FA-27720 / HTTP ranges / Member archive

A remote archive reader locates the central directory from a suffix range response: an exhausted backward scan cannot fall through to an unchecked first tail byte · case 05

A remote archive reader locates the central directory from a suffix range response: an exhausted backward scan cannot fall through to an unchecked first tail byte.

Member previewVariant 5 · 3 implementations · 16 checks per implementation

Case contract

x has total representation length, requested suffix length and the hex bytes of the suffix response (the last min(total,suffix) bytes). Emit the suffix Range value (null when it would be zero bytes). Scan backward for the end record signature PK\x05\x06 whose little-endian comment length makes the 22-byte record plus comment end exactly at the tail end. Reject multi-disk archives (disk or directory disk nonzero, or differing entry counts) and a directory that extends past the end record. A directory starting inside the tail is ["local",tail-index,size]; otherwise request only the missing prefix before the tail as ["fetch",inclusive range]. Output [suffix-range,plan-or-null].

Why this case matters

Range responses combine representation identity, conditional requests, framing, and partial-object state.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
scan-first-offset fixture 12	`["bytes=-30", ["local", 0, 0]]`	`["bytes=-30", null]`	Failed

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