Add base URI handling to Turtle decoder

lib/rdf/serialization/parse_helper.ex

@@ -6,6 +6,7 @@ defmodule RDF.Serialization.ParseHelper do
   @rdf_type RDF.uri("http://www.w3.org/1999/02/22-rdf-syntax-ns#type")
   def rdf_type, do: @rdf_type
 
+
   def to_uri_string({:iriref, line, value}), do: value
 
   def to_uri({:iriref, line, value}) do
@@ -15,6 +16,14 @@ defmodule RDF.Serialization.ParseHelper do
     end
   end
 
+  def to_absolute_or_relative_uri({:iriref, line, value}) do
+    case URI.parse(value) do
+      uri = %URI{scheme: scheme} when not is_nil(scheme) -> uri
+      _ -> {:relative_uri, value}
+    end
+  end
+
+
   def to_bnode({:blank_node_label, _line, value}), do: RDF.bnode(value)
   def to_bnode({:anon, _line}), do: RDF.bnode # TODO:
 

lib/rdf/serializations/turtle_decoder.ex

@@ -20,10 +20,16 @@ defmodule RDF.Turtle.Decoder do
     end
   end
 
-  def decode(content, _opts \\ []) do
+  def decode(content, opts \\ %{})
+
+  def decode(content, opts) when is_list(opts),
+    do: decode(content, Map.new(opts))
+
+  def decode(content, opts) do
     with {:ok, tokens, _} <- tokenize(content),
-         {:ok, ast}       <- parse(tokens) do
-      {:ok, build_graph(ast)}
+         {:ok, ast}       <- parse(tokens),
+         base = Map.get(opts, :base) do
+      {:ok, build_graph(ast, base && RDF.uri(base))}
     else
       {:error, {error_line, :turtle_lexer, error_descriptor}, _error_line_again} ->
         {:error, "Turtle scanner error on line #{error_line}: #{inspect error_descriptor}"}
@@ -37,9 +43,9 @@ defmodule RDF.Turtle.Decoder do
   defp parse([]),     do: {:ok, []}
   defp parse(tokens), do: tokens |> :turtle_parser.parse
 
-  defp build_graph(ast) do
+  defp build_graph(ast, base) do
     {graph, _} =
-      Enum.reduce ast, {RDF.Graph.new, %State{}}, fn
+      Enum.reduce ast, {RDF.Graph.new, %State{base_uri: base}}, fn
         {:triples, triples_ast}, {graph, state} ->
           with {statements, state} = triples(triples_ast, state) do
             {RDF.Graph.add(graph, statements), state}
@@ -57,7 +63,7 @@ defmodule RDF.Turtle.Decoder do
   end
 
   defp directive({:base, uri}, state) do
-    %State{state | base_uri: uri}
+    %State{state | base_uri: RDF.uri(uri)}
   end
 
 
@@ -85,6 +91,14 @@ defmodule RDF.Turtle.Decoder do
     {RDF.uri(State.ns(state, prefix) <> name), statements, state}
   end
 
+  defp resolve_node({:relative_uri, relative_uri}, _, %State{base_uri: nil}) do
+    raise "Could not resolve resolve relative IRI '#{relative_uri}', no base uri provided"
+  end
+
+  defp resolve_node({:relative_uri, relative_uri}, statements, state) do
+    {RDF.URI.Helper.absolute_iri(relative_uri, state.base_uri), statements, state}
+  end
+
   defp resolve_node({:anon}, statements, state) do
     with {node, state} = State.next_bnode(state) do
       {node, statements, state}

