{ "id": "P117", "slug": "message-queue", "key": "P117-message-queue", "title": "Message queue", "summary": "A broker that sends a message again when its acknowledgement is lost, four handlers over the same deliveries - add, replay, check and a window of keys - and every choice of lost acks counted, with a key reused for another request refused.", "entry": "main.eml", "ui": "terminal", "readme": "# P117 - Message queue\n\nA broker delivers every message at least once. When a consumer's ack is\nlost, the broker sends the message again, and the work is done twice\nunless the handler notices. Each message carries an idempotency key.\n\n- `main.eml` - the menu, the messages, the deliveries with four handlers\n side by side, every choice of lost acks, and the settings\n- `broker.eml` - the messages, the right result, the broker's order of\n deliveries, the four handlers, and the count over every choice\n\nHow each part works:\n\n- A message is a key, an account and an amount; every account starts at\n 0. A lost ack sends the message again a set number of deliveries later,\n or sooner when nothing else is waiting. The ack can be lost again.\n- The right result applies each key's first message once. A later message\n with the same key and the same request is a retry, answered done; with\n another request, it is refused.\n- The four handlers, as in the corpus cases `at-least-once-delivery` and\n `idempotency-key-reuse`:\n - add applies every delivery, so a duplicate is applied again;\n - replay keeps every key and answers a key it has seen with the first\n answer: the balances are right, but a reused key is told done;\n - check keeps every key with its request and refuses another request\n under it: right on every run, and it keeps every key;\n - a window keeps only the last few keys, so it is right only while\n every duplicate comes back before its key has left. When a key has\n left and come back with another request, the window can even refuse\n a right one.\n- Every choice: each message loses its first ack or not, 128 runs for the\n seven messages. With a message sent again 3 deliveries later, the first\n window right on every run keeps 3 keys; 6 deliveries later, 4. For\n every delay from 1 to 9 it is 2, 3, 3, 4, 4, 4, 5, 5 and 5 keys.\n\nWhat is checked: menu choices 1 to 7; lost acks as message numbers, at\nmost 3 for one message, or none; a key of up to 8 letters and digits, an\naccount of up to 10 lowercase letters, an amount from -999 to 999 but not\n0, and at most 8 messages; a delay and a window from 1 to 9. An empty\nanswer cancels.\n\nSessions: `sessions/basic.in` gives:\n- the messages, with one key reused for another request and one retry;\n- deliveries losing the acks of messages 2 and 5, of message 1 (the window\n of 2 is too small), and of none;\n- every choice at a delay of 3, and of 6;\n- a window of 4, with message 1's ack lost once and message 2's twice;\n- message 8, a late retry of message 1, after which only a window of all\n 5 keys is right on every run.\n\n`sessions/bad-input.in` gives:\n- menu choices 0 and x;\n- lost acks: a cancel, 0, 8, x, 2,5 and 1 four times;\n- new messages: a cancel, the keys k 1, toolongkey and k-1, a cancel, the\n accounts Bob and averyverylongname, a cancel, the amounts 0, 1000, +-3\n and x, then dave -15, and a ninth message;\n- the delay: a cancel, 0, 10 and x; the window: a cancel and 0.\n\nBuilt on the verified corpus cases `at-least-once-delivery` (duplicates\nare the handler's problem, and a bounded window is an assumption about\nlateness) and `idempotency-key-reuse` (a reused key with another request\nis refused only when the request is kept).\n", "modules": [ { "name": "main.eml", "eml": "# P117 message queue: a broker that sends a message again when its\n# acknowledgement is lost, four handlers side by side over the same\n# deliveries, and every choice of lost acknowledgements counted.\nimport broker\n\ndef plain(s):\n 0 => i\n len(s) => j\n while i < j and s[i] == \" \":\n i + 1 => i\n while j > i and s[j - 1] == \" \":\n j - 1 => j\n return s[i:j]\n\ndef pad(s, n):\n s => out\n while len(out) < n:\n out + \" \" => out\n return out\n\ndef lpad(s, n):\n s => out\n while len(out) < n:\n \" \" + out => out\n return out\n\ndef is_digits(s):\n if len(s) == 0:\n return False\n for c in s:\n if c < \"0\" or c > \"9\":\n return False\n return True\n\ndef numbers_text(ns):\n \"\" => out\n for i in [0:len(ns) - 1]:\n if i > 0 and i == len(ns) - 1:\n out + \" and \" => out\n elif i > 0:\n out + \", \" => out\n out + str(ns[i]) => out\n return out\n\ndef balances_text(msgs, bal):\n \"\" => out\n for a in broker.accounts(msgs):\n if out != \"\":\n out + \", \" => out\n out + a + \" \" + str(bal[a]) => out\n