BUG: Send() Fails with Error WSAENOBUFS Over Blocking Socket

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This article was previously published under Q201213

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SYMPTOMS

When large blocks of data (for example, 3-4 MB) are sent over a blocking socket, send eventually fails with error 10055, WSAENOBUFS.

The online documentation indicates that send over a blocking socket should block if there is no system buffer space available:

If no buffer space is available within the transport system to hold the data to be transmitted, send will block unless the socket has been placed in a nonblocking mode. On nonblocking stream oriented sockets, the number of bytes written can be between 1 and the requested length, depending on buffer availability on both client and server machines.

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RESOLUTION

When you encounter the problem described in the "Symptoms" section, please consider using one of the following workarounds:

Use the socket in nonblocking or asynchronous mode.
Break large-size data blocks into small ones and specify a relatively small buffer in send for blocking sockets, preferably no larger than 64K.
Set the SO_SNDBUF socket option to 0 (zero) to allow the stack to send from your application buffer directly.

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