Running the server

from the command line you can use

gradle run -PappArgs="['<IPAddress>', '<port>', '<directory>']"

For Example

gradle run -PappArgs="['127.0.0.1', '8080', './tmp/']"

will execute the program. Note that the directory must end in a '/' character.

Alternatively you can use an IDE such as eclipse to build and run the server.

Communication Protocol

The server uses a wire protocol similair to HTTP 1.0 to communicate.

The Server accepts 5 commands:

READ - Read an entire file.

NEW_TXN - Start a new transaction.

WRITE - Write a chunk of a file as part of a transaction.

COMMIT - Commit all writen files in a transaction to permanaent storage.

ABORT - Abort a transaction.

The server will respond with one of these 3 commands:

ACK - Server Responds to the client when a NEW_TXN or COMMIT message has been received and executed.

ASK_RESEND - Server Requests that the client resend a write message for a specific transaction.

ERROR - Server informs the client that there was an error when processing a message. The specific error is indicated by the error code.

Error codes:

201 - Invalid transaction ID. Occurs when a write or commit message is received with an transaction ID that the server is not currently processing.

202 - Invalid operation. Occurs when a command other than the 5 valid commands are recieved, or if a malformed message is received.

205 - File I/O error.

206 - File not found.

Wire Protocol

Each message in the wire protocol is broken up into two sections, the header followed by the data.

Commands sent to the server must be in the following format:

• The header contains 4 fields, each seperated by a space.
• If the data field is not empty then the header is followed by a "\r\n\r\n" sequence.
• If the data field is empty then the header is followed by a "\r\n\r\n\r\n" sequence.

The 4 header fields are: Command, Transaction ID, Message Sequence Number and data length.

Command Field - contains the operation that the server will perform (listed above)

Transaction ID Field - specifies which transaction the message relates to.

Message Sequence Number Field - specifies the current position of the message in a transaction. NEW_TXN messages have a sequence number of 0.

Data Length Field - specifies the length of the data field. Should be 0 if the data field is empty.

Data Field - if the command is a write then the data field contains the data to be written to the file. If the command is a read then the data field contains the name of the file to be read.

Examples:

• READ -1 0 8\r\n\r\ntest.txt
• NEW_TXN -1 0 0\r\n\r\n\r\n
• WRITE 1 1 11\r\n\r\nhello world

Responses sent from the server will be in the following format:

• The header contains 5 fields, each seperated by a space.
• If the data field is not empty then the header is followed by a "\r\n\r\n" sequence.
• If the data field is empty then the header is followed by a "\r\n\r\n\r\n" sequence.

The 5 header fields are: Command, Transaction ID, Message Sequence Number, Error Code, and Data Length

Command Field - contains the type of response. All valid response commands are listed above.

Transaction ID Field - Specifies which transaction the response relates to.

Message Sequence Number Field - Only relevant for an ASK_RESEND message. For an ASK_RESEND message it specifies which write message needs to be resent to the server.

Error Code - Specifies the error code assosiated with the response. All valid error codes are listed above.

Data Length Field - specifies the length of the data field. Should be 0 if the data field is empty.

Data Field - Contains an easy to understand explanation of what caused the error.