Document RPC error codes

Replace all "magic values" in RPCError(...) by constants.

src/bitcoinrpc.h

@@ -18,6 +18,42 @@ class CBlockIndex;
 
 #include "util.h"
 
+// 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
+};
+
 json_spirit::Object JSONRPCError(int code, const std::string& message);
 
 void ThreadRPCServer(void* parg);