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