I've read that Redis (https://github.com/antirez/redis) has well written code, in C.
It's definitely not uncommon, but yes, that file is on the long side. However, it is rather clean and well-organized.
It may be due to the poor module system (header files) of C where you end up making files slightly longer than ideal because splitting into two files means also adding some header files and thus adding to the maintenance burden.
When writing C code, I usually strive to put a whole "module" in a single file, so that no "private" interfaces have to be put in header files. Everything that needs to be exposed in order to test a module goes in the public interface.
It's a tradeoff and C being C doesn't help (and C++ wouldn't really help here IMO), but I see nothing wrong with the file you picked. It's a bit long but it looks well done to my C programmer eyes.
I also see lots of prototypes (all?!) defined at the top of the file instead of in a header file. They could be made static.
Also, the generic type "int" isn't a good idea because it can change, it helps avoid porting problems to specify the size (int32_t, uint64_t, etc.)
And the memcpy()'s should be changed to memcpy_s().
On the bright side, the comments are quite good and plentiful. Refreshing!