terraform/vendor/github.com/exponent-io/jsonpath/decoder.go

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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
}
}
}
}
}