Winsock Error Codes
The following is a list of error codes returned by the
WSAGetLastErrorcall, along with their descriptions. Errors are listed in alphabetical
order by name.
An attempt was made to access a socket in a way forbidden by its access
permissions. An example is using a broadcast address for sendto without broadcast
permission being set using setsockopt(SO_BROADCAST).
Address already in use.
Only one usage of each socket address (protocol/IP address/port) is normally
permitted. This error occurs if an application attempts to bind a socket to an IP
address/port that has already been used for an existing socket, or a socket that wasn't
closed properly, or one that is still in the process of closing. For server applications
that need to bind multiple sockets to the same port number, consider using
setsockopt(SO_REUSEADDR). Client applications usually need not call bind at all - connect
will choose an unused port automatically.
Cannot assign requested address.
The requested address is not valid in its context. Normally results from an attempt
to bind to an address that is not valid for the local machine, or connect/sendto an
address or port that is not valid for a remote machine (e.g. port 0).
Address family not supported by protocol family.
An address incompatible with the requested protocol was used. All sockets are
created with an associated "address family" (i.e. AF_INET for Internet
Protocols) and a generic protocol type (i.e. SOCK_STREAM). This error will be returned if
an incorrect protocol is explicitly requested in the socket call, or if an address of the
wrong family is used for a socket, e.g. in sendto.
Operation already in progress.
An operation was attempted on a non-blocking socket that already had an operation
in progress - i.e. calling connect a second time on a non-blocking socket that is already
connecting, or canceling an asynchronous request (WSAAsyncGetXbyY) that has already been
canceled or completed.
Software caused connection abort.
An established connection was aborted by the software in your host machine,
possibly due to a data transmission timeout or protocol error.
No connection could be made because the target machine actively refused it. This
usually results from trying to connect to a service that is inactive on the foreign host -
i.e. one with no server application running.
Connection reset by peer.
An existing connection was forcibly closed by the remote host. This normally
results if the peer application on the remote host is suddenly stopped, the host is
rebooted, or the remote host used a "hard close" (see setsockopt for more
information on the SO_LINGER option on the remote socket.)
Destination address required.
A required address was omitted from an operation on a socket. For example, this
error will be returned if sendto is called with the remote address of ADDR_ANY.
The system detected an invalid pointer address in attempting to use a pointer
argument of a call. This error occurs if an application passes an invalid pointer value,
or if the length of the buffer is too small. For instance, if the length of an argument
which is a struct sockaddr is smaller than sizeof(struct sockaddr).
Host is down.
A socket operation failed because the destination host was down. A socket operation
encountered a dead host. Networking activity on the local host has not been initiated.
These conditions are more likely to be indicated by the error WSAETIMEDOUT.
No route to host.
A socket operation was attempted to an unreachable host. This error also occurs
when your ISP is intentionally blocking port 25 (the SMTP port) in an attempt to reduce
spamming through their systems. See WSAENETUNREACH
Operation now in progress.
A blocking operation is currently executing. Windows Sockets only allows a single
blocking operation to be outstanding per task (or thread), and if any other function call
is made (whether or not it references that or any other socket) the function fails with
the WSAEINPROGRESS error.
Interrupted function call.
A blocking operation was interrupted by a call to WSACancelBlockingCall.
Some invalid argument was supplied (for example, specifying an invalid level to the
setsockopt function). In some instances, it also refers to the current state of the socket
- for instance, calling accept on a socket that is not listening.
Socket is already connected.
A connect request was made on an already connected socket. Some implementations
also return this error if sendto is called on a connected SOCK_DGRAM socket (For
SOCK_STREAM sockets, the to parameter in sendto is ignored), although other
implementations treat this as a legal occurrence.
Too many open files.
Too many open sockets. Each implementation may have a maximum number of socket
handles available, either globally, per process or per thread.
Message too long.
A message sent on a datagram socket was larger than the internal message buffer or
some other network limit, or the buffer used to receive a datagram into was smaller than
the datagram itself.
Network is down.
A socket operation encountered a dead network. This could indicate a serious
failure of the network system (i.e. the protocol stack that the WinSock DLL runs over),
the network interface, or the local network itself.
Network dropped connection on reset.
The host you were connected to crashed and rebooted. May also be returned by
setsockopt if an attempt is made to set SO_KEEPALIVE on a connection that has already
Network is unreachable.
A socket operation was attempted to an unreachable network. This usually means the
local software knows no route to reach the remote host.
No buffer space available.
An operation on a socket could not be performed because the system lacked
sufficient buffer space or because a queue was full.
Bad protocol option.
An unknown, invalid or unsupported option or level was specified in a getsockopt or
Socket is not connected.
A request to send or receive data was disallowed because the socket is not
connected and (when sending on a datagram socket using sendto) no address was supplied.
Any other type of operation might also return this error - for example, setsockoptsetting
SO_KEEPALIVE if the connection has been reset.
Socket operation on non-socket.
An operation was attempted on something that is not a socket. Either the socket
handle parameter did not reference a valid socket, or for select, a member of an fd_set
was not valid.
Operation not supported.
The attempted operation is not supported for the type of object referenced. Usually
this occurs when a socket descriptor to a socket that cannot support this operation, for
example, trying to accept a connection on a datagram socket.
Protocol family not supported.
The protocol family has not been configured into the system or no implementation
for it exists. Has a slightly different meaning to WSAEAFNOSUPPORT, but is interchangeable
in most cases, and all Windows Sockets functions that return one of these specify
Too many processes.
A Windows Sockets implementation may have a limit on the number of applications
that may use it simultaneously. WSAStartup may fail with this error if the limit has been
Protocol not supported.
