From c5768e07bca2ba1e6671a90951230ce178bbcb0c Mon Sep 17 00:00:00 2001
From: Alexey Andreev <konsoletyper@gmail.com>
Date: Thu, 26 Oct 2023 11:50:27 +0200
Subject: [PATCH] classlib: fix issue in InputStreamReader

---
 .../classlib/java/io/TInputStreamReader.java  |  5 ++++-
 .../java/io/InputStreamReaderTest.java        | 20 +++++++++++++++++++
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/classlib/src/main/java/org/teavm/classlib/java/io/TInputStreamReader.java b/classlib/src/main/java/org/teavm/classlib/java/io/TInputStreamReader.java
index 73f6d527a..fae9e251b 100644
--- a/classlib/src/main/java/org/teavm/classlib/java/io/TInputStreamReader.java
+++ b/classlib/src/main/java/org/teavm/classlib/java/io/TInputStreamReader.java
@@ -110,8 +110,11 @@ public class TInputStreamReader extends TReader {
             if (!inBuffer.hasRemaining() && !fillReadBuffer()) {
                 break;
             }
-            if (decoder.decode(inBuffer, outBuffer, streamEof).isOverflow()) {
+            var result = decoder.decode(inBuffer, outBuffer, streamEof);
+            if (result.isOverflow()) {
                 break;
+            } else if (result.isUnderflow()) {
+                fillReadBuffer();
             }
         }
         if (!inBuffer.hasRemaining() && streamEof && decoder.flush(outBuffer).isUnderflow()) {
diff --git a/tests/src/test/java/org/teavm/classlib/java/io/InputStreamReaderTest.java b/tests/src/test/java/org/teavm/classlib/java/io/InputStreamReaderTest.java
index dabe966c0..e901609ba 100644
--- a/tests/src/test/java/org/teavm/classlib/java/io/InputStreamReaderTest.java
+++ b/tests/src/test/java/org/teavm/classlib/java/io/InputStreamReaderTest.java
@@ -17,8 +17,10 @@ package org.teavm.classlib.java.io;
 
 import static org.junit.Assert.assertEquals;
 import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.io.InputStreamReader;
+import java.nio.charset.StandardCharsets;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.teavm.junit.TeaVMTestRunner;
@@ -78,4 +80,22 @@ public class InputStreamReaderTest {
             assertEquals(str.charAt(i), chars[i]);
         }
     }
+
+    @Test
+    public void underflowWhileFillingBuffer() throws IOException {
+        var bos = new ByteArrayOutputStream();
+        bos.write(0x24);
+        for (var i = 0; i < 20000; ++i) {
+            bos.write(0xC2);
+            bos.write(0xA2);
+        }
+
+        var bis = new ByteArrayInputStream(bos.toByteArray());
+        var reader = new InputStreamReader(bis, StandardCharsets.UTF_8);
+        assertEquals(0x24, reader.read());
+        for (var i = 0; i < 20000; ++i) {
+            assertEquals(0xA2, reader.read());
+        }
+        assertEquals(-1, reader.read());
+    }
 }