open-standards/wai/live-conformance/carousel_moq_fec_verify.py

#!/usr/bin/env python3
"""carousel_moq_fec_verify.py: a second implementation of the MoQ FEC catalog binding
(extensions/carousel.md §8.3) and of the multicast endpoint reading (bearer-receipts §9.7).

    carousel_moq_fec_verify.py [CORPUS_DIR]

Written from those sections and from draft-ramadan-moq-fec-catalog-00, -fec-core-00 and
-fec-block-codes-00; it shares no code with wai-rs. For live-conformance/carousel-moq-fec/ it
binds every group's entries itself and requires the instances, the catalog tracks, each
object's SS_ID and block, its Protected Object Unit, its symbol-track objects and the header of
every repair object; reads every catalog back and compares it with the schedule; rebuilds every
object from its symbol track and holds it to its entry's content hash; gives every entry that
does not bind, every catalog and every endpoint its outcome; plants a symbol of another object
in the ways that need no decoding; and changes cases and requires each change to be caught.

It does not implement RFC 6330: the values of the repair symbols are checked by
wai-rs's tests/carousel_moq_fec.rs alone, against an independent implementation of that RFC.
K' is read from carousel.md Appendix A, and the content hash is claim-conformance's BLAKE3
(_blake3.py, written from its specification).

Exit 0 when everything holds, 1 with one line a finding otherwise. Standard library only.
"""
import copy
import ipaddress
import json
import os
import re
import sys

HERE = os.path.dirname(os.path.abspath(__file__))
sys.path.insert(0, os.path.join(HERE, "..", "claim-conformance"))
from _blake3 import blake3  # noqa: E402  (written from its specification; no package)

K_MAX, MAX_ESI, MAX_LAYERS = 56403, (1 << 24) - 1, 256
DOMAIN_OBJECT = b"moq-jwp:object\x01"
GEOMETRY = ("scheme", "blockProfile", "mmtpMode", "timescale", "symbolSize", "interleaveDepthMs", "reorderToleranceMs", "sourceSymbols", "fec")


class Refuse(Exception):
    pass


def k_primes():
    with open(os.path.join(HERE, "..", "extensions", "carousel.md"), encoding="utf-8") as fh:
        text = fh.read()
    a, b = text.index("<!-- k-prime:begin -->"), text.index("<!-- k-prime:end -->")
    return [int(x) for x in re.findall(r"[0-9]+", text[a + len("<!-- k-prime:begin -->"):b])]


K_PRIME = k_primes()


def k_prime(k):
    return next((v for v in K_PRIME if v >= k), None)


def ceil_div(a, b):
    return -(-a // b)


def varint_bytes(v):
    for n in range(1, 9):
        if v < 1 << (7 * n):
            b = v.to_bytes(n, "big")
            return bytes([b[0] | (0xFF << (9 - n)) & 0xFF if n > 1 else b[0]]) + b[1:]
    return b"\xff" + v.to_bytes(8, "big")


def read_varint(b, at):
    ones = 0
    while ones < 8 and b[at] & (0x80 >> ones):
        ones += 1
    n = 9 if ones == 8 else ones + 1
    if at + n > len(b):
        raise IndexError
    if n == 9:
        return int.from_bytes(b[at + 1:at + 9], "big"), at + 9
    return int.from_bytes(bytes([b[at] & (0xFF >> n)]) + b[at + 1:at + n], "big"), at + n


def immutable_properties(instance, ss_id):
    """fec-core §5.6: the FEC Source Info Property alone, type 0x11."""
    value = (bytes([instance]) if instance else b"") + ss_id.to_bytes(4, "big")
    return varint_bytes(0x11) + varint_bytes(len(value)) + value


