Handling EINTR errors for I/O operations

[MeanSquaredError]

Hi,

After looking into the library's source code it seems that the library does not handle EINTR errors that happen when:

• The program has established a handler for some interrupt.
• The interrupt is signaled while the process is sleeping on a "slow" I/O operation, e.g. socket poll or socket read.
• The interrupt handler is set without the SA_RESTART flag or the flag is set, but the operation is not restartable automatically, e.g. socket recv with a timeout.
• The handler processes the interrupt and then returns without terminating the program.

If these conditions are met, then the I/O operation fails with an EINTR error code.

This problem can happen easily when the program has established a handler for SIGINT in order to shutdown gracefully or re-read its configuration when it receives the signal.

The usual workaround for this issue is just retrying the I/O operation when it returns EINTR. In pseudocode it looks like this:

do {
    auto error_code = read (...);
} while (error_code == EINTR);

[rbeeli]

Hi,

Where did you check, and which socket client implementation did you consider?

Both built-in synchronous socket clients TcpSocket and OpenSslSocket have a check for EINTR:

https://github.com/rbeeli/websocketclient-cpp/blob/main/include/ws_client/transport/builtin/OpenSslSocket.hpp#L257

https://github.com/rbeeli/websocketclient-cpp/blob/main/include/ws_client/transport/builtin/TcpSocket.hpp#L248

If you experience a specific error or unexpected result, please provide a MWE.

[MeanSquaredError]

Indeed I did not notice that tcp/ssl reads and writes have the check for EINTR. However the connect() and SSL_connect() calls are lacking the checks for EINTR and they can fail with EINTR too.

[rbeeli]

You are right, those function slipped my attention regarding EINTR, will look into it next week. Thanks.

[rbeeli]

connect and SSL_connect are now checked for EINTR in TcpSocket and OpenSslSocket.

[MeanSquaredError]

Thank you for fixing that!