Introduction
Apache Geode is a data management platform that provides real-time, consistent access to data-intensive applications throughout widely distributed cloud architectures. While it currently has high-speed client interfaces for Java, C++ and .NET there is both a need to create lighter-weight clients and a demand to access Geode from other programming languages. Unfortunately, the existing client-server protocol is undocumented. It evolved over time and is overly complex to meet either of these needs.
This document describes a new, lighter-weight client/server protocol that may be implemented in phases, moving from a "basic client" to a more advanced "smart client". It endeavors to provide a protocol that is also more amenable to more modern APIs such as those using asynchronous or reactive patterns.
You will notice that this document describes the protocol down to the level of byte-ordering and "bytes on the wire". This is a description of the native serialization of the protocol that will be used for the initial implementation. It is our intent to make this pluggable so that alternative serialization technologies may be used instead, such as Protobuf or Apache Thrift. How that is done will be left as a goal for the architecture of the server component, with an additional goal of providing an IDL description of the protocol.
At the same time, we realize that serialization of application keys, values, callback arguments, function parameters and so forth are a separate matter and are not necessarily tied to the serialization protocol used for client/server messaging. The initial protocol will support primitive types such as scalars, strings, and byte arrays. It will also support JSON documents as values and convert between these and Geode PDX-serialized objects in the servers.
Goals
The high-level goals for the protocol are defined here.
Message Definition
A message is a series of bytes which contains the request or response. If the message is large, then we will have provision to divide the message into small messages. In that case, client/server needs to collect all messages to parse the request/response. The message will be sent in following way. A client can send the multiple messages on the connection and the server will respond to those messages in same order.
Message definition grammar
In order to consistently define messages the Extended Backus–Naur form grammar will be used.
Usage | Notation |
---|---|
definition | = |
alteration | | |
optional | [ ... ] |
repetition | { ... } |
Generic Message definition
Every message will adhere to the following generic message definition.
Message => MessageHeader (Request | Response) |
---|
MessageHeader => defined below |
Request => defined below |
Response => defined below |
Protocol Terminology
Any binary protocol requires the following things:
Version: This indicates the API version.
Correlation Id: This should be different per request sent. It allows correlation of request and response.
Object Type: The type of a serialized object.
Response Type: It indicates whether a response is partial or complete.
ErrorCodes: It indicates the problem with API invocation.
Chunk Response: Send large response in multiple chunks.
Continuous Response: Client can register(Observer pattern) for events and then server notify the client if those events occur.
Request: It indicates client's message
Response: It indicates server's message.
Request Format: Format of request API and its parameters, which client wants to invoke.
Response Format: Format for API return value, which client invoked.
Message: Set of bytes which contain the Message Header and Request/Response.
Serialized Byte Order: Big Endian
Connect
In order to fit into the existing Geode client/server infrastructure, we will be leveraging the current Geode "cache server" component. It accepts an initial byte that tells it what type of client is connecting to the server and how the client should be handled. A client using the new protocol can connect with the Geode server by sending a protocol byte. Initially, we will support the following two protocols:
- byte - 110: Message will contain the whole request or response.
- byte - 111: If the message is large then client or server can divide the message into the set of small messages. Then they need to collect all the small message and parse the whole request or response.
We may add additional protocol definitions here to indicate the use of an alternative serialization mechanism. For instance bytes 112 & 113 might indicate the but require the server to use Protobuf for serialization of client/server messages. How we handle other serialization libraries will be addressed when the pluggable-serialization architecture is roughed out.
API Id
The ApiId recognizes the API, a client wants to invoke on the server. The request format will contain the 2-byte(int16) for API id. It will be marked as ApiId in the request format.
API Version
API version will be associated with the request API. The request format will contain a 1-byte(int8) for the version. It will be marked as ApiVersion in the request format. Its current value will be 1.
Correlation Id
The purpose of correlation id to match the request and its corresponding response. The request format will contain the 4-bytes(int32) for correlation Id. It will be marked as CorrelationId in the request and response format. The client needs to send correlation id with the request and server will send the same id with the response.
