Modifying Protocol Buffers (or Thrift, or MessagePack, or any of the free ASN.1 implementations I could find) to support length constraints was more work than writing a custom serialisation format, so I wrote a custom format.

api/net/sf/briar/api/protocol/Transport.proto

@@ -1,13 +0,0 @@
-package protocol;
-
-option java_package = "net.sf.briar.api.protocol";
-
-message TransportDetails {
-
-	message TransportDetail {
-		required string key = 1;
-		optional string value = 2;
-	}
-
-	repeated TransportDetail details = 1;
-}

api/net/sf/briar/api/serial/FormatException.java

@@ -0,0 +1,9 @@
+package net.sf.briar.api.serial;
+
+import java.io.IOException;
+
+public class FormatException extends IOException {
+
+	private static final long serialVersionUID = 2274966775687766337L;
+
+}

api/net/sf/briar/api/serial/Raw.java

@@ -0,0 +1,6 @@
+package net.sf.briar.api.serial;
+
+public interface Raw {
+
+	byte[] getBytes();
+}

api/net/sf/briar/api/serial/Reader.java

@@ -0,0 +1,54 @@
+package net.sf.briar.api.serial;
+
+import java.io.IOException;
+import java.util.List;
+import java.util.Map;
+
+public interface Reader {
+
+	boolean eof() throws IOException;
+
+	boolean hasBoolean() throws IOException;
+	boolean readBoolean() throws IOException;
+
+	boolean hasUint7() throws IOException;
+	byte readUint7() throws IOException;
+	boolean hasInt8() throws IOException;
+	byte readInt8() throws IOException;
+	boolean hasInt16() throws IOException;
+	short readInt16() throws IOException;
+	boolean hasInt32() throws IOException;
+	int readInt32() throws IOException;
+	boolean hasInt64() throws IOException;
+	long readInt64() throws IOException;
+	boolean hasIntAny() throws IOException;
+	long readIntAny() throws IOException;
+
+	boolean hasFloat32() throws IOException;
+	float readFloat32() throws IOException;
+	boolean hasFloat64() throws IOException;
+	double readFloat64() throws IOException;
+
+	boolean hasUtf8() throws IOException;
+	String readUtf8() throws IOException;
+	String readUtf8(int maxLength) throws IOException;
+
+	boolean hasRaw() throws IOException;
+	byte[] readRaw() throws IOException;
+	byte[] readRaw(int maxLength) throws IOException;
+
+	// FIXME: Add type-safe readers and iterator readers
+
+	boolean hasList(boolean definite) throws IOException;
+	List<?> readList(boolean definite) throws IOException;
+	boolean hasList() throws IOException;
+	List<?> readList() throws IOException;
+
+	boolean hasMap(boolean definite) throws IOException;
+	Map<?, ?> readMap(boolean definite) throws IOException;
+	boolean hasMap() throws IOException;
+	Map<?, ?> readMap() throws IOException;
+
+	boolean hasNull() throws IOException;
+	void readNull() throws IOException;
+}

api/net/sf/briar/api/serial/ReaderFactory.java

@@ -0,0 +1,8 @@
+package net.sf.briar.api.serial;
+
+import java.io.InputStream;
+
+public interface ReaderFactory {
+
+	Reader createReader(InputStream in);
+}

api/net/sf/briar/api/serial/Tag.java

@@ -0,0 +1,13 @@
+package net.sf.briar.api.serial;
+
+public interface Tag {
+
+	// FIXME: Definite lists and maps
+	public static final byte FALSE = -1, TRUE = -2;
+	public static final byte INT8 = -3, INT16 = -4, INT32 = -5, INT64 = -6;
+	public static final byte FLOAT32 = -7, FLOAT64 = -8;
+	public static final byte UTF8 = -9, RAW = -10;
+	public static final byte LIST_DEF = -11, MAP_DEF = -12;
+	public static final byte LIST_INDEF = -13, MAP_INDEF = -14, END = -15;
+	public static final byte NULL = -16;
+}

api/net/sf/briar/api/serial/Writer.java

@@ -0,0 +1,32 @@
+package net.sf.briar.api.serial;
+
+import java.io.IOException;
+import java.util.List;
+import java.util.Map;
+
+public interface Writer {
+
+	void writeBoolean(boolean b) throws IOException;
+
+	void writeUint7(byte b) throws IOException;
+	void writeInt8(byte b) throws IOException;
+	void writeInt16(short s) throws IOException;
+	void writeInt32(int i) throws IOException;
+	void writeInt64(long l) throws IOException;
+	void writeIntAny(long l) throws IOException;
+
+	void writeFloat32(float f) throws IOException;
+	void writeFloat64(double d) throws IOException;
+
+	void writeUtf8(String s) throws IOException;
+	void writeRaw(byte[] b) throws IOException;
+	void writeRaw(Raw r) throws IOException;
+
+	void writeList(List<?> l, boolean definite) throws IOException;
+	void writeList(List<?> l) throws IOException;
+
+	void writeMap(Map<?, ?> m, boolean definite) throws IOException;
+	void writeMap(Map<?, ?> m) throws IOException;
+
+	void writeNull() throws IOException;
+}

api/net/sf/briar/api/serial/WriterFactory.java

@@ -0,0 +1,8 @@
+package net.sf.briar.api.serial;
+
+import java.io.OutputStream;
+
+public interface WriterFactory {
+
+	Writer createWriter(OutputStream out);
+}