feat: add resourcename.Validate

Includes a copied implementation of the not-yet-public (due to some edge
cases) implementation of domain name validation in go/src/net.

resourcename/isdomainname.go

@@ -0,0 +1,54 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package resourcename
+
+// isDomainName is copied from go/src/net/dnsclient.go pending resolution of the following issues:
+// - https://github.com/golang/go/issues/31671
+// - https://github.com/golang/go/issues/17659
+func isDomainName(s string) bool {
+	// See RFC 1035, RFC 3696.
+	// Presentation format has dots before every label except the first, and the
+	// terminal empty label is optional here because we assume fully-qualified
+	// (absolute) input. We must therefore reserve space for the first and last
+	// labels' length octets in wire format, where they are necessary and the
+	// maximum total length is 255.
+	// So our _effective_ maximum is 253, but 254 is not rejected if the last
+	// character is a dot.
+	l := len(s)
+	if l == 0 || l > 254 || l == 254 && s[l-1] != '.' {
+		return false
+	}
+	last := byte('.')
+	partlen := 0
+	for i := 0; i < len(s); i++ {
+		c := s[i]
+		switch {
+		default:
+			return false
+		case 'a' <= c && c <= 'z' || 'A' <= c && c <= 'Z' || c == '_' || '0' <= c && c <= '9':
+			partlen++
+		case c == '-':
+			// Byte before dash cannot be dot.
+			if last == '.' {
+				return false
+			}
+			partlen++
+		case c == '.':
+			// Byte before dot cannot be dot, dash.
+			if last == '.' || last == '-' {
+				return false
+			}
+			if partlen > 63 || partlen == 0 {
+				return false
+			}
+			partlen = 0
+		}
+		last = c
+	}
+	if last == '-' || partlen > 63 {
+		return false
+	}
+	return true
+}

resourcename/validate.go

@@ -0,0 +1,32 @@
+package resourcename
+
+import (
+	"fmt"
+)
+
+// Validate that a resource name conforms to the restrictions outlined in AIP-122, primarily that each segment
+// must be a valid DNS name.
+// See: https://google.aip.dev/122
+func Validate(name string) error {
+	if name == "" {
+		return fmt.Errorf("resource name is empty")
+	}
+	var sc Scanner
+	sc.Init(name)
+	var i int
+	for sc.Scan() {
+		i++
+		switch {
+		case sc.Segment() == "":
+			return fmt.Errorf("segment %d is empty", i)
+		case sc.Segment() == Wildcard:
+			continue
+		case !isDomainName(string(sc.Segment())):
+			return fmt.Errorf("segment '%s': not a valid DNS name", sc.Segment())
+		}
+	}
+	if sc.Full() && !isDomainName(sc.ServiceName()) {
+		return fmt.Errorf("service '%s': not a valid DNS name", sc.Segment())
+	}
+	return nil
+}

resourcename/validate_test.go

@@ -0,0 +1,96 @@
+package resourcename
+
+import (
+	"testing"
+
+	"gotest.tools/v3/assert"
+)
+
+func TestValidate(t *testing.T) {
+	t.Parallel()
+	for _, tt := range []struct {
+		name          string
+		input         string
+		errorContains string
+	}{
+		{
+			name:          "empty",
+			input:         "",
+			errorContains: "empty",
+		},
+
+		{
+			name:          "invalid DNS characters",
+			input:         "ice cream is best",
+			errorContains: "not a valid DNS name",
+		},
+
+		{
+			name:          "invalid DNS characters in segment",
+			input:         "foo/bar/ice cream is best",
+			errorContains: "not a valid DNS name",
+		},
+
+		{
+			name:          "invalid DNS characters in domain",
+			input:         "//ice cream is best.com/foo/bar",
+			errorContains: "not a valid DNS name",
+		},
+
+		{
+			name:  "singleton",
+			input: "foo",
+		},
+
+		{
+			name:  "singleton wildcard",
+			input: "-",
+		},
+
+		{
+			name:  "multi",
+			input: "foo/bar",
+		},
+
+		{
+			name:  "multi wildcard at start",
+			input: "-/bar",
+		},
+
+		{
+			name:  "multi wildcard at end",
+			input: "foo/-",
+		},
+
+		{
+			name:  "multi wildcard at middle",
+			input: "foo/-/bar",
+		},
+
+		{
+			name:  "numeric",
+			input: "foo/1234/bar",
+		},
+
+		{
+			name:  "camelCase",
+			input: "FOO/1234/bAr",
+		},
+
+		{
+			name:  "full",
+			input: "//example.com/foo/bar",
+		},
+	} {
+		tt := tt
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+			err := Validate(tt.input)
+			if tt.errorContains != "" {
+				assert.ErrorContains(t, err, tt.errorContains)
+			} else {
+				assert.NilError(t, err)
+			}
+		})
+	}
+}