System.ConsolePal.Read C# (CSharp) Method

        internal static unsafe int Read(SafeFileHandle fd, byte[] buffer, int offset, int count)
        {
            fixed (byte* bufPtr = buffer)
            {
                int result = Interop.CheckIo(Interop.Sys.Read(fd, (byte*)bufPtr + offset, count));
                Debug.Assert(result <= count);
                return result;
            }
        }

            /// <summary>Read the database for the specified terminal from the specified directory.</summary>
            /// <param name="term">The identifier for the terminal.</param>
            /// <param name="directoryPath">The path to the directory containing terminfo database files.</param>
            /// <returns>The database, or null if it could not be found.</returns>
            private static Database?ReadDatabase(string?term, string?directoryPath)
            {
                if (string.IsNullOrEmpty(term) || string.IsNullOrEmpty(directoryPath))
                {
                    return(null);
                }

                Span <char>    stackBuffer = stackalloc char[256];
                SafeFileHandle?fd;

                if (!TryOpen(string.Create(null, stackBuffer, $"{directoryPath}/{term[0]}/{term}"), out fd) &&       // /directory/termFirstLetter/term      (Linux)
                    !TryOpen(string.Create(null, stackBuffer, $"{directoryPath}/{(int)term[0]:X}/{term}"), out fd))  // /directory/termFirstLetterAsHex/term (Mac)
                {
                    return(null);
                }

                using (fd)
                {
                    // Read in all of the terminfo data
                    long termInfoLength = Interop.CheckIo(Interop.Sys.LSeek(fd, 0, Interop.Sys.SeekWhence.SEEK_END)); // jump to the end to get the file length
                    Interop.CheckIo(Interop.Sys.LSeek(fd, 0, Interop.Sys.SeekWhence.SEEK_SET));                       // reset back to beginning
                    const int MaxTermInfoLength = 4096;                                                               // according to the term and tic man pages, 4096 is the terminfo file size max
                    const int HeaderLength      = 12;
                    if (termInfoLength <= HeaderLength || termInfoLength > MaxTermInfoLength)
                    {
                        throw new InvalidOperationException(SR.IO_TermInfoInvalid);
                    }

                    byte[] data = new byte[(int)termInfoLength];
                    if (ConsolePal.Read(fd, data) != data.Length)
                    {
                        throw new InvalidOperationException(SR.IO_TermInfoInvalid);
                    }

                    // Create the database from the data
                    return(new Database(term, data));
                }
            }