fix: panic in browser redirect handler for unexpected r.Host (#14844)

```
panic: "GET /": invalid hostname
goroutine 148 [running]:
runtime/debug.Stack()
	runtime/debug/stack.go:24 +0x65
github.com/minio/minio/cmd.setCriticalErrorHandler.func1.1()
	github.com/minio/minio/cmd/generic-handlers.go:469 +0x8e
panic({0x2201f00, 0xc001f1ddd0})
	runtime/panic.go:1038 +0x215
github.com/minio/pkg/net.URL.String({{0x25aa417, 0x5}, {0x0, 0x0}, 0x0, {0xc000174380, 0xd7}, {0x0, 0x0}, {0x0, ...}, ...})
	github.com/minio/pkg@v1.1.23/net/url.go:97 +0xfe
github.com/minio/minio/cmd.setBrowserRedirectHandler.func1({0x49af080, 0xc0003c20e0}, 0xc00002ea00)
	github.com/minio/minio/cmd/generic-handlers.go:136 +0x118
net/http.HandlerFunc.ServeHTTP(0xc00002ea00, {0x49af080, 0xc0003c20e0}, 0xa)
	net/http/server.go:2047 +0x2f
github.com/minio/minio/cmd.setAuthHandler.func1({0x49af080, 0xc0003c20e0}, 0xc00002ea00)
	github.com/minio/minio/cmd/auth-handler.go:525 +0x3d8
net/http.HandlerFunc.ServeHTTP(0xc00002e900, {0x49af080, 0xc0003c20e0}, 0xc001f33701)
	net/http/server.go:2047 +0x2f
github.com/gorilla/mux.(*Router).ServeHTTP(0xc0025d0780, {0x49af080, 0xc0003c20e0}, 0xc00002e800)
	github.com/gorilla/mux@v1.8.0/mux.go:210 +0x1cf
github.com/rs/cors.(*Cors).Handler.func1({0x49af080, 0xc0003c20e0}, 0xc00002e800)
	github.com/rs/cors@v1.7.0/cors.go:219 +0x1bd
net/http.HandlerFunc.ServeHTTP(0x0, {0x49af080, 0xc0003c20e0}, 0xc00068d9f8)
	net/http/server.go:2047 +0x2f
github.com/minio/minio/cmd.setCriticalErrorHandler.func1({0x49af080, 0xc0003c20e0}, 0x4a5cd3)
	github.com/minio/minio/cmd/generic-handlers.go:476 +0x83
net/http.HandlerFunc.ServeHTTP(0x72, {0x49af080, 0xc0003c20e0}, 0x0)
	net/http/server.go:2047 +0x2f
github.com/minio/minio/internal/http.(*Server).Start.func1({0x49af080, 0xc0003c20e0}, 0x10000c001f1dda0)
	github.com/minio/minio/internal/http/server.go:105 +0x1b6
net/http.HandlerFunc.ServeHTTP(0x0, {0x49af080, 0xc0003c20e0}, 0x46982e)
	net/http/server.go:2047 +0x2f
net/http.serverHandler.ServeHTTP({0xc003dc1950}, {0x49af080, 0xc0003c20e0}, 0xc00002e800)
	net/http/server.go:2879 +0x43b
net/http.(*conn).serve(0xc000514d20, {0x49cfc38, 0xc0010c0e70})
	net/http/server.go:1930 +0xb08
created by net/http.(*Server).Serve
	net/http/server.go:3034 +0x4e8
```

cmd/generic-handlers.go

@@ -141,6 +141,14 @@ func setBrowserRedirectHandler(h http.Handler) http.Handler {
 	})
 }
 
