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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/cayley/quad"
"github.com/linkeddata/gojsonld"
)
// 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 {
options := gojsonld.NewOptions("")
options.DocumentLoader = gojsonld.NewDocumentLoader()
data, err := gojsonld.ToRDF(o, options)
if err != nil {
return &Reader{err: err}
}
return &Reader{
graphs: data.Graphs,
}
}
type Reader struct {
err error
name string
n int
graphs map[string][]*gojsonld.Triple
}
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
}
func (r *Reader) Close() error {
r.graphs = nil
return r.err
}
func NewWriter(w io.Writer) *Writer {
return &Writer{w: w, ds: gojsonld.NewDataset()}
}
type Writer struct {
w io.Writer
ds *gojsonld.Dataset
ctx interface{}
}
func (w *Writer) SetLdContext(ctx interface{}) {
w.ctx = ctx
}
func (w *Writer) WriteQuad(q quad.Quad) error {
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, gojsonld.NewTriple(
toTerm(q.Subject),
toTerm(q.Predicate),
toTerm(q.Object),
))
w.ds.Graphs[graph] = g
return nil
}
func (w *Writer) Close() error {
opts := gojsonld.NewOptions("")
var data interface{}
data = gojsonld.FromRDF(w.ds, opts)
if w.ctx != nil {
out, err := gojsonld.Compact(data, w.ctx, opts)
if err != nil {
return err
}
data = out
}
return json.NewEncoder(w.w).Encode(data)
}
func toTerm(v quad.Value) gojsonld.Term {
switch v := v.(type) {
case quad.IRI:
return gojsonld.NewResource(string(v))
case quad.BNode:
return gojsonld.NewBlankNode(string(v))
case quad.String:
return gojsonld.NewLiteralWithDatatype(
string(v),
gojsonld.NewResource(gojsonld.XSD_STRING),
)
case quad.TypedString:
return gojsonld.NewLiteralWithDatatype(
string(v.Value),
gojsonld.NewResource(string(v.Type)),
)
case quad.LangString:
return gojsonld.NewLiteralWithLanguageAndDatatype(
string(v.Value),
string(v.Lang),
gojsonld.NewResource(gojsonld.XSD_STRING),
)
case quad.TypedStringer:
return toTerm(v.TypedString())
default:
return gojsonld.NewLiteralWithDatatype(v.String(), gojsonld.NewResource(gojsonld.XSD_STRING))
}
}
func toValue(t gojsonld.Term) quad.Value {
switch t := t.(type) {
case *gojsonld.Resource:
return quad.IRI(t.URI)
case *gojsonld.BlankNode:
return quad.BNode(t.ID)
case *gojsonld.Literal:
if t.Language != "" {
return quad.LangString{
Value: quad.String(t.Value),
Lang: t.Language,
}
} else if t.Datatype != nil {
ts := quad.TypedString{
Value: quad.String(t.Value),
Type: quad.IRI(t.Datatype.RawValue()),
}
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))
}
}