Object Type
We will support all the object types which Geode understands. This would include all the primitive java types, an array of primitive types, collections, java serialization, data serializable, pdx serialization and custom user data serializers. The client needs to serialize objects as described here. This might be extended as part of making the Geode storage format pluggable.
ObjectKeyType
Geode supports only few object types as the region Key. The region key will be marked as Key in the request format. the client needs to serialize key as described here.
ResponseType
The Response Type indicates whether the response is partial or complete. The response with the FullResponse type id indicates the completion of that request. And the response with PartialResponse type id indicates the response is partial. The response format will contain the 2-bytes(int16) for response type. It will be marked as ResponseTypeId in the response format.
ResponseType | ResponseTypeId |
---|---|
FullResponse | 1 |
PartialResponse | 2 |
Error Codes
The Error codes indicate the issue with the invocation of API at the server. We have defined the error code for various issues here. The response format will contain the 2-bytes(int16) for error codes. It will be marked as ErrorCode in the response format.
ProtocolType
The protocol descriptions use the following types. These may be mapped to a pluggable serialization description language but their native serialization is described here. The native serialization uses network byte order ("big-endian").
Type | Number Of Bytes | Value | SerializedBytes |
---|---|---|---|
boolean | Fixed = 1 | true | 0x01 |
boolean | Fixed = 1 | false | 0x00 |
int8 | Fixed = 1 | 1 | 0x01 |
int16 | Fixed = 2 | 1 | 0x00 0x01 |
int32 | Fixed = 4 | 1 | 0x00 0x00 0x00 0x01 |
int64 | Fixed = 8 | 1 | 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x01 |
String(modified UTF 8 ) | Variable
| "Geode" | 0x00 0x05 (length) 0x47 0x65 0x6f 0x64 0x65 (utf encoding) |
byte[] | Variable
| {1,2} | 0x00 0x02 (length) 0x01 0x02 |
bytes | Variable: series of bytes containing a serialized value. |
MessageHeader
The Message header is a fixed size header which contains the size of a message, boolean flag to indicates whether a message is partial, and correlation id for that request message. The correlation id is used for the dual purpose here.
- If a message is sent in multiple sub-messages, then it will be used for combining the whole message.
- It will be used for correlating the request to its response.
MessageHeader => Size CorrelationId isPartialMessage hasMetaData | Description |
---|---|
Size => fixedSize = 4 bytes, type = int32 | Size of request or response |
CorrelationId => fixedSize = 4 bytes, type = int32 | The correlationID used to track a request/response |
isPartialMessage => fixedSize = 1 byte, type = boolean | Is this a partial message |
hasMetaData => fixedSize = 1 byte, type = boolean | Does the message have meta data associated with it |
Request
The request would contain the fixed size request header, optional metadata and request api parameters.
Request => RequestHeader [MetaData] RequestAPI |
---|
RequestHeader => defined below |
MetaData => optional |
RequestAPI => (PutRequest | GetRequest | PutAllRequest | GetAllRequest |ServerConfigRequest | ClientConfigRequest | AuthRequest) |
RequestHeader
The request header contains the ApiId, ApiVersion, and hasMetaData flag to indicate whether the request contains some metadata.
RequestHeader => ApiId apiVersion | Description |
---|---|
ApiId => fixedSize = 2 bytes, type = int16 | |
apiVersion => fixedSize = 1 byte, type = int8 |
Response
The response would contain the fixed size response header, optional metadata and return values.
Response => ResponseHeader [MetaData] APIResponse |
---|
ResponseHeader => defined below |
MetaData => Optional |
APIResponse => (PutResponse | GetResponse | PutAllResponse | GetAllResponse | ServerConfigResposne | ClientConfigResponse | AuthResponse | ErrorResponse) |
ResponseHeader
The response header will have resposneType, which indicates its partial response, full response or error. A hasMetaData flag indicates whether the response contains some metadata.
ResponseHeader => (ResponseTypeId | ErrorCode) hasMetaData CorrelationId | Description |
---|---|
ResponseTypeId => fixedSize = 2 bytes, type = int16 | |
ErrorCode => fixedSize = 2 bytes, type = int16 | When there is error response will have error message(String) for it |
ErrorResponse
The server will raise the error when it failed to execute api request from the client. The error code and message should help the client to diagnose the issue.
