1 /*
2 *
3 * Copyright 2019 gRPC authors.
4 *
5 * Licensed under the Apache License, Version 2.0 (the "License");
6 * you may not use this file except in compliance with the License.
7 * You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 *
17 */
18 19 // Package attributes defines a generic key/value store used in various gRPC
20 // components.
21 //
22 // # Experimental
23 //
24 // Notice: This package is EXPERIMENTAL and may be changed or removed in a
25 // later release.
26 package attributes
27 28 import (
29 "fmt"
30 "strings"
31 )
32 33 // Attributes is an immutable struct for storing and retrieving generic
34 // key/value pairs. Keys must be hashable, and users should define their own
35 // types for keys. Values should not be modified after they are added to an
36 // Attributes or if they were received from one. If values implement 'Equal(o
37 // any) bool', it will be called by (*Attributes).Equal to determine whether
38 // two values with the same key should be considered equal.
39 type Attributes struct {
40 m map[any]any
41 }
42 43 // New returns a new Attributes containing the key/value pair.
44 func New(key, value any) *Attributes {
45 return &Attributes{m: map[any]any{key: value}}
46 }
47 48 // WithValue returns a new Attributes containing the previous keys and values
49 // and the new key/value pair. If the same key appears multiple times, the
50 // last value overwrites all previous values for that key. To remove an
51 // existing key, use a nil value. value should not be modified later.
52 func (a *Attributes) WithValue(key, value any) *Attributes {
53 if a == nil {
54 return New(key, value)
55 }
56 n := &Attributes{m: make(map[any]any, len(a.m)+1)}
57 for k, v := range a.m {
58 n.m[k] = v
59 }
60 n.m[key] = value
61 return n
62 }
63 64 // Value returns the value associated with these attributes for key, or nil if
65 // no value is associated with key. The returned value should not be modified.
66 func (a *Attributes) Value(key any) any {
67 if a == nil {
68 return nil
69 }
70 return a.m[key]
71 }
72 73 // Equal returns whether a and o are equivalent. If 'Equal(o any) bool' is
74 // implemented for a value in the attributes, it is called to determine if the
75 // value matches the one stored in the other attributes. If Equal is not
76 // implemented, standard equality is used to determine if the two values are
77 // equal. Note that some types (e.g. maps) aren't comparable by default, so
78 // they must be wrapped in a struct, or in an alias type, with Equal defined.
79 func (a *Attributes) Equal(o *Attributes) bool {
80 if a == nil && o == nil {
81 return true
82 }
83 if a == nil || o == nil {
84 return false
85 }
86 if len(a.m) != len(o.m) {
87 return false
88 }
89 for k, v := range a.m {
90 ov, ok := o.m[k]
91 if !ok {
92 // o missing element of a
93 return false
94 }
95 if eq, ok := v.(interface{ Equal(o any) bool }); ok {
96 if !eq.Equal(ov) {
97 return false
98 }
99 } else if v != ov {
100 // Fallback to a standard equality check if Value is unimplemented.
101 return false
102 }
103 }
104 return true
105 }
106 107 // String prints the attribute map. If any key or values throughout the map
108 // implement fmt.Stringer, it calls that method and appends.
109 func (a *Attributes) String() string {
110 var sb strings.Builder
111 sb.WriteString("{")
112 first := true
113 for k, v := range a.m {
114 if !first {
115 sb.WriteString(", ")
116 }
117 sb.WriteString(fmt.Sprintf("%q: %q ", str(k), str(v)))
118 first = false
119 }
120 sb.WriteString("}")
121 return sb.String()
122 }
123 124 func str(x any) (s string) {
125 if v, ok := x.(fmt.Stringer); ok {
126 return fmt.Sprint(v)
127 } else if v, ok := x.(string); ok {
128 return v
129 }
130 return fmt.Sprintf("<%p>", x)
131 }
132 133 // MarshalJSON helps implement the json.Marshaler interface, thereby rendering
134 // the Attributes correctly when printing (via pretty.JSON) structs containing
135 // Attributes as fields.
136 //
137 // Is it impossible to unmarshal attributes from a JSON representation and this
138 // method is meant only for debugging purposes.
139 func (a *Attributes) MarshalJSON() ([]byte, error) {
140 return []byte(a.String()), nil
141 }
142