return out\n\ndef note(msgs, i):\n broker.first_with_key(msgs, i) => f\n if f == i:\n return \"\"\n if broker.same_request(msgs[f], msgs[i]):\n return \"a retry of message \" + str(f + 1)\n return \"the key of message \" + str(f + 1) + \", for another request\"\n\ndef widths(msgs):\n 0 => kw\n 0 => bw\n for m in msgs:\n if len(m[0]) > kw:\n len(m[0]) => kw\n if len(broker.body_text(m)) > bw:\n len(broker.body_text(m)) => bw\n return [kw, bw]\n\ndef right_text(msgs):\n broker.expected(msgs) => want\n [] => refused\n for i in [0:len(msgs) - 1]:\n if want[1][i] == \"refused\":\n refused + [i + 1] => refused\n \"Right: \" + balances_text(msgs, want[0]) => out\n if len(refused) == 1:\n out + \"; message \" + numbers_text(refused) + \" refused\" => out\n elif len(refused) > 1:\n out + \"; messages \" + numbers_text(refused) + \" refused\" => out\n return out + \".\"\n\ndef show(msgs, delay, k):\n (\"Messages (a message whose ack is lost is sent again \" + str(delay) + \" deliveries later; the window keeps \" + str(k) + \" keys):\") ^0\n widths(msgs) => w\n for i in [0:len(msgs) - 1]:\n msgs[i] => m\n \" \" + lpad(str(i + 1), 2) + \" \" + pad(m[0], w[0]) + \" \" => line\n note(msgs, i) => n\n if n == \"\":\n (line + broker.body_text(m)) ^0\n else:\n (line + pad(broker.body_text(m), w[1]) + \" \" + n) ^0\n right_text(msgs) ^0\n\ndef handler_line(msgs, name, kind, k, seq):\n broker.handle(kind, k, msgs, seq) => r\n broker.problems(msgs, r) => p\n [] => parts\n if p[0] > 0:\n parts + [str(p[0]) + \" applied again\"] => parts\n for x in p[1]:\n \"message \" + str(x[0] + 1) => who\n if x[1] == \"applied\":\n parts + [who + \" applied under message \" + str(x[2] + 1) + \"'s key\"] => parts\n elif x[1] == \"told\":\n parts + [who + \" told done with message \" + str(x[2] + 1) + \"'s answer\"] => parts\n else:\n parts + [who + \" wrongly refused\"] => parts\n if len(parts) == 0 and not broker.balances_right(msgs, r):\n parts + [\"balances wrong\"] => parts\n \"\" => verdict\n if len(parts) == 0:\n \"right\" => verdict\n if kind == \"replay\":\n verdict + \", keeping \" + str(r[4]) + \" keys\" => verdict\n elif kind != \"add\":\n verdict + \", keeping \" + str(r[4]) + \" keys with their requests\" => verdict\n else:\n for q in parts:\n if verdict != \"\":\n verdict + \"; \" => verdict\n verdict + q => verdict\n (\" \" + pad(name, 10) + balances_text(msgs, r[0]) + \": \" + verdict + \".\") ^0\n\ndef deliver(msgs, delay, k):\n (\"Acks lost: message numbers from 1 to \" + str(len(msgs)) + \" such as 2 5 (a number twice loses two), or none.\") ^0\n plain(input(\"acks lost> \")) => t\n if t == \"\":\n \"Cancelled.\" ^0\n return\n [] => lost\n for m in msgs:\n lost + [0] => lost\n if t != \"none\":\n \"\" => w\n for c in t + \" \":\n if c == \" \":\n if w != \"\":\n if not is_digits(w) or len(w) > 2 or int(w) < 1 or int(w) > len(msgs):\n (\"Type message numbers from 1 to \" + str(len(msgs)) + \", or none.\") ^0\n return\n lost[int(w) - 1] + 1 => lost[int(w) - 1]\n if lost[int(w) - 1] > 3:\n \"At most 3 lost acks for one message.\" ^0\n return\n \"\" => w\n else:\n w + c => w\n broker.deliveries(msgs, lost, delay) => seq\n widths(msgs) => wd\n \"Deliveries:\" ^0\n for d in [0:len(seq) - 1]:\n seq[d] => e\n msgs[e[0]] => m\n \"\" => tag\n if e[2]:\n \"sent again\" => tag\n if e[1]:\n if tag != \"\":\n tag + \", \" => tag\n tag + \"ack lost\" => tag\n \" \" + lpad(str(d + 1), 2) + \" message \" + str(e[0] + 1) + \" \" + pad(m[0], wd[0]) + \" \" => line\n if tag == \"\":\n (line + broker.body_text(m)) ^0\n else:\n (line + pad(broker.body_text(m), wd[1]) + \" \" + tag) ^0\n right_text(msgs) ^0\n handler_line(msgs, \"add\", \"add\", k, seq)\n handler_line(msgs, \"replay\", \"replay\", k, seq)\n handler_line(msgs, \"check\", \"check\", k, seq)\n handler_line(msgs, \"window \" + str(k), \"window\", k, seq)\n\ndef every(msgs, delay):\n broker.census(msgs, delay) => c\n (\"Every choice of which messages lose their first ack: \" + str(c[0]) + \" runs, each lost one sent again \" + str(delay) + \" deliveries later, or sooner at the end.\") ^0\n \" handler right applied twice reuse mishandled keys kept\" ^0\n 0 => kept\n for row in c[1]:\n (\" \" + pad(row[0], 10) + lpad(str(row[1]), 8) + lpad(str(row[2]), 15) + lpad(str(row[3]), 18) + lpad(str(row[4]), 11)) ^0\n if row[0] == \"check\":\n row[4] => kept\n \" applied twice: some request was applied more than once.\" ^0\n \" reuse mishandled: a key reused for another request was not refused, or a message was wrongly refused.\" ^0\n c[1][len(c[1]) - 1] => last\n (\"The first window right on every run keeps \" + str(last[4]) + \" keys; check keeps \" + str(kept) + \". How small a window can be depends on how late a message comes back.