/**
* Reads the identification string from the SSH server. This is the very first string that is sent
* upon connection by the server. It takes the form of, e.g. "SSH-2.0-OpenSSH_ver".
*
* <p>Several concerns are taken care of here, e.g. verifying protocol version, correct line
* endings as specified in RFC and such.
*
* <p>This is not efficient but is only done once.
*
* @param buffer The buffer to read from.
* @return empty string if full ident string has not yet been received
* @throws IOException
*/
private String readIdentification(Buffer.PlainBuffer buffer) throws IOException {
String ident;
byte[] data = new byte[256];
for (; ; ) {
int savedBufPos = buffer.rpos();
int pos = 0;
boolean needLF = false;
for (; ; ) {
if (buffer.available() == 0) {
// Need more data, so undo reading and return null
buffer.rpos(savedBufPos);
return "";
}
byte b = buffer.readByte();
if (b == '\r') {
needLF = true;
continue;
}
if (b == '\n') break;
if (needLF) throw new TransportException("Incorrect identification: bad line ending");
if (pos >= data.length)
throw new TransportException("Incorrect identification: line too long");
data[pos++] = b;
}
ident = new String(data, 0, pos);
if (ident.startsWith("SSH-")) break;
if (buffer.rpos() > 16 * 1024)
throw new TransportException("Incorrect identification: too many header lines");
}
if (!ident.startsWith("SSH-2.0-") && !ident.startsWith("SSH-1.99-"))
throw new TransportException(
DisconnectReason.PROTOCOL_VERSION_NOT_SUPPORTED,
"Server does not support SSHv2, identified as: " + ident);
return ident;
}
