Concepts

The Outline SDK is built upon some basic concepts, defined as interoperable interfaces that allow for composition and easy reuse.

Connections

Connections enable communication between two endpoints over an abstract transport. There are two types of connections:

• transport.StreamConn: stream-based connection, like TCP and the SOCK_STREAM Posix socket type.
• transport.PacketConn: datagram-based connection, like UDP and the SOCK_DGRAM Posix socket type. We use "Packet" instead of "Datagram" because that is the convention in the Go standard library.

Connections can be wrapped to create nested connections over a new transport. For example, a StreamConn could be over TCP, over TLS over TCP, over HTTP over TLS over TCP, over QUIC, among other options.

Dialers

Dialers enable the creation of connections given a host:port address while encapsulating the underlying transport or proxy protocol. The StreamDialer and PacketDialer types create StreamConn and PacketConn connections, respectively, given an address. Dialers can also be nested. For example, a TLS Stream Dialer can use a TCP dialer to create a StreamConn backed by a TCP connection, then create a TLS StreamConn backed by the TCP StreamConn. A SOCKS5-over-TLS Dialer could use the TLS Dialer to create the TLS StreamConn to the proxy before doing the SOCKS5 connection to the target address.

Resolvers

Resolvers (dns.Resolver) enable the answering of DNS questions while encapsulating the underlying algorithm or protocol. Resolvers are primarily used to map domain names to IP addresses.