ErrorResponse => errorMessage |
---|
errorMessage => (variable size, type = String) |
Value
The Value is serialized bytes for the Geode region value. It contains value header and series of bytes. Using value header, we can send a big serialized object in more than one chunk.
Value => ValueHeader value {ValueHeader value} | Description |
---|---|
ValueHeader => defined below | |
value => bytes | Serialized Value Object which Geode can understand |
ValueHeader
The value header contains the value bytes size, and a flag indicates whether it contains all the value bytes.
ValueHeader => Size hasPartialBytes | Description |
---|---|
Size => fixedSize = 4 bytes, type = int32 | Number of serialized bytes |
hasPartialBytes => fixedSize = 1 byte, type = boolean | Whether this contains partial bytes of value |
Metadata
The purpose of a metadata to pass defined key value pair with request and response. That will be optional for a client. If there is any metadata associated with request or response, then need to set "hasMetadata" flag to "true" in request or response header. After that send metadata in the following format.
MetaData => NumberOfMetadata MetadataKeyId MetadataKeyValue { MetadataKeyId MetadataKeyValue} | |
---|---|
NumberOfMetadata=> fixedSize = 2 bytes, type = int16 | |
MetadataKeyId => fixedSize = 2 bytes, type = int16 | |
MetadataKeyValue => variable, Value as defined in table below |
We would have following pre-defined key and value for a metadata. Note this list will grow over time.
Request MetaData Key | MetaData KeyId | MetaData Value | Description |
---|---|---|---|
JSON_KEY | 1 fixedSize = 2 bytes, type = int16 | true fixedSize = 1 byte, type = boolean | Geode will expect key as JSON string(or bytes) and it will convert that string into pdx key. If the response requires a key, then it will convert the pdx key to JSON string(or bytes) back. |
JSON_VALUE | 2 fixedSize = 2 bytes, type = int16 | true fixedSize = 1 byte, type = boolean | Geode will expect Value as JSON string(or bytes) and it will convert that string into pdx value. If the response requires a value, then it will convert pdx value to JSON string(or bytes) back. |
EVENT_ID | 3 fixedSize = 2 bytes, type = int16 | EventId { uniqueId: type = String ThreadId:type=int64 SequenceId: type=int64 } | The eventid is used to identify same region event in Geode. Geode keeps map of "uniqueId + threadId" Vs "SequenceId" to know whether region event has been already seen or not.
|
Response MetaData Key | MetaData KeyId | MetaData Value | Description |
---|---|---|---|
UPDATE_PR_META_DATA | 1 fixedSize = 2 bytes, type = int16 | true fixedSize = 1 byte, type = boolean | [optional]The server accepted and forwarded the request to the appropriate node holding the affected cache entry. A smart client should refresh its partitioned region location metadata for higher performance. |
ServerConfigRequest
The purpose of ServerConfigRequest request to get a server config from the server. The client needs to send this request after connecting to the server. If the client knows server properties, then there is no need to send this request.
ServerConfigRequest => {} |
---|
ServerConfigResponse =>NumberOfProperties PropertyId PropertyValue{ PropertyId PropertyValue} | |
---|---|
NumberOfProperties => fixedSize = 2 bytes, type = int16 | |
Propertyid => fixedSize = 2 bytes, type = int16 | |
PropertyValue => variable, Value as defined in table below |
Server Response Properties | PropertyId | PropertyValue | Description |
---|---|---|---|
SECURITY_ENABLED | 1 | boolean | Whether security is enabled at server |
DIFFIE_HELLMAN_KEY | 2 | byte[] | The server Diffie-Hellman key if the credential is required to encrypt. |
MAX_TIME_BETWEEN_CLIENT_PING | 3 | int32 | If the client connection is idle for MAX_TIME_BETWEEN_CLIENT_PING seconds then the server will close that connection. |
ClientConfigRequest
The Purpose of ClientConfigRequest request to send a client config to a server. The client needs to send this request after connecting to the server. This request is optional for a client unless a server is configured for the Diffie-hellman algorithm.