def source_info(immutable, instance):
    """The SS_ID the properties give the object in `instance`, or None."""
    at, ty, found = 0, 0, None
    try:
        while at < len(immutable):
            d, at = read_varint(immutable, at)
            ty += d
            if ty % 2 == 0:
                _, at = read_varint(immutable, at)
                continue
            n, at = read_varint(immutable, at)
            if n > 0xFFFF or at + n > len(immutable):
                return None
            v, at = immutable[at:at + n], at + n
            if ty == 0x0B or (ty == 0x11 and found is not None):
                return None
            if ty == 0x11:
                found = v
    except IndexError:
        return None
    if found is None:
        return None
    if len(found) == 4:
        return int.from_bytes(found, "big") if instance == 0 else None
    entries = [found[i:i + 5] for i in range(0, len(found), 5)]
    if not found or len(found) % 5 or (len(entries) == 1 and entries[0][0] == 0) or any(a[0] >= b[0] for a, b in zip(entries, entries[1:])):
        return None
    for e in entries:
        if e[0] == instance:
            return int.from_bytes(e[1:], "big")
    return None


def unit(group, obj, immutable, payload):
    """fec-core §5.2."""
    return group.to_bytes(8, "big") + obj.to_bytes(8, "big") + len(immutable).to_bytes(2, "big") + immutable + len(payload).to_bytes(4, "big") + payload


def symbols(u, t):
    return [u[i:i + t].ljust(t, b"\0") for i in range(0, len(u), t)]


def geometry(e, instance):
    """§8.3: (T, s, layers) for an entry whose object goes to `instance`."""
    o = e["oti"]
    if e["fec"] != "raptorq" or o["source_blocks"] != 1 or o["sub_blocks"] != 1:
        raise Refuse("binding_no_form")
    f, t = o["transfer_length"], o["symbol_size"]
    if t % 8 or o["alignment"] != 8:
        raise Refuse("binding_symbol_size")
    k = ceil_div(f, t)
    s = ceil_div(22 + (6 if instance == 0 else 7) + f, t)
    if s > K_MAX or k_prime(s) != k_prime(k):
        raise Refuse("binding_block_differs")
    m = k + e["repair"]
    if m - s < 1:
        raise Refuse("binding_no_repair")
    if e["esi"] == "repeat":
        layers = [m - s]
    else:
        if e["count"] > MAX_LAYERS:
            raise Refuse("binding_no_form")
        layers = [m - s] + [m] * (e["count"] - 1)
    return t, s, layers


def bind(entries, first_ss_id):
    """§8.3 Instances and layers: (instances, objects)."""
    instances, nxt, objects = [], [], []
    for e in entries:
        g, at = None, None
        try:
            zero = geometry(e, 0)
            if not instances or (instances[0]["symbol_size"], instances[0]["layers"]) == (zero[0], zero[2]):
                g, at = zero, 0
        except Refuse:
            if not instances:
                raise
        if g is None:
            g = geometry(e, 1)
            at = next((i for i in range(1, len(instances)) if (instances[i]["symbol_size"], instances[i]["layers"]) == (g[0], g[2])), len(instances))
        t, s, layers = g
        if at == len(instances):
            if at > 255:
                raise Refuse("binding_too_many_instances")
            instances.append({"id": at, "symbol_size": t, "source_symbols": 0, "layers": layers, "span_ms": 0})
            nxt.append(first_ss_id)
        i = instances[at]
        i["source_symbols"], i["span_ms"] = max(i["source_symbols"], s), max(i["span_ms"], e["duration_ms"])
        if i["source_symbols"] + sum(i["layers"]) - 1 > MAX_ESI:
            raise Refuse("binding_no_form")
        objects.append({"leaf_index": e["leaf_index"], "instance": at, "ss_id": nxt[at] % (1 << 32), "block_group": nxt[at], "symbols": s})
        nxt[at] += s
    if not objects:
        raise Refuse("binding_no_form")
    return instances, objects


def catalog_tracks(instances, track):
    def rname(i, layer):
        mid = "" if i == 0 else "/i%d" % i
        return track + mid + "/repair" + ("" if layer == 0 else "/%d" % layer)

    def sname(i):
        return track + ("" if i == 0 else "/i%d" % i) + "/symbols"

    fec, tracks = [], []
    for i in instances:
        fec.append({"instanceId": i["id"], "scheme": "raptorq", "blockProfile": "moq-object-v1", "sourceSymbols": i["source_symbols"],
                    "symbolSize": i["symbol_size"], "repairSymbols": i["layers"][0], "interleaveDepthMs": i["span_ms"],
                    "repairTrack": rname(i["id"], 0), "symbolTrack": sname(i["id"])})
        tracks.append({"name": sname(i["id"]), "packaging": "fec-source", "isLive": True, "source": track, "instanceId": i["id"], "priority": 128})
        for layer, p in enumerate(i["layers"]):
            tracks.append({"name": rname(i["id"], layer), "packaging": "fec-repair", "isLive": True, "source": track,
                           "instanceId": i["id"], "repairLayer": layer, "repairSymbols": p, "priority": min(240 + layer, 255)})
    return fec, tracks


