Don Newton | 379ae25 | 2019-04-01 12:17:06 -0400 | [diff] [blame^] | 1 | // Copyright (C) MongoDB, Inc. 2017-present. |
| 2 | // |
| 3 | // Licensed under the Apache License, Version 2.0 (the "License"); you may |
| 4 | // not use this file except in compliance with the License. You may obtain |
| 5 | // a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 |
| 6 | |
| 7 | package bsoncodec |
| 8 | |
| 9 | import ( |
| 10 | "reflect" |
| 11 | "strings" |
| 12 | ) |
| 13 | |
| 14 | // StructTagParser returns the struct tags for a given struct field. |
| 15 | type StructTagParser interface { |
| 16 | ParseStructTags(reflect.StructField) (StructTags, error) |
| 17 | } |
| 18 | |
| 19 | // StructTagParserFunc is an adapter that allows a generic function to be used |
| 20 | // as a StructTagParser. |
| 21 | type StructTagParserFunc func(reflect.StructField) (StructTags, error) |
| 22 | |
| 23 | // ParseStructTags implements the StructTagParser interface. |
| 24 | func (stpf StructTagParserFunc) ParseStructTags(sf reflect.StructField) (StructTags, error) { |
| 25 | return stpf(sf) |
| 26 | } |
| 27 | |
| 28 | // StructTags represents the struct tag fields that the StructCodec uses during |
| 29 | // the encoding and decoding process. |
| 30 | // |
| 31 | // In the case of a struct, the lowercased field name is used as the key for each exported |
| 32 | // field but this behavior may be changed using a struct tag. The tag may also contain flags to |
| 33 | // adjust the marshalling behavior for the field. |
| 34 | // |
| 35 | // The properties are defined below: |
| 36 | // |
| 37 | // OmitEmpty Only include the field if it's not set to the zero value for the type or to |
| 38 | // empty slices or maps. |
| 39 | // |
| 40 | // MinSize Marshal an integer of a type larger than 32 bits value as an int32, if that's |
| 41 | // feasible while preserving the numeric value. |
| 42 | // |
| 43 | // Truncate When unmarshaling a BSON double, it is permitted to lose precision to fit within |
| 44 | // a float32. |
| 45 | // |
| 46 | // Inline Inline the field, which must be a struct or a map, causing all of its fields |
| 47 | // or keys to be processed as if they were part of the outer struct. For maps, |
| 48 | // keys must not conflict with the bson keys of other struct fields. |
| 49 | // |
| 50 | // Skip This struct field should be skipped. This is usually denoted by parsing a "-" |
| 51 | // for the name. |
| 52 | // |
| 53 | // TODO(skriptble): Add tags for undefined as nil and for null as nil. |
| 54 | type StructTags struct { |
| 55 | Name string |
| 56 | OmitEmpty bool |
| 57 | MinSize bool |
| 58 | Truncate bool |
| 59 | Inline bool |
| 60 | Skip bool |
| 61 | } |
| 62 | |
| 63 | // DefaultStructTagParser is the StructTagParser used by the StructCodec by default. |
| 64 | // It will handle the bson struct tag. See the documentation for StructTags to see |
| 65 | // what each of the returned fields means. |
| 66 | // |
| 67 | // If there is no name in the struct tag fields, the struct field name is lowercased. |
| 68 | // The tag formats accepted are: |
| 69 | // |
| 70 | // "[<key>][,<flag1>[,<flag2>]]" |
| 71 | // |
| 72 | // `(...) bson:"[<key>][,<flag1>[,<flag2>]]" (...)` |
| 73 | // |
| 74 | // An example: |
| 75 | // |
| 76 | // type T struct { |
| 77 | // A bool |
| 78 | // B int "myb" |
| 79 | // C string "myc,omitempty" |
| 80 | // D string `bson:",omitempty" json:"jsonkey"` |
| 81 | // E int64 ",minsize" |
| 82 | // F int64 "myf,omitempty,minsize" |
| 83 | // } |
| 84 | // |
| 85 | // A struct tag either consisting entirely of '-' or with a bson key with a |
| 86 | // value consisting entirely of '-' will return a StructTags with Skip true and |
| 87 | // the remaining fields will be their default values. |
| 88 | var DefaultStructTagParser StructTagParserFunc = func(sf reflect.StructField) (StructTags, error) { |
| 89 | key := strings.ToLower(sf.Name) |
| 90 | tag, ok := sf.Tag.Lookup("bson") |
| 91 | if !ok && !strings.Contains(string(sf.Tag), ":") && len(sf.Tag) > 0 { |
| 92 | tag = string(sf.Tag) |
| 93 | } |
| 94 | var st StructTags |
| 95 | if tag == "-" { |
| 96 | st.Skip = true |
| 97 | return st, nil |
| 98 | } |
| 99 | |
| 100 | for idx, str := range strings.Split(tag, ",") { |
| 101 | if idx == 0 && str != "" { |
| 102 | key = str |
| 103 | } |
| 104 | switch str { |
| 105 | case "omitempty": |
| 106 | st.OmitEmpty = true |
| 107 | case "minsize": |
| 108 | st.MinSize = true |
| 109 | case "truncate": |
| 110 | st.Truncate = true |
| 111 | case "inline": |
| 112 | st.Inline = true |
| 113 | } |
| 114 | } |
| 115 | |
| 116 | st.Name = key |
| 117 | |
| 118 | return st, nil |
| 119 | } |