Preserve leading and trailing slashes on proxy subpaths

Kubernetes-commit: 04eede9b2a2a24571cb084fcb952c6a2a2a2bdd1

pkg/util/net/http.go

@@ -26,13 +26,34 @@ import (
 	"net/http"
 	"net/url"
 	"os"
+	"path"
 	"strconv"
 	"strings"
 
 	"github.com/golang/glog"
 	"golang.org/x/net/http2"
 )
 
+// JoinPreservingTrailingSlash does a path.Join of the specified elements,
+// preserving any trailing slash on the last non-empty segment
+func JoinPreservingTrailingSlash(elem ...string) string {
+	// do the basic path join
+	result := path.Join(elem...)
+
+	// find the last non-empty segment
+	for i := len(elem) - 1; i >= 0; i-- {
+		if len(elem[i]) > 0 {
+			// if the last segment ended in a slash, ensure our result does as well
+			if strings.HasSuffix(elem[i], "/") && !strings.HasSuffix(result, "/") {
+				result += "/"
+			}
+			break
+		}
+	}
+
+	return result
+}
+
 // IsProbableEOF returns true if the given error resembles a connection termination
 // scenario that would justify assuming that the watch is empty.
 // These errors are what the Go http stack returns back to us which are general

pkg/util/net/http_test.go

@@ -20,6 +20,7 @@ package net
 
 import (
 	"crypto/tls"
+	"fmt"
 	"net"
 	"net/http"
 	"net/url"
@@ -218,3 +219,40 @@ func TestTLSClientConfigHolder(t *testing.T) {
 		t.Errorf("didn't find tls config")
 	}
 }
+
+func TestJoinPreservingTrailingSlash(t *testing.T) {
+	tests := []struct {
+		a    string
+		b    string
+		want string
+	}{
+		// All empty
+		{"", "", ""},
+
+		// Empty a
+		{"", "/", "/"},
+		{"", "foo", "foo"},
+		{"", "/foo", "/foo"},
+		{"", "/foo/", "/foo/"},
+
+		// Empty b
+		{"/", "", "/"},
+		{"foo", "", "foo"},
+		{"/foo", "", "/foo"},
+		{"/foo/", "", "/foo/"},
+
+		// Both populated
+		{"/", "/", "/"},
+		{"foo", "foo", "foo/foo"},
+		{"/foo", "/foo", "/foo/foo"},
+		{"/foo/", "/foo/", "/foo/foo/"},
+	}
+	for _, tt := range tests {
+		name := fmt.Sprintf("%q+%q=%q", tt.a, tt.b, tt.want)
+		t.Run(name, func(t *testing.T) {
+			if got := JoinPreservingTrailingSlash(tt.a, tt.b); got != tt.want {
+				t.Errorf("JoinPreservingTrailingSlash() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}