Dynamic multipart boundary

Ensure multipart boundary does not collide with content.
marchof · Nov 17, 2023 · e4d7023 · e4d7023
1 parent b87051d
commit e4d7023
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Showing 3 changed files with 85 additions and 33 deletions.
diff --git a/src/main/java/com/mountainminds/three4j/Gateway.java b/src/main/java/com/mountainminds/three4j/Gateway.java
@@ -20,9 +20,7 @@
 import static com.mountainminds.three4j.GatewayException.STATUS_PAYLOADTOOLARGE;
 import static com.mountainminds.three4j.GatewayException.STATUS_PAYMENTREQUIRED;
 import static com.mountainminds.three4j.GatewayException.STATUS_UNAUTHORIZED;
-import static com.mountainminds.three4j.HttpSupport.MULTIPART_BOUNDARY;
 import static com.mountainminds.three4j.HttpSupport.UNKNOWN_RESPONSE;
-import static com.mountainminds.three4j.HttpSupport.blobBody;
 import static java.util.Arrays.stream;
 import static java.util.function.Function.identity;
 import static java.util.stream.Collectors.toMap;
@@ -41,6 +39,7 @@
 import java.util.Map;
 import java.util.Set;
 
+import com.mountainminds.three4j.HttpSupport.MultipartEncoder;
 import com.mountainminds.three4j.HttpSupport.StatusHandler;
 
 /**
@@ -361,9 +360,10 @@ public MessageId sendMessage(ThreemaId toThreemid, EncryptedMessage msg) throws
 	 * @throws IOException      when a technical communication problem occurs
 	 */
 	public BlobId uploadBlob(byte[] encryptedcontent) throws GatewayException, IOException {
+		var encoder = new MultipartEncoder(encryptedcontent);
 		var request = gwRequest(auth(), "upload_blob") //
-				.header("Content-Type", "multipart/form-data;boundary=" + MULTIPART_BOUNDARY) //
-				.POST(BodyPublishers.ofByteArray(blobBody(encryptedcontent))).build();
+				.header("Content-Type", encoder.getContentType()) //
+				.POST(BodyPublishers.ofByteArray(encoder.getBody())).build();
 		return BlobId.of(send(request, BodyHandlers.ofString(), DEFAULT_STATUS //
 				.error(STATUS_BADREQUEST, "required parameters missing or blob empty") //
 				.error(STATUS_PAYLOADTOOLARGE, "blob is too big")));

diff --git a/src/main/java/com/mountainminds/three4j/HttpSupport.java b/src/main/java/com/mountainminds/three4j/HttpSupport.java
@@ -18,14 +18,14 @@
 
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
-import java.io.PrintWriter;
 import java.net.URLDecoder;
 import java.net.URLEncoder;
 import java.net.http.HttpRequest;
 import java.net.http.HttpRequest.BodyPublisher;
 import java.nio.charset.StandardCharsets;
 import java.util.Arrays;
 import java.util.Map;
+import java.util.Random;
 import java.util.function.Supplier;
 import java.util.stream.Collectors;
 
@@ -67,33 +67,73 @@ default StatusHandler ok() {
 		}
 	}
 
-	static final String MULTIPART_BOUNDARY = "xZK2aOVCeCybl1bbgvCEas6n4cdntpzkpcLWA12SahAiBrDrkIBj3W2HMPghi3Bo";
-
 	/**
 	 * Encode binary content as multipart/form-data body according to
 	 * <a href="https://tools.ietf.org/html/rfc2046">RFC 2046</a>.
 	 */
-	static byte[] blobBody(byte[] blob) {
-		try (var out = new ByteArrayOutputStream(); var printer = new PrintWriter(out, true, US_ASCII) {
-			@Override
-			public void println() {
-				// Ensure CRLF line endings on every platform
-				write('\r');
-				write('\n');
-				flush();
-			};
-		}) {
-			printer.println("--" + MULTIPART_BOUNDARY);
-			printer.println("Content-Disposition: form-data;name=\"blob\";filename=\"blob\"");
-			printer.println();
-			out.write(blob);
-			printer.println();
-			printer.println("--" + MULTIPART_BOUNDARY + "--");
-			return out.toByteArray();
-		} catch (IOException e) {
-			// Must not happen with ByteArrayOutputStream
-			throw new RuntimeException(e);
+	static class MultipartEncoder {
+
+		private static final String CHARS = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
+
+		private final byte[] content;
+		private final String boundary;
+
+		MultipartEncoder(byte[] content) {
+			this.content = content;
+			this.boundary = getBoundary(content);
+		}
+
+		private static String getBoundary(byte[] content) {
+			// deterministic pseudo random for testing
+			var rand = new Random(0L);
+			var boundary = new StringBuilder();
+			while (boundary.length() < 16 || contains(boundary.toString().getBytes(US_ASCII), content)) {
+				boundary.append(CHARS.charAt(rand.nextInt(CHARS.length())));
+			}
+			return boundary.toString();
+		}
+
+		private static boolean contains(byte[] substr, byte[] str) {
+			outer: for (int i = 0; i < str.length - substr.length; i++) {
+				for (int j = 0; j < substr.length; j++) {
+					if (str[i + j] != substr[j]) {
+						continue outer;
+					}
+				}
+				return true;
+			}
+			return false;
+		}
+
+		String getContentType() {
+			return "multipart/form-data;boundary=" + boundary;
 		}
+
+		byte[] getBody() {
+			try (var out = new ByteArrayOutputStream() {
+				public void println() throws IOException {
+					write('\r');
+					write('\n');
+				};
+
+				public void println(String text) throws IOException {
+					write(text.getBytes(US_ASCII));
+					println();
+				};
+			}) {
+				out.println("--" + boundary);
+				out.println("Content-Disposition: form-data;name=\"blob\";filename=\"blob\"");
+				out.println();
+				out.write(content);
+				out.println();
+				out.println("--" + boundary + "--");
+				return out.toByteArray();
+			} catch (IOException e) {
+				// Must not happen with ByteArrayOutputStream
+				throw new RuntimeException(e);
+			}
+		}
+
 	}
 
