add support structured tag fields

tags.go is copied from encoding/json in the go standard library.  We're
not doing anything with the field options yet, just parsing them out.

Author: willnorris

query/encode.go

@@ -20,7 +20,8 @@ func Values(v interface{}) (url.Values, error) {
 	for i := 0; i < typ.NumField(); i++ {
 		sf := typ.Field(i)
 
-		name := sf.Tag.Get("url")
+		tag := sf.Tag.Get("url")
+		name, _ := parseTag(tag)
 		if name == "" {
 			name = sf.Name
 		}

query/encode_test.go

@@ -9,7 +9,7 @@ import (
 
 func TestValues(t *testing.T) {
 	s := struct {
-		A string `url:"a"`
+		A string `url:"a,omitempty"`
 		B int
 	}{"abc", 1}
 	v, err := Values(s)

query/tags.go

@@ -0,0 +1,42 @@
+// Copyright 2011 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 query
+
+import "strings"
+
+// tagOptions is the string following a comma in a struct field's "json"
+// tag, or the empty string. It does not include the leading comma.
+type tagOptions string
+
+// parseTag splits a struct field's json tag into its name and
+// comma-separated options.
+func parseTag(tag string) (string, tagOptions) {
+	if idx := strings.Index(tag, ","); idx != -1 {
+		return tag[:idx], tagOptions(tag[idx+1:])
+	}
+	return tag, tagOptions("")
+}
+
+// Contains returns whether checks that a comma-separated list of options
+// contains a particular substr flag. substr must be surrounded by a
+// string boundary or commas.
+func (o tagOptions) Contains(optionName string) bool {
+	if len(o) == 0 {
+		return false
+	}
+	s := string(o)
+	for s != "" {
+		var next string
+		i := strings.Index(s, ",")
+		if i >= 0 {
+			s, next = s[:i], s[i+1:]
+		}
+		if s == optionName {
+			return true
+		}
+		s = next
+	}
+	return false
+}

query/tags_test.go

@@ -0,0 +1,26 @@
+// Copyright 2011 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 query
+
+import "testing"
+
+func TestTagParsing(t *testing.T) {
+	name, opts := parseTag("field,foobar,foo")
+	if name != "field" {
+		t.Fatalf("name = %q, want field", name)
+	}
+	for _, tt := range []struct {
+		opt  string
+		want bool
+	}{
+		{"foobar", true},
+		{"foo", true},
+		{"bar", false},
+	} {
+		if opts.Contains(tt.opt) != tt.want {
+			t.Errorf("Contains(%q) = %v", tt.opt, !tt.want)
+		}
+	}
+}