// Copyright 2013 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 implements encoding of structs into URL query parameters.
//
// As a simple example:
//
// type Options struct {
// Query string `url:"q"`
// ShowAll bool `url:"all"`
// Page int `url:"page"`
// }
//
// opt := Options{ "foo", true, 2 }
// v, _ := query.Values(opt)
// fmt.Print(v.Encode()) // will output: "q=foo&all=true&page=2"
//
// The exact mapping between Go values and url.Values is described in the
// documentation for the Values() function.
package query
import (
"bytes"
"fmt"
"net/url"
"reflect"
"strconv"
"strings"
"time"
)
var timeType = reflect.TypeOf(time.Time{})
var encoderType = reflect.TypeOf(new(Encoder)).Elem()
// Encoder is an interface implemented by any type that wishes to encode
// itself into URL values in a non-standard way.
type Encoder interface {
EncodeValues(key string, v *url.Values) error
}
// Values returns the url.Values encoding of v.
//
// Values expects to be passed a struct, and traverses it recursively using the
// following encoding rules.
//
// Each exported struct field is encoded as a URL parameter unless
//
// - the field's tag is "-", or
// - the field is empty and its tag specifies the "omitempty" option
//
// The empty values are false, 0, any nil pointer or interface value, any array
// slice, map, or string of length zero, and any time.Time that returns true
// for IsZero().
//
// The URL parameter name defaults to the struct field name but can be
// specified in the struct field's tag value. The "url" key in the struct
// field's tag value is the key name, followed by an optional comma and
// options. For example:
//
// // Field is ignored by this package.
// Field int `url:"-"`
//
// // Field appears as URL parameter "myName".
// Field int `url:"myName"`
//
// // Field appears as URL parameter "myName" and the field is omitted if
// // its value is empty
// Field int `url:"myName,omitempty"`
//
// // Field appears as URL parameter "Field" (the default), but the field
// // is skipped if empty. Note the leading comma.
// Field int `url:",omitempty"`
//
// For encoding individual field values, the following type-dependent rules
// apply:
//
// Boolean values default to encoding as the strings "true" or "false".
// Including the "int" option signals that the field should be encoded as the
// strings "1" or "0".
//
// time.Time values default to encoding as RFC3339 timestamps. Including the
// "unix" option signals that the field should be encoded as a Unix time (see
// time.Unix())
//
// Slice and Array values default to encoding as multiple URL values of the
// same name. Including the "comma" option signals that the field should be
// encoded as a single comma-delimited value. Including the "space" option
// similarly encodes the value as a single space-delimited string. Including
// the "semicolon" option will encode the value as a semicolon-delimited string.
// Including the "brackets" option signals that the multiple URL values should
// have "[]" appended to the value name. "numbered" will append a number to
// the end of each incidence of the value name, example:
// name0=value0&name1=value1, etc.
//
// Anonymous struct fields are usually encoded as if their inner exported
// fields were fields in the outer struct, subject to the standard Go
// visibility rules. An anonymous struct field with a name given in its URL
// tag is treated as having that name, rather than being anonymous.
//
// Non-nil pointer values are encoded as the value pointed to.
//
// Nested structs are encoded including parent fields in value names for
// scoping. e.g:
//
// "user[name]=acme&user[addr][postcode]=1234&user[addr][city]=SFO"
//
// All other values are encoded using their default string representation.
//
// Multiple fields that encode to the same URL parameter name will be included
// as multiple URL values of the same name.
func Values(v interface{}) (url.Values, error) {
values := make(url.Values)
val := reflect.ValueOf(v)
for val.Kind() == reflect.Ptr {
if val.IsNil() {
return values, nil
}
val = val.Elem()
}
if v == nil {
return values, nil
}
if val.Kind() != reflect.Struct {
return nil, fmt.Errorf("query: Values() expects struct input. Got %v", val.Kind())
}
err := reflectValue(values, val, "")
return values, err
}
// reflectValue populates the values parameter from the struct fields in val.
