RPC包格式：
這圖是從別人那拿過來的 留着自己看，主要是對如下這段代碼的理解有幫助：
/**
* 請求報文: 4字節hrpc + 1字節Current_version + 1字節authMethod
* 4字節Header_len + connection_header
* 4字節Data_len + call.id + writable
*
* connection_header長度不定 call.id + writable長度不等
*
* 返回報文： call.id + status.state + writable
* errorClass + error
* @return
* @throws IOException
* @throws InterruptedException
*/
public int readAndProcess() throws IOException, InterruptedException {
while (true) {
/* Read at most one RPC. If the header is not read completely yet
* then iterate until we read first RPC or until there is no data left.
*/
int count = -1;
//讀取hrpc信息
if (dataLengthBuffer.remaining() > 0) {
count = channelRead(channel, dataLengthBuffer);
if (count < 0 || dataLengthBuffer.remaining() > 0)
return count;
}
if (!rpcHeaderRead) {//一次連接 只會讀一次
//Every connection is expected to send the header.
if (rpcHeaderBuffer == null) {
rpcHeaderBuffer = ByteBuffer.allocate(2);
}
count = channelRead(channel, rpcHeaderBuffer);
if (count < 0 || rpcHeaderBuffer.remaining() > 0) {
return count;
}
//讀取current_version信息
int version = rpcHeaderBuffer.get(0);
//讀取authMethod（認證方法）信息
byte[] method = new byte[] {rpcHeaderBuffer.get(1)};
authMethod = AuthMethod.read(new DataInputStream(new ByteArrayInputStream(method)));
dataLengthBuffer.flip();
if (!HEADER.equals(dataLengthBuffer) || version != CURRENT_VERSION) {
//Warning is ok since this is not supposed to happen.
LOG.warn("Incorrect header or version mismatch from " + hostAddress + ":" + remotePort +
" got version " + version + " expected version " + CURRENT_VERSION);
return -1;
}
dataLengthBuffer.clear();
if (authMethod == null) {
throw new IOException("Unable to read authentication method");
}
if (isSecurityEnabled && authMethod == AuthMethod.SIMPLE) {
AccessControlException ae = new AccessControlException("Authentication is required");
setupResponse(authFailedResponse, authFailedCall, Status.FATAL, null, ae.getClass().getName(), ae.getMessage());
responder.doRespond(authFailedCall);
throw ae;
}
if (!isSecurityEnabled && authMethod != AuthMethod.SIMPLE) {
doSaslReply(SaslStatus.SUCCESS, new IntWritable(SaslRpcServer.SWITCH_TO_SIMPLE_AUTH), null, null);
authMethod = AuthMethod.SIMPLE;
// client has already sent the initial Sasl message and we
// should ignore it. Both client and server should fall back
// to simple auth from now on.
skipInitialSaslHandshake = true;
}
if (authMethod != AuthMethod.SIMPLE) {
useSasl = true;
}
rpcHeaderBuffer = null;
rpcHeaderRead = true;
continue;
}
//讀取connection連接信息及真正的Data信息
if (data == null) {
dataLengthBuffer.flip();
dataLength = dataLengthBuffer.getInt();
if (dataLength == Client.PING_CALL_ID) {//如果此RPC調用爲ping則 直接返回
if(!useWrap) { //covers the !useSasl too
dataLengthBuffer.clear();
return 0; //ping message
}
}
if (dataLength < 0) {
LOG.warn("Unexpected data length " + dataLength + "!! from " + getHostAddress());
}
data = ByteBuffer.allocate(dataLength);
}
count = channelRead(channel, data);
//當data沒有空位置時 說明已經讀完
if (data.remaining() == 0) {
dataLengthBuffer.clear();
data.flip();
if (skipInitialSaslHandshake) {
data = null;
skipInitialSaslHandshake = false;
continue;
}
boolean isHeaderRead = headerRead;
if (useSasl) {
saslReadAndProcess(data.array());
} else {//此處具體處理Data信息及Header信息
processOneRpc(data.array());
}
data = null;
if (!isHeaderRead) {//如果只讀取了Header信息 繼續循環讀取Data信息
continue;
}
}
return count;
}
} private void processOneRpc(byte[] buf) throws IOException, InterruptedException {
if (headerRead) {//讀取Data信息
processData(buf);
} else {//讀取Header信息
processHeader(buf);
headerRead = true;
if (!authorizeConnection()) {
throw new AccessControlException("Connection from " + this
+ " for protocol " + header.getProtocol()
+ " is unauthorized for user " + user);
}
}
} private void processData(byte[] buf) throws IOException, InterruptedException {
DataInputStream dis = new DataInputStream(new ByteArrayInputStream(buf));
int id = dis.readInt(); // try to read an id
if (LOG.isDebugEnabled())
LOG.debug(" got #" + id);
Writable param = ReflectionUtils.newInstance(paramClass, conf);//read param
param.readFields(dis);
Call call = new Call(id, param, this);
callQueue.put(call); // queue the call; maybe blocked here
incRpcCount(); // Increment the rpc count
} /// Reads the connection header following version
private void processHeader(byte[] buf) throws IOException {
DataInputStream in = new DataInputStream(new ByteArrayInputStream(buf));
header.readFields(in);
try {
String protocolClassName = header.getProtocol();
if (protocolClassName != null) {
protocol = getProtocolClass(header.getProtocol(), conf);
}
} catch (ClassNotFoundException cnfe) {
throw new IOException("Unknown protocol: " + header.getProtocol());
}
UserGroupInformation protocolUser = header.getUgi();
if (!useSasl) {
user = protocolUser;
if (user != null) {
user.setAuthenticationMethod(AuthMethod.SIMPLE.authenticationMethod);
}
} else {
// user is authenticated
user.setAuthenticationMethod(authMethod.authenticationMethod);
//Now we check if this is a proxy user case. If the protocol user is
//different from the 'user', it is a proxy user scenario. However,
//this is not allowed if user authenticated with DIGEST.
if ((protocolUser != null)
&& (!protocolUser.getUserName().equals(user.getUserName()))) {
if (authMethod == AuthMethod.DIGEST) {
// Not allowed to doAs if token authentication is used
throw new AccessControlException("Authenticated user (" + user
+ ") doesn't match what the client claims to be ("
+ protocolUser + ")");
} else {
// Effective user can be different from authenticated user
// for simple auth or kerberos auth
// The user is the real user. Now we create a proxy user
UserGroupInformation realUser = user;
user = UserGroupInformation.createProxyUser(protocolUser
.getUserName(), realUser);
// Now the user is a proxy user, set Authentication method Proxy.
user.setAuthenticationMethod(AuthenticationMethod.PROXY);
}
}
}
}具體查看鏈接：http://fengshenwu.com/blog/2012/11/13/hadoop-rpc_develop/
我的hadoop源碼(有一些我看代碼時留下的註釋):https://github.com/heipacker/hadoop-1.0.3-linux