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jsonld.go
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jsonld.go
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// Package jsonld provides an encoder/decoder for JSON-LD quad format
package jsonld
import (
"encoding/json"
"fmt"
"io"
"github.com/cayleygraph/quad"
"github.com/cayleygraph/quad/voc"
"github.com/cayleygraph/quad/voc/xsd"
"github.com/piprate/json-gold/ld"
)
// AutoConvertTypedString allows to convert TypedString values to native
// equivalents directly while parsing. It will call ToNative on all TypedString values.
//
// If conversion error occurs, it will preserve original TypedString value.
var AutoConvertTypedString = true
func init() {
quad.RegisterFormat(quad.Format{
Name: "jsonld",
Ext: []string{".jsonld"},
Mime: []string{"application/ld+json"},
Writer: func(w io.Writer) quad.WriteCloser { return NewWriter(w) },
Reader: func(r io.Reader) quad.ReadCloser { return NewReader(r) },
})
}
// NewReader returns quad reader for JSON-LD stream.
func NewReader(r io.Reader) *Reader {
var o interface{}
if err := json.NewDecoder(r).Decode(&o); err != nil {
return &Reader{err: err}
}
return NewReaderFromMap(o)
}
// NewReaderFromMap returns quad reader for JSON-LD map object.
func NewReaderFromMap(o interface{}) *Reader {
opts := ld.NewJsonLdOptions("")
processor := ld.NewJsonLdProcessor()
data, err := processor.ToRDF(o, opts)
if err != nil {
return &Reader{err: err}
}
return &Reader{
graphs: data.(*ld.RDFDataset).Graphs,
}
}
var _ quad.Reader = &Reader{}
// Reader implements the quad.Reader interface
type Reader struct {
err error
name string
n int
graphs map[string][]*ld.Quad
}
// ReadQuad implements the quad.Reader interface
func (r *Reader) ReadQuad() (quad.Quad, error) {
if r.err != nil {
return quad.Quad{}, r.err
}
next:
if len(r.graphs) == 0 {
return quad.Quad{}, io.EOF
}
if r.name == "" {
for gname := range r.graphs {
r.name = gname
break
}
}
if r.n >= len(r.graphs[r.name]) {
r.n = 0
delete(r.graphs, r.name)
r.name = ""
goto next
}
cur := r.graphs[r.name][r.n]
r.n++
var graph quad.Value
if r.name != "@default" {
graph = quad.IRI(r.name)
}
return quad.Quad{
Subject: toValue(cur.Subject),
Predicate: toValue(cur.Predicate),
Object: toValue(cur.Object),
Label: graph,
}, nil
}
// Close implements quad.Reader
func (r *Reader) Close() error {
r.graphs = nil
return r.err
}
var _ quad.Writer = &Writer{}
// Writer implements quad.Writer
type Writer struct {
w io.Writer
ds *ld.RDFDataset
ctx interface{}
}
// NewWriter constructs a new Writer
func NewWriter(w io.Writer) *Writer {
return &Writer{w: w, ds: ld.NewRDFDataset()}
}
// SetLdContext defines a context for the emitted JSON-LD data
// See: https://json-ld.org/spec/latest/json-ld/#the-context
func (w *Writer) SetLdContext(ctx interface{}) {
w.ctx = ctx
}
// WriteQuad implements quad.Writer
func (w *Writer) WriteQuad(q quad.Quad) error {
if !q.IsValid() {
return quad.ErrInvalid
}
var graph string
if q.Label == nil {
graph = "@default"
} else if iri, ok := q.Label.(quad.IRI); ok {
graph = string(iri)
} else {
graph = q.Label.String()
}
g := w.ds.Graphs[graph]
g = append(g, ld.NewQuad(
toTerm(q.Subject),
toTerm(q.Predicate),
toTerm(q.Object),
graph,
))
