// Eventually this will define stuff client code will use to
// construct messages to StorageManager.

#ifndef MESSAGEFORMAT_H_
#define MESSAGEFORMAT_H_

namespace storagemanager
{

static const uint SM_MSG_START=0xbf65a7e1;
static const char *socket_name = "\0storagemanager";

enum Opcodes {
    OPEN,
    READ,
    WRITE,
    STAT,
    UNLINK,
    APPEND,
    TRUNCATE,
    LIST_DIRECTORY,
    PING
};

/*
    All commands sent to and from StorageManager begin with
    SM_MSG_START, and a uint32_t for the length of the payload.
    
    In the payload, all responses from StorageManager begin with
    a return code, which is the same as the corresponding syscall.
    If the return code is an error (usually < 0), then a 4-byte
    value for errno follows.  On success, no errno is sent.

    On success, what follows is any output parameters from the call.

    OPEN
    ----
    command format:
    opcode|4-byte filename length|filename|4-byte openmode

    response format:
    struct stat

    READ
    ----
    command format:
    opcode|4-byte filename length|filename|size_t count|off_t offset

    response format:
    data (size is stored in the return code)

    WRITE
    -----
    command format:
    opcode|4-byte filename length|filename|size_t count|off_t offset|data

    response format:

    APPEND
    ------
    command format:
    opcode|4-byte filename length|filename|size_t count|data

    response format:

    UNLINK
    ------
    command format:
    opcode|4-byte filename length|filename

    response format:
    
    STAT
    ----
    command format:
    opcode|4-byte filename length|filename

    response format:
    struct stat

    TRUNCATE
    --------
    command format:
    opcode|4-byte filename length|filename|off64_t length
   
    response format:
    
    LIST_DIRECTORY
    --------------
    command format:
    opcode|4-byte path length|pathname

    response format:
    4-byte num elements|
    (4-byte filename length|filename) * num elements
    
    PING
    ----
    command format:
    opcode

    reponse format:

#endif