Corrected logic error that was failing tests as per P2P review

Author: gitnes94

src/main/java/org/example/http/HttpResponseBuilder.java

@@ -45,14 +45,31 @@ public void setContentTypeFromFilename(String filename) {
     public String build(){
         StringBuilder sb = new StringBuilder();
         String reason = REASON_PHRASES.getOrDefault(statusCode, "OK");
+
+        // Status line
         sb.append(PROTOCOL).append(" ").append(statusCode).append(" ").append(reason).append(CRLF);
+
+        // User-defined headers
         headers.forEach((k,v) -> sb.append(k).append(": ").append(v).append(CRLF));
-        sb.append("Content-Length: ")
-                .append(body.getBytes(StandardCharsets.UTF_8).length);
-        sb.append(CRLF);
-        sb.append("Connection: close").append(CRLF);
+
+        // Only adds Content-Length if not already set
+        if (!headers.containsKey("Content-Length")) {
+            sb.append("Content-Length: ")
+                    .append(body.getBytes(StandardCharsets.UTF_8).length)
+                    .append(CRLF);
+        }
+
+        // Only adds Connection if not already set
+        if (!headers.containsKey("Connection")) {
+            sb.append("Connection: close").append(CRLF);
+        }
+
+        // Blank line before body
         sb.append(CRLF);
+
+        // Body
         sb.append(body);
+
         return sb.toString();
     }
 }