Ensure input length is not overflown after a match

alllex · Oct 7, 2023 · 4876834 · 4876834
1 parent d1e0b33
commit 4876834
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Showing 2 changed files with 19 additions and 2 deletions.
diff --git a/src/commonMain/kotlin/me/alllex/parsus/parser/ParsingContext.kt b/src/commonMain/kotlin/me/alllex/parsus/parser/ParsingContext.kt
@@ -20,6 +20,8 @@ internal class ParsingContext(
     private val debugMode: Boolean = false
 ) : ParsingScope {
 
+    private val inputLength = tokenizer.input.length
+
     private var backtrackCont: Continuation<ParseError>? = null
     private var cont: Continuation<Any?>? = null
     private var position: Int = 0
@@ -63,10 +65,10 @@ internal class ParsingContext(
         val match = tokenizer.findMatchOf(fromIndex, token)
             ?: return UnmatchedToken(token, fromIndex, getParseErrorContextProviderOrNull())
 
-        // TODO: clean up, as this should not happen anymore
+        // This can only happen with EagerTokenizer
         if (match.token != token) return MismatchedToken(token, match, getParseErrorContextProviderOrNull())
 
-        val newPosition = match.nextOffset
+        val newPosition = match.nextOffset.coerceAtMost(inputLength)
         this.position = newPosition
         this.lastTokenMatchContext.currentOffset = newPosition
         this.lastTokenMatchContext.lastMatch = match

diff --git a/src/commonTest/kotlin/me/alllex/parsus/TokenTests.kt b/src/commonTest/kotlin/me/alllex/parsus/TokenTests.kt
@@ -83,4 +83,19 @@ class TokenTests {
         }
     }
 
+    @Test
+    fun explicitEofMatchesDoNotOverflowInputLength() {
+        object : Grammar<List<TokenMatch>>() {
+            val ab by literalToken("ab")
+            val eof by EofToken
+            override val root by ab * eof * eof map { it.toList() }
+        }.run {
+            assertParsed("ab").isEqualTo(listOf(
+                TokenMatch(ab, 0, 2),
+                TokenMatch(EofToken, 2, 1),
+                TokenMatch(EofToken, 2, 1),
+            ))
+        }
+    }
+
 }