pkg/httputil: configure HTTP transport timeouts

[thaJeztah]

• (slightly) related to Rootless: each GET /version leaks a connection to the RootlessKit API moby/moby#53814

Configure a timeout for connecting to the RootlessKit API socket, and set an idle connection timeout on the HTTP transport.

Previously, idle connections had no expiration because IdleConnTimeout was left at its zero value. This could leave connections open indefinitely for callers that create short-lived clients without explicitly closing idle connections.

Use the same dial and idle connection timeouts as http.DefaultTransport.

[thaJeztah]

cc @AkihiroSuda

[AkihiroSuda]

Should this be passed from the caller as an option like WithTimeout() ?

[AkihiroSuda]

ping @thaJeztah

[thaJeztah]

Don't think so (or at least it would be a separate feature) I used the same defaults as http.DefaultTransport. Or at least to my understanding, this client is created as the equivalent to the default, but with the connection-string modified.

For timeouts, callers can already use context cancellation.

Same for the other timeout, which also aligns with stdlib.

[AkihiroSuda]

I used the same defaults as http.DefaultTransport

Please add a comment line to refer to it?

[thaJeztah]

Updated; I slightly rewrote the code, and added a unixDialContext helper, so that the code here more closely resembles the implementation of http.DefaultTransport in stdlib;

var DefaultTransport RoundTripper = &Transport{
	Proxy: ProxyFromEnvironment,
	DialContext: defaultTransportDialContext(&net.Dialer{
		Timeout:   30 * time.Second,
		KeepAlive: 30 * time.Second,
	}),
	ForceAttemptHTTP2:     true,
	MaxIdleConns:          100,
	IdleConnTimeout:       90 * time.Second,
	TLSHandshakeTimeout:   10 * time.Second,
	ExpectContinueTimeout: 1 * time.Second,
}

[AkihiroSuda]

maybe:

Suggested change

	IdleConnTimeout: 90 * time.Second,
	IdleConnTimeout: dialer.Timeout * 3

[AkihiroSuda]

Thanks