def integer(m, k, lo, hi):
    if k not in m:
        return None
    v = m[k]
    if isinstance(v, bool) or not isinstance(v, int) or not lo <= v <= hi:
        raise Refuse("binding_catalog_malformed")
    return v


def text(m, k):
    if k not in m:
        return None
    if not isinstance(m[k], str):
        raise Refuse("binding_catalog_malformed")
    return m[k]


def read_catalog(tracks, track):
    """§8.3 And back: the instances a catalog declares for `track`, failing closed."""
    bad = Refuse("binding_catalog_malformed")
    if any(not isinstance(t, dict) or "enhancementRepair" in t or any(isinstance(i, dict) and "enhancementRepair" in i for i in (t.get("fec") if isinstance(t.get("fec"), list) else [])) for t in tracks):
        raise bad

    def entry(name):
        got = [t for t in tracks if t.get("name") == name]
        if len(got) != 1:
            raise bad
        return got[0]

    source = entry(track)
    fec = source.get("fec")
    if not isinstance(fec, list) or not fec:
        raise bad
    out, named, served = [], [], []
    for f in fec:
        if not isinstance(f, dict):
            raise bad
        iid = integer(f, "instanceId", 0, 255) or 0
        if any(i["id"] == iid for i in out):
            raise bad
        if (text(f, "scheme"), text(f, "blockProfile")) != ("raptorq", "moq-object-v1"):
            raise Refuse("binding_no_form")
        k, t, p0 = integer(f, "sourceSymbols", 1, K_MAX), integer(f, "symbolSize", 8, 65535), integer(f, "repairSymbols", 1, MAX_ESI)
        if k is None or t is None or t % 8 or p0 is None:
            raise bad
        span = integer(f, "interleaveDepthMs", 1, (1 << 64) - 1) or 0
        if "reorderToleranceMs" in f and (isinstance(f["reorderToleranceMs"], bool) or not isinstance(f["reorderToleranceMs"], (int, float)) or f["reorderToleranceMs"] < 0 or f["reorderToleranceMs"] != f["reorderToleranceMs"]):
            raise bad
        if "label" in f and not isinstance(f["label"], str):
            raise bad
        layer0, sym = text(f, "repairTrack"), text(f, "symbolTrack")
        if layer0 is None:
            raise bad
        for n in (layer0, sym):
            if n is not None:
                if n in named:
                    raise bad
                named.append(n)
        layers = {}
        for tr in tracks:
            name = text(tr, "name")
            if name is None:
                raise bad
            is0 = name == layer0
            if text(tr, "packaging") != "fec-repair":
                if is0:
                    raise bad
                continue
            src = text(tr, "source")
            if src is None:
                serves = is0
            else:
                tid = integer(tr, "instanceId", 0, 255)
                serves = src == track and (tid if tid is not None else (iid if is0 else 0)) == iid
            if not serves:
                if is0:
                    raise bad
                continue
            if any(g in tr for g in GEOMETRY):
                raise bad
            layer = integer(tr, "repairLayer", 0, MAX_ESI)
            if layer is None:
                if not is0:
                    raise bad
                layer = 0
            if (layer == 0) != is0:
                raise bad
            p = integer(tr, "repairSymbols", 1, MAX_ESI)
            if p is None:
                if layer != 0:
                    raise bad
                p = p0
            elif layer == 0 and p != p0:
                raise bad
            prio = integer(tr, "priority", 192, 255)
            if layer in layers:
                raise bad
            layers[layer] = (name, p, 240 if prio is None else prio)
        order = sorted(layers)
        if not order or order != list(range(len(order))) or any(layers[a][2] > layers[b][2] for a, b in zip(order, order[1:])):
            raise bad
        if sym is not None:
            st = entry(sym)
            if text(st, "packaging") != "fec-source" or text(st, "source") not in (None, track) or integer(st, "instanceId", 0, 255) not in (None, iid) \
                    or "repairLayer" in st or "repairSymbols" in st or any(g in st for g in GEOMETRY):
                raise bad
            integer(st, "priority", 0, 255)
            served.append(sym)
        inst = {"id": iid, "symbol_size": t, "source_symbols": k, "layers": [layers[x][1] for x in order], "span_ms": span}
        if k + sum(inst["layers"]) - 1 > MAX_ESI:
            raise bad
        served += [layers[x][0] for x in order]
        out.append(inst)
    for tr in tracks:
        if text(tr, "packaging") in ("fec-repair", "fec-source") and text(tr, "source") in (None, track) and text(tr, "name") not in served:
            raise bad
    return sorted(out, key=lambda i: i["id"])


