Details
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Bug
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Status: Closed
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Major
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Resolution: Fixed
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proton-0.7
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None
Description
Our team is currently using Proton 0.7 and ran into an issue on Windows while testing where we could not successfully reconnect to a broker once it was taken down and brought back up (we are using a pn_driver_t in C). It appears that having the ability to clear the pn_error_t stored in the driver struct would have solved the issue for us. I'll include some of the details below that were also sent to the mailing list but the solution is probably a pretty easy fix that just involves adding a function to the driver that simply returns its pn_error_t field.
Details
The Proton library's Driver Module (both Posix and Windows) does not supply a mechanism to clear an error that was detected. In contrast, other modules such as Connection supply a method to obtain the pn_error_t structure (see pn_connection_error()). This method can be used in combination with pn_error_clear() to clear an error.
It was observed that when establishing a connection from Windows to a potential broker on Linux that a WSAECONNREFUSED can be returned from the connect() call if the broker is not running. This results in a call to select() with a -1 file descriptor. The select() returns a socket error which is recorded in the Error Module. The error number can be obtained using the pn_driver_errno() call. Deleting the Connection and therefore removing the erroneous -1 file description results in subsequent successful select() calls. However, querying the Driver module for an error will perpetually return the last error. There is no mechanism to clear that error.
A small patch to the driver.c below is working for us currently but we wanted input on what the best or more general solution to the problem should be:
< return d ? pn_error_code(d->error) : PN_ARG_ERR;
—
> int rtn = PN_ARG_ERR;
> if (d)
> return rtn;
On the mailing list, Rafael said his preference would be to expose the driver's pn_error_t as the other modules do so it can be cleared rather than auto-clearing it as we do in the sample patch above. However, the pn_driver_error function already exists so either we need to break convention with the other modules in terms of the function name or break compatibility.