mps/middleware/singleHostReverseProxy.go

package middleware

import (
	"net/http"
	"net/url"
	"strings"

	"github.com/telanflow/mps"
)

// SingleHostReverseProxy returns a mps.Middleware
// URLs to the scheme, host, and base path provided in target. If the
// target's path is "/base" and the incoming request was for "/dir",
// the target request will be for /base/dir.
// SingleHostReverseProxy does not rewrite the Host header.
// To rewrite Host headers, use ReverseProxy directly with a custom
// Director policy.
func SingleHostReverseProxy(target *url.URL) mps.MiddlewareFunc {
	targetQuery := target.RawQuery
	return func(req *http.Request, ctx *mps.Context) (*http.Response, error) {
		// changed request Host
		req.Host = target.Host
		// changed request URL
		req.URL.Scheme = target.Scheme
		req.URL.Host = target.Host
		req.URL.Path = singleJoiningSlash(target.Path, req.URL.Path)
		if targetQuery == "" || req.URL.RawQuery == "" {
			req.URL.RawQuery = targetQuery + req.URL.RawQuery
		} else {
			req.URL.RawQuery = targetQuery + "&" + 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", "")
		}
		return ctx.Next(req)
	}
}

func singleJoiningSlash(a, b string) string {
	aslash := strings.HasSuffix(a, "/")
	bslash := strings.HasPrefix(b, "/")
	switch {
	case aslash && bslash:
		return a + b[1:]
	case !aslash && !bslash:
		return a + "/" + b
	}
	return a + b
}