\") ^0\n\ndef add_message(msgs):\n if len(msgs) >= 8:\n \"8 messages is the most.\" ^0\n return msgs\n plain(input(\"key (up to 8 letters and digits)> \")) => key\n if key == \"\":\n \"Cancelled.\" ^0\n return msgs\n if len(key) > 8:\n \"Type a key of up to 8 letters and digits.\" ^0\n return msgs\n for c in key:\n if not ((c >= \"a\" and c <= \"z\") or (c >= \"A\" and c <= \"Z\") or (c >= \"0\" and c <= \"9\")):\n \"Type a key of up to 8 letters and digits.\" ^0\n return msgs\n plain(input(\"account (up to 10 lowercase letters)> \")) => acct\n if acct == \"\":\n \"Cancelled.\" ^0\n return msgs\n if len(acct) > 10:\n \"Type an account of up to 10 lowercase letters.\" ^0\n return msgs\n for c in acct:\n if c < \"a\" or c > \"z\":\n \"Type an account of up to 10 lowercase letters.\" ^0\n return msgs\n plain(input(\"amount (a whole number from -999 to 999, not 0)> \")) => t\n if t == \"\":\n \"Cancelled.\" ^0\n return msgs\n 1 => sign\n t => digits\n if t[0] == \"-\" or t[0] == \"+\":\n if t[0] == \"-\":\n 0 - 1 => sign\n t[1:len(t)] => digits\n if not is_digits(digits) or len(digits) > 3 or int(digits) == 0:\n \"Type a whole number from -999 to 999, not 0.\" ^0\n return msgs\n msgs + [[key, acct, sign * int(digits)]] => out\n note(out, len(out) - 1) => n\n if n == \"\":\n (\"Added message \" + str(len(out)) + \": \" + key + \" \" + broker.body_text(out[len(out) - 1]) + \".\") ^0\n else:\n (\"Added message \" + str(len(out)) + \": \" + key + \" \" + broker.body_text(out[len(out) - 1]) + \", \" + n + \".\") ^0\n return out\n\ndef one_to_nine(prompt):\n plain(input(prompt)) => t\n if t == \"\":\n \"Cancelled.\" ^0\n return 0\n if len(t) != 1 or t < \"1\" or t > \"9\":\n \"Type a number from 1 to 9.\" ^0\n return 0\n return int(t)\n\nbroker.default_messages() => msgs\n3 => delay\n2 => k\n\n\"== Message queue ==\" ^0\n\"A broker delivers every message at least once: when an ack is lost, it sends the message again. Each message carries an idempotency key.\" ^0\nTrue => running\nwhile running:\n \"\" ^0\n \"1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\" ^0\n plain(input(\"choice> \")) => choice\n if choice == \"1\":\n show(msgs, delay, k)\n elif choice == \"2\":\n deliver(msgs, delay, k)\n elif choice == \"3\":\n every(msgs, delay)\n elif choice == \"4\":\n add_message(msgs) => msgs\n elif choice == \"5\":\n one_to_nine(\"sent again after (1 to 9 deliveries)> \") => n\n if n > 0:\n n => delay\n (\"A message whose ack is lost is now sent again \" + str(delay) + \" deliveries later.\") ^0\n elif choice == \"6\":\n one_to_nine(\"window (1 to 9 keys)> \") => n\n if n > 0:\n n => k\n (\"The window now keeps \" + str(k) + \" keys.\") ^0\n elif choice == \"7\":\n False => running\n else:\n \"Pick a number from 1 to 7.\" ^0\n\"Bye.\" ^0\n", "python": "import broker\n\ndef plain(s):\n i = 0\n j = len(s)\n while i < j and s[i] == \" \":\n i = i + 1\n while j > i and s[j - 1] == \" \":\n j = j - 1\n return s[i:j]\n\ndef pad(s, n):\n out = s\n while len(out) < n:\n out = out + \" \"\n return out\n\ndef lpad(s, n):\n out = s\n while len(out) < n:\n out = \" \" + out\n return out\n\ndef is_digits(s):\n if len(s) == 0:\n return False\n for c in s:\n if c < \"0\" or c > \"9\":\n return False\n return True\n\ndef numbers_text(ns):\n out = \"\"\n for i in range(0, len(ns)):\n if i > 0 and i == len(ns) - 1:\n out = out + \" and \"\n elif i > 0:\n out = out + \", \"\n out = out + str(ns[i])\n return out\n\ndef balances_text(msgs, bal):\n out = \"\"\n for a in broker.accounts(msgs):\n if out != \"\":\n out = out + \", \"\n out = out + a + \" \" + str(bal[a])\n return out\n\ndef note(msgs, i):\n f = broker.first_with_key(msgs, i)\n if f == i:\n return \"\"\n if broker.same_request(msgs[f], msgs[i]):\n return \"a retry of message \" + str(f + 1)\n return \"the key of message \" + str(f + 1) + \", for another request\"\n\ndef widths(msgs):\n kw = 0\n bw = 0\n for m in msgs:\n if len(m[0]) > kw:\n kw = len(m[0])\n if len(broker.body_text(m)) > bw:\n bw = len(broker.body_text(m))\n return [kw, bw]\n\ndef right_text(msgs):\n want = broker.expected(msgs)\n refused = []\n for i in range(0, len(msgs)):\n if want[1][i] == \"refused\":\n refused = refused + [i + 1]\n out = \"Right: \" + balances_text(msgs, want[0])\n if len(refused) == 1:\n out = out + \"; message \" + numbers_text(refused) + \" refused\"\n elif len(refused) > 1:\n out = out + \"; messages \" + numbers_text(refused) + \" refused\"\n return out + \".