TCP

Transmission Control Protocol (TCP) is a primary communication protocol of the internet, though that is changing with HTTP3 (which is not built on TCP) gaining adoption.

TCP is great because it allows ordered data to be safely sent across the internet. For example, let's say we want to send the message "i am live":

text	binary
i	01101001
a	01100001
m	01101101
l	01101100
i	01101001
v	01110110
e	01100101

When data is sent over a network, it is sent in packets. Each message is split into packets, the packets are sent, they arrive (potentially) out of order, and they are reassembled on the other side. And without a protocol like TCP, you can't guarantee that the order is correct...

You might end up with "i am evil" instead of "i am live"! TCP solves this problem.

Assignment

We're building our own HTTP, not our own TCP. We'll use the Go standard library's TCP implementation. Luckily Go doesn't have a built-in HTTP package or TheStartup™ would be out of business... /s

Instead of reading lines from a file, our program will now read lines from a TCP connection.

Remove all logic that reads from a file. Instead, use net.Listen to set up a TCP listener on port :42069.
- Don't forget to .Close() the listener when the program exits.
With the listener created, start an infinite loop that:
- Starts by waiting to .Accept a connection.
- Prints a message to the console that a connection has been accepted.
- Uses our getLinesChannel function to read lines from the connection.
- Prints each line to the console with no additional formatting (aside from a terminating newline).
- Prints a message to the console that the connection has been closed when the channel is closed.
You can terminate the program by pressing ctrl+c.
Run the server again and tee the output (copies the stdout) to a new temporary file called tcp.txt.

When printing lines to the console, use fmt.Println() rather than log.Println(). The log package writes to stderr by default, which won't be captured by the tee command used in testing.

go run . | tee /tmp/tcp.txt

Run and submit the CLI tests while the server is running.

For linux users, the tests expect openbsd-netcat, not gnu-netcat.

We haven't shipped a way to customize the port on these CLI shell-command lesson types... admittedly, Prime is probably the only person that might have conflicts on port 42069, so it should be fine.