def same_instances(bound, read):
    return len(bound) == len(read) and all(
        a["id"] == b["id"] and a["symbol_size"] == b["symbol_size"] and a["layers"] == b["layers"] and a["source_symbols"] <= b["source_symbols"] and (b["span_ms"] == 0 or a["span_ms"] <= b["span_ms"])
        for a, b in zip(bound, read))


def rebuild(block, inst, ss_start):
    """fec-core §9.2: the objects of a block's source symbols."""
    bad = Refuse("binding_unit_malformed")
    t = inst["symbol_size"]
    if not block or len(block) % t:
        raise bad
    out, at = [], 0
    while at < len(block):
        if at + 18 > len(block):
            raise bad
        group, obj, il = int.from_bytes(block[at:at + 8], "big"), int.from_bytes(block[at + 8:at + 16], "big"), int.from_bytes(block[at + 16:at + 18], "big")
        if at + 22 + il > len(block):
            raise bad
        immutable = block[at + 18:at + 18 + il]
        pl = int.from_bytes(block[at + 18 + il:at + 22 + il], "big")
        if at + 22 + il + pl > len(block):
            raise bad
        payload = block[at + 22 + il:at + 22 + il + pl]
        nxt = at + ceil_div(22 + il + pl, t) * t
        if nxt > len(block) or any(block[at + 22 + il + pl:nxt]):
            raise bad
        if source_info(immutable, inst["id"]) != (ss_start + at // t) % (1 << 32) or any((o[0], o[1]) == (group, obj) for o in out):
            raise bad
        out.append((group, obj, immutable, payload))
        at = nxt
    return out


def check_object(o, group, e):
    if (o[0], o[1]) != (group, e["leaf_index"]):
        raise Refuse("binding_unit_malformed")
    if len(o[3]) != e["oti"]["transfer_length"] or blake3(DOMAIN_OBJECT + o[3]).hex() != e["content_hash"]:
        raise Refuse("binding_content_mismatch")


def read_repair(b, t):
    if len(b) != 13 + t:
        return None
    return {"ss_start": int.from_bytes(b[:4], "big"), "rsb": int.from_bytes(b[4:7], "big"), "rs_id": int.from_bytes(b[7:10], "big"), "ssb": int.from_bytes(b[10:13], "big"), "symbol": b[13:]}


def accept_repair(inst, block, layer, group, obj, payload):
    """§8.3 Symbols: whether a repair object fits the block (its Group and, once known, SSB_length)."""
    r = read_repair(payload, inst["symbol_size"])
    return not (r is None or group != block["group"] or group % (1 << 32) != r["ss_start"] or r["ssb"] == 0 or r["ssb"] > inst["source_symbols"]
                or (block["ssb"] is not None and block["ssb"] != r["ssb"]) or r["rsb"] != sum(inst["layers"]) or layer >= len(inst["layers"])
                or obj >= inst["layers"][layer] or r["rs_id"] != sum(inst["layers"][:layer]) + obj)


def accept_symbol(inst, block, group, obj, payload):
    limit = block["ssb"] if block["ssb"] is not None else inst["source_symbols"]
    return group == block["group"] and len(payload) == inst["symbol_size"] and obj < limit


def in_mode(group, ssm):
    if group.version == 4:
        return group.is_multicast and (group.packed[0] == 232) == ssm
    p = group.packed
    return p[0] == 0xFF and (p[1] >> 4 == 3 and p[2] == 0 and p[3] == 0) == ssm


