Issue #60 - Reduce the memory used to read the response body

src/main/java/org/metricshub/http/HttpClient.java

@@ -109,7 +109,7 @@
 		try {
 			sc = SSLContext.getInstance("SSL");
 			sc.init(null, LOUSY_TRUST_MANAGER, new java.security.SecureRandom());
 		} catch (NoSuchAlgorithmException | KeyManagementException e) {}
 		BASE_SOCKET_FACTORY = sc.getSocketFactory();
 		DEFAULT_SSL_PROTOCOLS = sc.getDefaultSSLParameters().getProtocols();
 	}
@@ -363,7 +363,8 @@
 					}
 				}
 			}
-			response.appendBody(new String(bodyBytes.toByteArray(), charset));
+			// Decode straight from the buffer (toByteArray() would copy it first)
+			response.appendBody(bodyBytes.toString(charset.name()));
 
 			// Return
 			return response;

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

@@ -31,7 +31,8 @@
 public class HttpResponse {
 
 	private int statusCode;
-	private StringBuilder body;
+	// The body is kept as a String: a StringBuilder would copy it once when appended and once more in getBody()
+	private String body;
 	private StringBuilder header;
 
 	/**
@@ -40,7 +41,7 @@ public class HttpResponse {
 	public HttpResponse() {
 		statusCode = 0;
 		header = new StringBuilder();
-		body = new StringBuilder();
+		body = "";
 	}
 
 	/**
@@ -86,23 +87,27 @@ public void appendHeader(String name, String value) {
 	 * @return the body of the HTTP response
 	 */
 	public String getBody() {
-		return body.toString();
+		return body;
 	}
 
 	/**
 	 * Append content to the body of the HTTP response
+	 * <p>
+	 * Each call after the first copies the whole body: the body is meant to be set by a single call.
 	 *
-	 * @param data Data to append
+	 * @param data Data to append ("null" is appended for null, as StringBuilder.append() does)
 	 */
 	public void appendBody(String data) {
-		body.append(data);
+		String value = String.valueOf(data);
+		body = body.isEmpty() ? value : body.concat(value);
 	}
 
 	/**
 	 * @return the entire HTTP response, header and body
 	 */
 	@Override
 	public String toString() {
-		return new StringBuilder().append(header).append("\n").append(body).toString();
+		// concat() copies the body once, where a StringBuilder copies it twice
+		return header.toString().concat("\n").concat(body);
 	}
 }

src/test/java/org/metricshub/http/HttpClientTest.java

@@ -0,0 +1,138 @@
+package org.metricshub.http;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import com.sun.net.httpserver.HttpServer;
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.OutputStream;
+import java.net.InetSocketAddress;
+import java.nio.charset.StandardCharsets;
+import java.util.zip.GZIPOutputStream;
+import org.junit.jupiter.api.AfterAll;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Reading of the response body, against a local server
+ */
+class HttpClientTest {
+
+	private static final String TEXT = "{\"name\":\"café 中 😀\",\"list\":[1,2,3]}";
+
+	private static HttpServer server;
+	private static String baseUrl;
+
+	@BeforeAll
+	static void startServer() throws IOException {
+		server = HttpServer.create(new InetSocketAddress("127.0.0.1", 0), 0);
+		respond("/length", 200, "application/json", null, TEXT.getBytes(StandardCharsets.UTF_8), false);
+		respond("/chunked", 200, "application/json", null, TEXT.getBytes(StandardCharsets.UTF_8), true);
+		respond(
+			"/latin1",
+			200,
+			"text/plain; charset=ISO-8859-1",
+			null,
+			"café".getBytes(StandardCharsets.ISO_8859_1),
+			false
+		);
+		respond("/gzip", 200, "application/json", "gzip", gzip(TEXT.getBytes(StandardCharsets.UTF_8)), true);
+		respond("/empty", 200, "application/json", null, new byte[0], false);
+		respond("/error", 404, "text/plain", null, "not found".getBytes(StandardCharsets.UTF_8), false);
+		server.start();
+		baseUrl = "http://127.0.0.1:" + server.getAddress().getPort();
+	}
+
+	@AfterAll
+	static void stopServer() {
+		server.stop(0);
+	}
+
+	private static void respond(
+		String path,
+		int status,
+		String contentType,
+		String contentEncoding,
+		byte[] content,
+		boolean chunked
+	) {
+		server.createContext(
+			path,
+			exchange -> {
+				exchange.getResponseHeaders().add("Content-Type", contentType);
+				if (contentEncoding != null) {
+					exchange.getResponseHeaders().add("Content-Encoding", contentEncoding);
+				}
+				// Length 0 means chunked, -1 means no body
+				exchange.sendResponseHeaders(status, chunked ? 0 : content.length == 0 ? -1 : content.length);
+				try (OutputStream os = exchange.getResponseBody()) {
+					if (content.length > 0) {
+						os.write(content);
+					}
+				}
+			}
+		);
+	}
+
+	private static byte[] gzip(byte[] content) throws IOException {
+		ByteArrayOutputStream out = new ByteArrayOutputStream();
+		try (GZIPOutputStream gzip = new GZIPOutputStream(out)) {
+			gzip.write(content);
+		}
+		return out.toByteArray();
+	}
+
+	private static HttpResponse get(String path) throws IOException {
+		return HttpClient.sendRequest(
+			baseUrl + path,
+			"GET",
+			null,
+			null,
+			null,
+			null,
+			0,
+			null,
+			null,
+			null,
+			null,
+			null,
+			10,
+			null
+		);
+	}
+
+	@Test
+	void testBodyWithContentLength() throws IOException {
+		HttpResponse response = get("/length");
+		assertEquals(200, response.getStatusCode());
+		assertEquals(TEXT, response.getBody());
+	}
+
+	@Test
+	void testBodyChunked() throws IOException {
+		assertEquals(TEXT, get("/chunked").getBody());
+	}
+
+	@Test
+	void testBodyCharsetFromContentType() throws IOException {
+		assertEquals("café", get("/latin1").getBody());
+	}
+
+	@Test
+	void testBodyGzip() throws IOException {
+		assertEquals(TEXT, get("/gzip").getBody());
+	}
+
+	@Test
+	void testBodyEmpty() throws IOException {
+		assertEquals("", get("/empty").getBody());
+	}
+
+	@Test
+	void testBodyOfError() throws IOException {
+		HttpResponse response = get("/error");
+		assertEquals(404, response.getStatusCode());
+		assertEquals("not found", response.getBody());
+		assertEquals(response.getHeader() + "\nnot found", response.toString());
+	}
+}

src/test/java/org/metricshub/http/HttpResponseTest.java

@@ -1,6 +1,7 @@
 package org.metricshub.http;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertSame;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import org.junit.jupiter.api.Test;
@@ -35,6 +36,16 @@ void testGetBody() {
 		r.appendBody("abc");
 		r.appendBody("def");
 		assertEquals("abcdef", r.getBody());
+		r.appendBody(null);
+		r.appendBody("");
+		assertEquals("abcdefnull", r.getBody());
+
+		// The body is not copied
+		HttpResponse single = new HttpResponse();
+		String body = "single";
+		single.appendBody(body);
+		assertSame(body, single.getBody());
+		assertSame(single.getBody(), single.getBody());
 	}
 
 	@Test