Add actions to parse select chunks of a JSON stream while scanning fo…

…rward.

decoder.go

@@ -83,8 +83,8 @@ func (d *Decoder) Path() JsonPath {
 }
 
 // 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 the
-// KeyString type rather than as a bare string type.
+// 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 {
@@ -155,3 +155,41 @@ func (d *Decoder) Token() (json.Token, error) {
 
 	return t, err
 }
+
+func (d *Decoder) Scan(ext *PathActions) (bool, error) {
+
+	matched := false
+	rootPath := d.Path()
+	if rootPath.inferContext() == arrValue {
+		rootPath.incTop()
+	}
+
+	for {
+		_, err := d.Token()
+		if err != nil {
+			return matched, err
+		}
+
+	match:
+		path := d.Path()
+		relPath := JsonPath{}
+
+		// fmt.Printf("rootPath: %v path: %v rel: %v\n", rootPath, path, relPath)
+
+		if len(path) > len(rootPath) {
+			relPath = path[len(rootPath):]
+		} else {
+			return matched, nil
+		}
+
+		if node, ok := ext.node.match(relPath); ok {
+			if node.action != nil {
+				matched = true
+				node.action(d)
+				if d.context == arrValue && d.Decoder.More() {
+					goto match
+				}
+			}
+		}
+	}
+}

path.go

@@ -12,6 +12,9 @@ const (
 	arrValue
 )
 
+// AnyIndex can be used in a pattern to match any array index.
+const AnyIndex = -2
+
 // JsonPath is a slice of strings and/or integers. Each string specifies an JSON object key, and
 // each integer specifies an index into a JSON array.
 type JsonPath []interface{}
@@ -53,3 +56,12 @@ func (p *JsonPath) Equal(o JsonPath) bool {
 	}
 	return true
 }
+
+func (p *JsonPath) HasPrefix(o JsonPath) bool {
+	for i, v := range o {
+		if v != (*p)[i] {
+			return false
+		}
+	}
+	return true
+}

pathaction.go

@@ -0,0 +1,56 @@
+package jsonpath
+
+type pathNode struct {
+	matchOn    interface{} // string, or integer
+	childNodes []pathNode
+	action     DecodeAction
+}
+
+func (n *pathNode) match(path JsonPath) (*pathNode, bool) {
+	var node *pathNode = n
+	for _, ps := range path {
+		found := false
+		for i, n := range node.childNodes {
+			if n.matchOn == ps {
+				node = &node.childNodes[i]
+				found = true
+				break
+			} else if _, ok := ps.(int); ok && n.matchOn == AnyIndex {
+				node = &node.childNodes[i]
+				found = true
+				break
+			}
+		}
+		if !found {
+			return nil, false
+		}
+	}
+	return node, true
+}
+
+type PathActions struct {
+	node pathNode
+}
+
+type DecodeAction func(d *Decoder)
+
+// Action specifies an action to call on the Decoder when a particular path is encountered.
+func (je *PathActions) Action(action DecodeAction, path ...interface{}) {
+
+	var node *pathNode = &je.node
+	for _, ps := range path {
+		found := false
+		for i, n := range node.childNodes {
+			if n.matchOn == ps {
+				node = &node.childNodes[i]
+				found = true
+				break
+			}
+		}
+		if !found {
+			node.childNodes = append(node.childNodes, pathNode{matchOn: ps})
+			node = &node.childNodes[len(node.childNodes)-1]
+		}
+	}
+	node.action = action
+}