w.ds.Graphs[graph] = g
return nil
}
// WriteQuads implements quad.Writer
func (w *Writer) WriteQuads(buf []quad.Quad) (int, error) {
for i, q := range buf {
if err := w.WriteQuad(q); err != nil {
return i, err
}
}
return len(buf), nil
}
// Close implements quad.Writer
func (w *Writer) Close() error {
opts := ld.NewJsonLdOptions("")
api := ld.NewJsonLdApi()
processor := ld.NewJsonLdProcessor()
var data interface{}
data, err := api.FromRDF(w.ds, opts)
if err != nil {
return err
}
if w.ctx != nil {
out, err := processor.Compact(data, w.ctx, opts)
if err != nil {
return err
}
data = out
}
return json.NewEncoder(w.w).Encode(data)
}
func toTerm(v quad.Value) ld.Node {
switch v := v.(type) {
case quad.IRI:
return ld.NewIRI(string(v))
case quad.BNode:
return ld.NewBlankNode(string(v))
case quad.String:
return ld.NewLiteral(string(v), "", "")
case quad.TypedString:
return ld.NewLiteral(string(v.Value), string(v.Type), "")
case quad.LangString:
return ld.NewLiteral(string(v.Value), "", string(v.Lang))
case quad.TypedStringer:
return toTerm(v.TypedString())
default:
return ld.NewLiteral(v.String(), "", "")
}
}
// FromValue converts quad value to a JSON-LD compatible object.
func FromValue(v quad.Value) interface{} {
switch v := v.(type) {
case quad.IRI:
return map[string]interface{}{
"@id": string(v),
}
case quad.BNode:
return map[string]interface{}{
"@id": v.String(),
}
case quad.String:
return string(v)
case quad.LangString:
return map[string]interface{}{
"@value": string(v.Value),
"@language": string(v.Lang),
}
case quad.TypedString:
return typedStringToJSON(v)
case quad.TypedStringer:
return typedStringToJSON(v.TypedString())
default:
return v.String()
}
}
// ToNode transforms a quad.Value to ld.Node
func ToNode(value quad.Value) (ld.Node, error) {
switch v := value.(type) {
case quad.IRI:
return ld.NewIRI(string(v)), nil
case quad.BNode:
return ld.NewBlankNode(string(v)), nil
case quad.String:
return ld.NewLiteral(string(v), "", ""), nil
case quad.TypedString:
return ld.NewLiteral(string(v.Value), string(v.Type), ""), nil
case quad.LangString:
return ld.NewLiteral(string(v.Value), "", v.Lang), nil
default:
return nil, fmt.Errorf("Can not convert %v to ld.Node", value)
}
}
func isKnownTimeType(dataType quad.IRI) bool {
for _, iri := range quad.KnownTimeTypes {
if iri == dataType {
return true
}
}
return false
}
func typedStringToJSON(v quad.TypedString) interface{} {
if AutoConvertTypedString && quad.HasStringConversion(v.Type) && !isKnownTimeType(v.Type) {
return v.Native()
}
return map[string]interface{}{
"@value": string(v.Value),
"@type": string(v.Type),
}
}
var stringDataType = voc.FullIRI(xsd.String)
func toValue(t ld.Node) quad.Value {
switch t := t.(type) {
case *ld.IRI:
return quad.IRI(t.Value)
case *ld.BlankNode:
return quad.BNode(t.Attribute)
case *ld.Literal:
if t.Language != "" {
return quad.LangString{
Value: quad.String(t.Value),
Lang: t.Language,
}
} else if t.Datatype != "" && t.Datatype != stringDataType {
ts := quad.TypedString{
Value: quad.String(t.Value),
Type: quad.IRI(t.Datatype),
}
if AutoConvertTypedString {
if v, err := ts.ParseValue(); err == nil {
return v
}
}
return ts
}
return quad.String(t.Value)
default:
panic(fmt.Errorf("unexpected term type: %T", t))
}
}