gunjan5 | c79837e | 2016-07-09 03:31:27 -0700 | [diff] [blame] | 1 | // Copyright (c) 2013 Kelsey Hightower. All rights reserved. |
| 2 | // Use of this source code is governed by the MIT License that can be found in |
| 3 | // the LICENSE file. |
| 4 | |
| 5 | package envconfig |
| 6 | |
| 7 | import ( |
| 8 | "errors" |
| 9 | "fmt" |
| 10 | "reflect" |
| 11 | "strconv" |
| 12 | "strings" |
| 13 | "syscall" |
| 14 | "time" |
| 15 | ) |
| 16 | |
| 17 | // ErrInvalidSpecification indicates that a specification is of the wrong type. |
| 18 | var ErrInvalidSpecification = errors.New("specification must be a struct pointer") |
| 19 | |
| 20 | // A ParseError occurs when an environment variable cannot be converted to |
| 21 | // the type required by a struct field during assignment. |
| 22 | type ParseError struct { |
| 23 | KeyName string |
| 24 | FieldName string |
| 25 | TypeName string |
| 26 | Value string |
| 27 | } |
| 28 | |
| 29 | // A Decoder is a type that knows how to de-serialize environment variables |
| 30 | // into itself. |
| 31 | type Decoder interface { |
| 32 | Decode(value string) error |
| 33 | } |
| 34 | |
| 35 | func (e *ParseError) Error() string { |
| 36 | return fmt.Sprintf("envconfig.Process: assigning %[1]s to %[2]s: converting '%[3]s' to type %[4]s", e.KeyName, e.FieldName, e.Value, e.TypeName) |
| 37 | } |
| 38 | |
| 39 | // Process populates the specified struct based on environment variables |
| 40 | func Process(prefix string, spec interface{}) error { |
| 41 | s := reflect.ValueOf(spec) |
| 42 | |
| 43 | if s.Kind() != reflect.Ptr { |
| 44 | return ErrInvalidSpecification |
| 45 | } |
| 46 | s = s.Elem() |
| 47 | if s.Kind() != reflect.Struct { |
| 48 | return ErrInvalidSpecification |
| 49 | } |
| 50 | typeOfSpec := s.Type() |
| 51 | for i := 0; i < s.NumField(); i++ { |
| 52 | f := s.Field(i) |
| 53 | if !f.CanSet() || typeOfSpec.Field(i).Tag.Get("ignored") == "true" { |
| 54 | continue |
| 55 | } |
| 56 | |
| 57 | if typeOfSpec.Field(i).Anonymous && f.Kind() == reflect.Struct { |
| 58 | embeddedPtr := f.Addr().Interface() |
| 59 | if err := Process(prefix, embeddedPtr); err != nil { |
| 60 | return err |
| 61 | } |
| 62 | f.Set(reflect.ValueOf(embeddedPtr).Elem()) |
| 63 | } |
| 64 | |
| 65 | alt := typeOfSpec.Field(i).Tag.Get("envconfig") |
| 66 | fieldName := typeOfSpec.Field(i).Name |
| 67 | if alt != "" { |
| 68 | fieldName = alt |
| 69 | } |
| 70 | key := strings.ToUpper(fmt.Sprintf("%s_%s", prefix, fieldName)) |
| 71 | // `os.Getenv` cannot differentiate between an explicitly set empty value |
| 72 | // and an unset value. `os.LookupEnv` is preferred to `syscall.Getenv`, |
| 73 | // but it is only available in go1.5 or newer. |
| 74 | value, ok := syscall.Getenv(key) |
| 75 | if !ok && alt != "" { |
| 76 | key := strings.ToUpper(fieldName) |
| 77 | value, ok = syscall.Getenv(key) |
| 78 | } |
| 79 | |
| 80 | def := typeOfSpec.Field(i).Tag.Get("default") |
| 81 | if def != "" && !ok { |
| 82 | value = def |
| 83 | } |
| 84 | |
| 85 | req := typeOfSpec.Field(i).Tag.Get("required") |
| 86 | if !ok && def == "" { |
| 87 | if req == "true" { |
| 88 | return fmt.Errorf("required key %s missing value", key) |
