TCP/IP for DOS Socket Library Reference

Appendix C. Socket Error Codes

This appendix lists and explains error codes that are returned if a socket function is unsuccessful.

Most socket library functions, if unsuccessful, store an error code in a variable to report the results of a function call. Application programs, therefore, can make error-handling decisions based on this value. Programs that use the DOS socket library can access these global variables directly. Programs that use the Windows socket library can use the appropriate function (GetErmo(), GetHErmo(), or GetDNSErmo()) to access the values maintained in the Windows DLL. Header files define names for these error codes. The application program should refer to those names, instead of the actual numerical values.

Table C-l lists in numerical order the socket library error codes stored in the variable errno and explains their meanings. These symbolic constants are defined in SOCKET.H.

Table C-1. Socket Library Error Codes

Code	Label	Explanation
9	EBADF	Bad socket number, probably because the socket() function has not yet been called and the specified socket does not yet exist.
22	EINVAL	The request contained an invalid argument.
35	EWOULDBLOCK	The socket is synchronous nonblocking and no connection is established yet or no bytes were available to be read. Retry the request.
36	EINPROGRESS	Operation now in progress; try the request again. With a close request, the socket will eventually be closed so no further action is required.
37	EALREADY	The operation is currently in progress.
41	EPROTOTYPE	Protocol is the wrong type for the socket.
42	ENOPROTOOPT	Protocol is not available.
43	ENOPROTONOSUPPORT	The protocol type is not supported.
45	EOPNOTSUPP	The operation is not supported on the socket. Connectionless socket types, such as SOCK_DGRAM, never support this operation. Only passive SOCK_STREAM sockets support this operation.
46	EPFNOSUPPORT	The protocol family is not supported.
47	EAFNOSUPPORT	Addresses in the specified address family cannot be used with this socket.
48	EADDRINUSE	An attempt was made to create a socket with a port that is already being used, or a connection already exists on the same socket pair.
53	ECONNABORTED	A connection was aborted before it could be accepted.
54	ECONNRESET	The other end has aborted the connection to this SOCK_STREAM socket. Close the socket.
55	ENOBUFS	No buffer space is available, and the socket cannot be created.
56	EISCONN	The socket is already connected. This is not necessarily an error if the socket is synchronous nonblocking, because it can indicate a successful connection request.
57	ENOTCONN	For a SOCK_STREAM socket, a connection has not yet been established, and therefore the socket is not ready for data.
58	ESHUTDOWN	Cannot send data after socket is closed.
60	ETIMEOUT	An attempt to establish a connection timed out without establishing a connection. This error typically occurs with TCP when IP communications with the peer system do not work. This failure can be caused by anything from a broken cable to an IP address mismatch. Close the socket.
61	ECONNREFUSED	An attempt to establish a connection was rejected. This error typically occurs with TCP when no passive open on the address is pending on the peer system.
66	ENOTINSTLD	The requested protocol is not installed.
67	EASYNCNOTSUPP	The requested asynchronous operation cannot be performed. This error occurs when standard DOS applications run under Windows or DESQview and request asynchronous services.
68	ESYNCNOTSUPP	The requested synchronous function cannot be called from within an asynchronous function.
69	ENO_RCB	The socket library has run out of internal resources because there are too many outstanding socket function calls.

Table C-2 lists in numerical order the transport database function error codes stored in the h_errno variable and explains their meanings. These symbolic constants are defined in SOCKET.H.