\"\n\ndef show(msgs, delay, k):\n print(\"Messages (a message whose ack is lost is sent again \" + str(delay) + \" deliveries later; the window keeps \" + str(k) + \" keys):\")\n w = widths(msgs)\n for i in range(0, len(msgs)):\n m = msgs[i]\n line = \" \" + lpad(str(i + 1), 2) + \" \" + pad(m[0], w[0]) + \" \"\n n = note(msgs, i)\n if n == \"\":\n print(line + broker.body_text(m))\n else:\n print(line + pad(broker.body_text(m), w[1]) + \" \" + n)\n print(right_text(msgs))\n\ndef handler_line(msgs, name, kind, k, seq):\n r = broker.handle(kind, k, msgs, seq)\n p = broker.problems(msgs, r)\n parts = []\n if p[0] > 0:\n parts = parts + [str(p[0]) + \" applied again\"]\n for x in p[1]:\n who = \"message \" + str(x[0] + 1)\n if x[1] == \"applied\":\n parts = parts + [who + \" applied under message \" + str(x[2] + 1) + \"'s key\"]\n elif x[1] == \"told\":\n parts = parts + [who + \" told done with message \" + str(x[2] + 1) + \"'s answer\"]\n else:\n parts = parts + [who + \" wrongly refused\"]\n if len(parts) == 0 and not broker.balances_right(msgs, r):\n parts = parts + [\"balances wrong\"]\n verdict = \"\"\n if len(parts) == 0:\n verdict = \"right\"\n if kind == \"replay\":\n verdict = verdict + \", keeping \" + str(r[4]) + \" keys\"\n elif kind != \"add\":\n verdict = verdict + \", keeping \" + str(r[4]) + \" keys with their requests\"\n else:\n for q in parts:\n if verdict != \"\":\n verdict = verdict + \"; \"\n verdict = verdict + q\n print(\" \" + pad(name, 10) + balances_text(msgs, r[0]) + \": \" + verdict + \".\")\n\ndef deliver(msgs, delay, k):\n print(\"Acks lost: message numbers from 1 to \" + str(len(msgs)) + \" such as 2 5 (a number twice loses two), or none.\")\n t = plain(input(\"acks lost> \"))\n if t == \"\":\n print(\"Cancelled.\")\n return\n lost = []\n for m in msgs:\n lost = lost + [0]\n if t != \"none\":\n w = \"\"\n for c in t + \" \":\n if c == \" \":\n if w != \"\":\n if not is_digits(w) or len(w) > 2 or int(w) < 1 or int(w) > len(msgs):\n print(\"Type message numbers from 1 to \" + str(len(msgs)) + \", or none.\")\n return\n lost[int(w) - 1] = lost[int(w) - 1] + 1\n if lost[int(w) - 1] > 3:\n print(\"At most 3 lost acks for one message.\")\n return\n w = \"\"\n else:\n w = w + c\n seq = broker.deliveries(msgs, lost, delay)\n wd = widths(msgs)\n print(\"Deliveries:\")\n for d in range(0, len(seq)):\n e = seq[d]\n m = msgs[e[0]]\n tag = \"\"\n if e[2]:\n tag = \"sent again\"\n if e[1]:\n if tag != \"\":\n tag = tag + \", \"\n tag = tag + \"ack lost\"\n line = \" \" + lpad(str(d + 1), 2) + \" message \" + str(e[0] + 1) + \" \" + pad(m[0], wd[0]) + \" \"\n if tag == \"\":\n print(line + broker.body_text(m))\n else:\n print(line + pad(broker.body_text(m), wd[1]) + \" \" + tag)\n print(right_text(msgs))\n handler_line(msgs, \"add\", \"add\", k, seq)\n handler_line(msgs, \"replay\", \"replay\", k, seq)\n handler_line(msgs, \"check\", \"check\", k, seq)\n handler_line(msgs, \"window \" + str(k), \"window\", k, seq)\n\ndef every(msgs, delay):\n c = broker.census(msgs, delay)\n print(\"Every choice of which messages lose their first ack: \" + str(c[0]) + \" runs, each lost one sent again \" + str(delay) + \" deliveries later, or sooner at the end.\")\n print(\" handler right applied twice reuse mishandled keys kept\")\n kept = 0\n for row in c[1]:\n print(\" \" + pad(row[0], 10) + lpad(str(row[1]), 8) + lpad(str(row[2]), 15) + lpad(str(row[3]), 18) + lpad(str(row[4]), 11))\n if row[0] == \"check\":\n kept = row[4]\n print(\" applied twice: some request was applied more than once.\")\n print(\" reuse mishandled: a key reused for another request was not refused, or a message was wrongly refused.\")\n last = c[1][len(c[1]) - 1]\n print(\"The first window right on every run keeps \" + str(last[4]) + \" keys; check keeps \" + str(kept) + \". How small a window can be depends on how late a message comes back.\")\n\ndef add_message(msgs):\n if len(msgs) >= 8:\n print(\"8 messages is the most.\")\n return msgs\n key = plain(input(\"key (up to 8 letters and digits)> \"))\n if key == \"\":\n print(\"Cancelled.\")\n return msgs\n if len(key) > 8:\n print(\"Type a key of up to 8 letters and digits.\")\n return msgs\n for c in key:\n if not (c >= \"a\" and c <= \"z\" or c >= \"A\" and c <= \"Z\" or c >= \"0\" and c <= \"9\"):\n print(\"Type a key of up to 8 letters and digits.\")\n return msgs\n acct = plain(input(\"account (up to 10 lowercase letters)> \"))\n if acct == \"\":\n print(\"Cancelled.\")\n return msgs\n if len(acct) > 10:\n print(\"Type an account of up to 10 lowercase letters.\")\n return msgs\n for c in acct:\n if c < \"a\" or c > \"z\":\n print(\"Type an account of up to 10 lowercase letters.\")\n return msgs\n t = plain(input(\"amount (a whole number from -999 to 999, not 0)> \"))\n if t == \"\":\n print(\"Cancelled.\")\n return msgs\n sign = 1\n digits = t\n if t[0] == \"-\" or t[0] == \"+\":\n if t[0] == \"-\":\n sign = 0 - 1\n digits = t[1:len(t)]\n if not is_digits(digits) or len(digits) > 3 or int(digits) == 0:\n print(\"Type a whole number from -999 to 999, not 0.