The Wire Answers in Files
The Wire Answers in Files
Seed: Plan 9 /net — the IP stack as a file tree.
Every other system asks a program to reach for a special call to open a connection — a socket, its own kind of object, living outside the ordinary rules of files, needing its own functions to read it, write it, close it, ask it questions. Plan 9 refuses the special case. Under /net sits tcp, udp, ip, arp, ipifc — an entire protocol stack laid out as an ordinary directory tree, and a connection is not a handle returned by a privileged call. It is a directory, made the same way any other resource on this system is made: by opening a clone file.
Open /net/tcp/clone and the system reserves you a connection before you have said who it is for. Reading the file descriptor back hands you a number; that number is now a subdirectory, /net/tcp/3, holding ctl to command it, data to carry the actual bytes, status and local and remote to describe what it currently is. Dialing an address is just writing a string into ctl. Sending data is just writing into data. There is no send(), no recv(), no distinct socket namespace to learn — only the read and write every file already answers to.
This is not merely economy of syntax. It means every tool that already knows how to handle a file automatically knows how to handle a network connection: it can be passed between processes as a file descriptor, imported into another machine's namespace over 9P, inspected with cat and ls without a single network-aware line of code written for the purpose. A firewall, a proxy, a debugger for a new IP stack — all of these become questions of which directory you bind where, not which new API you must first invent.
The wire was never a separate kind of thing. It only looked that way because other systems built a wall around it. Plan 9's answer was to take the wall down and discover the wire had been a file all along.