Swap:Custom Protocol

SWAP has a custom protocol available that is used for management and inter-node communication. This is a persistent socket connection between nodes. This is not run over http due to the small size of most messages and overhead in establishing a connection for each message.

Mina

SWAP uses mina to manage socket communication. Protocol decoding is handled through a set of filters and a final handler to dispatch command.

Wire-level message Structure

Each SWAP command is sent as a list of a single SWAP message. This is done to allow efficient packing of small messages (ie, results of stat, etc)

Int - size of message (type + reps + content) short - message type (See MessageType enum) short - repetitions of message byte[] - content

Content is the list of packed messages. Each message is composed of a set of primitive segments (long, string, uuid, long[], etc). What segments comprise a message are described in the MessageType enum. Allowable types of segments are defined in MessageSegment.

For example, the GET_PATH_DETAILS request has the following structure: UUID - uuid of file group STRING[] - list of paths for details w/in that file group.

To request for just one group the message would have the following information: size=message size type=13, reps=1 UUID of file group "path1","path2"

Since we can issue multiple requests of the same message, in one message, we could include a request for files from two different groups. This message would look slightly different:

size=message size type=13 reps=2 UUID of group 1 "path1","path2" UUID of group 2 "path3","path4"

This packing and unpacking is handled by the two mina filters, SwapProtocolEncoder and SwapProtocolDecoder. These two filters encode/decode messages to and from an array of SwapMessage. A SwapMessage is a simple container holding the type of message along w/ the an array of Objects representing the message content. The size of the content is equal to the number of segments in a message * the number of repetitions in a message.

Authentication

Due to how swap authenticates against LDAP, clients must supply a clear-text username and password to the server. To secure this, an ssl tunnel is established during the initial connection to a swap server. Once authentication has finished the client may tell the server to disable the tunnel.