\")\n return msgs\n out = msgs + [[key, acct, sign * int(digits)]]\n n = note(out, len(out) - 1)\n if n == \"\":\n print(\"Added message \" + str(len(out)) + \": \" + key + \" \" + broker.body_text(out[len(out) - 1]) + \".\")\n else:\n print(\"Added message \" + str(len(out)) + \": \" + key + \" \" + broker.body_text(out[len(out) - 1]) + \", \" + n + \".\")\n return out\n\ndef one_to_nine(prompt):\n t = plain(input(prompt))\n if t == \"\":\n print(\"Cancelled.\")\n return 0\n if len(t) != 1 or t < \"1\" or t > \"9\":\n print(\"Type a number from 1 to 9.\")\n return 0\n return int(t)\n\nmsgs = broker.default_messages()\ndelay = 3\nk = 2\nprint(\"== Message queue ==\")\nprint(\"A broker delivers every message at least once: when an ack is lost, it sends the message again. Each message carries an idempotency key.\")\nrunning = True\nwhile running:\n print(\"\")\n print(\"1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\")\n choice = plain(input(\"choice> \"))\n if choice == \"1\":\n show(msgs, delay, k)\n elif choice == \"2\":\n deliver(msgs, delay, k)\n elif choice == \"3\":\n every(msgs, delay)\n elif choice == \"4\":\n msgs = add_message(msgs)\n elif choice == \"5\":\n n = one_to_nine(\"sent again after (1 to 9 deliveries)> \")\n if n > 0:\n delay = n\n print(\"A message whose ack is lost is now sent again \" + str(delay) + \" deliveries later.\")\n elif choice == \"6\":\n n = one_to_nine(\"window (1 to 9 keys)> \")\n if n > 0:\n k = n\n print(\"The window now keeps \" + str(k) + \" keys.\")\n elif choice == \"7\":\n running = False\n else:\n print(\"Pick a number from 1 to 7.\")\nprint(\"Bye.\")\n" }, { "name": "broker.eml", "eml": "# P117 message queue - a broker that delivers every message at least once:\n# when a consumer's acknowledgement is lost, the broker sends the message\n# again a few deliveries later. As in the corpus case at-least-once-delivery,\n# what a duplicate does is up to the handler. Each message carries an\n# idempotency key, and as in the corpus case idempotency-key-reuse, a client\n# that reuses a key for another request has to be refused, which needs the\n# request kept beside the key.\n#\n# A message is [key, account, amount]; every account starts at 0.\n\ndef default_messages():\n return [[\"k1\", \"alice\", 30], [\"k2\", \"bob\", 20], [\"k3\", \"alice\", 0 - 10], [\"k2\", \"bob\", 25], [\"k4\", \"carol\", 50], [\"k4\", \"carol\", 50], [\"k5\", \"bob\", 0 - 5]]\n\ndef signed(n):\n if n < 0:\n return \"-\" + str(0 - n)\n return \"+\" + str(n)\n\ndef body_text(m):\n return m[1] + \" \" + signed(m[2])\n\ndef same_request(a, b):\n return a[1] == b[1] and a[2] == b[2]\n\ndef member(xs, x):\n for y in xs:\n if y == x:\n return True\n return False\n\ndef accounts(msgs):\n [] => out\n for m in msgs:\n if not member(out, m[1]):\n out + [m[1]] => out\n return out\n\ndef first_with_key(msgs, i):\n # the first message carrying message i's key\n for j in [0:i]:\n if msgs[j][0] == msgs[i][0]:\n return j\n return i\n\ndef expected(msgs):\n # each key's first message applied once; a later message with the same\n # key and the same request is a retry and is answered done; with another\n # request it is refused: [balances, answer per message]\n {} => bal\n for a in accounts(msgs):\n 0 => bal[a]\n [] => answers\n for i in [0:len(msgs) - 1]:\n msgs[i] => m\n first_with_key(msgs, i) => f\n if f == i:\n bal[m[1]] + m[2] => bal[m[1]]\n answers + [\"done\"] => answers\n elif same_request(msgs[f], m):\n answers + [\"done\"] => answers\n else:\n answers + [\"refused\"] => answers\n return [bal, answers]\n\ndef deliveries(msgs, lost, delay):\n # the broker's deliveries, in order, as [message, ack lost, sent before];\n # lost[i] is how many of message i's acks are lost. A message whose ack\n # is lost is sent again delay deliveries later, or sooner when nothing\n # else is waiting.\n [] => pending\n [] => left\n for i in [0:len(msgs) - 1]:\n pending + [i] => pending\n left + [lost[i]] => left\n [] => again\n [] => sent\n [] => out\n 0 => d\n while len(pending) > 0 or len(again) > 0:\n d + 1 => d\n 0 - 1 => best\n for j in [0:len(again) - 1]:\n if best == 0 - 1 or again[j][0] < again[best][0]:\n j => best\n if best != 0 - 1 and (again[best][0] <= d or len(pending) == 0):\n again[best][1] => m\n [] => rest\n for j in [0:len(again) - 1]:\n if j != best:\n rest + [again[j]] => rest\n rest => again\n else:\n pending[0] => m\n pending[1:len(pending)] => pending\n left[m] > 0 => lose\n if lose:\n left[m] - 1 => left[m]\n again + [[d + delay, m]] => again\n out + [[m, lose, member(sent, m)]] => out\n sent + [m] => sent\n return out\n\ndef handle(kind, k, msgs, seq):\n # one handler over the deliveries:\n # add applies every delivery;\n # replay keeps every key, and answers a key it has seen with the\n # first answer, applying nothing;\n # check keeps every key with its request: the same request again is\n # answered done, another request under it is refused;\n # window like check, but keeps only the last k keys it applied.