add UnmarshalPartially

decode.go

@@ -117,7 +117,7 @@ func (p *hjsonParser) readString(allowML bool) (string, error) {
 				return "", p.errAt("Bad escape \\" + string(p.ch))
 			}
 		} else if p.ch == '\n' || p.ch == '\r' {
-			return "", p.errAt("Bad string containing newline");
+			return "", p.errAt("Bad string containing newline")
 		} else {
 			res.WriteByte(p.ch)
 		}
@@ -425,7 +425,7 @@ func (p *hjsonParser) rootValue() (interface{}, error) {
 	}
 
 	// assume we have a root object without braces
-	res, err := p.checkTrailing(p.readObject(true));
+	res, err := p.checkTrailing(p.readObject(true))
 	if err == nil {
 		return res, nil
 	}
@@ -479,3 +479,42 @@ func Unmarshal(data []byte, v interface{}) (err error) {
 	rv.Set(reflect.ValueOf(value))
 	return err
 }
+
+func (p *hjsonParser) rootValueWithTrail() (interface{}, error) {
+	// Braces for the root object are optional
+
+	p.white()
+	switch p.ch {
+	case '{':
+		return p.readObject(false)
+	case '[':
+		return p.readArray()
+	}
+
+	// assume we have a root object without braces
+	res, err := p.readObject(true)
+	if err == nil {
+		return res, nil
+	}
+
+	// test if we are dealing with a single JSON value instead (true/false/null/num/"")
+	p.resetAt()
+	if res2, err2 := p.readValue(); err2 == nil {
+		return res2, nil
+	}
+	return res, err
+}
+
+// UnmarshalPartially try to partially parse the Hjson-encoded data,
+// return the value and the start position of unprocessed parts.
+func UnmarshalPartially(data []byte) (v interface{}, next int, err error) {
+	parser := &hjsonParser{data, 0, ' '}
+	parser.resetAt()
+
+	v, err = parser.rootValueWithTrail()
+	if err != nil {
+		return
+	}
+	next = parser.at + 1
+	return
+}

hjson_test.go

@@ -105,3 +105,34 @@ func TestInvalidDestinationType(t *testing.T) {
 		panic("An error should occur")
 	}
 }
+
+func TestUnmarshalPartially(t *testing.T) {
+	var src = `
+	{
+		database:
+		{
+		  host: 127.0.0.1
+		  port: 555
+		}
+	  }
+	@@there is sth cannot be parsed as hijson.
+	`
+	v, next, err := UnmarshalPartially([]byte(src))
+	if err != nil {
+		panic(err)
+	}
+	if next != strings.Index(src, "@") {
+		panic("wrong next value")
+	}
+	if v == nil {
+		panic("v is nil")
+	}
+	val, ok := v.(map[string]interface{})
+	if !ok {
+		panic("v has wrong type")
+	}
+	_, ok = val["database"]
+	if !ok {
+		panic("v has wrong value")
+	}
+}