Document RPC error codes #1908

I performed some code archeology to retroactively name and document the JSONRPC error codes.

This pull has no code changes.

Feel free to suggest other names for the errors.

// Bitcoin RPC error codes
enum RPCErrorCode
{
    // Standard JSON-RPC 2.0 errors
    RPC_INVALID_REQUEST  = -32600,
    RPC_METHOD_NOT_FOUND = -32601,
    RPC_INVALID_PARAMS   = -32602,
    RPC_INTERNAL_ERROR   = -32603,
    RPC_PARSE_ERROR      = -32700,

    // General application defined errors
    RPC_MISC_ERROR                  = -1,  // std::exception thrown in command handling
    RPC_FORBIDDEN_BY_SAFE_MODE      = -2,  // Server is in safe mode, and command is not allowed in safe mode
    RPC_TYPE_ERROR                  = -3,  // Unexpected type was passed as parameter
    RPC_INVALID_ADDRESS_OR_KEY      = -5,  // Invalid address or key
    RPC_OUT_OF_MEMORY               = -7,  // Ran out of memory during operation
    RPC_INVALID_PARAMETER           = -8,  // Invalid, missing or duplicate parameter
    RPC_DATABASE_ERROR              = -20, // Database error
    RPC_DESERIALIZATION_ERROR       = -22, // Error parsing or validating structure in raw format

    // P2P client errors
    RPC_CLIENT_NOT_CONNECTED        = -9,  // Bitcoin is not connected
    RPC_CLIENT_IN_INITIAL_DOWNLOAD  = -10, // Still downloading initial blocks

    // Wallet errors
    RPC_WALLET_ERROR                = -4,  // Unspecified problem with wallet (key not found etc.)
    RPC_WALLET_INSUFFICIENT_FUNDS   = -6,  // Not enough funds in wallet or account
    RPC_WALLET_INVALID_ACCOUNT_NAME = -11, // Invalid account name
    RPC_WALLET_KEYPOOL_RAN_OUT      = -12, // Keypool ran out, call keypoolrefill first
    RPC_WALLET_UNLOCK_NEEDED        = -13, // Enter the wallet passphrase with walletpassphrase first
    RPC_WALLET_PASSPHRASE_INCORRECT = -14, // The wallet passphrase entered was incorrect
    RPC_WALLET_WRONG_ENC_STATE      = -15, // Command given in wrong wallet encryption state (encrypting an encrypted wallet etc.)
    RPC_WALLET_ENCRYPTION_FAILED    = -16, // Failed to encrypt the wallet
    RPC_WALLET_ALREADY_UNLOCKED     = -17, // Wallet is already unlocked
};

This pull reveals some inconsistencies in the error codes thrown, for example, -3 is sometimes used for "Invalid bitcoin address" sometimes i.s.o -5, but as to not change the interface I decided against addressing this. This can be left for a later pull (or never, and just documented as part of the API).

I've also added constants for the HTTP status codes.

I love it as it makes the code so much more readable, great pull IMO.

ACK.

ACK

ACK