ClientConfigRequest | NumberOfProperties PropertyId PropertyValue{ PropertyId PropertyValue} |
---|---|
NumberOfProperties | fixedSize = 2 bytes, type = int16 |
Propertyid | fixedSize = 2 bytes, type = int16 |
PropertyValue | variable, Value as defined in table below |
ClientConfigResponse ==> Success |
---|
Success => fixedSize = 1 byte, type = boolean |
Client Request Properties | PropertyId | PropertyValue | Description | |
---|---|---|---|---|
CLIENT_ID | 1 | string | Unique id for the client; if a client doesn't send this property then the server will just create id (client-host, client-port, server-host, server-port). | optional |
ClIENT_READ_TIMEOUT | 2 | int32 | The client will wait for ClIENT_READ_TIMEOUT for a server response. It's an optional property. | optional |
DIFFIE_HELLMAN_KEY | 3 | byte[] | The client Diffie-Hellman key is required to encrypt the credential. | If a server is configured with it then the client should send this. |
AuthRequest
The purpose of AuthRequest to authenticate the client connection. A client can send the auth request in the following format. Before sending the auth request a client can verify the server config by sending the ServerConfigRequest. A client can send a key-value pair of credentials to authenticate itself.
Those pair needs to serialized in following way. If Diffie-Hellman encryption is enabled on the server side then need to encrypt those serialized bytes. And then send those encrypted bytes to the server. The server will decrypt those bytes and create the key-value pair.
AuthRequest | isDiffieHellmanEnabled ( NumberOfProperties PropertyId PropertyValue{ PropertyId PropertyValue} | NumberOfEncryptedBytes EncryptedCredentials ) |
---|---|
isDiffieHellmanEnabled | fixedSize = 1 byte, type = boolean |
NumberOfProperties | fixedSize = 2 bytes, type = int16 |
Propertyid | bytes |
PropertyValue | bytes |
EncrptedCredentials | bytes |
AuthResponse => Success |
---|
Success => fixedSize = 1 byte, type = boolean |
Examples
PutRequest
string regionName = "ExampleRegion"
Key = 101
Value = "New Geode Client Server Protocol"
CallbackArg = Null
MessageHeader
| RequestHeader | PutRequest | |
---|---|---|---|
Size PartialMessage CorrelationId | RequestType apiVersion hasMetaData | RegionName Key CallbackArg | Value ( ValueHeader value ) |
Size = Size of Request (65) 0x00 0x00 0x00 0x42 | RequestType (PutRequestType = 3) 0x00 0x03 | RegionName(type:String, value:"ExampleRegion" ) len = 0x00 0x0d Utf Encoding = 0x45 0x78 0x61 0x6d 0x70 0x6c 0x65 0x52 0x65 0x67 0x69 0x6f 0x6e | Size = (number of serialized bytes = 35) 0x00 0x00 0x00 0x23 |
PartialMessage = (type = Boolean, value = false) 0x00 | apiVersion (1) 0x01 | Key (Serialzied using geode types, value = 101) Geode Int type = 0x39 Value = 0x00 0x00 0x00 0x65 | isPartialBytes = (It contains all serialized bytes, type = boolean) 0x00 |
CorrelationId = 1 0x00 0x00 0x00 0x01 | hasMetaData (false) 0x00 | CallbackArg (Serialzied using geode types, value = null) Value = 0x29 | value (Serialized as Geode String type, value = "New Geode Client Server Protocol") Geode String type = 0x57 Serialized Encoded length = 0x00 0x20 Encoded String = 0x4e 0x65 0x77 0x20 0x47 0x65 0x6f 0x64 0x65 0x20 0x43 0x6c 0x69 0x65 0x6e 0x74 0x20 0x53 0x65 0x72 0x76 0x65 0x72 0x20 0x50 0x72 0x6f 0x74 0x6f 0x63 0x6f 0x6c |
PutResponse
MessageHeader | ResponseHeader | PutResponse |
---|---|---|
Size PartialMessage CorrelationId | ResponseTypeId hasMetaData | Success |
