fix: Write resources using the charset defined in a Content-Type header

If a resource is returned using "application/javascript; charset=UTF-8" it should not be written as ISO-8859-1

Author: Artur-

aws-serverless-java-container-core/src/main/java/com/amazonaws/serverless/proxy/internal/servlet/AwsHttpServletResponse.java

@@ -213,7 +213,11 @@ public void addDateHeader(String s, long l) {
     @Override
     public void setHeader(String s, String s1) {
         if (!canSetHeader()) return;
-        setHeader(s, s1, true);
+        if ("Content-Type".equalsIgnoreCase(s)) {
+            setContentType(s1);
+        } else {
+            setHeader(s, s1, true);
+        }
     }
 
 

aws-serverless-java-container-core/src/test/java/com/amazonaws/serverless/proxy/internal/servlet/AwsHttpServletResponseTest.java

@@ -12,6 +12,7 @@
 
 import java.io.IOException;
 import java.io.PrintWriter;
+import java.nio.charset.StandardCharsets;
 import java.text.ParseException;
 import java.text.SimpleDateFormat;
 import java.time.Instant;
@@ -38,6 +39,7 @@ public class AwsHttpServletResponseTest {
     private static final Pattern EXPIRES_PATTERN = Pattern.compile("Expires=(.*)$");
 
     private static final String CONTENT_TYPE_WITH_CHARSET = "application/json; charset=UTF-8";
+    private static final String JAVASCRIPT_CONTENT_TYPE_WITH_CHARSET = "application/javascript; charset=UTF-8";
 
     @Test
     void cookie_addCookie_verifyPath() {
@@ -325,6 +327,18 @@ void characterEncoding_setCharacterEncodingInContentType_overridesDefault() {
         assertEquals("UTF-8", resp.getCharacterEncoding());
     }
 
+    @Test
+    void characterEncoding_encodingInContentTypeHeader_writesCorrectData() throws IOException {
+        AwsHttpServletResponse resp = new AwsHttpServletResponse(null, new CountDownLatch(1));
+        resp.setHeader("Content-Type", JAVASCRIPT_CONTENT_TYPE_WITH_CHARSET);
+        resp.getOutputStream().write("ü".getBytes(StandardCharsets.UTF_8));
+        resp.flushBuffer();
+
+        assertEquals(JAVASCRIPT_CONTENT_TYPE_WITH_CHARSET, resp.getContentType());
+        assertEquals(JAVASCRIPT_CONTENT_TYPE_WITH_CHARSET, resp.getHeader("Content-Type"));
+        assertEquals("ü",resp.getAwsResponseBodyString());
+    }
+
     private int getMaxAge(String header) {
         Matcher ageMatcher = MAX_AGE_PATTERN.matcher(header);
         assertTrue(ageMatcher.find());