| 89 | } |
| 90 | continue |
| 91 | } |
| 92 | |
| 93 | err := processField(value, f) |
| 94 | if err != nil { |
| 95 | return &ParseError{ |
| 96 | KeyName: key, |
| 97 | FieldName: fieldName, |
| 98 | TypeName: f.Type().String(), |
| 99 | Value: value, |
| 100 | } |
| 101 | } |
| 102 | } |
| 103 | return nil |
| 104 | } |
| 105 | |
| 106 | // MustProcess is the same as Process but panics if an error occurs |
| 107 | func MustProcess(prefix string, spec interface{}) { |
| 108 | if err := Process(prefix, spec); err != nil { |
| 109 | panic(err) |
| 110 | } |
| 111 | } |
| 112 | |
| 113 | func processField(value string, field reflect.Value) error { |
| 114 | typ := field.Type() |
| 115 | |
| 116 | decoder := decoderFrom(field) |
| 117 | if decoder != nil { |
| 118 | return decoder.Decode(value) |
| 119 | } |
| 120 | |
| 121 | if typ.Kind() == reflect.Ptr { |
| 122 | typ = typ.Elem() |
| 123 | if field.IsNil() { |
| 124 | field.Set(reflect.New(typ)) |
| 125 | } |
| 126 | field = field.Elem() |
| 127 | } |
| 128 | |
| 129 | switch typ.Kind() { |
| 130 | case reflect.String: |
| 131 | field.SetString(value) |
| 132 | case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64: |
| 133 | var ( |
| 134 | val int64 |
| 135 | err error |
| 136 | ) |
| 137 | if field.Kind() == reflect.Int64 && typ.PkgPath() == "time" && typ.Name() == "Duration" { |
| 138 | var d time.Duration |
| 139 | d, err = time.ParseDuration(value) |
| 140 | val = int64(d) |
| 141 | } else { |
| 142 | val, err = strconv.ParseInt(value, 0, typ.Bits()) |
| 143 | } |
| 144 | if err != nil { |
| 145 | return err |
| 146 | } |
| 147 | |
| 148 | field.SetInt(val) |
| 149 | case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64: |
| 150 | val, err := strconv.ParseUint(value, 0, typ.Bits()) |
| 151 | if err != nil { |
| 152 | return err |
| 153 | } |
| 154 | field.SetUint(val) |
| 155 | case reflect.Bool: |
| 156 | val, err := strconv.ParseBool(value) |
| 157 | if err != nil { |
| 158 | return err |
| 159 | } |
| 160 | field.SetBool(val) |
| 161 | case reflect.Float32, reflect.Float64: |
| 162 | val, err := strconv.ParseFloat(value, typ.Bits()) |
| 163 | if err != nil { |
| 164 | return err |
| 165 | } |
| 166 | field.SetFloat(val) |
| 167 | case reflect.Slice: |
| 168 | vals := strings.Split(value, ",") |
| 169 | sl := reflect.MakeSlice(typ, len(vals), len(vals)) |
| 170 | for i, val := range vals { |
| 171 | err := processField(val, sl.Index(i)) |
| 172 | if err != nil { |
| 173 | return err |
| 174 | } |
| 175 | } |
| 176 | field.Set(sl) |
| 177 | } |
| 178 | |
| 179 | return nil |
| 180 | } |
| 181 | |
| 182 | func decoderFrom(field reflect.Value) Decoder { |
| 183 | if field.CanInterface() { |
| 184 | dec, ok := field.Interface().(Decoder) |
| 185 | if ok { |
| 186 | return dec |
| 187 | } |
| 188 | } |
| 189 | |
| 190 | // also check if pointer-to-type implements Decoder, |
| 191 | // and we can get a pointer to our field |
| 192 | if field.CanAddr() { |
| 193 | field = field.Addr() |
| 194 | dec, ok := field.Interface().(Decoder) |
| 195 | if ok { |
| 196 | return dec |
| 197 | } |
| 198 | } |
| 199 | |
| 200 | return nil |
| 201 | } |