Size = Size of Request (4) 0x00 0x00 0x00 0x04 | ResponseTypeId (FullResponse, type=int16, value =1) 0x00 0x01 | Success(type=boolean, value = true) 0x01 |
PartialMessage = (type = Boolean, value = false) 0x00 | hasMetaData (false) 0x00 | |
CorrelationId = 1 0x00 0x00 0x00 0x01 |
Messages
PutRequestMessage | PutResponseMessage |
---|---|
PutRequestMessage { MessageHeader { Size, 4 byte, int32 isPartialMessage, 1 byte, boolean CorrelationId, 4 byte, int32 } RequestHeader { ApiId, 2 byte, int16 ApiVersion, 1 byte, int8 hasMetaData, 1 byte, boolean } PutRequest { regionName, varaible , String { len, 2 byte, int16 variable, utf encoding } key, variable, bytes CallbaclArg, variable, bytes Value { ValueHeader { Size, 4 byte, int32 hasPartialBytes, 1 byte, boolean } value { bytes, series of bytes } } } } | PutResponseMessage { MessageHeader { Size, 4 byte, int32 isPartialMessage, 1 byte, boolean CorrelationId, 4 byte, int32 } ResponseHeader { ResponseTypeId, 2 byte, int16 hasMetaData, 1 byte, boolean } Success, 1 byte, boolean } |
GetRequestMessage | GetResponseMessage |
GetRequestMessage { MessageHeader { Size, 4 byte, int32 isPartialMessage, 1 byte, boolean CorrelationId, 4 byte, int32 } RequestHeader { ApiId, 2 byte, int16 ApiVersion, 1 byte, int8 hasMetaData, 1 byte, boolean } GetRequest { regionName, varaible , String { len, 2 byte, int16 variable, utf encoding } key, variable, bytes CallbaclArg, variable, bytes } } | GetResponseMessage { MessageHeader { Size, 4 byte, int32 isPartialMessage, 1 byte, boolean CorrelationId, 4 byte, int32 } ResponseHeader { ResponseTypeId, 2 byte, int16 hasMetaData, 1 byte, boolean } Result, variable, bytes } |
PutAllRequestMessage | PutAllResponseMessage |
PutAllRequestMessage { MessageHeader { Size, 4 byte, int32 isPartialMessage, 1 byte, boolean CorrelationId, 4 byte, int32 } RequestHeader { ApiId, 2 byte, int16 ApiVersion, 1 byte, int8 hasMetaData, 1 byte, boolean } PutRequest { regionName, varaible , String { len, 2 byte, int16 variable, utf encoding } NumberOfKeyValuePair, 4 byte, int32 KeyValuePair { key, variable, bytes Value { ValueHeader { Size, 4 byte, int32 hasPartialBytes, 1 byte, boolean } value { bytes, series of bytes } } } CallbaclArg, variable, bytes } } | PutAllResponseMessage { MessageHeader { Size, 4 byte, int32 isPartialMessage, 1 byte, boolean CorrelationId, 4 byte, int32 } ResponseHeader { ResponseTypeId, 2 byte, int16 hasMetaData, 1 byte, boolean } NumberOfKeysFailed , 4 byte, int32 } |
GetAllRequestMessage | GetAllResponseMessage |
GetAllRequestMessage { MessageHeader { Size, 4 byte, int32 isPartialMessage, 1 byte, boolean CorrelationId, 4 byte, int32 } RequestHeader { ApiId, 2 byte, int16 ApiVersion, 1 byte, int8 hasMetaData, 1 byte, boolean } GetRequest { regionName, varaible , String { len, 2 byte, int16 variable, utf encoding } NumberOfKeys, 4 byte, int32 keys { key, variable, bytes } CallbaclArg, variable, bytes } } | GetAllResponseMessage { MessageHeader { Size, 4 byte, int32 isPartialMessage, 1 byte, boolean CorrelationId, 4 byte, int32 } ResponseHeader { ResponseTypeId, 2 byte, int16 hasMetaData, 1 byte, boolean } NumberOfKeyValuePair, 4 byte, int32 KeyValuePair { key, variable, bytes value, variable, bytes } } |
RPC Frameworks
RPC frameworks such as Thrift or Apache Avro provide tools to generate client -server library based on a message schema. We are talking about how we may support various RPC frameworks to facilitate quick creation of GEODE clients in various languages supported by popular RPC frameworks.
Glossary
- Partial Response
- Full Response