v0.07

AmigaOS 3 opens WeKan's files: SQLite no longer seeks past the end of a file

• wena6 log: both AmigaOS 3 builds (RTG and AGA) stopped on WeKan's
  database with no reason given. Running the released
  wena-amigaos-m68k under vamos (amitools' AmigaOS emulator) traced
  it. SQLite's first look at the header of the new, empty
  wekan.sqlite seeked to offset 24. AmigaDOS cannot Seek() past the
  end of a file, and libnix's lseek() makes up for it by writing the
  gap from memory it never cleared. The file became 24 stray bytes
  ("ar(0)) = 0 AND card_id N"), and ATTACH failed with "file is not a
  database", on that start and every start after it.
• The Amiga builds' SQLite (-DUSE_PREAD, with pread and pwrite
  from server/sqlite_amiga_vfs.c, declared by
  server/sqlite_amiga_io.h) now reads and writes at an offset without
  seeking past the end. A read there is the end of the file; a write
  there pads with zeros first. This covers AmigaOS 3, AmigaOS 4 and
  AROS alike.
• A wekan.sqlite already spoiled this way (not empty, under 512
  bytes, without SQLite's header) is renamed to
  wekan.sqlite.not-a-database, never removed, and a new database is
  made.
• So that the next failure says why, a failed open now names its step
  and SQLite's reason:
  • each step of opening WeKan's files is logged on its own;
  • wena_sqlite_open and the attach record why they failed;
  • SQLite's own error log (the OS call, errno and file of a failed
    open, the SQL of a failed statement) goes to the debug log.
• Tests:
  • amiga-desktop builds SQLite with the Amiga options over an lseek()
    that behaves like libnix's. A fresh attached file is a sound
    database. The same build without the new options fails "file is
    not a database", as on the Amiga.
  • wekan-files: the spoiled file is set aside twice under two names;
    a real header, an empty file, a large file and a missing one stay.

Thanks to xet7.