net/url: add JoinPath, URL.JoinPath

Builds on CL 332209.

Fixes #47005

Change-Id: I82708dede05d79a196ca63f5a4e7cb5ac9a041ea
GitHub-Last-Rev: 51b735066e
GitHub-Pull-Request: golang/go#50383
Reviewed-on: https://go-review.googlesource.com/c/go/+/374654
Reviewed-by: Russ Cox <rsc@golang.org>
Auto-Submit: Russ Cox <rsc@golang.org>
Trust: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Damien Neil <dneil@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>

api/next.txt

@@ -3,3 +3,5 @@ pkg encoding/binary, type AppendByteOrder interface, AppendUint16([]uint8, uint1
 pkg encoding/binary, type AppendByteOrder interface, AppendUint32([]uint8, uint32) []uint8
 pkg encoding/binary, type AppendByteOrder interface, AppendUint64([]uint8, uint64) []uint8
 pkg encoding/binary, type AppendByteOrder interface, String() string
+pkg net/url, func JoinPath(string, ...string) (string, error)
+pkg net/url, method (*URL) JoinPath(...string) *URL

src/net/url/url.go

@@ -13,6 +13,7 @@ package url
 import (
 	"errors"
 	"fmt"
+	"path"
 	"sort"
 	"strconv"
 	"strings"
@@ -1176,6 +1177,17 @@ func (u *URL) UnmarshalBinary(text []byte) error {
 	return nil
 }
 
+// JoinPath returns a new URL with the provided path elements joined to
+// any existing path and the resulting path cleaned of any ./ or ../ elements.
+func (u *URL) JoinPath(elem ...string) *URL {
+	url := *u
+	if len(elem) > 0 {
+		elem = append([]string{u.Path}, elem...)
+		url.setPath(path.Join(elem...))
+	}
+	return &url
+}
+
 // validUserinfo reports whether s is a valid userinfo string per RFC 3986
 // Section 3.2.1:
 //     userinfo    = *( unreserved / pct-encoded / sub-delims / ":" )
@@ -1216,3 +1228,14 @@ func stringContainsCTLByte(s string) bool {
 	}
 	return false
 }
+
+// JoinPath returns a URL string with the provided path elements joined to
+// the existing path of base and the resulting path cleaned of any ./ or ../ elements.
+func JoinPath(base string, elem ...string) (result string, err error) {
+	url, err := Parse(base)
+	if err != nil {
+		return
+	}
+	result = url.JoinPath(elem...).String()
+	return
+}

src/net/url/url_test.go

@@ -2062,3 +2062,59 @@ func BenchmarkPathUnescape(b *testing.B) {
 		})
 	}
 }
+
+func TestJoinPath(t *testing.T) {
+	tests := []struct {
+		base string
+		elem []string
+		out  string
+	}{
+		{
+			base: "https://go.googlesource.com",
+			elem: []string{"go"},
+			out:  "https://go.googlesource.com/go",
+		},
+		{
+			base: "https://go.googlesource.com/a/b/c",
+			elem: []string{"../../../go"},
+			out:  "https://go.googlesource.com/go",
+		},
+		{
+			base: "https://go.googlesource.com/",
+			elem: []string{"./go"},
+			out:  "https://go.googlesource.com/go",
+		},
+		{
+			base: "https://go.googlesource.com//",
+			elem: []string{"/go"},
+			out:  "https://go.googlesource.com/go",
+		},
+		{
+			base: "https://go.googlesource.com//",
+			elem: []string{"/go", "a", "b", "c"},
+			out:  "https://go.googlesource.com/go/a/b/c",
+		},
+		{
+			base: "http://[fe80::1%en0]:8080/",
+			elem: []string{"/go"},
+		},
+	}
+	for _, tt := range tests {
+		wantErr := "nil"
+		if tt.out == "" {
+			wantErr = "non-nil error"
+		}
+		if out, err := JoinPath(tt.base, tt.elem...); out != tt.out || (err == nil) != (tt.out != "") {
+			t.Errorf("JoinPath(%q, %q) = %q, %v, want %q, %v", tt.base, tt.elem, out, err, tt.out, wantErr)
+		}
+		var out string
+		u, err := Parse(tt.base)
+		if err == nil {
+			u = u.JoinPath(tt.elem...)
+			out = u.String()
+		}
+		if out != tt.out || (err == nil) != (tt.out != "") {
+			t.Errorf("Parse(%q).JoinPath(%q) = %q, %v, want %q, %v", tt.base, tt.elem, out, err, tt.out, wantErr)
+		}
+	}
+}