// Embedded structs are followed recursively (using the rules defined in the
// Values function documentation) breadth-first.
func reflectValue(values url.Values, val reflect.Value, scope string) error {
var embedded []reflect.Value
typ := val.Type()
for i := 0; i < typ.NumField(); i++ {
sf := typ.Field(i)
if sf.PkgPath != "" && !sf.Anonymous { // unexported
continue
}
sv := val.Field(i)
tag := sf.Tag.Get("url")
if tag == "-" {
continue
}
name, opts := parseTag(tag)
if name == "" {
if sf.Anonymous && sv.Kind() == reflect.Struct {
// save embedded struct for later processing
embedded = append(embedded, sv)
continue
}
name = sf.Name
}
if scope != "" {
name = scope + "[" + name + "]"
}
if opts.Contains("omitempty") && isEmptyValue(sv) {
continue
}
if sv.Type().Implements(encoderType) {
if !reflect.Indirect(sv).IsValid() {
sv = reflect.New(sv.Type().Elem())
}
m := sv.Interface().(Encoder)
if err := m.EncodeValues(name, &values); err != nil {
return err
}
continue
}
if sv.Kind() == reflect.Slice || sv.Kind() == reflect.Array {
var del byte
if opts.Contains("comma") {
del = ','
} else if opts.Contains("space") {
del = ' '
} else if opts.Contains("semicolon") {
del = ';'
} else if opts.Contains("brackets") {
name = name + "[]"
}
if del != 0 {
s := new(bytes.Buffer)
first := true
for i := 0; i < sv.Len(); i++ {
if first {
first = false
} else {
s.WriteByte(del)
}
s.WriteString(valueString(sv.Index(i), opts))
}
values.Add(name, s.String())
} else {
for i := 0; i < sv.Len(); i++ {
k := name
if opts.Contains("numbered") {
k = fmt.Sprintf("%s%d", name, i)
}
values.Add(k, valueString(sv.Index(i), opts))
}
}
continue
}
for sv.Kind() == reflect.Ptr {
if sv.IsNil() {
break
}
sv = sv.Elem()
}
if sv.Type() == timeType {
values.Add(name, valueString(sv, opts))
continue
}
if sv.Kind() == reflect.Struct {
reflectValue(values, sv, name)
continue
}
values.Add(name, valueString(sv, opts))
}
for _, f := range embedded {
if err := reflectValue(values, f, scope); err != nil {
return err
}
}
return nil
}
// valueString returns the string representation of a value.
func valueString(v reflect.Value, opts tagOptions) string {
for v.Kind() == reflect.Ptr {
if v.IsNil() {
return ""
}
v = v.Elem()
}
if v.Kind() == reflect.Bool && opts.Contains("int") {
if v.Bool() {
return "1"
}
return "0"
}
if v.Type() == timeType {
t := v.Interface().(time.Time)
if opts.Contains("unix") {
return strconv.FormatInt(t.Unix(), 10)
}
return t.Format(time.RFC3339)
}
return fmt.Sprint(v.Interface())
}
// isEmptyValue checks if a value should be considered empty for the purposes
// of omitting fields with the "omitempty" option.
func isEmptyValue(v reflect.Value) bool {
switch v.Kind() {
case reflect.Array, reflect.Map, reflect.Slice, reflect.String:
return v.Len() == 0
case reflect.Bool:
return !v.Bool()
case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
return v.Int() == 0
case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
return v.Uint() == 0
case reflect.Float32, reflect.Float64:
return v.Float() == 0
case reflect.Interface, reflect.Ptr:
return v.IsNil()
}
if v.Type() == timeType {
return v.Interface().(time.Time).IsZero()
}
return false
}
// tagOptions is the string following a comma in a struct field's "url" tag, or
// the empty string. It does not include the leading comma.
type tagOptions []string
// parseTag splits a struct field's url tag into its name and comma-separated
// options.
func parseTag(tag string) (string, tagOptions) {
s := strings.Split(tag, ",")
return s[0], s[1:]
}
// Contains checks whether the tagOptions contains the specified option.
func (o tagOptions) Contains(option string) bool {
for _, s := range o {
if s == option {
return true
}
}
return false
}