\n # [balances, applied again, times applied per message, last answer per\n # message, keys kept]\n {} => bal\n for a in accounts(msgs):\n 0 => bal[a]\n {} => kept\n [] => window\n [] => applied\n 0 => again\n [] => times\n [] => answers\n for m in msgs:\n times + [0] => times\n answers + [\"\"] => answers\n for e in seq:\n e[0] => i\n msgs[i] => m\n \"apply\" => act\n if kind == \"replay\" or kind == \"check\":\n if m[0] in kept:\n if same_request(msgs[kept[m[0]]], m):\n \"repeat\" => act\n elif kind == \"replay\":\n \"told\" => act\n else:\n \"refused\" => act\n elif kind == \"window\":\n for w in window:\n if w[0] == m[0]:\n if same_request(msgs[w[1]], m):\n \"repeat\" => act\n else:\n \"refused\" => act\n if act == \"apply\":\n if member(applied, [m[0], m[1], m[2]]):\n again + 1 => again\n applied + [[m[0], m[1], m[2]]] => applied\n bal[m[1]] + m[2] => bal[m[1]]\n times[i] + 1 => times[i]\n \"done\" => answers[i]\n if kind == \"replay\" or kind == \"check\":\n i => kept[m[0]]\n if kind == \"window\":\n window + [[m[0], i]] => window\n if len(window) > k:\n window[1:len(window)] => window\n elif act == \"repeat\":\n \"done\" => answers[i]\n else:\n act => answers[i]\n 0 => n\n if kind == \"window\":\n len(window) => n\n else:\n len(kept) => n\n return [bal, again, times, answers, n]\n\ndef problems(msgs, r):\n # what went wrong, as [applied again, list of [message, what, first]]\n expected(msgs) => want\n [] => out\n for i in [0:len(msgs) - 1]:\n first_with_key(msgs, i) => f\n if want[1][i] == \"refused\":\n if r[2][i] > 0:\n out + [[i, \"applied\", f]] => out\n elif r[3][i] == \"told\":\n out + [[i, \"told\", f]] => out\n elif r[3][i] == \"refused\":\n out + [[i, \"refused\", f]] => out\n return [r[1], out]\n\ndef balances_right(msgs, r):\n expected(msgs)[0] => want\n for a in accounts(msgs):\n if r[0][a] != want[a]:\n return False\n return True\n\ndef right(msgs, r):\n problems(msgs, r) => p\n return p[0] == 0 and len(p[1]) == 0 and balances_right(msgs, r)\n\ndef lost_choices(n):\n # every choice of which messages lose their first ack\n [[]] => out\n for i in [1:n]:\n [] => more\n for c in out:\n more + [c + [0]] => more\n more + [c + [1]] => more\n more => out\n return out\n\ndef census(msgs, delay):\n # over every choice of lost first acks, for add, replay, check and the\n # windows from 1 key up to the first that is right on every run:\n # [runs, rows of [name, right, applied twice, reuse mishandled, kept]]\n lost_choices(len(msgs)) => choices\n [] => runs\n for c in choices:\n runs + [deliveries(msgs, c, delay)] => runs\n [] => rows\n [\"add\", \"replay\", \"check\"] => kinds\n 0 => k\n True => going\n while going:\n if len(kinds) > 0:\n kinds[0] => kind\n kinds[1:len(kinds)] => kinds\n kind => name\n else:\n \"window\" => kind\n k + 1 => k\n \"window \" + str(k) => name\n 0 => good\n 0 => twice\n 0 => reuse\n 0 => most\n for seq in runs:\n handle(kind, k, msgs, seq) => r\n problems(msgs, r) => p\n if p[0] == 0 and len(p[1]) == 0 and balances_right(msgs, r):\n good + 1 => good\n if p[0] > 0:\n twice + 1 => twice\n if len(p[1]) > 0:\n reuse + 1 => reuse\n if r[4] > most:\n r[4] => most\n rows + [[name, good, twice, reuse, most]] => rows\n if kind == \"window\" and good == len(runs):\n False => going\n return [len(runs), rows]\n", "python": "def default_messages():\n return [[\"k1\", \"alice\", 30], [\"k2\", \"bob\", 20], [\"k3\", \"alice\", 0 - 10], [\"k2\", \"bob\", 25], [\"k4\", \"carol\", 50], [\"k4\", \"carol\", 50], [\"k5\", \"bob\", 0 - 5]]\n\ndef signed(n):\n if n < 0:\n return \"-\" + str(0 - n)\n return \"+\" + str(n)\n\ndef body_text(m):\n return m[1] + \" \" + signed(m[2])\n\ndef same_request(a, b):\n return a[1] == b[1] and a[2] == b[2]\n\ndef member(xs, x):\n for y in xs:\n if y == x:\n return True\n return False\n\ndef accounts(msgs):\n out = []\n for m in msgs:\n if not member(out, m[1]):\n out = out + [m[1]]\n return out\n\ndef first_with_key(msgs, i):\n for j in range(0, i+1):\n if msgs[j][0] == msgs[i][0]:\n return j\n return i\n\ndef expected(msgs):\n bal = {}\n for a in accounts(msgs):\n bal[a] = 0\n answers = []\n for i in range(0, len(msgs)):\n m = msgs[i]\n f = first_with_key(msgs, i)\n if f == i:\n bal[m[1]] = bal[m[1]] + m[2]\n answers = answers + [\"done\"]\n elif same_request(msgs[f], m):\n answers = answers + [\"done\"]\n else:\n answers = answers + [\"refused\"]\n return [bal, answers]\n\ndef