def read_endpoint(e, tracks, auth):
    """bearer-receipts §9.7, in its order: "stands" or the label the endpoint is ignored with."""
    if not isinstance(e, dict) or not isinstance(e.get("groupAddress"), str) or not isinstance(e.get("tracks"), list) or not e["tracks"] \
            or any(not isinstance(t, dict) for t in e["tracks"]) or any(k in e and not isinstance(e[k], str) for k in ("sourceAddress", "protocol")):
        return "endpoint_malformed"
    bw = e.get("bandwidth")
    if "bandwidth" in e and (isinstance(bw, bool) or not isinstance(bw, int) or not 0 <= bw < 1 << 53):
        return "endpoint_malformed"
    try:
        group = ipaddress.ip_address(e["groupAddress"])
        source = ipaddress.ip_address(e["sourceAddress"]) if "sourceAddress" in e else None
    except ValueError:
        return "endpoint_address"
    if (source is not None and source.version != group.version) or not in_mode(group, source is not None):
        return "endpoint_address"
    if "protocol" in e and e["protocol"] != ("ssm" if source is not None else "asm"):
        return "endpoint_mode"
    port = e.get("port")
    if isinstance(port, bool) or not isinstance(port, int) or not 1 <= port <= 65535:
        return "endpoint_port"
    for t in e["tracks"]:
        pid = t.get("packetId")
        if not isinstance(t.get("name"), str) or isinstance(pid, bool) or not isinstance(pid, int) or not 1 <= pid <= 65535:
            return "endpoint_packet_id"

    def find(name):
        got = [t for t in tracks if isinstance(t, dict) and t.get("name") == name]
        return got[0] if len(got) == 1 else None

    for t in e["tracks"]:
        tr = find(t["name"])
        if tr is None or "namespace" in tr:
            return "endpoint_track"
        if tr.get("packaging") == "mmtp":
            continue
        src = find(tr.get("source")) if tr.get("packaging") == "fec-repair" and isinstance(tr.get("source"), str) else None
        if src is None or src.get("packaging") != "mmtp":
            return "endpoint_track"
    if ("auth" in e) != auth or ("auth" in e and "bandwidth" not in e):
        return "endpoint_auth"
    return "stands"


def read_endpoints(catalog):
    if "multicast" not in catalog:
        return []
    mc = catalog["multicast"]
    eps = mc.get("endpoints") if isinstance(mc, dict) else None
    if not isinstance(eps, list) or not eps:
        return "endpoints_malformed"
    tracks = catalog.get("tracks") if isinstance(catalog.get("tracks"), list) else []
    return [read_endpoint(e, tracks, "auth" in mc) for e in eps]


def outcome(f, *a):
    try:
        return f(*a)
    except Refuse as r:
        return str(r)


