1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
|
package jsonpath
import (
"encoding/json"
"io"
)
// KeyString is returned from Decoder.Token to represent each key in a JSON object value.
type KeyString string
// Decoder extends the Go runtime's encoding/json.Decoder to support navigating in a stream of JSON tokens.
type Decoder struct {
json.Decoder
path JsonPath
context jsonContext
}
// NewDecoder creates a new instance of the extended JSON Decoder.
func NewDecoder(r io.Reader) *Decoder {
return &Decoder{Decoder: *json.NewDecoder(r)}
}
// SeekTo causes the Decoder to move forward to a given path in the JSON structure.
//
// The path argument must consist of strings or integers. Each string specifies an JSON object key, and
// each integer specifies an index into a JSON array.
//
// Consider the JSON structure
//
// { "a": [0,"s",12e4,{"b":0,"v":35} ] }
//
// SeekTo("a",3,"v") will move to the value referenced by the "a" key in the current object,
// followed by a move to the 4th value (index 3) in the array, followed by a move to the value at key "v".
// In this example, a subsequent call to the decoder's Decode() would unmarshal the value 35.
//
// SeekTo returns a boolean value indicating whether a match was found.
//
// Decoder is intended to be used with a stream of tokens. As a result it navigates forward only.
func (d *Decoder) SeekTo(path ...interface{}) (bool, error) {
if len(path) == 0 {
return len(d.path) == 0, nil
}
last := len(path) - 1
if i, ok := path[last].(int); ok {
path[last] = i - 1
}
for {
if d.path.Equal(path) {
return true, nil
}
_, err := d.Token()
if err == io.EOF {
return false, nil
} else if err != nil {
return false, err
}
}
}
// Decode reads the next JSON-encoded value from its input and stores it in the value pointed to by v. This is
// equivalent to encoding/json.Decode().
func (d *Decoder) Decode(v interface{}) error {
switch d.context {
case objValue:
d.context = objKey
break
case arrValue:
d.path.incTop()
break
}
return d.Decoder.Decode(v)
}
// Path returns a slice of string and/or int values representing the path from the root of the JSON object to the
// position of the most-recently parsed token.
func (d *Decoder) Path() JsonPath {
p := make(JsonPath, len(d.path))
copy(p, d.path)
return p
}
// Token is equivalent to the Token() method on json.Decoder. The primary difference is that it distinguishes
// between strings that are keys and and strings that are values. String tokens that are object keys are returned as a
// KeyString rather than as a native string.
func (d *Decoder) Token() (json.Token, error) {
t, err := d.Decoder.Token()
if err != nil {
return t, err
}
if t == nil {
switch d.context {
case objValue:
d.context = objKey
break
case arrValue:
d.path.incTop()
break
}
return t, err
}
switch t := t.(type) {
case json.Delim:
switch t {
case json.Delim('{'):
if d.context == arrValue {
d.path.incTop()
}
d.path.push("")
d.context = objKey
break
case json.Delim('}'):
d.path.pop()
d.context = d.path.inferContext()
break
case json.Delim('['):
if d.context == arrValue {
d.path.incTop()
}
d.path.push(-1)
d.context = arrValue
break
case json.Delim(']'):
d.path.pop()
d.context = d.path.inferContext()
break
}
case float64, json.Number, bool:
switch d.context {
case objValue:
d.context = objKey
break
case arrValue:
d.path.incTop()
break
}
break
case string:
switch d.context {
case objKey:
d.path.nameTop(t)
d.context = objValue
return KeyString(t), err
case objValue:
d.context = objKey
case arrValue:
d.path.incTop()
}
break
}
return t, err
}
// Scan moves forward over the JSON stream consuming all the tokens at the current level (current object, current array)
// invoking each matching PathAction along the way.
//
// Scan returns true if there are more contiguous values to scan (for example in an array).
func (d *Decoder) Scan(ext *PathActions) (bool, error) {
rootPath := d.Path()
// If this is an array path, increment the root path in our local copy.
if rootPath.inferContext() == arrValue {
rootPath.incTop()
}
for {
// advance the token position
_, err := d.Token()
if err != nil {
return false, err
}
match:
var relPath JsonPath
// capture the new JSON path
path := d.Path()
if len(path) > len(rootPath) {
// capture the path relative to where the scan started
relPath = path[len(rootPath):]
} else {
// if the path is not longer than the root, then we are done with this scan
// return boolean flag indicating if there are more items to scan at the same level
return d.Decoder.More(), nil
}
// match the relative path against the path actions
if node := ext.node.match(relPath); node != nil {
if node.action != nil {
// we have a match so execute the action
err = node.action(d)
if err != nil {
return d.Decoder.More(), err
}
// The action may have advanced the decoder. If we are in an array, advancing it further would
// skip tokens. So, if we are scanning an array, jump to the top without advancing the token.
if d.path.inferContext() == arrValue && d.Decoder.More() {
goto match
}
}
}
}
}
|
