Fix snet.UDPAddress parsing & serialization

[oncilla]

Allow :port without [] for IPv4.
Use net library functions instead of manual parsing.

Recommended:
  - isd-as,ipv4:port   (e.g., 1-ff00:0:300,192.168.1.1:8080)
  - isd-as,[ipv6]:port (e.g., 1-ff00:0:300,[f00d::1337]:808)

 Others:
  - isd-as,[ipv4]:port (e.g., 1-ff00:0:300,[192.168.1.1]:80)
  - isd-as,[ipv4]      (e.g., 1-ff00:0:300,[192.168.1.1])
  - isd-as,[ipv6]      (e.g., 1-ff00:0:300,[f00d::1337])
  - isd-as,ipv4        (e.g., 1-ff00:0:300,192.168.1.1)
  - isd-as,ipv6        (e.g., 1-ff00:0:300,f00d::1337)

 Not supported:
  - isd-as,ipv6:port    (caveat if ipv6:port builds a valid ipv6 address,
                         it will successfully parse as ipv6 without error)

Fixes #3647

based on #3648

---

This change is 

[lukedirtwalker]

Reviewed 2 of 2 files at r2.
Reviewable status: all files reviewed, 3 unresolved discussions (waiting on @oncilla)

---

go/lib/snet/udpaddr.go, line 70 at r2 (raw file):

	}
	hostPortPart := parts["host"]
	host, portS, err := net.SplitHostPort(hostPortPart)

Just use net.ResolveUDPAddr(...) here then we can remove the code below.

---

go/lib/snet/udpaddr.go, line 151 at r2 (raw file):

I

lower case start of error message

---

go/lib/snet/udpaddr.go, line 165 at r2 (raw file):

// If the input is invalid, or also contains a port, nil is returned.
func hostOnly(s string) net.IP {
	left, right := strings.Count(s, "["), strings.Count(s, "]")

I think the bracket checks could be done separately in the beginning as a validation function. If any of those 2 conditions fail, it is an error and the format is wrong. SplitHostPort will also fail. hostOnly is really only the last line of this function, at which point I don't see the need for a separate function.

[oncilla]

Reviewable status: 0 of 2 files reviewed, 3 unresolved discussions (waiting on @lukedirtwalker)

---

go/lib/snet/udpaddr.go, line 70 at r2 (raw file):

Previously, lukedirtwalker (Lukas Vogel) wrote…

Just use net.ResolveUDPAddr(...) here then we can remove the code below.

Done.

---

go/lib/snet/udpaddr.go, line 151 at r2 (raw file):

Previously, lukedirtwalker (Lukas Vogel) wrote…

I

lower case start of error message

Done.

---

go/lib/snet/udpaddr.go, line 165 at r2 (raw file):

Previously, lukedirtwalker (Lukas Vogel) wrote…

I think the bracket checks could be done separately in the beginning as a validation function. If any of those 2 conditions fail, it is an error and the format is wrong. SplitHostPort will also fail. hostOnly is really only the last line of this function, at which point I don't see the need for a separate function.

Done.

[lukedirtwalker]

Reviewed 2 of 2 files at r3.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @oncilla)

---

go/lib/snet/udpaddr.go, line 157 at r3 (raw file):

// hostOnly parses the input in the case it only contains a host.
// If the input is invalid, or also contains a port, nil is returned.
func hostOnly(s string) net.IP {

remove?

[oncilla]

Reviewable status: 1 of 2 files reviewed, 1 unresolved discussion (waiting on @lukedirtwalker)

---

go/lib/snet/udpaddr.go, line 157 at r3 (raw file):

Previously, lukedirtwalker (Lukas Vogel) wrote…

remove?

Done.

[lukedirtwalker]

Reviewed 1 of 1 files at r4.
Reviewable status: complete! all files reviewed, all discussions resolved

[lukedirtwalker]

Reviewable status: complete! all files reviewed, all discussions resolved