Implementing TCP in Rust (part 1)

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- Published on Feb 23, 2019๐ŸŒ Public

In this stream, we started implementing the ubiquitous TCP protocol that underlies much of the traffic on the internet! In particular, we followed RFC 793 โ€” โ€” which describes the original protocol, with the goal of being able to set up and tear down a connection with a "real" TCP stack at the other end (netcat in particular). We're writing it using a user-space networking interface (see and the Rust bindings at We got decently far, and are now able to both establish an incoming TCP connection (i.e., perform the TCP three-way handshake) and terminate the connection cleanly. You can find the current code at There's still a long way to go though, as we still need to add support for data segments, retransmissions, and timers; so that's what we'll cover in the next stream! Eventually, we will also want to implement RFC 1122 โ€” โ€” which lays out a number of further enhancements that must be made in order to interoperate nicely on the internet. This is also discussed in RFC 7414:, which we're also aiming to support. You can see the live version with comments at