RFC6066 defines server name indication in extension of type server_name. The extension_data field of this extension SHALL contain ServerNameList where:
struct {
NameType name_type;
select (name_type) {
case host_name: HostName;
} name;
} ServerName;
enum {
host_name(0), (255)
} NameType;
opaque HostName<1..2^16-1>;
struct {
ServerName server_name_list<1..2^16-1>
} ServerNameList;
Would be nice to have step by step explanation of this data structure. Also, here is the sample code, could be found here, how to read the extension data:
private static List<SNIServerName> exploreSNIExt(ByteBuffer input,
int extLen) throws IOException {
Map<Integer, SNIServerName> sniMap = new LinkedHashMap<>();
int remains = extLen;
if (extLen >= 2) { // "server_name" extension in ClientHello
int listLen = getInt16(input); // length of server_name_list
if (listLen == 0 || listLen + 2 != extLen) {
throw new SSLProtocolException(
"Invalid server name indication extension");
}
remains -= 2; // 0x02: the length field of server_name_list
while (remains > 0) {
int code = getInt8(input); // name_type
int snLen = getInt16(input); // length field of server name
if (snLen > remains) {
throw new SSLProtocolException(
"Not enough data to fill declared vector size");
}
byte[] encoded = new byte[snLen];
input.get(encoded);
SNIServerName serverName;
switch (code) {
case StandardConstants.SNI_HOST_NAME: // 0x00
if (encoded.length == 0) {
throw new SSLProtocolException(
"Empty HostName in server name indication");
}
serverName = new SNIHostName(encoded);
break;
default:
serverName = new UnknownServerName(code, encoded);
}
// check for duplicated server name type
if (sniMap.put(serverName.getType(), serverName) != null) {
throw new SSLProtocolException(
"Duplicated server name of type "
+ serverName.getType());
}
remains -= encoded.length + 3; // NameType: 1 byte
// HostName length: 2 bytes
}
} else if (extLen == 0) { // "server_name" extension in ServerHello
throw new SSLProtocolException(
"Not server name indication extension in client");
}
if (remains != 0) {
throw new SSLProtocolException(
"Invalid server name indication extension");
}
return Collections.<SNIServerName>unmodifiableList(
new ArrayList<>(sniMap.values()));
}
Byte reader:
private static int getInt16(ByteBuffer input) {
return ((input.get() & 0xFF) << 8) | (input.get() & 0xFF);
}
Here is good example how data should be read. For example, extension type is defined by reading 2 bytes - so another question is - which RFC defines it?
