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Expose the encryption and authentication overhead without breaking

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encapsulation.

This should allow callers to calculate maximum packet sizes without
knowing the details of the transport protocol.
This commit is contained in:
akwizgran
2011-09-21 15:22:25 +01:00
parent 7e58b25618
commit 10c3b21726
10 changed files with 115 additions and 35 deletions
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7
components/net/sf/briar/transport/ConnectionEncrypter.java
View File

@@ -11,4 +11,11 @@ interface ConnectionEncrypter {
/** Encrypts and writes the MAC for the current frame. */
void writeMac(byte[] mac) throws IOException;
/**
* Returns the number of encrypted bytes that can be written without
* writing more than the given number of bytes, including encryption
* overhead.
*/
long getCapacity(long capacity);
}

5
components/net/sf/briar/transport/ConnectionEncrypterImpl.java
View File

@@ -58,6 +58,11 @@ implements ConnectionEncrypter {
betweenFrames = true;
}
public long getCapacity(long capacity) {
if(capacity < 0L) throw new IllegalArgumentException();
return ivWritten ? capacity : Math.max(0L, capacity - IV_LENGTH);
}
@Override
public void write(int b) throws IOException {
if(!ivWritten) writeIv();

24
components/net/sf/briar/transport/ConnectionWriterImpl.java
View File

@@ -20,13 +20,13 @@ import net.sf.briar.util.ByteUtils;
class ConnectionWriterImpl extends FilterOutputStream
implements ConnectionWriter {
private final ConnectionEncrypter encrypter;
private final Mac mac;
private final int maxPayloadLength;
private final ByteArrayOutputStream buf;
private final byte[] header;
protected final ConnectionEncrypter encrypter;
protected final Mac mac;
protected final int maxPayloadLength;
protected final ByteArrayOutputStream buf;
protected final byte[] header;
private long frame = 0L;
protected long frame = 0L;
ConnectionWriterImpl(ConnectionEncrypter encrypter, Mac mac) {
super(encrypter.getOutputStream());
@@ -41,6 +41,18 @@ implements ConnectionWriter {
return this;
}
public long getCapacity(long capacity) {
if(capacity < 0L) throw new IllegalArgumentException();
// Subtract the encryption overhead
capacity = encrypter.getCapacity(capacity);
// If there's any data buffered, subtract it and its auth overhead
int overheadPerFrame = header.length + mac.getMacLength();
if(buf.size() > 0) capacity -= buf.size() + overheadPerFrame;
// Subtract the auth overhead from the remaining capacity
long frames = (long) Math.ceil((double) capacity / MAX_FRAME_LENGTH);
return Math.max(0L, capacity - frames * overheadPerFrame);
}
@Override
public void flush() throws IOException {
if(buf.size() > 0) writeFrame();

26
components/net/sf/briar/transport/PaddedConnectionWriter.java
View File

@@ -1,16 +1,11 @@
package net.sf.briar.transport;
import static net.sf.briar.api.transport.TransportConstants.MAX_FRAME_LENGTH;
import static net.sf.briar.util.ByteUtils.MAX_32_BIT_UNSIGNED;
import java.io.ByteArrayOutputStream;
import java.io.FilterOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import javax.crypto.Mac;
import net.sf.briar.api.transport.ConnectionWriter;
import net.sf.briar.util.ByteUtils;
/**
@@ -19,33 +14,18 @@ import net.sf.briar.util.ByteUtils;
* padding inserted if necessary. Calls to the writer's write() methods will
* block until there is space to buffer the data.
*/
class PaddedConnectionWriter extends FilterOutputStream
implements ConnectionWriter {
class PaddedConnectionWriter extends ConnectionWriterImpl {
private final ConnectionEncrypter encrypter;
private final Mac mac;
private final int maxPayloadLength;
private final ByteArrayOutputStream buf;
private final byte[] header, padding;
private final byte[] padding;
private long frame = 0L;
private boolean closed = false;
private IOException exception = null;
PaddedConnectionWriter(ConnectionEncrypter encrypter, Mac mac) {
super(encrypter.getOutputStream());
this.encrypter = encrypter;
this.mac = mac;
maxPayloadLength = MAX_FRAME_LENGTH - 4 - mac.getMacLength();
buf = new ByteArrayOutputStream(maxPayloadLength);
header = new byte[4];
super(encrypter, mac);
padding = new byte[maxPayloadLength];
}
public OutputStream getOutputStream() {
return this;
}
@Override
public synchronized void close() throws IOException {
if(exception != null) throw exception;