Allow a connection attempt to timeout and keep trying resolved addresses

[ex-nihil]

Before this change connect_host only attempted to connect to the first resolved SocketAddr.

My interpretation was that this was the indented use of agent.config.timeout_connect but, I'm unsure as the default value seems to be 30 sec.

Breaking change for any projects depending on the timeout_connect config, maybe introduce a separate configuration for this timeout.

[algesten]

The intention is that connect_timeout is regardless of how many SocketAddr there might be.

Is your problem that the failing socket address takes longer than 30 seconds to fail?

[ex-nihil]

My problem is that there's no SocketAddr failover.
Whatever connect_timeout is set to will be the amount of time we wait for the first SocketAddr connection attempt.

And when that fails the request is aborted by this line.

ureq/src/stream.rs

Line 372 in ec663fa

Some(deadline) => Some(time_until_deadline(deadline)?),

edit: My first address never responds

[algesten]

edit: My first address never responds

As far as I know all OSes will timeout socket connection attempts at some point. Some quick googling seems to say for windows it's 72 seconds and for Linux 60 seconds. In many cases I would image the timeout to be shorter. For example, if the host is there, but port closed, the SYN would be responded with an RST and the fail be instant.

The 30 second value is for the overall the connection attempt, not per socket addr. On your host, could you try lowering the OS default timeout and see if that helps?

I wonder what cURL does here, does it fail faster than the OS so it can try more addresses?

[ex-nihil]

I wonder what cURL does here, does it fail faster than the OS so it can try more addresses?

Curl failed over pretty much instantly when it was happening.

It seems the Spotify server is no longer non-responsive for the first host, so unable to recreate right now.
I will try to setup a test the behavior later tonight.

[ex-nihil]

Added a testcase to this PR socket_addr_fail_over recreating it. Your suggestion with lowering the OS timeout should absolutely work, but the question is how curl was able to figure it out.

I would need to setup a DNS server to compare.

[ex-nihil]

Well, found why curl worked. It attempts the first two entries at the same time.
https://github.com/curl/curl/blob/faebcee349d45f46638add6dda3185425c7afac6/lib/connect.c#L752

They also set the addr connection attempt to timeoutms/2 if there's multiple addresses.
https://github.com/curl/curl/blob/faebcee349d45f46638add6dda3185425c7afac6/lib/connect.c#L504

[algesten]

Right. That seems reasonable. We could do that too. if there are at least two addresses, split connect_timeout in 2 and try both after each other.

[ex-nihil]

Updated the PR.
The behavior for multiple addresses is now that a socket connection gets half of the remaining time until the deadline.
So as an example a timeout of 10sec with 3 resolved SocketAddr will result in.

Timeouts
1st after 5 sec
2nd after 2.5 sec
3rd after 1.25 sec

[algesten]

Let's land this.

Thanks!