12.3 The response contract

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All rsi_respond_* helpers return 0, or -1 with errno. A set of rules applies to every helper, and violating one is an EINVAL caller-contract error:

  • (ptr, len) pairs: a pointer may be NULL only when its length/count is zero.
  • Boolean fields (volatile_key, symlink, target types) must be exactly 0 or 1.
  • Hidden path targets (RSI_PATH_TARGET_HIDDEN) must carry an all-zero target_guid.
  • LOOKUP/ENUM_CHILDREN metadata must exactly cover the GUID path targets referenced — no missing metadata, no duplicates, no unreferenced entries.
  • DELETE_LAYER orphan GUIDs must be nonzero and unique.

Beyond EINVAL, any helper can also fail with ENOMEM (during validation or frame allocation), EOVERFLOW (validation arithmetic or the assembled frame too large), EIO (a short write), or the raw write(2) errno. Per-helper EINVAL additions are noted below.

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