Add method for escaping single-quoted newline chars

Author: rmosolgo

lib/graphql/language.rb

@@ -12,6 +12,7 @@
 require "graphql/language/token"
 require "graphql/language/visitor"
 require "graphql/language/definition_slice"
+require "strscan"
 
 module GraphQL
   module Language
@@ -33,5 +34,41 @@ def self.serialize(value)
         JSON.generate(value, quirks_mode: true)
       end
     end
+
+    # Returns a new string if any single-quoted newlines were escaped.
+    # Otherwise, returns `query_str` unchanged.
+    # @return [String]
+    def self.escape_single_quoted_newlines(query_str)
+      scanner = StringScanner.new(query_str)
+      inside_single_quoted_string = false
+      new_query_str = nil
+      while !scanner.eos?
+        if (match = scanner.scan(/(?:\\"|[^"\n\r]|""")+/m)) && new_query_str
+          new_query_str << match
+        elsif scanner.scan('"')
+          new_query_str && (new_query_str << '"')
+          inside_single_quoted_string = !inside_single_quoted_string
+        elsif scanner.scan("\n")
+          if inside_single_quoted_string
+            new_query_str ||= query_str[0, scanner.pos - 1]
+            new_query_str << '\\n'
+          else
+            new_query_str && (new_query_str << "\n")
+          end
+        elsif scanner.scan("\r")
+          if inside_single_quoted_string
+            new_query_str ||= query_str[0, scanner.pos - 1]
+            new_query_str << '\\r'
+          else
+            new_query_str && (new_query_str << "\r")
+          end
+        elsif scanner.eos?
+          break
+        else
+          raise ArgumentError, "Unmatchable string scanner segment: #{scanner.rest.inspect}"
+        end
+      end
+      new_query_str || query_str
+    end
   end
 end

spec/graphql/language/parser_spec.rb

@@ -16,15 +16,35 @@
     assert_equal expected_message, err.message
   end
 
-  it "rejects newlines in single-quoted strings" do
+  it "rejects newlines in single-quoted strings unless escaped" do
+    nl_query_string_1 = "{ doStuff(arg: \"
+    abc\") }"
+    nl_query_string_2 = "{ doStuff(arg: \"\rabc\") }"
+
     assert_raises(GraphQL::ParseError) {
-      GraphQL.parse("{ doStuff(arg: \"
-abc\") }"
-      )
+      GraphQL.parse(nl_query_string_2)
     }
     assert_raises(GraphQL::ParseError) {
-      GraphQL.parse("{ doStuff(arg: \"\rabc\") }")
+      GraphQL.parse(nl_query_string_2)
     }
+
+    assert GraphQL.parse(GraphQL::Language.escape_single_quoted_newlines(nl_query_string_1))
+    assert GraphQL.parse(GraphQL::Language.escape_single_quoted_newlines(nl_query_string_2))
+  end
+
+  it "can replace single-quoted newlines" do
+    replacements = {
+      "{ a(\"\n abc\n\") }" => '{ a("\\n abc\\n") }',
+      "{ a(\"\r\n ab\rc\n\") }" => '{ a("\\r\\n ab\\rc\\n") }',
+      "{ a(\"\n abc\n\") b(\"\n \\\"abc\n\") }" => '{ a("\\n abc\\n") b("\\n \\"abc\\n") }',
+      # No modification to block strings:
+      "{ a(\"\"\"\n abc\n\"\"\") }" => "{ a(\"\"\"\n abc\n\"\"\") }",
+      "{ a(\"\"\"\r\n abc\r\n\"\"\") }" => "{ a(\"\"\"\r\n abc\r\n\"\"\") }",
+    }
+
+    replacements.each_with_index do |(before_str, after_str), idx|
+      assert_equal after_str, GraphQL::Language.escape_single_quoted_newlines(before_str), "It works for example pair ##{idx + 1} (#{after_str})"
+    end
   end
 
   describe "when there are no selections" do