Add basic HTTP response support (#24)

Rebased 4 commits in this PR.

Author: addee1

src/main/java/org/juv25d/SocketServer.java

@@ -11,7 +11,6 @@
 import java.util.logging.Logger;
 
 public class SocketServer {
-
     private final HttpParser httpParser;
 
     public SocketServer(HttpParser httpParser) {

src/main/java/org/juv25d/http/HttpResponse.java

@@ -0,0 +1,41 @@
+package org.juv25d.http;
+
+import java.util.Collections;
+import java.util.LinkedHashMap;
+import java.util.Map;
+import java.util.Objects;
+
+public class HttpResponse {
+
+    private final int statusCode;
+    private final String statusText;
+    private final Map<String, String> headers;
+    private final byte[] body;
+
+    public HttpResponse(int statusCode, String statusText, Map<String, String> headers, byte[] body) {
+        Objects.requireNonNull(statusText, "statusText must not be null");
+        Objects.requireNonNull(headers, "headers must not be null");
+        Objects.requireNonNull(body, "body must not be null");
+        this.statusCode = statusCode;
+        this.statusText = statusText;
+        this.headers = Collections.unmodifiableMap(new LinkedHashMap<>(headers));
+        this.body = body.clone();
+    }
+
+    public int statusCode(){
+        return statusCode;
+    }
+
+    public String statusText(){
+        return statusText;
+    }
+
+    public Map<String, String> headers() {
+        return headers;
+    }
+
+    public byte[] body(){
+        return body.clone();
+    }
+
+}

src/main/java/org/juv25d/http/HttpResponseWriter.java

@@ -0,0 +1,50 @@
+package org.juv25d.http;
+
+import java.io.IOException;
+import java.io.OutputStream;
+import java.nio.charset.StandardCharsets;
+import java.util.Map;
+
+public class HttpResponseWriter {
+
+    private HttpResponseWriter() {
+    }
+
+    // This method should be called by SocketServer/ConnectionHandler later
+    public static void write(OutputStream out, HttpResponse response) throws IOException {
+        writeStatusLine(out, response);
+        writeHeaders(out, response.headers(), response.body());
+        writeBody(out, response.body());
+        out.flush();
+    }
+
+    private static void writeStatusLine(OutputStream out, HttpResponse response) throws IOException {
+        String statusLine =
+            "HTTP/1.1 " + response.statusCode() + " " + response.statusText() + "\r\n";
+        out.write(statusLine.getBytes(StandardCharsets.UTF_8));
+    }
+
+    private static void writeHeaders(
+        OutputStream out,
+        Map<String, String> headers,
+        byte[] body
+    ) throws IOException {
+
+        for (Map.Entry<String, String> header : headers.entrySet()) {
+            if (!header.getKey().equalsIgnoreCase("Content-Length")) {
+                String line = header.getKey() + ": " + header.getValue() + "\r\n";
+                out.write(line.getBytes(StandardCharsets.UTF_8));
+            }
+        }
+
+        String contentLength = "Content-Length: " + body.length + "\r\n";
+        out.write(contentLength.getBytes(StandardCharsets.UTF_8));
+
+        out.write("\r\n".getBytes(StandardCharsets.UTF_8));
+    }
+
+
+    private static void writeBody(OutputStream out, byte[] body) throws IOException {
+        out.write(body);
+    }
+}

src/test/java/org/juv25d/http/HttpResponseWriterTest.java

@@ -0,0 +1,59 @@
+package org.juv25d.http;
+
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+
+import java.io.ByteArrayOutputStream;
+import java.nio.charset.StandardCharsets;
+import java.util.Map;
+
+import static org.assertj.core.api.AssertionsForClassTypes.assertThat;
+
+public class HttpResponseWriterTest {
+
+
+    @Test
+    @DisplayName("Should write a valid HTTP 200 OK response ")
+    void writesValidHttp200Response() throws Exception {
+        // Arrange
+        HttpResponse response = new HttpResponse(
+            200,
+            "OK",
+            Map.of("Content-Type", "text/plain"),
+            "Hello World".getBytes(StandardCharsets.UTF_8)
+        );
+
+        ByteArrayOutputStream out = new ByteArrayOutputStream();
+
+        // Act
+        HttpResponseWriter.write(out, response);
+
+        // Assert
+        String result = out.toString(StandardCharsets.UTF_8);
+
+        assertThat(result).startsWith("HTTP/1.1 200 OK");
+        assertThat(result).contains("Content-Type: text/plain");
+        assertThat(result).contains("Content-Length: 11");
+        assertThat(result).endsWith("Hello World");
+    }
+
+    @Test
+    @DisplayName("Should write a valid HTTP 404 Not Found Response")
+    void writes404NotFoundResponse() throws Exception {
+        HttpResponse response = new HttpResponse(
+            404,
+            "Not Found",
+            Map.of("Content-Type", "text/plain"),
+            "Not found".getBytes(StandardCharsets.UTF_8)
+        );
+
+        ByteArrayOutputStream out = new ByteArrayOutputStream();
+
+        HttpResponseWriter.write(out, response);
+
+        String result = out.toString(StandardCharsets.UTF_8);
+
+        assertThat(result).startsWith("HTTP/1.1 404 Not Found");
+    }
+
+}