def check(doc):
    fails = []
    for g in doc["groups"]:
        what = g["what"]
        got = outcome(bind, g["entries"], g["first_ss_id"])
        if isinstance(got, str):
            fails.append("%s: does not bind: %s" % (what, got))
            continue
        instances, objects = got
        fec, tracks = catalog_tracks(instances, g["track"])
        if (fec, tracks) != (g["fec"], g["tracks"]):
            fails.append("%s: the catalog tracks are not the ones stated" % what)
        read = outcome(read_catalog, [{"name": g["track"], "packaging": "wai", "isLive": True, "fec": g["fec"]}] + g["tracks"], g["track"])
        if read != instances or not same_instances(instances, read):
            fails.append("%s: the catalog does not read back to the schedule's instances: %s" % (what, read))
        for o, w, e, env in zip(objects, g["objects"], g["entries"], g["envelopes"]):
            inst = instances[o["instance"]]
            t = inst["symbol_size"]
            at = "%s, object %d" % (what, o["leaf_index"])
            if any(o[k] != w[k] for k in o):
                fails.append("%s: its instance or block is not the one stated" % at)
                continue
            payload = bytes.fromhex(env)
            imm = immutable_properties(o["instance"], o["ss_id"])
            u = unit(g["group_id"], o["leaf_index"], imm, payload)
            src = symbols(u, t)
            if imm.hex() != w["immutable"] or u.hex() != w["unit"] or [s.hex() for s in src] != w["symbol_track"] or len(src) != o["symbols"]:
                fails.append("%s: its unit or its source symbols are not the ones stated" % at)
            # Everything §6 derives from the entry holds of the block: the count a pass, and K'.
            k = ceil_div(e["oti"]["transfer_length"], t)
            if o["symbols"] + inst["layers"][0] != k + e["repair"] or k_prime(o["symbols"]) != k_prime(k):
                fails.append("%s: a pass does not send the schedule's symbols" % at)
            # The repair objects' headers, Locations and layers.
            block = {"group": o["block_group"], "ssb": None}
            total = sum(inst["layers"])
            if len(w["repair"]) != total:
                fails.append("%s: %d repair objects for %d repair symbols" % (at, len(w["repair"]), total))
            for rs, r in enumerate(w["repair"]):
                layer = max(x for x in range(len(inst["layers"])) if sum(inst["layers"][:x]) <= rs)
                hdr = read_repair(bytes.fromhex(r["hex"]), t)
                if (r["layer"], r["group"], r["object"]) != (layer, o["block_group"], rs - sum(inst["layers"][:layer])) or hdr is None \
                        or (hdr["ss_start"], hdr["rsb"], hdr["rs_id"], hdr["ssb"]) != (o["ss_id"], total, rs, o["symbols"]) \
                        or not accept_repair(inst, block, r["layer"], r["group"], r["object"], bytes.fromhex(r["hex"])):
                    fails.append("%s: repair object %d is not where §8.3 puts it" % (at, rs))
                block["ssb"] = o["symbols"]
            # Rebuilt from its symbol track, it is the object its entry signs.
            held = b"".join(bytes.fromhex(s) for s in w["symbol_track"])
            got = outcome(rebuild, held, inst, o["ss_id"])
            if isinstance(got, str) or len(got) != 1 or got[0][3] != payload or outcome(check_object, got[0], g["group_id"], e) is not None:
                fails.append("%s: it does not rebuild to the object scheduled" % at)
            # And back: the entry's code members from the instance and the block.
            if (inst["symbol_size"], o["symbols"] + inst["layers"][0] - k) != (e["oti"]["symbol_size"], e["repair"]):
                fails.append("%s: the entry's members do not come back" % at)
        # A symbol of another object, in the ways that need no decoding.
        first = [i for i, o in enumerate(objects) if o["instance"] == objects[0]["instance"]]
        if len(first) >= 2:
            a, b = objects[first[0]], objects[first[1]]
            wa, wb = g["objects"][first[0]], g["objects"][first[1]]
            inst = instances[a["instance"]]
            block = {"group": a["block_group"], "ssb": a["symbols"]}
            other = bytes.fromhex(wb["repair"][0]["hex"])
            forged = a["ss_id"].to_bytes(4, "big") + other[4:]
            if accept_symbol(inst, block, b["block_group"], 0, bytes.fromhex(wb["symbol_track"][0])) or accept_repair(inst, block, 0, b["block_group"], 0, other) \
                    or accept_repair(inst, block, 0, a["block_group"], 0, other) or accept_repair(inst, block, 0, a["block_group"], 0, forged) \
                    or accept_symbol(inst, block, a["block_group"], a["symbols"], bytes.fromhex(wa["symbol_track"][0])):
                fails.append("%s: a symbol of another object was placed" % what)
            for esi, want in ((0, "binding_unit_malformed"), (min(6, a["symbols"] - 2), "binding_content_mismatch")):
                held = [bytes.fromhex(s) for s in wa["symbol_track"]]
                held[esi] = bytes.fromhex(wb["symbol_track"][esi])
                got = outcome(rebuild, b"".join(held), inst, a["ss_id"])
                if not isinstance(got, str):
                    got = outcome(check_object, got[0], g["group_id"], g["entries"][first[0]])
                if got != want:
                    fails.append("%s: the other object's symbol %d in place gave %s, not %s" % (what, esi, got, want))
    for c in doc["unbound"]:
        got = outcome(bind, [c["entry"]], 0)
        if got != c["reason"]:
            fails.append("unbound %r: %s, stated %s" % (c["what"], got if isinstance(got, str) else "bound", c["reason"]))
    for c in doc["catalogs"]:
        got = outcome(read_catalog, c["tracks"], c["tracks"][0]["name"])
        got = got if isinstance(got, str) else "accept"
        if got != c["outcome"]:
            fails.append("catalog %r: %s, stated %s" % (c["what"], got, c["outcome"]))
    for c in doc["endpoints"]:
        got = read_endpoints(c["catalog"])
        if got != c["outcome"]:
            fails.append("endpoints %r: %s, stated %s" % (c["what"], got, c["outcome"]))
    if len(doc["groups"]) < 3 or len(doc["unbound"]) < 9 or len(doc["catalogs"]) < 30 or len(doc["endpoints"]) < 6:
        fails.append("the corpus is smaller than it was written to be")
    return fails


