it's recommended to increase sysctl parameters:

```
sudo sysctl net.ipv4.tcp_max_orphans=128000
sudo sysctl 'net.ipv4.tcp_mem=179200 256000 384000'
```

Values for `tcp_mem` are in pages. Size of one page can be found by `getconf PAGESIZE` and is most
likely 4kb.

If you have installed proxy via Docker or use some NAT firewall settings, you may want to increase
netfilter conntrack limits to be at least the max number of connections you expect:

```
sudo sysctl net.netfilter.nf_conntrack_max=128000
```


Helpers
-------

Number of connections

```bash
/opt/mtp_proxy/bin/mtp_proxy eval 'lists:sum([proplists:get_value(all_connections, L) || {_, L} <- ranch:info()]).'
```
