Fixed issue 3883. Add according unit test.

wenshao · wenshao · commit 73df32d342a4 · 2025-12-26T09:55:09.000+08:00
diff --git a/core/src/main/java/com/alibaba/fastjson2/JSONReaderUTF16.java b/core/src/main/java/com/alibaba/fastjson2/JSONReaderUTF16.java
@@ -3599,6 +3599,9 @@ public void readNumber0() {
 
         if (ch == '.') {
             valueType = JSON_TYPE_DEC;
+            if (offset == end) {
+                throw new JSONException(info("illegal input"));
+            }
             ch = chars[offset++];
             while (ch >= '0' && ch <= '9') {
                 valid = true;
diff --git a/core/src/main/java/com/alibaba/fastjson2/JSONReaderUTF8.java b/core/src/main/java/com/alibaba/fastjson2/JSONReaderUTF8.java
@@ -3298,6 +3298,9 @@ public final void readNumber0() {
 
         if (ch == '.') {
             valueType = JSON_TYPE_DEC;
+            if (offset == end) {
+                throw new JSONException(info("illegal input"));
+            }
             ch = bytes[offset++];
             while (ch >= '0' && ch <= '9') {
                 valid = true;
diff --git a/core/src/test/java/com/alibaba/fastjson2/issues_3800/Issue3883.java b/core/src/test/java/com/alibaba/fastjson2/issues_3800/Issue3883.java
@@ -0,0 +1,19 @@
+package com.alibaba.fastjson2.issues_3800;
+
+import com.alibaba.fastjson2.JSON;
+import com.alibaba.fastjson2.JSONException;
+import org.junit.jupiter.api.Test;
+
+import java.nio.charset.StandardCharsets;
+
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+public class Issue3883 {
+    @Test
+    public void jsonReaderUTF8ArrayOOBTest() {
+        String str = ".";
+        assertThrows(JSONException.class, () -> JSON.parse(str.toCharArray())); // UTF16
+        assertThrows(JSONException.class, () -> JSON.parse(str.getBytes(StandardCharsets.UTF_8))); // UTF8
+        assertThrows(JSONException.class, () -> JSON.parse(str)); // JDK 8 UTF16, JDK 9+ UTF8
+    }
+}
