Add generic method to set Decoder options

Not as elegant as functional options, but it allows for adding
more options later without increasing the API surface.

Author: boutros

decoder.go

@@ -6,6 +6,14 @@ import (
 	"runtime"
 )
 
+// A ParseOption allows to customize the behaviour of decoders.
+type ParseOption int
+
+// Options which can configure the decoders.
+const (
+	Base ParseOption = iota // Base IRI to resolve relative IRIs against.
+)
+
 // TripleDecoder parses RDF documents (serializations of an RDF graph).
 //
 // For streaming parsing, use the Decode() method to decode a single Triple
@@ -19,10 +27,9 @@ type TripleDecoder interface {
 	// triples, or an error.
 	DecodeAll() ([]Triple, error)
 
-	// SetBase sets the base IRI which will be used for resolving relative IRIs.
-	// For formats that doesn't allow relative IRIs (N-Triples), this is a no-op.
-	// TODO strip #fragment in implementations? - check w3.org spec.
-	SetBase(IRI)
+	// SetOption sets a parsing option to the given value. Not all options
+	// are supported by all decoders.
+	SetOption(ParseOption, interface{}) error
 }
 
 // NewTripleDecoder returns a new TripleDecoder capable of parsing triples

nt.go

@@ -99,8 +99,13 @@ func (d *ntDecoder) DecodeAll() ([]Triple, error) {
 	return ts, nil
 }
 
-// SetBase does nothing, but is needed to implement the TripleDecoder interface.
-func (d *ntDecoder) SetBase(i IRI) {}
+// SetOption sets a ParseOption to the give value
+func (d *ntDecoder) SetOption(o ParseOption, v interface{}) error {
+	switch o {
+	default:
+		return fmt.Errorf("N-Triples decoder doesn't support option: %v", o)
+	}
+}
 
 // Parsing functions:
 

rdfxml.go

@@ -70,9 +70,19 @@ func newRDFXMLDecoder(r io.Reader) *rdfXMLDecoder {
 	return &rdfXMLDecoder{dec: xml.NewDecoder(r), nextState: parseXMLTopElem}
 }
 
-// SetBase sets the base IRI of the decoder, to be used resolving relative IRIs.
-func (d *rdfXMLDecoder) SetBase(i IRI) {
-	d.ctx.Base = i.str
+// SetOption sets a ParseOption to the give value
+func (d *rdfXMLDecoder) SetOption(o ParseOption, v interface{}) error {
+	switch o {
+	case Base:
+		iri, ok := v.(IRI)
+		if !ok {
+			return fmt.Errorf("ParseOption \"Base\" must be an IRI.")
+		}
+		d.ctx.Base = iri.str
+	default:
+		return fmt.Errorf("RDF/XML decoder doesn't support option: %v", o)
+	}
+	return nil
 }
 
 // Decode parses a RDF/XML document, and returns the next available triple,

rdfxml_test.go

@@ -9,7 +9,7 @@ import (
 func TestRDFXMLExamples(t *testing.T) {
 	for i, test := range rdfxmlExamples {
 		dec := NewTripleDecoder(bytes.NewBufferString(test.rdfxml), FormatRDFXML)
-		dec.SetBase(IRI{str: "http://www.w3.org/2013/RDFXMLTests/" + test.file})
+		dec.SetOption(Base, IRI{str: "http://www.w3.org/2013/RDFXMLTests/" + test.file})
 		ts, err := dec.DecodeAll()
 		if err != nil {
 			t.Fatalf("[%d] parseRDFXML(%s).Serialize(FormatNT) => %v, want %q", i, test.rdfxml, err, test.nt)
@@ -32,7 +32,7 @@ func TestRDFXMLExamples(t *testing.T) {
 func TestRDFXML(t *testing.T) {
 	for i, test := range rdfxmlTestSuite {
 		dec := NewTripleDecoder(bytes.NewBufferString(test.rdfxml), FormatRDFXML)
-		dec.SetBase(IRI{str: "http://www.w3.org/2013/RDFXMLTests/" + test.file})
+		dec.SetOption(Base, IRI{str: "http://www.w3.org/2013/RDFXMLTests/" + test.file})
 		ts, err := dec.DecodeAll()
 		if test.err == "TODO" {
 			continue

ttl.go

@@ -37,9 +37,19 @@ func newTTLDecoder(r io.Reader) *ttlDecoder {
 	}
 }
 
-// SetBase sets the base IRI of the decoder, to be used resolving relative IRIs.
-func (d *ttlDecoder) SetBase(i IRI) {
-	d.base = i
+// SetOption sets a ParseOption to the give value
+func (d *ttlDecoder) SetOption(o ParseOption, v interface{}) error {
+	switch o {
+	case Base:
+		iri, ok := v.(IRI)
+		if !ok {
+			return fmt.Errorf("ParseOption \"Base\" must be an IRI.")
+		}
+		d.base = iri
+	default:
+		return fmt.Errorf("RDF/XML decoder doesn't support option: %v", o)
+	}
+	return nil
 }
 
 // Decode parses a Turtle document, and returns the next valid triple, or an error.