Merge pull request #144 from typelevel/fix/143

Fix #143

parser/src/main/scala/jawn/Parser.scala

@@ -90,6 +90,23 @@ abstract class Parser[J] {
   protected[this] def die(i: Int, msg: String): Nothing =
     die(i, msg, ErrorContext)
 
+  /**
+   * A version of `at` that returns as much of the indicated substring as
+   * possible without throwing exceptions.
+   *
+   * This method is necessary because `at(i, j)` may fail with an exception even
+   * when `atEof(i, j)` returns false (see #143 for an example). This method is
+   * a workaround; it is not optimized or robust against invalid input and
+   * should not be used outside of the context of `die`.
+   */
+  @tailrec private[this] def safeAt(i: Int, j: Int): CharSequence =
+    if (j <= i) "" else {
+      try at(i, j) catch {
+        case _: Exception =>
+          safeAt(i, j - 1)
+      }
+    }
+
   /**
    * Used to generate error messages with character info and offsets.
    *
@@ -108,7 +125,7 @@ abstract class Parser[J] {
       } else {
         var offset = 0
         while (offset < chars && !atEof(i + offset)) offset += 1
-        val txt = at(i, i + offset)
+        val txt = safeAt(i, i + offset)
         if (atEof(i + offset)) s"'$txt'" else s"'$txt...'"
       }
     val s = "%s got %s (line %d, column %d)" format (msg, got, y, x)

parser/src/test/scala/jawn/SyntaxCheck.scala

@@ -100,6 +100,7 @@ class SyntaxCheck extends PropSpec with Matchers with PropertyChecks {
   }
 
   property("empty is invalid") { isValidSyntax("") shouldBe false }
+  property("} is invalid") { isValidSyntax("}") shouldBe false }
 
   property("literal TAB is invalid") { isValidSyntax(qs("\t")) shouldBe false }
   property("literal NL is invalid") { isValidSyntax(qs("\n")) shouldBe false }
@@ -220,4 +221,16 @@ class SyntaxCheck extends PropSpec with Matchers with PropertyChecks {
   property("error location 2") { testErrorLoc("[1, 2,    \n   x3]", 2, 4) }
   property("error location 3") { testErrorLoc("[1, 2,\n\n\n\n\nx3]", 6, 1) }
   property("error location 4") { testErrorLoc("[1, 2,\n\n3,\n4,\n\n x3]", 6, 2) }
+
+  property("absorb should fail fast on bad inputs") {
+    def absorbFails(in: String): Boolean = {
+      val async = AsyncParser[Unit](AsyncParser.UnwrapArray)
+      async.absorb("}")(NullFacade).isLeft
+    }
+
+    val badInputs = Seq("}", "fälse", "n0ll", "try", "0x", "0.x", "0ex", "[1; 2]", "{\"a\"; 1}", "{1: 2}")
+    badInputs.foreach { input =>
+      absorbFails(input) shouldBe true
+    }
+  }
 }