bson_reader_read_func_t man page
bson_reader_read_func_t — bson_reader_read_func_t
typedef ssize_t (*bson_reader_read_func_t) (void *handle, void *buf, size_t count);
handle: The handle to read from.
buf: The buffer to read into.
count: The number of bytes to read.
A callback function that will be called by bson_reader_t to read the next chunk of data from the underlying opaque file descriptor.
This function is meant to operate similar to the read(2) function as part of libc on UNIX-like systems.
0 for end of stream.
-1 for a failure on read.
A value greater than zero for the number of bytes read into buf.
2017, MongoDB, Inc