Escape JSON pointer tokens

When building `data_pointer` and `schema_pointer` in error objects.

[JSON Pointer RFC][0]:

```
Because the characters '~' (%x7E) and '/' (%x2F) have special
meanings in JSON Pointer, '~' needs to be encoded as '~0' and '/'
needs to be encoded as '~1' when these characters appear in a
reference token.
```

Fixes: #121

[0]: https://www.rfc-editor.org/rfc/rfc6901#section-3

Author: davishmcclurg

lib/json_schemer/schema/base.rb

@@ -44,6 +44,9 @@ def merge(
         end
       end
 
+      JSON_POINTER_TOKEN_ESCAPE_CHARS = { '~' => '~0', '/' => '~1' }
+      JSON_POINTER_TOKEN_ESCAPE_REGEXP = Regexp.union(JSON_POINTER_TOKEN_ESCAPE_CHARS.keys)
+
       def initialize(
         schema,
         format: true,
@@ -531,7 +534,8 @@ def validate_object(instance, &block)
           dependencies.each do |key, value|
             next unless data.key?(key)
             subschema = value.is_a?(Array) ? { 'required' => value } : value
-            subinstance = instance.merge(schema: subschema, schema_pointer: "#{instance.schema_pointer}/dependencies/#{key}")
+            escaped_key = escape_json_pointer_token(key)
+            subinstance = instance.merge(schema: subschema, schema_pointer: "#{instance.schema_pointer}/dependencies/#{escaped_key}")
             validate_instance(subinstance, &block)
           end
         end
@@ -545,6 +549,8 @@ def validate_object(instance, &block)
 
         regex_pattern_properties = nil
         data.each do |key, value|
+          escaped_key = escape_json_pointer_token(key)
+
           unless property_names.nil?
             subinstance = instance.merge(
               data: key,
@@ -559,9 +565,9 @@ def validate_object(instance, &block)
           if properties && properties.key?(key)
             subinstance = instance.merge(
               data: value,
-              data_pointer: "#{instance.data_pointer}/#{key}",
+              data_pointer: "#{instance.data_pointer}/#{escaped_key}",
               schema: properties[key],
-              schema_pointer: "#{instance.schema_pointer}/properties/#{key}"
+              schema_pointer: "#{instance.schema_pointer}/properties/#{escaped_key}"
             )
             validate_instance(subinstance, &block)
             matched_key = true
@@ -572,12 +578,13 @@ def validate_object(instance, &block)
               [pattern, resolve_regexp(pattern), property_schema]
             end
             regex_pattern_properties.each do |pattern, regex, property_schema|
+              escaped_pattern = escape_json_pointer_token(pattern)
               if regex.match?(key)
                 subinstance = instance.merge(
                   data: value,
-                  data_pointer: "#{instance.data_pointer}/#{key}",
+                  data_pointer: "#{instance.data_pointer}/#{escaped_key}",
                   schema: property_schema,
-                  schema_pointer: "#{instance.schema_pointer}/patternProperties/#{pattern}"
+                  schema_pointer: "#{instance.schema_pointer}/patternProperties/#{escaped_pattern}"
                 )
                 validate_instance(subinstance, &block)
                 matched_key = true
@@ -590,7 +597,7 @@ def validate_object(instance, &block)
           unless additional_properties.nil?
             subinstance = instance.merge(
               data: value,
-              data_pointer: "#{instance.data_pointer}/#{key}",
+              data_pointer: "#{instance.data_pointer}/#{escaped_key}",
               schema: additional_properties,
               schema_pointer: "#{instance.schema_pointer}/additionalProperties"
             )
@@ -614,6 +621,10 @@ def safe_strict_decode64(data)
         nil
       end
 
+      def escape_json_pointer_token(token)
+        token.gsub(JSON_POINTER_TOKEN_ESCAPE_REGEXP, JSON_POINTER_TOKEN_ESCAPE_CHARS)
+      end
+
       def join_uri(a, b)
         b = URI.parse(b) if b
         if a && b && a.relative? && b.relative?

test/json_schemer_test.rb

@@ -1156,4 +1156,21 @@ def test_it_handles_multiple_of_floats
     refute(JSONSchemer.schema({ 'multipleOf' => 0.01 }).valid?(8.666))
     assert(JSONSchemer.schema({ 'multipleOf' => 0.001 }).valid?(8.666))
   end
+
+  def test_it_escapes_json_pointer_tokens
+    schemer = JSONSchemer.schema(
+      {
+        'type' => 'object',
+        'properties' => {
+          'foo/bar~' => {
+            'type' => 'string'
+          }
+        }
+    }
+    )
+    errors = schemer.validate({ 'foo/bar~' => 1 }).to_a
+    assert_equal(1, errors.size)
+    assert_equal('/foo~1bar~0', errors.first.fetch('data_pointer'))
+    assert_equal('/properties/foo~1bar~0', errors.first.fetch('schema_pointer'))
+  end
 end