update host.ProxyHandler to compatiable with different hosts in target url and request host

[tuhao1020]

#1702

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[kataras]

Hello @tuhao1020, how are you?

I think we must not introduce changes to that function, as it may be used by many applications and it was not updated for the past versions. I think it's better to introduce a new function for that e.g. ProxyHandlerRemote , please do it and don't forget to use gofmt :P

[tuhao1020]

@kataras I have added ProxyHandlerRemote and NewProxyRemote, and code has formatted :)

[kataras]

LGTM, thanks @tuhao1020 (although there is space for improvements there, e.g. remove the code duplication on the ProxyHandlerRemote, the 95% of the code is identical to the existing ProxyHandler one, but I will fix it later on)

[tuhao1020]

iris/core/host/proxy.go

Lines 40 to 55 in 6c823e4

	func modifyProxiedRequest(req *http.Request, target *url.URL) {
	req.URL.Scheme = target.Scheme
	req.URL.Host = target.Host
	req.Host = target.Host
	if target.RawQuery == "" || req.URL.RawQuery == "" {
	req.URL.RawQuery = target.RawQuery + req.URL.RawQuery
	} else {
	req.URL.RawQuery = target.RawQuery + "&" + req.URL.RawQuery
	}
	if _, ok := req.Header["User-Agent"]; !ok {
	// explicitly disable User-Agent so it's not set to default value
	req.Header.Set("User-Agent", "")
	}
	}

Line 43: req.Host = target.Host
this line will make below code useless

iris/core/host/proxy.go

Lines 70 to 72 in 6c823e4

	if req.Host != target.Host {
	req.URL.Path = target.Path
	} else {

req.Host = target.Host should be placed after above code.

[kataras]

Oh you are totally right, merging the 2nd one now @tuhao1020 .