291 lines
7.5 KiB
Go
291 lines
7.5 KiB
Go
// Package query implements encoding of structs into http.Header fields.
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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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// ContentType string `header:"Content-Type"`
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// Length int
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// }
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//
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// opt := Options{"application/json", 2}
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// h, _ := httpheader.Header(opt)
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// fmt.Printf("%#v", h)
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// // will output:
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// // http.Header{"Content-Type":[]string{"application/json"},"Length":[]string{"2"}}
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//
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// The exact mapping between Go values and http.Header is described in the
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// documentation for the Header() function.
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package httpheader
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import (
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"fmt"
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"net/http"
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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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const tagName = "header"
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// Version ...
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const Version = "0.2.1"
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var timeType = reflect.TypeOf(time.Time{})
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var headerType = reflect.TypeOf(http.Header{})
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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 Header fields in a non-standard way.
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type Encoder interface {
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EncodeHeader(key string, v *http.Header) error
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}
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// Header returns the http.Header encoding of v.
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//
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// Header 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 Header field 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 Header field name defaults to the struct field name but can be
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// specified in the struct field's tag value. The "header" 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 `header:"-"`
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//
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// // Field appears as Header field "X-Name".
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// Field int `header:"X-Name"`
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//
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// // Field appears as Header field "X-Name" and the field is omitted if
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// // its value is empty
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// Field int `header:"X-Name,omitempty"`
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//
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// // Field appears as Header field "Field" (the default), but the field
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// // is skipped if empty. Note the leading comma.
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// Field int `header:",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 RFC1123("Mon, 02 Jan 2006 15:04:05 GMT")
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// timestamps. Including the "unix" option signals that the field should be
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// encoded as a Unix time (see time.Unix())
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//
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// Slice and Array values default to encoding as multiple Header values of the
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// same name. example:
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// X-Name: []string{"Tom", "Jim"}, etc.
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//
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// http.Header values will be used to extend the Header fields.
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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 Header
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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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// 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 Header filed name will be included
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// as multiple Header values of the same name.
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func Header(v interface{}) (http.Header, error) {
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h := make(http.Header)
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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 h, 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 h, nil
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}
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if val.Kind() != reflect.Struct {
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return nil, fmt.Errorf("httpheader: Header() expects struct input. Got %v", val.Kind())
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}
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err := reflectValue(h, val)
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return h, err
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}
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// reflectValue populates the header fields 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(header http.Header, val reflect.Value) 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(tagName)
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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 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.EncodeHeader(name, &header); 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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for i := 0; i < sv.Len(); i++ {
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k := name
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header.Add(k, valueString(sv.Index(i), opts))
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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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header.Add(name, valueString(sv, opts))
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continue
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}
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if sv.Type() == headerType {
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h := sv.Interface().(http.Header)
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for k, vs := range h {
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for _, v := range vs {
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header.Add(k, v)
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}
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}
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continue
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}
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if sv.Kind() == reflect.Struct {
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reflectValue(header, sv)
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continue
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}
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header.Add(name, valueString(sv, opts))
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}
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for _, f := range embedded {
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if err := reflectValue(header, f); 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(http.TimeFormat)
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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 "header" 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 header 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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