The requested protocol has not been configured into the system, or no
implementation for it exists. For example, a socketcall requests a SOCK_DGRAM socket, but
specifies a stream protocol.
Protocol wrong type for socket.
A protocol was specified in the socketfunction call that does not support the
semantics of the socket type requested. For example, the ARPA Internet UDP protocol cannot
be specified with a socket type of SOCK_STREAM.
Cannot send after socket shutdown.
A request to send or receive data was disallowed because the socket had already
been shut down in that direction with a previous shutdown call. By calling shutdown a
partial close of a socket is requested, which is a signal that sending or receiving or
both has been discontinued.
Socket type not supported.
The support for the specified socket type does not exist in this address family.
For example, the optional type SOCK_RAW might be selected in a socketcall, and the
implementation does not support SOCK_RAW sockets at all.
Connection timed out.
A connection attempt failed because the connected party did not properly respond
after a period of time, or established connection failed because connected host has failed
Resource temporarily unavailable.
This error is returned from operations on non-blocking sockets that cannot be
completed immediately, for example recv when no data is queued to be read from the socket.
It is a non-fatal error, and the operation should be retried later. It is normal for
WSAEWOULDBLOCK to be reported as the result from calling connect on a non-blocking
SOCK_STREAM socket, since some time must elapse for the connection to be established.
Host not found.
No such host is known. The name is not an official hostname or alias, or it cannot
be found in the database(s) being queried. This error may also be returned for protocol
and service queries, and means the specified name could not be found in the relevant
WSA_INVALID_HANDLE (OS dependent)
Specified event object handle is invalid.
An application attempts to use an event object, but the specified handle is not
WSA_INVALID_PARAMETER (OS dependent)
One or more parameters are invalid.
An application used a Windows Sockets function which directly maps to a Win32
function. The Win32 function is indicating a problem with one or more parameters.
WSAINVALIDPROCTABLE (OS dependent)
Invalid procedure table from service provider.
A service provider returned a bogus proc table to WS2_32.DLL. (Usually caused by
one or more of the function pointers being NULL.)
WSAINVALIDPROVIDER (OS dependent)
Invalid service provider version number.
A service provider returned a version number other than 2.0.
WSA_IO_PENDING (OS dependent)
Overlapped operations will complete later.
The application has initiated an overlapped operation which cannot be completed
immediately. A completion indication will be given at a later time when the operation has
WSA_IO_INCOMPLETE (OS dependent)
Overlapped I/O event object not in signaled state.
The application has tried to determine the status of an overlapped operation which
is not yet completed. Applications that use WSAWaitForMultipleEvents in a polling mode to
determine when an overlapped operation has completed will get this error code until the
operation is complete.
WSA_NOT_ENOUGH_MEMORY (OS dependent)
Insufficient memory available.
An application used a Windows Sockets function which directly maps to a Win32
function. The Win32 function is indicating a lack of required memory resources.
Successful WSAStartup not yet performed.
Either the application hasn't called WSAStartup, or WSAStartup failed. The
application may be accessing a socket which the current active task does not own (i.e.
trying to share a socket between tasks), or WSACleanup has been called too many times.
Valid name, no data record of requested type.
The requested name is valid and was found in the database, but it does not have the
correct associated data being resolved for. The usual example for this is a hostname ->
address translation attempt (using gethostbyname or WSAAsyncGetHostByName) which uses the
DNS (Domain Name Server), and an MX record is returned but no A record - indicating the
host itself exists, but is not directly reachable.
This is a non-recoverable error.
This indicates some sort of non-recoverable error occurred during a database
lookup. This may be because the database files (e.g. BSD-compatible HOSTS, SERVICES or
PROTOCOLS files) could not be found, or a DNS request was returned by the server with a
WSAPROVIDERFAILEDINIT (OS dependent)
Unable to initialize a service provider.
Either a service provider's DLL could not be loaded (LoadLibrary failed) or the
provider's WSPStartup/NSPStartupfunction failed.
WSASYSCALLFAILURE (OS dependent)
System call failure.
Returned when a system call that should never fail does. For example, if a call to
WaitForMultipleObjects fails or one of the registry functions fails trying to manipulate
the protocol/namespace catalogs.
Network subsystem is unavailable.
This error is returned by WSAStartup if the Windows Sockets implementation cannot function
at this time because the underlying system it uses to provide network services is
currently unavailable. Users should check:
- that the WINSOCK.DLL file is in the current path,
- that the WINSOCK.DLL file is from the same vendor as the underlying protocol stack. They
cannot be mixed and matched (WinSock DLLs must be supplied by the same vendor that
provided the underlying protocol stack).
- that they are not trying to use more than one Windows Sockets implementation
simultaneously. If there is more than one WINSOCK DLL on your system, be sure the first
one in the path is appropriate for the network subsystem currently loaded.
- the Windows Sockets implementation documentation to be sure all necessary components are
currently installed and configured correctly.
Non-authoritative host not found.
This is usually a temporary error during hostname resolution and means that the local
server did not receive a response from an authoritative server. A retry at some time later
may be successful.
WINSOCK.DLL version out of range.
The current Windows Sockets implementation does not support the Windows Sockets
specification version requested by the application. Check that no old WINSOCK.DLL files
are being accessed, or contact the stack vendor to see if an updated WINSOCK.DLL exists.
Graceful shutdown in progress.
Returned by recv, WSARecvto indicate the remote party has initiated a graceful
WSA_OPERATION_ABORTED (OS dependent)
Overlapped operation aborted.
An overlapped operation was canceled due to the closure of the socket, or the execution of
the SIO_FLUSH command in WSAIoctl.
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