Golang does not support the 'socks5h://' schema for http[s]_proxy
env variable: https://github.com/golang/go/blob/9123221ccf3c80c741ead5b6f2e960573b1676b9/src/vendor/golang.org/x/net/http/httpproxy/proxy.go#L152-L159,
while libcurl supports it: https://github.com/curl/curl/blob/ae98b85020094fb04eee7e7b4ec4eb1a38a98b98/docs/libcurl/opts/CURLOPT_PROXY.3#L48-L59.
So, if a 'https_proxy=socks5h://127.0.0.1:1080' env has been set in the
make.conf to make curl (assuming curl is the current download command) to
download all packages through the proxy, go-module_live_vendor will
fail.

The only difference between these two schemas is, 'socks5h' will solve
the hostname via the proxy while 'socks5' will not. I think it's ok to
fallback 'socks5h' to 'socks5' for `go vendor` command and warn user,
until golang supports it.

related to issue: golang/go#24135

Golang does not support the 'socks5h://' schema for http[s]_proxy
env variable: https://github.com/golang/go/blob/9123221ccf3c80c741ead5b6f2e960573b1676b9/src/vendor/golang.org/x/net/http/httpproxy/proxy.go#L152-L159,
while libcurl supports it: https://github.com/curl/curl/blob/ae98b85020094fb04eee7e7b4ec4eb1a38a98b98/docs/libcurl/opts/CURLOPT_PROXY.3#L48-L59.
So, if a 'https_proxy=socks5h://127.0.0.1:1080' env has been set in the
make.conf to make curl (assuming curl is the current download command) to
download all packages through the proxy, go-module_live_vendor will
fail.

The only difference between these two schemas is, 'socks5h' will solve
the hostname via the proxy while 'socks5' will not. I think it's ok to
fallback 'socks5h' to 'socks5' for `go vendor` command and warn user,
until golang supports it.

related to issue: golang/go#24135

Signed-off-by: Ryan Qian <i@bitbili.net>

currently only http/https/socks5 scheme are allowed. However, any scheme could
be possible if user provides their own implementation. Specifically, the widely
used `socks5h://localhost` is parsed as Scheme="http" Host="socks5h:", which
does not make sense because host name cannot contain ":".

This patch allows any scheme to appear in the proxy config. And only fallback
to http scheme if parsed scheme or host is empty.

`url.Parse` result of fallback cases:

localhost      => Scheme="localhost"
localhost:1234 => Scheme="localhost" Opaque="1234"
example.com    => Path="example.com"

Updates golang/go#24135

currently only http/https/socks5 scheme are allowed. However, any scheme
could be possible if user provides their own implementation.
Specifically, the widely used "socks5h://localhost" is parsed as
Scheme="http" Host="socks5h:", which does not make sense because host
name cannot contain ":".

This patch allows any scheme to appear in the proxy config. And only
fallback to http scheme if parsed scheme or host is empty.

url.Parse() result of fallback cases:

localhost      => Scheme="localhost"
localhost:1234 => Scheme="localhost" Opaque="1234"
example.com    => Path="example.com"

Updates golang/go#24135

Change-Id: Ia2c041e37e2ac61be16220fd41d6cb6fabeeca3d
Reviewed-on: https://go-review.googlesource.com/c/net/+/525257
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Run-TryBot: Damien Neil <dneil@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Damien Neil <dneil@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Damien Neil <dneil@google.com>

Extend the net/http Transport to recognize the 'socks5h' schema as an alias for 'socks5'. Traditionally, the 'socks5h' schema indicates that the hostname should be resolved by the proxy server, which is behavior already implemented in Go for 'socks5'.

The update requires upgrading the golang.org/x/net dependency to support any proxy schema, including 'socks5h', specified through environment variables.

Fixes golang#24135

Commands run (in both src and src/cmd):
	go get golang.org/x/net@master
	go mod tidy
	go mod vendor

For #24135

Change-Id: I88084d174c15a65350be1b43e27de619dc6d4dd6
Reviewed-on: https://go-review.googlesource.com/c/go/+/570156
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: 胡玮文 <huww98@outlook.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>