optimize read nil/true/false

feature_iter_skip.go

@@ -0,0 +1,202 @@
+package jsoniter
+
+import "fmt"
+
+// ReadNil reads a json object as nil and
+// returns whether it's a nil or not
+func (iter *Iterator) ReadNil() (ret bool) {
+	c := iter.nextToken()
+	if c == 'n' {
+		iter.skipFixedBytes(3) // null
+		return true
+	}
+	iter.unreadByte()
+	return false
+}
+
+// ReadBool reads a json object as Bool
+func (iter *Iterator) ReadBool() (ret bool) {
+	c := iter.nextToken()
+	if c == 't' {
+		iter.skipFixedBytes(3)
+		return true
+	}
+	if c == 'f' {
+		iter.skipFixedBytes(4)
+		return false
+	}
+	iter.reportError("ReadBool", "expect t or f")
+	return
+}
+
+
+// Skip skips a json object and positions to relatively the next json object
+func (iter *Iterator) Skip() {
+	c := iter.nextToken()
+	switch c {
+	case '"':
+		iter.skipString()
+	case 'n', 't':
+		iter.skipFixedBytes(3) // null or true
+	case 'f':
+		iter.skipFixedBytes(4) // false
+	case '-', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
+		iter.skipUntilBreak()
+	case '[':
+		iter.skipArray()
+	case '{':
+		iter.skipObject()
+	default:
+		iter.reportError("Skip", fmt.Sprintf("do not know how to skip: %v", c))
+		return
+	}
+}
+
+func (iter *Iterator) skipString() {
+	for {
+		end, escaped := iter.findStringEnd()
+		if end == -1 {
+			if !iter.loadMore() {
+				return
+			}
+			if escaped {
+				iter.head = 1 // skip the first char as last char read is \
+			}
+		} else {
+			iter.head = end
+			return
+		}
+	}
+}
+
+// adapted from: https://github.com/buger/jsonparser/blob/master/parser.go
+// Tries to find the end of string
+// Support if string contains escaped quote symbols.
+func (iter *Iterator) findStringEnd() (int, bool) {
+	escaped := false
+	for i := iter.head; i < iter.tail; i++ {
+		c := iter.buf[i]
+		if c == '"' {
+			if !escaped {
+				return i + 1, false
+			}
+			j := i - 1
+			for {
+				if j < iter.head || iter.buf[j] != '\\' {
+					// even number of backslashes
+					// either end of buffer, or " found
+					return i + 1, true
+				}
+				j--
+				if j < iter.head || iter.buf[j] != '\\' {
+					// odd number of backslashes
+					// it is \" or \\\"
+					break
+				}
+				j--
+			}
+		} else if c == '\\' {
+			escaped = true
+		}
+	}
+	j := iter.tail - 1
+	for {
+		if j < iter.head || iter.buf[j] != '\\' {
+			// even number of backslashes
+			// either end of buffer, or " found
+			return -1, false // do not end with \
+		}
+		j--
+		if j < iter.head || iter.buf[j] != '\\' {
+			// odd number of backslashes
+			// it is \" or \\\"
+			break
+		}
+		j--
+
+	}
+	return -1, true // end with \
+}
+
+func (iter *Iterator) skipArray() {
+	level := 1
+	for {
+		for i := iter.head; i < iter.tail; i++ {
+			switch iter.buf[i] {
+			case '"': // If inside string, skip it
+				iter.head = i + 1
+				iter.skipString()
+				i = iter.head - 1 // it will be i++ soon
+			case '[': // If open symbol, increase level
+				level++
+			case ']': // If close symbol, increase level
+				level--
+
+				// If we have returned to the original level, we're done
+				if level == 0 {
+					iter.head = i + 1
+					return
+				}
+			}
+		}
+		if !iter.loadMore() {
+			return
+		}
+	}
+}
+
+func (iter *Iterator) skipObject() {
+	level := 1
+	for {
+		for i := iter.head; i < iter.tail; i++ {
+			switch iter.buf[i] {
+			case '"': // If inside string, skip it
+				iter.head = i + 1
+				iter.skipString()
+				i = iter.head - 1 // it will be i++ soon
+			case '{': // If open symbol, increase level
+				level++
+			case '}': // If close symbol, increase level
+				level--
+
+				// If we have returned to the original level, we're done
+				if level == 0 {
+					iter.head = i + 1
+					return
+				}
+			}
+		}
+		if !iter.loadMore() {
+			return
+		}
+	}
+}
+
+func (iter *Iterator) skipUntilBreak() {
+	// true, false, null, number
+	for {
+		for i := iter.head; i < iter.tail; i++ {
+			c := iter.buf[i]
+			switch c {
+			case ' ', '\n', '\r', '\t', ',', '}', ']':
+				iter.head = i
+				return
+			}
+		}
+		if !iter.loadMore() {
+			return
+		}
+	}
+}
+
+func (iter *Iterator) skipFixedBytes(n int) {
+	iter.head += n;
+	if (iter.head >= iter.tail) {
+		more := iter.head - iter.tail;
+		if !iter.loadMore() {
+			iter.reportError("skipFixedBytes", "unexpected end");
+			return
+		}
+		iter.head += more;
+	}
+}