ross-spencer / eyeglass

Sample file format for teaching the principles file format development in the digital preservation community

eyeglass

Sample 'file format' specification and applications for understanding issues in digital preservation. The format stores the information required for an eyeglass prescription for a single patient.

Specification

Eyeglass Format Specification 1.0
---
Magic number    - 14 bytes  - String
Version         - 1 bytes   - Unsigned Char
Big-endian      - 1 byte    - Bool
Date/time       - 19 bytes  - String #YYYY-MM-DDTHH:MM:SS
Expansion room  - 88 bytes  - Undefined
Sphere          - 8 bytes   - R: Float   L: Float
Cylinder        - 8 bytes   - R: Float   L: Float
Axis            - 8 bytes   - R: Integer L: Integer
Prism           - 8 bytes   - R: Float   L: Float
Base            - 8 bytes   - R: Float   L: Float
Distance acuity - 8 bytes   - R: Float   L: Float
Near acuity     - 8 bytes   - R: Integer L: Integer
Purpose         - 140 bytes - String
Observation     - 255 bytes - String
Next checkup    - 4 bytes   - Float
End of file     - 4 bytes   - String

The ‘magic number’ identifying the file format will be as follows:

'\xBB\x0D\x0A\x65\x79\x65\x67\x6C\x61\x73\x73\x1A\x0A\xAB'

The ‘end of file’ sequence terminating the stream will be as follows:

'\xBB\x65\x6f\x66'

Further reading

• exponentialdecay.co.uk/blog/genesis-of-a-file-format.
• exponentialdecay.co.uk/blog/shattering-the-eyeglass.