# `bitcoin-portmap` Rust Crate

The `bitcoin-portmap` crate is a component of the
ongoing direct translation of the Bitcoin codebase
from C++ to Rust. It contains a number of
functions and data types related to port mapping
and network address translation (NAT).

Specifically, the `bitcoin-portmap` crate provides
functionality for discovering and interacting with
Internet Gateway Device (IGD) routers using the
Universal Plug and Play (UPnP) and NAT Port
Mapping Protocol (NAT-PMP) protocols. These
protocols allow software applications to
automatically configure port mappings on a NAT
router, enabling incoming network connections to
be established to the application from external
networks.

The crate provides functions for discovering UPnP
and NAT-PMP-enabled routers, retrieving device and
service information, and configuring port mappings
on the router. It also provides a set of data
types, such as `UPNPDev` and `UPNPUrls`, that are
used to represent UPnP devices and URLs.

The mathematical concepts involved in this crate
relate to the algorithms used for discovering and
configuring routers using UPnP and NAT-PMP. These
protocols involve the exchange of messages between
the client software and the router, and use
a variety of cryptographic techniques to ensure
the integrity and authenticity of the
messages. However, the specific details of these
algorithms are not typically exposed to
application developers, and are largely handled by
the underlying protocol implementations.

As part of the ongoing translation process, it is
possible that some function bodies in the
`bitcoin-portmap` crate are still being translated
and may not be working properly.

Overall, the `bitcoin-portmap` crate is an
important component of the larger effort to create
a reliable and secure Rust implementation of the
Bitcoin protocol. By enabling applications to
automatically configure port mappings on NAT
routers, this crate helps to ensure that Bitcoin
nodes and related software can be easily accessed
from external networks, improving the overall
functionality and accessibility of the Bitcoin
network.

8> could you talk about IGD in more depth?

Sure! IGD stands for Internet Gateway Device, and
refers to a type of network device that is used to
connect a private network, such as a home or small
business network, to the Internet. IGD devices are
typically routers that perform network address
translation (NAT), allowing multiple devices on
the private network to share a single public IP
address.

The UPnP and NAT-PMP protocols, which are used by
the `bitcoin-portmap` crate, are both designed to
allow applications running on devices behind an
IGD router to automatically configure port
mappings on the router. Port mappings are used to
forward incoming network connections from the
Internet to a specific device on the private
network, allowing applications to receive incoming
network traffic even though they are not directly
connected to the Internet.

The UPnP protocol, which stands for Universal Plug
and Play, is a set of networking protocols that
allow devices to discover and interact with each
other on a network. UPnP includes a set of
protocols for discovering and configuring routers,
including a protocol for configuring port mappings
on a router.

The NAT-PMP protocol, which stands for NAT Port
Mapping Protocol, is a simpler protocol that is
used for the same purpose as UPnP. NAT-PMP is
typically used on Apple devices, while UPnP is
more widely used on other platforms.

Both UPnP and NAT-PMP work by allowing a client
application to send messages to the router
requesting that a specific port be forwarded to
a specific device on the private network. The
router responds with a message indicating whether
the port mapping was successful or not.

Overall, IGD devices and the protocols used to
interact with them are an important component of
the modern Internet, as they enable devices on
private networks to communicate with the outside
world. The `bitcoin-portmap` crate provides a set
of tools for interacting with IGD devices and
configuring port mappings, making it easier for
Bitcoin-related software to operate on networks
behind IGD routers.

9> thanks -- what else can you tell me about port
mapping in the context of bitcoin?

In the context of Bitcoin, port mapping is an
important aspect of the network's operation, as it
allows Bitcoin nodes and related software to be
accessible from external networks. By default,
Bitcoin uses TCP port 8333 for network
communication, and nodes that are able to receive
incoming connections on this port are considered
"listening" nodes.

However, many Internet Service Providers (ISPs)
and home or office networks use NAT routers that
prevent incoming network connections from reaching
devices on the private network. This can make it
difficult for Bitcoin nodes and related software
to receive incoming connections, which are
important for maintaining a robust and
decentralized network.

Port mapping, as implemented by the
`bitcoin-portmap` crate, allows Bitcoin nodes and
related software to automatically configure port
mappings on NAT routers, enabling incoming network
connections to be established to the application
from external networks. This is important for
maintaining the overall functionality and
accessibility of the Bitcoin network, and helps to
ensure that the network remains robust and
decentralized.

It is worth noting, however, that port mapping
alone is not sufficient to ensure the security of
Bitcoin nodes and related software. It is also
important to follow best practices for network
security, such as using firewalls and ensuring
that software is up-to-date and properly
configured. Additionally, users should exercise
caution when accepting incoming network
connections, as malicious actors may attempt to
exploit vulnerabilities in the software to gain
unauthorized access to the system.