From 81cfcff5d7d967c83f17695a94b7676f37dae03e Mon Sep 17 00:00:00 2001
From: Marcel Otto <marcelotto@gmx.de>
Date: Fri, 17 Aug 2018 01:31:08 +0200
Subject: [PATCH] Add default_base_iri configuration and use it for
 serialization readers

---
 CHANGELOG.md                    |  4 +++-
 README.md                       |  8 ++++++++
 lib/rdf/iri.ex                  | 13 +++++++++++++
 lib/rdf/serialization/reader.ex | 19 +++++++++++++++----
 4 files changed, 39 insertions(+), 5 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index e1b35d9..9cef6bf 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -19,7 +19,9 @@ This project adheres to [Semantic Versioning](http://semver.org/) and
 - the logical operators and the Effective Boolean Value (EBV) coercion algorithm 
   from the XPath and SPARQL specs on `RDF.Boolean`
 - `RDF.Term.equal?/2` and `RDF.Term.equal_value?/2`
-- `RDF.LangString.match_language?/2` 
+- `RDF.LangString.match_language?/2`
+- possibility to configure an application-specific default base IRI; for now it 
+  is used only on reading of RDF serializations (when no `base` specified)
 
 
 ### Changed
diff --git a/README.md b/README.md
index b116c2d..586651c 100644
--- a/README.md
+++ b/README.md
@@ -716,6 +716,14 @@ RDF.read_file!("/path/to/some_file.ttl")
 |> RDF.write_file!("/path/to/some_file.jsonld")
 ```
 
+For serialization formats which support it, you can provide a base IRI on the read functions with the `base` option. You can also provide a default base IRI in your application configuration, which will be used when no `base` option is given.
+
+```elixir
+config :rdf,
+  default_base_iri: "http://my_app.example/"
+```
+
+
 
 ## Getting help
 
diff --git a/lib/rdf/iri.ex b/lib/rdf/iri.ex
index 60a7b9c..0c37a00 100644
--- a/lib/rdf/iri.ex
+++ b/lib/rdf/iri.ex
@@ -25,6 +25,19 @@ defmodule RDF.IRI do
   # see https://tools.ietf.org/html/rfc3986#appendix-B
   @scheme_regex Regex.recompile!(~r/^([a-z][a-z0-9\+\-\.]*):/i)
 
+  @doc """
+  The default base IRI to be used when reading a serialization and no `base` option is provided.
+
+  The value can be set via the `default_base_iri` configuration. For example:
+
+      config :rdf,
+        default_base_iri: "http://my_app.example/"
+
+  See [section 5.1.4 of RFC 3987](https://tools.ietf.org/html/rfc3986#page-29)
+  """
+  @default_base Application.get_env(:rdf, :default_base_iri)
+  def default_base, do: @default_base
+
 
   @doc """
   Creates a `RDF.IRI`.
diff --git a/lib/rdf/serialization/reader.ex b/lib/rdf/serialization/reader.ex
index d07baf5..f60e77b 100644
--- a/lib/rdf/serialization/reader.ex
+++ b/lib/rdf/serialization/reader.ex
@@ -2,6 +2,9 @@ defmodule RDF.Serialization.Reader do
   @moduledoc """
   General functions for reading a `RDF.Graph` or `RDF.Dataset` from a serialization file or encoded-string.
 
+  If no base IRI is provided with the `base` option on any of these functions,
+  the `RDF.IRI.default_base/0` is used.
+
   You probably won't use these functions directly, but instead use the automatically
   generated functions with same name on a `RDF.Serialization.Format`, which implicitly
   use the proper `RDF.Serialization.Decoder` module.
@@ -15,7 +18,7 @@ defmodule RDF.Serialization.Reader do
   dataset, or `{:error, reason}` if an error occurs.
   """
   def read_string(decoder, content, opts \\ []) do
-    decoder.decode(content, opts)
+    decoder.decode(content, with_base(opts))
   end
 
   @doc """
@@ -24,7 +27,7 @@ defmodule RDF.Serialization.Reader do
   As opposed to `read_string`, it raises an exception if an error occurs.
   """
   def read_string!(decoder, content, opts \\ []) do
-    decoder.decode!(content, opts)
+    decoder.decode!(content, with_base(opts))
   end
 
   @doc """
@@ -35,7 +38,7 @@ defmodule RDF.Serialization.Reader do
   """
   def read_file(decoder, file, opts \\ []) do
     case File.read(file) do
-      {:ok,   content} -> read_string(decoder, content, opts)
+      {:ok,   content} -> read_string(decoder, content, with_base(opts))
       {:error, reason} -> {:error, reason}
     end
   end
@@ -47,7 +50,15 @@ defmodule RDF.Serialization.Reader do
   """
   def read_file!(decoder, file, opts \\ []) do
     with content = File.read!(file) do
-      read_string!(decoder, content, opts)
+      read_string!(decoder, content, with_base(opts))
+    end
+  end
+
+  defp with_base(opts) do
+    cond do
+      Keyword.has_key?(opts, :base) -> opts
+      base = RDF.IRI.default_base() -> Keyword.put(opts, :base, base)
+      true                          -> opts
     end
   end