Struct Tags functions

// Function - #1
func getStructInfo(st reflect.Type) (*structInfo, error) {
    structMapMutex.RLock()
    sinfo, found := structMap[st]
    structMapMutex.RUnlock()
    if found {
        return sinfo, nil
    }
    n := st.NumField()
    fieldsMap := make(map[string]fieldInfo)
    fieldsList := make([]fieldInfo, 0, n)
    inlineMap := -1
    for i := 0; i != n; i++ {
        field := st.Field(i)
        if field.PkgPath != "" && !field.Anonymous {
            continue // Private field
        }

        info := fieldInfo{Num: i}

        tag := field.Tag.Get("bson")
        if tag == "" && strings.Index(string(field.Tag), ":") < 0 {
            tag = string(field.Tag)
        }
        if tag == "-" {
            continue
        }

        inline := false
        fields := strings.Split(tag, ",")
        if len(fields) > 1 {
            for _, flag := range fields[1:] {
                switch flag {
                case "omitempty":
                    info.OmitEmpty = true
                case "minsize":
                    info.MinSize = true
                case "inline":
                    inline = true
                default:
                    msg := fmt.Sprintf("Unsupported flag %q in tag %q of type %s", flag, tag, st)
                    panic(externalPanic(msg))
                }
            }
            tag = fields[0]
        }

        if inline {
            switch field.Type.Kind() {
            case reflect.Map:
                if inlineMap >= 0 {
                    return nil, errors.New("Multiple ,inline maps in struct " + st.String())
                }
                if field.Type.Key() != reflect.TypeOf("") {
                    return nil, errors.New("Option ,inline needs a map with string keys in struct " + st.String())
                }
                inlineMap = info.Num
            case reflect.Struct:
                sinfo, err := getStructInfo(field.Type)
                if err != nil {
                    return nil, err
                }
                for _, finfo := range sinfo.FieldsList {
                    if _, found := fieldsMap[finfo.Key]; found {
                        msg := "Duplicated key '" + finfo.Key + "' in struct " + st.String()
                        return nil, errors.New(msg)
                    }
                    if finfo.Inline == nil {
                        finfo.Inline = []int{i, finfo.Num}
                    } else {
                        finfo.Inline = append([]int{i}, finfo.Inline...)
                    }
                    fieldsMap[finfo.Key] = finfo
                    fieldsList = append(fieldsList, finfo)
                }
            default:
                panic("Option ,inline needs a struct value or map field")
            }
            continue
        }

        if tag != "" {
            info.Key = tag
        } else {
            info.Key = strings.ToLower(field.Name)
        }

        if _, found = fieldsMap[info.Key]; found {
            msg := "Duplicated key '" + info.Key + "' in struct " + st.String()
            return nil, errors.New(msg)
        }

        fieldsList = append(fieldsList, info)
        fieldsMap[info.Key] = info
    }
    sinfo = &structInfo{
        fieldsMap,
        fieldsList,
        inlineMap,
        reflect.New(st).Elem(),
    }
    structMapMutex.Lock()
    structMap[st] = sinfo
    structMapMutex.Unlock()
    return sinfo, nil
}

// Function - #2
func (e *encoder) addStruct(v reflect.Value) {
    sinfo, err := getStructInfo(v.Type())
    if err != nil {
        panic(err)
    }
    var value reflect.Value
    if sinfo.InlineMap >= 0 {
        m := v.Field(sinfo.InlineMap)
        if m.Len() > 0 {
            for _, k := range m.MapKeys() {
                ks := k.String()
                if _, found := sinfo.FieldsMap[ks]; found {
                    panic(fmt.Sprintf("Can't have key %q in inlined map; conflicts with struct field", ks))
                }
                e.addElem(ks, m.MapIndex(k), false)
            }
        }
    }
    for _, info := range sinfo.FieldsList {
        if info.Inline == nil {
            value = v.Field(info.Num)
        } else {
            // as pointers to struct are allowed here,
            // there is no guarantee that pointer won't be nil.
            //
            // It is expected allowed behaviour
            // so info.Inline MAY consist index to a nil pointer
            // and that is why we safely call v.FieldByIndex and just continue on panic
            field, errField := safeFieldByIndex(v, info.Inline)
            if errField != nil {
                continue
            }

            value = field
        }
        if info.OmitEmpty && isZero(value) {
            continue
        }
        if useRespectNilValues &&
            (value.Kind() == reflect.Slice || value.Kind() == reflect.Map) &&
            value.IsNil() {
            e.addElem(info.Key, reflect.ValueOf(nil), info.MinSize)
            continue
        }
        e.addElem(info.Key, value, info.MinSize)
    }
}