dplatformid

Defines ID of current platform as a global constant PLATFORM_ID.

Overview

Sometimes it is necessary to save some data on disk for future use by the same program on the same PC, e.g. caches.

There is a risk that such local data will be transmitted from one PC to another by accident, so loader should be protected from reading incompatible raw binary data. Common protection strategy is to encode the data in platform-agnostic way, so the data can be read on any platform, but for that saver and loader spend time for encoding/decoding and become a little bit more complex (programmer should take into account sizes of integers types, little or big endian bytes order etc).

The dplatformid unit provides another strategy: save the ID with binary data and reject all data with different ID, so binary data can be saved "as is".

Usage

While saving: put the content of PLATFORM_ID with binary data. While loading: compare ID from some data with the PLATFORM_ID and reject the data if they differ. Pseudocode to demonstrate the idea:

  // In saver:
  Stream.Write(PLATFORM_ID[0], Length(PLATFORM_ID));

...

  // In loader:
  var
    PlatformID: TPlatformID;

  Steam.Read(PlatformID[0], Length(PLATFORM_ID));
  if CompareByte(PlatformID[0], PLATFORM_ID[0], Length(PLATFORM_ID)) <> 0 then begin
    ... ERROR! Data is not compatible, reject the data
  end;

Format of a ID is simple: first two bytes are ASCII characters of decimal digits for Size of the ID and other Size-2 bytes are any data (human readable or binary) that determines current platform (cpu, os etc).

Here is one possible example:

16_64L86_64linux
^  ^ ^^    ^
|  | ||    |
|  | ||    - OS
|  | |- cpu
|  | - endianness
|  - cpu bits
- size of the ID in bytes