lib/rdf/uri_helper.ex

@@ -0,0 +1,29 @@
+defmodule RDF.URI.Helper do
+  @moduledoc """
+  Some helpers functions for working with URIs.
+
+  These functions should be part of a dedicated RDF.IRI implementation.
+  """
+
+
+  @doc """
+  Resolves a relative IRI against a base IRI.
+
+  as specified in [section 5.1 Establishing a Base URI of RFC3986](http://tools.ietf.org/html/rfc3986#section-5.1).
+  Only the basic algorithm in [section 5.2 of RFC3986](http://tools.ietf.org/html/rfc3986#section-5.2)
+  is used; neither Syntax-Based Normalization nor Scheme-Based Normalization are performed.
+
+  Characters additionally allowed in IRI references are treated in the same way that unreserved
+  characters are treated in URI references, per [section 6.5 of RFC3987](http://tools.ietf.org/html/rfc3987#section-6.5)
+  """
+  def absolute_iri(value, base_iri) do
+    case URI.parse(value) do
+      # absolute?
+      uri = %URI{scheme: scheme} when not is_nil(scheme) -> uri
+      # relative
+      _ when is_nil(base_iri) -> nil
+      _ -> URI.merge(base_iri, value)
+    end
+  end
+
+end

src/turtle_parser.yrl

@@ -84,11 +84,7 @@ blankNode -> anon             : {anon} .
 Erlang code.
 
 to_uri_string(IRIREF) -> 'Elixir.RDF.Serialization.ParseHelper':to_uri_string(IRIREF) .
-to_uri(IRIREF) ->
-  case 'Elixir.RDF.Serialization.ParseHelper':to_uri(IRIREF) of
-    {ok, URI} -> URI;
-    {error, ErrorLine, Message} -> return_error(ErrorLine, Message)
-  end.
+to_uri(IRIREF) -> 'Elixir.RDF.Serialization.ParseHelper':to_absolute_or_relative_uri(IRIREF) .
 to_bnode(BLANK_NODE) -> 'Elixir.RDF.Serialization.ParseHelper':to_bnode(BLANK_NODE).
 to_literal(STRING_LITERAL_QUOTE) -> 'Elixir.RDF.Serialization.ParseHelper':to_literal(STRING_LITERAL_QUOTE).
 to_literal(STRING_LITERAL_QUOTE, Type) -> 'Elixir.RDF.Serialization.ParseHelper':to_literal(STRING_LITERAL_QUOTE, Type).

test/unit/turtle_decoder_test.exs

@@ -312,4 +312,58 @@ defmodule RDF.Turtle.DecoderTest do
     end
   end
 
+
+  describe "relative IRIs" do
+    test "without explicit in-doc base and no document_base option option given" do
+      assert_raise RuntimeError, fn ->
+        Turtle.Decoder.decode!(
+          "<#Aaron> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <#Person> .")
+      end
+    end
+
+    test "without explicit in-doc base, but document_base option given" do
+      assert Turtle.Decoder.decode!("""
+        <#Aaron> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <#Person> .
+      """, base: "http://example.org/") == Graph.new({EX.Aaron, RDF.type, EX.Person})
+    end
+
+    test "with @base given" do
+      assert Turtle.Decoder.decode!("""
+        @base <http://example.org/> .
+        <#Aaron> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <#Person> .
+      """) == Graph.new({EX.Aaron, RDF.type, EX.Person})
+
+      assert Turtle.Decoder.decode!("""
+        @base <http://example.org/#> .
+        <#Aaron> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <#Person> .
+      """) == Graph.new({EX.Aaron, RDF.type, EX.Person})
+    end
+
+    test "with BASE given" do
+      assert Turtle.Decoder.decode!("""
+        BASE <http://example.org/>
+        <#Aaron> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <#Person> .
+      """) == Graph.new({EX.Aaron, RDF.type, EX.Person})
+
+      assert Turtle.Decoder.decode!("""
+        base <http://example.org/#>
+        <#Aaron> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <#Person> .
+      """) == Graph.new({EX.Aaron, RDF.type, EX.Person})
+    end
+
+    test "when a given base is itself relative" do
+      assert_raise RDF.InvalidURIError, fn ->
+        Turtle.Decoder.decode!("""
+          @base <foo> .
+          <#Aaron> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <#Person> .
+          """)
+      end
+      assert_raise RDF.InvalidURIError, fn ->
+        Turtle.Decoder.decode!(
+          "<#Aaron> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <#Person> .",
+          base: "foo")
+      end
+    end
+  end
+
 end