fix: 누락된 ResponseHeaders 커밋 추가

tomcat/src/main/java/org/apache/coyote/http11/http/message/ResponseHeaders.java

@@ -0,0 +1,36 @@
+package org.apache.coyote.http11.http.message;
+
+import org.apache.coyote.http11.http.util.HttpResponseMessageHeader;
+
+import java.util.EnumMap;
+import java.util.Map;
+
+public class ResponseHeaders {
+
+    private static final String MESSAGE_HEADERS_DELIMITER = ": ";
+    private static final String SP = " ";
+    private static final String CRLF = "\r\n";
+
+    private final Map<HttpResponseMessageHeader, String> headerValues;
+
+    public ResponseHeaders() {
+        this.headerValues = new EnumMap<>(HttpResponseMessageHeader.class);
+    }
+
+    public void setAttribute(final HttpResponseMessageHeader headerType, final String value) {
+        headerValues.put(headerType, value);
+    }
+
+    @Override
+    public String toString() {
+        final StringBuilder stringBuilder = new StringBuilder();
+        for (final HttpResponseMessageHeader header : headerValues.keySet()) {
+            stringBuilder.append(header.getValue())
+                         .append(MESSAGE_HEADERS_DELIMITER)
+                         .append(headerValues.get(header))
+                         .append(SP)
+                         .append(CRLF);
+        }
+        return stringBuilder.toString();
+    }
+}