+var redirectPrefixes = map[string]struct{}{
+	"favicon-16x16.png": {},
+	"favicon-32x32.png": {},
+	"favicon-96x96.png": {},
+	"index.html":        {},
+	minioReservedBucket: {},
+}
+
 // Fetch redirect location if urlPath satisfies certain
 // criteria. Some special names are considered to be
 // redirectable, this is purely internal function and
@@ -151,32 +159,25 @@ func getRedirectLocation(r *http.Request) *xnet.URL {
 	if err != nil {
 		return nil
 	}
-	for _, prefix := range []string{
-		"favicon-16x16.png",
-		"favicon-32x32.png",
-		"favicon-96x96.png",
-		"index.html",
-		minioReservedBucket,
-	} {
-		bucket, _ := path2BucketObject(resource)
-		if path.Clean(bucket) == prefix || resource == slashSeparator {
-			if globalBrowserRedirectURL != nil {
-				return globalBrowserRedirectURL
-			}
-			hostname, _, _ := net.SplitHostPort(r.Host)
-			if hostname == "" {
-				hostname = r.Host
-			}
-			return &xnet.URL{
-				Host: net.JoinHostPort(hostname, globalMinioConsolePort),
-				Scheme: func() string {
-					scheme := "http"
-					if r.TLS != nil {
-						scheme = "https"
-					}
-					return scheme
-				}(),
-			}
+	bucket, _ := path2BucketObject(resource)
+	_, redirect := redirectPrefixes[path.Clean(bucket)]
+	if redirect || resource == slashSeparator {
+		if globalBrowserRedirectURL != nil {
+			return globalBrowserRedirectURL
+		}
+		xhost, err := xnet.ParseHost(r.Host)
+		if err != nil {
+			return nil
+		}
+		return &xnet.URL{
+			Host: net.JoinHostPort(xhost.Name, globalMinioConsolePort),
+			Scheme: func() string {
+				scheme := "http"
+				if r.TLS != nil {
+					scheme = "https"
+				}
+				return scheme
+			}(),
 		}
 	}
 	return nil

cmd/handler-utils.go

@@ -25,7 +25,6 @@ import (
 	"io"
 	"io/ioutil"
 	"mime/multipart"
-	"net"
 	"net/http"
 	"net/textproto"
 	"net/url"
@@ -37,6 +36,7 @@ import (
 	"github.com/minio/minio/internal/handlers"
 	xhttp "github.com/minio/minio/internal/http"
 	"github.com/minio/minio/internal/logger"
+	xnet "github.com/minio/pkg/net"
 )
 
 const (
@@ -395,26 +395,25 @@ func getResource(path string, host string, domains []string) (string, error) {
 	if len(domains) == 0 {
 		return path, nil
 	}
+
 	// If virtual-host-style is enabled construct the "resource" properly.
-	if strings.Contains(host, ":") {
-		// In bucket.mydomain.com:9000, strip out :9000
-		var err error
-		if host, _, err = net.SplitHostPort(host); err != nil {
-			reqInfo := (&logger.ReqInfo{}).AppendTags("host", host)
-			reqInfo.AppendTags("path", path)
-			ctx := logger.SetReqInfo(GlobalContext, reqInfo)
-			logger.LogIf(ctx, err)
-			return "", err
-		}
+	xhost, err := xnet.ParseHost(host)
+	if err != nil {
+		reqInfo := (&logger.ReqInfo{}).AppendTags("host", host)
+		reqInfo.AppendTags("path", path)
+		ctx := logger.SetReqInfo(context.Background(), reqInfo)
+		logger.LogIf(ctx, err)
+		return "", err
 	}
+
 	for _, domain := range domains {
-		if host == minioReservedBucket+"."+domain {
+		if xhost.Name == minioReservedBucket+"."+domain {
 			continue
 		}
-		if !strings.HasSuffix(host, "."+domain) {
+		if !strings.HasSuffix(xhost.Name, "."+domain) {
 			continue
 		}
-		bucket := strings.TrimSuffix(host, "."+domain)
+		bucket := strings.TrimSuffix(xhost.Name, "."+domain)
 		return SlashSeparator + pathJoin(bucket, path), nil
 	}
 	return path, nil

cmd/handler-utils_test.go

@@ -221,6 +221,9 @@ func TestGetResource(t *testing.T) {
 		expectedResource string
 	}{
 		{"/a/b/c", "test.mydomain.com", []string{"mydomain.com"}, "/test/a/b/c"},
+		{"/a/b/c", "[2001:0db8:85a3:0000:0000:8a2e:0370:7334]:17000", []string{"mydomain.com"}, "/a/b/c"},
+		{"/a/b/c", "[2001:0db8:85a3:0000:0000:8a2e:0370:7334]", []string{"mydomain.com"}, "/a/b/c"},
+		{"/a/b/c", "192.168.1.1:9000", []string{"mydomain.com"}, "/a/b/c"},
 		{"/a/b/c", "test.mydomain.com", []string{"notmydomain.com"}, "/a/b/c"},
 		{"/a/b/c", "test.mydomain.com", nil, "/a/b/c"},
 	}