Solves duplicate header issue

Author: gitnes94

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

@@ -0,0 +1,4 @@
+package org.example.http;
+
+public class BinaryResponseBuilder {
+}

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

@@ -41,17 +41,34 @@ public void setContentTypeFromFilename(String filename) {
             404, "Not Found",
             500, "Internal Server Error");
 
-    public String build(){
+    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);
-        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);
+
+        // User-defined headers
+        headers.forEach((k, v) -> sb.append(k).append(": ").append(v).append(CRLF));
+
+        // Only append 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 append 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();
     }
 }

src/test/java/org/example/http/HttpResponseBuilderTest.java

@@ -3,7 +3,11 @@
 import org.junit.jupiter.api.DisplayName;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
 import org.junit.jupiter.params.provider.CsvSource;
+import org.junit.jupiter.params.provider.MethodSource;
+
+import java.util.stream.Stream;
 
 import static org.assertj.core.api.AssertionsForClassTypes.assertThat;
 
@@ -123,17 +127,34 @@ void setContentTypeFromFilename_allCases(String filename, String expectedContent
             assertThat(result).contains("Content-Type: " + expectedContentType);
         }
 
-        @Test
-        @DisplayName("Should override previous Content-Type when set again")
-        void setContentTypeFromFilename_overridesPrevious() {
+        @ParameterizedTest
+        @MethodSource("provideHeaderDuplicationScenarios")
+        @DisplayName("Should not duplicate headers when manually set")
+        void build_doesNotDuplicateHeaders(String headerName, String manualValue, String bodyContent) {
             HttpResponseBuilder builder = new HttpResponseBuilder();
-            builder.setContentTypeFromFilename("file.txt");
-            builder.setContentTypeFromFilename("file.html");
-            builder.setBody("Test");
+            builder.setHeader(headerName, manualValue);
+            builder.setBody(bodyContent);
 
             String result = builder.build();
 
-            assertThat(result).contains("Content-Type: text/html; charset=UTF-8");
-            assertThat(result).doesNotContain("text/plain");
+            // Count occurrences of the header
+            long count = result.lines()
+                    .filter(line -> line.startsWith(headerName + ":"))
+                    .count();
+
+            assertThat(count).isEqualTo(1);
+            assertThat(result).contains(headerName + ": " + manualValue);
+        }
+
+        private static Stream<Arguments> provideHeaderDuplicationScenarios() {
+            return Stream.of(
+                    Arguments.of("Content-Length", "999", "Hello"),
+                    Arguments.of("Content-Length", "0", ""),
+                    Arguments.of("Content-Length", "12345", "Test content"),
+                    Arguments.of("Connection", "keep-alive", "Hello"),
+                    Arguments.of("Connection", "upgrade", "WebSocket data"),
+                    Arguments.of("Connection", "close", "Goodbye")
+            );
         }
+
     }