deliveries(msgs, lost, delay):\n pending = []\n left = []\n for i in range(0, len(msgs)):\n pending = pending + [i]\n left = left + [lost[i]]\n again = []\n sent = []\n out = []\n d = 0\n while len(pending) > 0 or len(again) > 0:\n d = d + 1\n best = 0 - 1\n for j in range(0, len(again)):\n if best == 0 - 1 or again[j][0] < again[best][0]:\n best = j\n if best != 0 - 1 and (again[best][0] <= d or len(pending) == 0):\n m = again[best][1]\n rest = []\n for j in range(0, len(again)):\n if j != best:\n rest = rest + [again[j]]\n again = rest\n else:\n m = pending[0]\n pending = pending[1:len(pending)]\n lose = left[m] > 0\n if lose:\n left[m] = left[m] - 1\n again = again + [[d + delay, m]]\n out = out + [[m, lose, member(sent, m)]]\n sent = sent + [m]\n return out\n\ndef handle(kind, k, msgs, seq):\n bal = {}\n for a in accounts(msgs):\n bal[a] = 0\n kept = {}\n window = []\n applied = []\n again = 0\n times = []\n answers = []\n for m in msgs:\n times = times + [0]\n answers = answers + [\"\"]\n for e in seq:\n i = e[0]\n m = msgs[i]\n act = \"apply\"\n if kind == \"replay\" or kind == \"check\":\n if m[0] in kept:\n if same_request(msgs[kept[m[0]]], m):\n act = \"repeat\"\n elif kind == \"replay\":\n act = \"told\"\n else:\n act = \"refused\"\n elif kind == \"window\":\n for w in window:\n if w[0] == m[0]:\n if same_request(msgs[w[1]], m):\n act = \"repeat\"\n else:\n act = \"refused\"\n if act == \"apply\":\n if member(applied, [m[0], m[1], m[2]]):\n again = again + 1\n applied = applied + [[m[0], m[1], m[2]]]\n bal[m[1]] = bal[m[1]] + m[2]\n times[i] = times[i] + 1\n answers[i] = \"done\"\n if kind == \"replay\" or kind == \"check\":\n kept[m[0]] = i\n if kind == \"window\":\n window = window + [[m[0], i]]\n if len(window) > k:\n window = window[1:len(window)]\n elif act == \"repeat\":\n answers[i] = \"done\"\n else:\n answers[i] = act\n n = 0\n if kind == \"window\":\n n = len(window)\n else:\n n = len(kept)\n return [bal, again, times, answers, n]\n\ndef problems(msgs, r):\n want = expected(msgs)\n out = []\n for i in range(0, len(msgs)):\n f = first_with_key(msgs, i)\n if want[1][i] == \"refused\":\n if r[2][i] > 0:\n out = out + [[i, \"applied\", f]]\n elif r[3][i] == \"told\":\n out = out + [[i, \"told\", f]]\n elif r[3][i] == \"refused\":\n out = out + [[i, \"refused\", f]]\n return [r[1], out]\n\ndef balances_right(msgs, r):\n want = expected(msgs)[0]\n for a in accounts(msgs):\n if r[0][a] != want[a]:\n return False\n return True\n\ndef right(msgs, r):\n p = problems(msgs, r)\n return p[0] == 0 and len(p[1]) == 0 and balances_right(msgs, r)\n\ndef lost_choices(n):\n out = [[]]\n for i in range(1, n+1):\n more = []\n for c in out:\n more = more + [c + [0]]\n more = more + [c + [1]]\n out = more\n return out\n\ndef census(msgs, delay):\n choices = lost_choices(len(msgs))\n runs = []\n for c in choices:\n runs = runs + [deliveries(msgs, c, delay)]\n rows = []\n kinds = [\"add\", \"replay\", \"check\"]\n k = 0\n going = True\n while going:\n if len(kinds) > 0:\n kind = kinds[0]\n kinds = kinds[1:len(kinds)]\n name = kind\n else:\n kind = \"window\"\n k = k + 1\n name = \"window \" + str(k)\n good = 0\n twice = 0\n reuse = 0\n most = 0\n for seq in runs:\n r = handle(kind, k, msgs, seq)\n p = problems(msgs, r)\n if p[0] == 0 and len(p[1]) == 0 and balances_right(msgs, r):\n good = good + 1\n if p[0] > 0:\n twice = twice + 1\n if len(p[1]) > 0:\n reuse = reuse + 1\n if r[4] > most:\n most = r[4]\n rows = rows + [[name, good, twice, reuse, most]]\n if kind == \"window\" and good == len(runs):\n going = False\n return [len(runs), rows]\n" } ], "sessions": [ { "name": "bad-input", "input": "0\nx\n2\n\n2\n0\n2\n8\n2\nx\n2\n2,5\n2\n1 1 1 1\n4\n\n4\nk 1\n4\ntoolongkey\n4\nk-1\n4\nk9\n\n4\nk9\nBob\n4\nk9\naveryverylongname\n4\nk9\ndave\n\n4\nk9\ndave\n0\n4\nk9\ndave\n1000\n4\nk9\ndave\n+-3\n4\nk9\ndave\nx\n4\nk9\ndave\n-15\n4\n5\n\n5\n0\n5\n10\n5\nx\n6\n\n6\n0\n7\n", "screen": "== Message queue ==\nA broker delivers every message at least once: when an ack is lost, it sends the message again. Each message carries an idempotency key.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> 0\nPick a number from 1 to 7.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> x\nPick a number from 1 to 7.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> 2\nAcks lost: message numbers from 1 to 7 such as 2 5 (a number twice loses two), or none.\nacks lost> \nCancelled.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> 2\nAcks lost: message numbers from 1 to 7 such as 2 5 (a number twice loses two), or none.\nacks lost> 0\nType message numbers from 1 to 7, or none.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> 2\nAcks lost: message numbers from 1 to 7 such as 2 5 (a number twice loses two), or none.