Escape non-source characters in the encoder

3 files changed, 16 insertions, 7 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5cc152c..fed2d47 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,7 @@ All notable changes to this project will be documented in this file.
 - Fragment spread is evaluated based on the `__typename` resolver. If the
   resolver is missing, it is assumed that the type condition is satisfied (all
   fragments are included).
+- Escaping characters during encoding.
 
 ### Added
 - Directive support (@skip and @include).
diff --git a/src/Language/GraphQL/AST/Encoder.hs b/src/Language/GraphQL/AST/Encoder.hs
index afc425f..056ae2c 100644
--- a/src/Language/GraphQL/AST/Encoder.hs
+++ b/src/Language/GraphQL/AST/Encoder.hs
@@ -18,6 +18,7 @@ import Data.Monoid ((<>))
 import qualified Data.List.NonEmpty as NonEmpty (toList)
 import Data.Text.Lazy (Text)
 import qualified Data.Text.Lazy as Text.Lazy
+import qualified Data.Text.Lazy.Builder as Builder
 import Data.Text.Lazy.Builder (toLazyText)
 import Data.Text.Lazy.Builder.Int (decimal)
 import Data.Text.Lazy.Builder.RealFloat (realFloat)
@@ -191,10 +192,18 @@ booleanValue True  = "true"
 booleanValue False = "false"
 
 stringValue :: Text -> Text
-stringValue
-    = quotes
-    . Text.Lazy.replace "\"" "\\\""
-    . Text.Lazy.replace "\\" "\\\\"
+stringValue string = Builder.toLazyText
+    $ quote
+    <> Text.Lazy.foldr replace quote string
+  where
+    replace '\\' = mappend $ Builder.fromLazyText "\\\\"
+    replace '\"' = mappend $ Builder.fromLazyText "\\\""
+    replace '\b' = mappend $ Builder.fromLazyText "\\b"
+    replace '\f' = mappend $ Builder.fromLazyText "\\f"
+    replace '\n' = mappend $ Builder.fromLazyText "\\n"
+    replace '\r' = mappend $ Builder.fromLazyText "\\r"
+    replace char = mappend $ Builder.singleton char
+    quote = Builder.singleton '\"'
 
 listValue :: Formatter -> [Full.Value] -> Text
 listValue formatter = bracketsCommas formatter $ value formatter
@@ -243,9 +252,6 @@ brackets = between '[' ']'
 braces :: Text -> Text
 braces = between '{' '}'
 
-quotes :: Text -> Text
-quotes = between '"' '"'
-
 spaces :: forall a. (a -> Text) -> [a] -> Text
 spaces f = Text.Lazy.intercalate "\SP" . fmap f
 
diff --git a/tests/Language/GraphQL/AST/EncoderSpec.hs b/tests/Language/GraphQL/AST/EncoderSpec.hs
index a418a61..acf8075 100644
--- a/tests/Language/GraphQL/AST/EncoderSpec.hs
+++ b/tests/Language/GraphQL/AST/EncoderSpec.hs
@@ -17,3 +17,5 @@ spec = describe "value" $ do
         value minified (String "\\") `shouldBe` "\"\\\\\""
     it "escapes quotes" $
         value minified (String "\"") `shouldBe` "\"\\\"\""
+    it "escapes backspace" $
+        value minified (String "a\bc") `shouldBe` "\"a\\bc\""