![The PTTH logo, a green box sitting on a black conveyor belt. The box has an arrow pointing left, and the text "PTTH", in white. The conveyor belt has an arrow pointing right, in white.](assets/logo-128-pixel.png)

# PTTH

An extroverted HTTP server that makes outgoing connections through
firewalls.

```
HTTP:

Client -> Firewall -> Server

PTTH:

Client -> Firewall -> Relay <- Firewall <- Server
```

The server can run behind a firewall, because it is actually a special HTTP
client. The relay acts as a facade, so the client is still a normal
HTTP client like Firefox, curl, or wget.

## Configuration

ptth_server:

- Copy ptth_server or ptth_server.exe onto the server
- Create ptth_server.toml in the server's working dir
- Add a human-readable name and a secret API key generated by diceware
- Run `ptth_server --print-tripcode` and copy the output into ptth_relay.toml

ptth_relay first-time config:

- Copy ptth_relay onto the server (A Dockerfile is provided with no guarantees)
- Create ptth_relay.toml in the relay's working dir

Example server config: (Won't run because the key is too weak)

```
name = "my_server"
api_key = "secretpassword"
relay_url = "http://127.0.0.1:4000"
file_server_root = "./data"
```

ptth_relay.toml:

```
[[servers]]
name = "my_server"
tripcode = "czpCob1t1T7IU9zIlYyoNRomyeN7pqKSg1R0EUPz6Pw="

[[servers]
name = "some_other_server"
tripcode = "su2wWbTyf5xih4yiCTfAzqDlASatV+0dI+UVKFBIsEI="
```

## Use

1. Start the relay
2. Start a server
3. Use a client to access a server through the relay

From the source code directory:

- `cargo run --bin ptth_relay`
- `cargo run --bin ptth_server`
- `firefox http://127.0.0.1:4000/servers/my_server/files/`

If you only have pre-built binaries:

- `./ptth_relay`
- `./ptth_server`
- `firefox http://127.0.0.1:4000/servers/my_server/files/`

To run the relay behind Nginx, these directives improve time-to-first-byte
when streaming:

```
client_max_body_size 0;
proxy_http_version 1.1;
proxy_request_buffering off;
proxy_buffering off;
```

## Glossary

(sorted alphabetically)

- **Backend API** - The HTTP API that ptth_server uses to establish the tunnel.
Noted in the code with the cookie "7ZSFUKGV".
- **Client** - Any client that connects to ptth_relay in order to reach a
destination server. Admins must terminate TLS between 
ptth_relay and all clients.
- **Frontend** - The human-friendly, browser-friendly HTTP+HTML interface 
that ptth_relay serves directly or relays from ptth_server. 
This interface has no auth by default. Admins must provide their own auth 
in front of ptth_relay. OAuth2 is recommended.
- **ptth_file_server** - A standalone file server. It uses the same code
as ptth_server, so production environments don't need it.
- **ptth_relay** or **Relay server** - The ptth_relay app. This must run on a server
that can accept incoming HTTP connections.
- **ptth_server** or **Destination server** - The ptth_server app. This should run behind
a firewall. It will connect out to the relay and accept incoming connections
through the PTTH tunnel.
- **Scraper API** - An optional HTTP API for scraper clients to access ptth_relay and
the destination servers using machine-friendly auth.
- **Tripcode** - The base64 hash of a server's private API key. When adding
a new server, the tripcode must be copied to ptth_relay.toml on the relay
server.
- **Tunnel** - The reverse HTTP tunnel between ptth_relay and ptth_server.
ptth_server connects out to ptth_relay, then ptth_relay forwards incoming
connections to ptth_server through the tunnel.

## Comparison with normal HTTP

Normal HTTP:

```
Client       Server

       H1
  O ---------> O
               | H2
  O <--------- O
          H3
```

1. The client connects to the server and sends a request
2. The server accepts the connection and processes the request
3. The server responds with a response

We'll call these steps "H1", "H2", and "H3" in the next section.

PTTH:

```
Client    Relay    Server

                P1
            O <----- O
    P2/H1   |
  O ------> O
            |   P3
            O -----> O
                     | P4/H2
            O <----- O
            |   P5
  O <------ O
      P6/H3 |   P7
            O -----> O
```

We'll call these steps "P1" through "P7".

1. The server makes a "listen" request to the relay, 
punching out through the server's firewall.
The server and relay are now in a long-polling state with each other, 
waiting for a client to make a request.
2. A client makes a request to the relay. (P2 == H1)
3. The relay packages the request and sends it as a response to the server,
completing the server's request in P1.
The client and relay are now in a long-polling state, waiting for the server
to respond.
4. The server processes the request. (P4 == H2)
5. The server packages its response in another request to the relay.
6. The relay unwraps the request and forwards it to the client. (P6 == H3)
7. When the full response body has been streamed through the relay and to the
client, the relay will respond to the server.

Every step of the normal HTTP process is inverted for the server:

- It must stay connected to the relay even when nothing is happening
- A request arrives packaged in a response
- A response is sent out packaged as a request

There are twice as many steps, and the per-connection and per-request overhead
is probably high. But once the connections are established, the only
overhead is that of using a relay, which is similar to many other file transfer
or remote desktop software.

## Comparison with similar software

PTTH is very similar to [PageKite](https://github.com/pagekite/PyPagekite).
PTTH's relay is equivalent to PageKite's front-end server, and PTTH's server
is equivalent to (I think) PageKite's backend.

WireGuard can also pierce firewalls, but it requires root permissions,
and the client must be a WireGuard node. PTTH allows any normal HTTP client
such as curl, Firefox, etc.

## Module overview

```
+------------+       +-------------+       +------------------+
| ptth_relay |       | ptth_server |       | ptth_file_server |
+------------+       +-------------+       +------------------+
            |         |           |          |
             \       /             \        /
              V     V               V      V
           +------------+       +-------------+
           | http_serde |       | file_server |
           +------------+       +-------------+
```

The top-level binaries are ptth_relay, ptth_server, and ptth_file_server.

ptth_relay should run on a well-known public server, behind an HTTPS proxy
such as Caddy, Nginx, or Apache.

ptth_file_server is a standalone HTTP file server, similar to Python2's
`-m SimpleHTTPServer` command, or Python3's `-m http.server`.

ptth_server and ptth_file_server use the `file_server` module. ptth_server
will connect out to a ptth_relay instance and serve files through the reverse
HTTP tunnel.

The `http_serde` module is shared by ptth_relay and ptth_server so that they
can communicate with each other easily.

## How should I report bugs or request features?

For now, either email me (if you know me personally) or make a pull request to add an item to [todo.md](todo.md).

## License

PTTH is licensed under the
[GNU AGPLv3](https://www.gnu.org/licenses/agpl-3.0.html)

Copyright 2020 "Trish"