The API: int read4(char *buf) reads 4 characters at a time from a file. The return value is the actual number of characters read. For example, it returns 3 if there is only 3 characters left in the file. By using the read4 API, implement the function int read(char *buf, int n) that reads n characters from the file.
Note: The read function will only be called once for each test case.
Hold buffer, keep track of current bufferPos, bufferLength, and eof