testfs

type FaultFile struct {
	// contains filtered or unexported fields
}

type Faults struct {
	// FailWritesAfterBytes causes Write to fail once the cumulative
	// bytes written to the file reaches this value. The partial write
	// up to the threshold is permitted; subsequent writes return
	// [ErrPartialWrite]. Zero disables this mode.
	FailWritesAfterBytes int64

	// ReturnENOSPC causes every Write call to return [syscall.ENOSPC]
	// regardless of the current write budget.
	ReturnENOSPC bool

	// FsyncDelay inserts a sleep of this duration before each Sync
	// call. Zero disables the delay.
	FsyncDelay time.Duration

	// FailSyncAfter causes Sync to fail once the given number of
	// calls have succeeded: the first FailSyncAfter Sync calls are
	// honoured, every subsequent call returns [ErrSyncFailed]. When
	// the fault fires, the bytes written since the last successful
	// Sync are discarded (the file is truncated back to its
	// durably-synced size). This mirrors the post-"fsyncgate" kernel
	// contract — after fsync(2) reports an error the previously-dirty
	// pages are marked clean and their content must be assumed lost —
	// so the file is left holding exactly the durable prefix a crash
	// would preserve. Zero disables this mode; use
	// [Faults.ReturnEIOOnSync] to fail every call.
	FailSyncAfter int

	// ReturnEIOOnSync causes every Sync call to return
	// [ErrSyncFailed] immediately, with the same
	// discard-unsynced-suffix semantics as [Faults.FailSyncAfter].
	ReturnEIOOnSync bool

	// CorruptOnRead, when non-nil, is called with the current file
	// offset and the number of bytes about to be read. Returning true
	// flips the MSB of the first byte in the result buffer to simulate
	// a bit-flip or CRC-corrupting storage error.
	CorruptOnRead func(offset, n int64) bool
}

type File interface {
	io.ReadWriter
	io.Seeker
	// Sync flushes the OS write buffer to durable storage (equivalent
	// to fsync(2)).
	Sync() error
	// Truncate resizes the file to size bytes. If size < current
	// length, the suffix is discarded; if size > current length, the
	// file is extended with zero bytes (implementation-defined).
	Truncate(size int64) error
	// Close releases any associated OS resources.
	Close() error
}