 	/**

diff --git a/src/test/java/com/mountainminds/three4j/HttpSupportTest.java b/src/test/java/com/mountainminds/three4j/HttpSupportTest.java
@@ -14,7 +14,6 @@
 package com.mountainminds.three4j;
 
 import static com.mountainminds.three4j.HttpSupport.UNKNOWN_RESPONSE;
-import static com.mountainminds.three4j.HttpSupport.blobBody;
 import static com.mountainminds.three4j.HttpSupport.decodeUrlParams;
 import static java.nio.charset.StandardCharsets.US_ASCII;
 import static org.junit.jupiter.api.Assertions.assertEquals;
@@ -25,6 +24,7 @@
 
 import org.junit.jupiter.api.Test;
 
+import com.mountainminds.three4j.HttpSupport.MultipartEncoder;
 import com.mountainminds.three4j.HttpSupport.UrlParams;
 
 public class HttpSupportTest {
@@ -61,13 +61,25 @@ public void StatusHandler_error_should_not_handle_other_codes() {
 	}
 
 	@Test
-	public void blobBody_should_create_correct_multipart_content() throws IOException {
-		var body = new String(blobBody("<content>".getBytes(US_ASCII)), US_ASCII);
-		assertEquals("--xZK2aOVCeCybl1bbgvCEas6n4cdntpzkpcLWA12SahAiBrDrkIBj3W2HMPghi3Bo\r\n" //
+	public void multipartEncoder_should_create_correct_multipart_content() throws IOException {
+		var encoder = new MultipartEncoder("hello".getBytes(US_ASCII));
+		assertEquals("multipart/form-data;boundary=22Pbd7157KhLr8Ry", encoder.getContentType());
+		assertEquals("--22Pbd7157KhLr8Ry\r\n" //
 				+ "Content-Disposition: form-data;name=\"blob\";filename=\"blob\"\r\n" //
 				+ "\r\n" //
-				+ "<content>\r\n" //
-				+ "--xZK2aOVCeCybl1bbgvCEas6n4cdntpzkpcLWA12SahAiBrDrkIBj3W2HMPghi3Bo--\r\n", body);
+				+ "hello\r\n" //
+				+ "--22Pbd7157KhLr8Ry--\r\n", new String(encoder.getBody(), US_ASCII));
+	}
+
+	@Test
+	public void multipartEncoder_should_extend_boundary_in_case_of_conflicts() throws IOException {
+		var encoder = new MultipartEncoder("hello 22Pbd7157KhLr8Ry8RZmz66!".getBytes(US_ASCII));
+		assertEquals("multipart/form-data;boundary=22Pbd7157KhLr8Ry8RZmz66h", encoder.getContentType());
+		assertEquals("--22Pbd7157KhLr8Ry8RZmz66h\r\n" //
+				+ "Content-Disposition: form-data;name=\"blob\";filename=\"blob\"\r\n" //
+				+ "\r\n" //
+				+ "hello 22Pbd7157KhLr8Ry8RZmz66!\r\n" //
+				+ "--22Pbd7157KhLr8Ry8RZmz66h--\r\n", new String(encoder.getBody(), US_ASCII));
 	}
 
 	@Test