The zzip_disk_findfirst function is the first call of all the zip access functions here. It contains the code to find the first entry of the zip central directory. Here we require the mmapped block to represent a real zip file where the disk_trailer is _last_ in the file area, so that its position would be at a fixed offset from the end of the file area if not for the comment field allowed to be of variable length (which needs us to do a little search for the disk_tailer). However, in this simple implementation we disregard any disk_trailer info telling about multidisk archives, so we just return a pointer to the zip central directory.

For an actual means, we are going to search backwards from the end of the mmaped block looking for the PK-magic signature of a disk_trailer. If we see one then we check the rootseek value to find the first disk_entry of the root central directory. If we find the correct PK-magic signature of a disk_entry over there then we assume we are done and we are going to return a pointer to that label.

The return value is a pointer to the first zzip_disk_entry being checked to be within the bounds of the file area specified by the arguments. If no disk_trailer was found then null is returned, and likewise we only accept a disk_trailer with a seekvalue that points to a disk_entry and both parts have valid PK-magic parts. Beyond some sanity check we try to catch a common brokeness with zip archives that still allows us to find the start of the zip central directory.

The zzip_disk_findnext function takes an existing disk_entry in the central root directory (e.g. from zzip_disk_findfirst) and returns the next entry within in the given bounds of the mmapped file area.

The zzip_disk_findmatch function uses a compare-function with an additional argument and it is called just like fnmatch(3) from POSIX.2 AD:1993), i.e. the argument filespec first and the ziplocal filename second with the integer-flags put in as third to the indirect call. If the platform has fnmatch available then null-compare will use that one and otherwise we fall back to mere strcmp, so if you need fnmatch searching then please provide an implementation somewhere else. - use null as argument for "after"-entry when searching the first matching entry, or the last disk_entry return-value to find the next entry matching the given filespec.