Add specific enum value to `pcap::Error` for an interface that has disappeared

[GyulyVGC]

Currently if you are capturing packets from an interface and such interface is taken down, the next_packet method will indefinitely throw a generic PcapError("The interface disappeared").

If possible, it'd be better to add a new enum value just for this specific error to better identify it in a robust and platform-independent way.
For example this could be useful to break the associated loop.
This is particularly significant since, at least on macOS, such capture will always return that error even in case the corresponding interface is brought back up.

Related issue that would benefit from this: GyulyVGC/sniffnet#1028

[Stargateur]

I think we could do better indeed but pcap doesn't really have a lot of rigorous error. pcap mostly define few general error code and than use string as error.

/*
 * Error codes for the pcap API.
 * These will all be negative, so you can check for the success or
 * failure of a call that returns these codes by checking for a
 * negative value.
 */
#define PCAP_ERROR			-1	/* generic error code */
#define PCAP_ERROR_BREAK		-2	/* loop terminated by pcap_breakloop */
#define PCAP_ERROR_NOT_ACTIVATED	-3	/* the capture needs to be activated */
#define PCAP_ERROR_ACTIVATED		-4	/* the operation can't be performed on already activated captures */
#define PCAP_ERROR_NO_SUCH_DEVICE	-5	/* no such device exists */
#define PCAP_ERROR_RFMON_NOTSUP		-6	/* this device doesn't support rfmon (monitor) mode */
#define PCAP_ERROR_NOT_RFMON		-7	/* operation supported only in monitor mode */
#define PCAP_ERROR_PERM_DENIED		-8	/* no permission to open the device */
#define PCAP_ERROR_IFACE_NOT_UP		-9	/* interface isn't up */
#define PCAP_ERROR_CANTSET_TSTAMP_TYPE	-10	/* this device doesn't support setting the time stamp type */
#define PCAP_ERROR_PROMISC_PERM_DENIED	-11	/* you don't have permission to capture in promiscuous mode */
#define PCAP_ERROR_TSTAMP_PRECISION_NOTSUP -12  /* the requested time stamp precision is not supported */
#define PCAP_ERROR_CAPTURE_NOTSUP	-13	/* capture mechanism not available */

/*
 * Warning codes for the pcap API.
 * These will all be positive and non-zero, so they won't look like
 * errors.
 */
#define PCAP_WARNING			1	/* generic warning code */
#define PCAP_WARNING_PROMISC_NOTSUP	2	/* this device doesn't support promiscuous mode */
#define PCAP_WARNING_TSTAMP_TYPE_NOTSUP	3	/* the requested time stamp type is not supported */

For example error The interface disappeared will return with PCAP_ERROR code so the only way would be to string compare the error and hope for the best. There is even a "The interface disappeared (error code %s)"

We could try to extract every possible error string from npcap code source, and try to improve error reporting