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cquads.go
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cquads.go
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// Copyright 2014 The Cayley Authors. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//go:generate ragel -Z -G2 parse.rl
// Package cquads implements parsing N-Quads like line-based syntax
// for RDF datasets.
//
// N-Quad parsing is performed as based on a simplified grammar derived from
// the N-Quads grammar defined by http://www.w3.org/TR/n-quads/.
//
// For a complete definition of the grammar, see cquads.rl.
package cquads
import (
"bufio"
"bytes"
"fmt"
"io"
"strconv"
"github.com/google/cayley/quad"
)
// Decoder implements simplified N-Quad document parsing.
type Decoder struct {
r *bufio.Reader
line []byte
}
// NewDecoder returns an N-Quad decoder that takes its input from the
// provided io.Reader.
func NewDecoder(r io.Reader) *Decoder {
return &Decoder{r: bufio.NewReader(r)}
}
// Unmarshal returns the next valid N-Quad as a quad.Quad, or an error.
func (dec *Decoder) Unmarshal() (quad.Quad, error) {
dec.line = dec.line[:0]
var line []byte
for {
for {
l, pre, err := dec.r.ReadLine()
if err != nil {
return quad.Quad{}, err
}
dec.line = append(dec.line, l...)
if !pre {
break
}
}
if line = bytes.TrimSpace(dec.line); len(line) != 0 && line[0] != '#' {
break
}
dec.line = dec.line[:0]
}
q, err := Parse(string(line))
if err != nil {
return quad.Quad{}, fmt.Errorf("failed to parse %q: %v", dec.line, err)
}
if !q.IsValid() {
return dec.Unmarshal()
}
return q, nil
}
func unEscape(r []rune, isQuoted, isEscaped bool) string {
if isQuoted {
r = r[1 : len(r)-1]
}
if len(r) >= 2 && r[0] == '<' && r[len(r)-1] == '>' {
return string(r[1 : len(r)-1])
}
if !isEscaped {
return string(r)
}
buf := bytes.NewBuffer(make([]byte, 0, len(r)))
for i := 0; i < len(r); {
switch r[i] {
case '\\':
i++
var c byte
switch r[i] {
case 't':
c = '\t'
case 'b':
c = '\b'
case 'n':
c = '\n'
case 'r':
c = '\r'
case 'f':
c = '\f'
case '"':
c = '"'
case '\'':
c = '\''
case '\\':
c = '\\'
case 'u':
rc, err := strconv.ParseInt(string(r[i+1:i+5]), 16, 32)
if err != nil {
panic(fmt.Errorf("internal parser error: %v", err))
}
buf.WriteRune(rune(rc))
i += 5
continue
case 'U':
rc, err := strconv.ParseInt(string(r[i+1:i+9]), 16, 32)
if err != nil {
panic(fmt.Errorf("internal parser error: %v", err))
}
buf.WriteRune(rune(rc))
i += 9
continue
}
buf.WriteByte(c)
default:
buf.WriteRune(r[i])
}
i++
}
return buf.String()
}