While the Oblivion file format is closely related to the Morrowind file format, the two formats also differ substantially both in structural elements and in details for most (all) record types. The introduction of groups, data compression and outsize field data handling all vastly complicate reading and writing of the file, while the introduction of formids greatly complicates the logic of integrating and relating changes to files.
File Parsing PseudocodeEdit
OblivionEdit
Basic pseudocode for parsing Oblivion's ESM/ESP files. Successfully tested on Oblivion.esm. Note that Header refers to the 20 byte record/group and the 6 byte field headers.
Read Header //Required TES4 record
Read Record
While Bytes Left in File
Read Header
Read Group
EndWhile
Read Group
While Bytes Left in Group
Read Header
if Name = GRUP
Read Group
else
Read Record
EndWhile
End Group
Read Record
Read Header
if IsCompressed
Read Compressed Record Data
else
Read Fields
End Record
Read Compressed Record Data
Read Deflated Data Size (dword)
Read Compressed Data (given by record size in header)
Deflate Data (zLib)
Read Fields (from the deflated data)
End Read Raw Data
Read Fields
While Bytes Left in Record
Read Field Header
if Name = XXXX
Read Field Data
Field data is the size of the next field
Read Next Field Header, ignoring size
Read Field Data
EndWhile
End Read Fields
MorrowindEdit
For comparison only, the pseudocode for parsing Morrowind's ESM/ESP/ESS files is trivial:
While Bytes Left in File
Read Record Header
While Bytes Left in Record
Read Field Header
Read Field Data
EndWhile
EndWhile
Simple is good...