refactor digests. (#161)

docs/client.md

@@ -68,6 +68,12 @@ client.on_cache_write do |request, payload|
 end
 ```
 
+All request digests use SHA2 by default. You can swap in [a faster algorithm](https://github.com/Shopify/blake3-rb) and/or add base scoping by reconfiguring the stitching library:
+
+```ruby
+GraphQL::Stitching.digest { |str| Digest::MD5.hexdigest("v2/#{str}") }
+```
+
 Note that inlined input data works against caching, so you should _avoid_ these input literals when possible:
 
 ```graphql

lib/graphql/stitching.rb

@@ -27,12 +27,24 @@ class CompositionError < StitchingError; end
     class ValidationError < CompositionError; end
 
     class << self
+      attr_writer :stitch_directive
+
+      # Proc used to compute digests; uses SHA2 by default.
+      # @returns [Proc] proc used to compute digests.
+      def digest(&block)
+        if block_given?
+          @digest = block
+        else
+          @digest ||= ->(str) { Digest::SHA2.hexdigest(str) }
+        end
+      end
+
+      # Name of the directive used to mark type resolvers.
+      # @returns [String] name of the type resolver directive.
       def stitch_directive
         @stitch_directive ||= "stitch"
       end
 
-      attr_writer :stitch_directive
-
       # Names of stitching directives to omit from the composed supergraph.
       # @returns [Array<String>] list of stitching directive names.
       def stitching_directive_names

lib/graphql/stitching/request.rb

@@ -75,12 +75,12 @@ def normalized_string
 
       # @return [String] a digest of the original document string. Generally faster but less consistent.
       def digest
-        @digest ||= Digest::SHA2.hexdigest(string)
+        @digest ||= Stitching.digest.call("#{Stitching::VERSION}/#{string}")
       end
 
       # @return [String] a digest of the normalized document string. Slower but more consistent.
       def normalized_digest
-        @normalized_digest ||= Digest::SHA2.hexdigest(normalized_string)
+        @normalized_digest ||= Stitching.digest.call("#{Stitching::VERSION}/#{normalized_string}")
       end
 
       # @return [GraphQL::Language::Nodes::OperationDefinition] The selected root operation for the request.

lib/graphql/stitching/type_resolver.rb

@@ -47,7 +47,7 @@ def list?
       end
 
       def version
-        @version ||= Digest::SHA2.hexdigest("#{Stitching::VERSION}/#{as_json.to_json}")
+        @version ||= Stitching.digest.call("#{Stitching::VERSION}/#{as_json.to_json}")
       end
 
       def ==(other)

test/graphql/stitching/request/request_test.rb

@@ -136,8 +136,8 @@ def test_provides_digest_and_normalized_digest
     |
 
     request = GraphQL::Stitching::Request.new(@supergraph, string)
-    expected = "ad4b4eb706f67020084a7927ed5bd73b7196e393e0af3535d25ae2d22df33232"
-    expected_normalized = "88908d0790f7b20afe4a7508a8bba6343c62f98abb9c5abff17345c64d90c0d0"
+    expected = "9f3c5afb51b7155611921d0e8537c8556b8d757ac90b63d85ea52964d18076d0"
+    expected_normalized = "71369fe5ee8f33e15b049991a294e6eeeb6e743310c339877f770fa8beb29f21"
 
     assert_equal expected, request.digest
     assert_equal expected_normalized, request.normalized_digest

test/graphql/stitching_test.rb

@@ -0,0 +1,32 @@
+# frozen_string_literal: true
+
+require "test_helper"
+
+describe "GraphQL::Stitching" do
+  def test_digest_gets_and_sets_hashing_implementation
+    expected_sha = "f5a163f364ac65dfd8ef60edb3ba39d6c2b44bccc289af3ced96b06e3f25df59"
+    expected_md5 = "fec9ff7a551c37ef692994407710fa54"
+
+    fn = GraphQL::Stitching.digest
+    assert_equal expected_sha, new_type_resolver.version
+
+    GraphQL::Stitching.digest { |str| Digest::MD5.hexdigest(str) }
+    assert_equal expected_md5, new_type_resolver.version
+
+    GraphQL::Stitching.digest(&fn)
+    assert_equal expected_sha, new_type_resolver.version
+  end
+
+  private
+
+  def new_type_resolver
+    GraphQL::Stitching::TypeResolver.new(
+      location: "a",
+      type_name: "Test",
+      list: false,
+      field: "a",
+      key: GraphQL::Stitching::TypeResolver.parse_key("id"),
+      arguments: GraphQL::Stitching::TypeResolver.parse_arguments_with_type_defs("id: $.id", "id: ID"),
+    )
+  end
+end