def main(argv):
    d = argv[1] if len(argv) > 1 else os.path.join(HERE, "carousel-moq-fec")
    with open(os.path.join(d, "vectors.json"), encoding="utf-8") as fh:
        doc = json.load(fh)
    if K_PRIME[0] != 10 or K_PRIME[-1] != K_MAX or len(K_PRIME) != 477:
        print("FAIL carousel.md Appendix A is not the table of K'")
        return 1
    fails = check(doc)
    def flip(h):
        return ("00" if h[:2] != "00" else "01") + h[2:]
    edits = [
        ("an envelope octet", lambda x: x["groups"][0]["envelopes"].__setitem__(0, flip(x["groups"][0]["envelopes"][0]))),
        ("a symbol-track object", lambda x: x["groups"][0]["objects"][1]["symbol_track"].__setitem__(3, flip(x["groups"][0]["objects"][1]["symbol_track"][3]))),
        ("an SS_ID", lambda x: x["groups"][0]["objects"][1].__setitem__("ss_id", x["groups"][0]["objects"][1]["ss_id"] + 1)),
        ("a repair object's RS_ID", lambda x: x["groups"][0]["objects"][0]["repair"][2].__setitem__("hex", x["groups"][0]["objects"][0]["repair"][3]["hex"])),
        ("a repair object's layer", lambda x: x["groups"][1]["objects"][0]["repair"][8].__setitem__("layer", 0)),
        ("an entry's repair", lambda x: x["groups"][0]["entries"][0].__setitem__("repair", 10)),
        ("an entry's content hash", lambda x: x["groups"][2]["entries"][0].__setitem__("content_hash", "00" * 32)),
        ("the catalog's repairSymbols", lambda x: x["groups"][0]["fec"][0].__setitem__("repairSymbols", 8)),
        ("a repair track's layer", lambda x: x["groups"][1]["tracks"][2].__setitem__("repairLayer", 2)),
        ("an unbound entry's reason", lambda x: x["unbound"][0].__setitem__("reason", "binding_symbol_size")),
        ("an unbound entry made good", lambda x: x["unbound"][4].__setitem__("entry", x["groups"][0]["entries"][0])),
        ("a catalog's outcome", lambda x: x["catalogs"][5].__setitem__("outcome", "accept")),
        ("a good catalog's outcome", lambda x: x["catalogs"][0].__setitem__("outcome", "binding_catalog_malformed")),
        ("an endpoint's outcome", lambda x: x["endpoints"][0]["outcome"].__setitem__(0, "endpoint_port")),
        ("an ignored endpoint stated to stand", lambda x: x["endpoints"][0]["outcome"].__setitem__(11, "stands")),
    ]
    for what, e in edits:
        changed = copy.deepcopy(doc)
        e(changed)
        if not check(changed):
            fails.append("a change went unnoticed: %s" % what)
    for f in fails:
        print("FAIL " + f)
    n = sum(len(g["objects"]) for g in doc["groups"])
    print("carousel-moq-fec: %d objects of %d groups, %d unbound, %d catalogs, %d endpoint lists, %d edits; %d failure(s)" % (n, len(doc["groups"]), len(doc["unbound"]), len(doc["catalogs"]), len(doc["endpoints"]), len(edits), len(fails)))
    return 1 if fails else 0


if __name__ == "__main__":
    sys.exit(main(sys.argv))