nx_ico_gate.nx

nx_ico_gate.nx -- proves the ICO writer/reader pair by ROUND-TRIP. T1 pins ZERO MEANS 256 in both directions. The width and height fields are one byte, so 256 -- the standard modern favicon size -- is stored as 0. A reader taking the byte at face value reports a 256x256 icon as 0x0, and this is the single most common ICO bug: it appears at exactly the one size that matters most today and nowhere else. T4 proves the payload sniff. Nothing in the directory says whether an entry is a DIB or a PNG, both are legal in the same file, and the bitCount field is routinely zero or wrong for PNG entries. The test builds a mixed file and requires each entry to be classified from its own bytes. T6 covers the crafted-file case: an entry whose offset or length points past the buffer, or back into the directory, must be REFUSED rather than followed. license_tier: ORIGINAL