https://github.com/cirocosta/http-ctx-cancellation

golang's request timeout from context cancellation exemplified in C
https://github.com/cirocosta/http-ctx-cancellation

c go http

Last synced: 11 days ago
JSON representation

golang's request timeout from context cancellation exemplified in C

• Host: GitHub
• URL: https://github.com/cirocosta/http-ctx-cancellation
• Owner: cirocosta
• Created: 2019-12-26T16:45:15.000Z (almost 5 years ago)
• Default Branch: master
• Last Pushed: 2019-12-27T23:10:38.000Z (almost 5 years ago)
• Last Synced: 2024-10-15T18:05:07.780Z (26 days ago)
• Topics: c, go, http
• Language: C
• Homepage: https://ops.tips
• Size: 344 KB
• Stars: 1
• Watchers: 2
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.txt

Awesome Lists containing this project

• awesome-golang-repositories - http-ctx-cancellation

README

        
WHAT'S THIS

	this repo is intended to play around w/ context cancellation in Go in

	the "context" of http requests.

	

	it contains:

		- http client in C that w/ a timeout of `n` seconds 

		  - plain use of epoll and timerfd

		- http client in Go w/ a timeout of `n` seconds 

		  - using ctx cancellation

		- http server in Go that sleeps for N seconds 

	by making the server not respond on a given amount of time, we can

	simulate cases where you'd want to timeout the request.

	using `go`, one can do so via `http.NewRequestWithContext()`, giving it

	a context that gets cancelled after a given deadline is reached.

	under the hood, such cancellation is done through a socket shutdown

	(plain `close(2)`) on a nonblocking socket that's part of an epoll

	facility

		strace -f -e 'trace=!futex,nanosleep' ./http

		1. non-blocking socket gets created

			[pid 17751] socket(AF_INET, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, IPPROTO_IP) = 3

			[pid 17751] setsockopt(3, SOL_SOCKET, SO_BROADCAST, [1], 4) = 0

			[pid 17751] connect(3, {sa_family=AF_INET, sin_port=htons(1337), sin_addr=inet_addr("127.0.0.1")}, 16) = -1 

				EINPROGRESS (Operation now in progress)

		2. socket gets added to epoll facility

			[pid 17751] epoll_ctl(4, EPOLL_CTL_ADD, 3, {

				EPOLLIN|EPOLLOUT|EPOLLRDHUP|EPOLLET, {u32=812239112, u64=139655968835848}}) = 0

		3. wait on the fds that were added - once `connect` finishes, we

		   should get an event for that fd

			[pid 17751] epoll_pwait(4, [{

				EPOLLOUT, {u32=812239112, u64=139655968835848}}], 128, 0, NULL, 824634156712) = 1

		4. check if there were any errors in the conn

			[pid 17751] getsockopt(3, SOL_SOCKET, SO_ERROR,  

		5. write to the socket

			[pid 17751] write(3, "GET / HTTP/1.1\r\nHost: localhost:"..., 95

		6. try to read from it

			[pid 17757] read(3,  

			[pid 17757] <... read resumed> 0xc00011e000, 4096) 

				-1 EAGAIN (Resource temporarily unavailable)

				// ...

		7. would block, so lets continue waiting ..

		8. deadline reached, all we gotta do is remove from the set and

		   close it

			[pid 17755] epoll_ctl(4, EPOLL_CTL_DEL, 3, 0xc000132984) = 0

			[pid 17755] close(3)                    = 0

	naturally, we can implement that in C - see ./http-client.c