\nacks lost> 8\nType message numbers from 1 to 7, or none.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> 2\nAcks lost: message numbers from 1 to 7 such as 2 5 (a number twice loses two), or none.\nacks lost> x\nType message numbers from 1 to 7, or none.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> 2\nAcks lost: message numbers from 1 to 7 such as 2 5 (a number twice loses two), or none.\nacks lost> 2,5\nType message numbers from 1 to 7, or none.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> 2\nAcks lost: message numbers from 1 to 7 such as 2 5 (a number twice loses two), or none.\nacks lost> 1 1 1 1\nAt most 3 lost acks for one message.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> 4\nkey (up to 8 letters and digits)> \nCancelled.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> 4\nkey (up to 8 letters and digits)> k 1\nType a key of up to 8 letters and digits.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> 4\nkey (up to 8 letters and digits)> toolongkey\nType a key of up to 8 letters and digits.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> 4\nkey (up to 8 letters and digits)> k-1\nType a key of up to 8 letters and digits.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> 4\nkey (up to 8 letters and digits)> k9\naccount (up to 10 lowercase letters)> \nCancelled.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> 4\nkey (up to 8 letters and digits)> k9\naccount (up to 10 lowercase letters)> Bob\nType an account of up to 10 lowercase letters.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> 4\nkey (up to 8 letters and digits)> k9\naccount (up to 10 lowercase letters)> averyverylongname\nType an account of up to 10 lowercase letters.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> 4\nkey (up to 8 letters and digits)> k9\naccount (up to 10 lowercase letters)> dave\namount (a whole number from -999 to 999, not 0)> \nCancelled.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> 4\nkey (up to 8 letters and digits)> k9\naccount (up to 10 lowercase letters)> dave\namount (a whole number from -999 to 999, not 0)> 0\nType a whole number from -999 to 999, not 0.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> 4\nkey (up to 8 letters and digits)> k9\naccount (up to 10 lowercase letters)> dave\namount (a whole number from -999 to 999, not 0)> 1000\nType a whole number from -999 to 999, not 0.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> 4\nkey (up to 8 letters and digits)> k9\naccount (up to 10 lowercase letters)> dave\namount (a whole number from -999 to 999, not 0)> +-3\nType a whole number from -999 to 999, not 0.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> 4\nkey (up to 8 letters and digits)> k9\naccount (up to 10 lowercase letters)> dave\namount (a whole number from -999 to 999, not 0)> x\nType a whole number from -999 to 999, not 0.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> 4\nkey (up to 8 letters and digits)> k9\naccount (up to 10 lowercase letters)> dave\namount (a whole number from -999 to 999, not 0)> -15\nAdded message 8: k9 dave -15.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> 4\n8 messages is the most.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> 5\nsent again after (1 to 9 deliveries)> \nCancelled.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> 5\nsent again after (1 to 9 deliveries)> 0\nType a number from 1 to 9.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> 5\nsent again after (1 to 9 deliveries)> 10\nType a number from 1 to 9.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> 5\nsent again after (1 to 9 deliveries)> x\nType a number from 1 to 9.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> 6\nwindow (1 to 9 keys)> \nCancelled.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> 6\nwindow (1 to 9 keys)> 0\nType a number from 1 to 9.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> 7\nBye.\n", "interpreter": "equal" }, { "name": "basic", "input": "1\n2\n2 5\n2\n1\n2\nnone\n3\n5\n6\n3\n6\n4\n2\n1 2 2\n4\nk1\nalice\n30\n1\n3\n7\n", "screen": "== Message queue ==\nA broker delivers every message at least once: when an ack is lost, it sends the message again. Each message carries an idempotency key.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> 1\nMessages (a message whose ack is lost is sent again 3 deliveries later; the window keeps 2 keys):\n 1 k1 alice +30\n 2 k2 bob +20\n 3 k3 alice -10\n 4 k2 bob +25 the key of message 2, for another request\n 5 k4 carol +50\n 6 k4 carol +50 a retry of message 5\n 7 k5 bob -5\nRight: alice 20, bob 15, carol 50; message 4 refused.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> 2\nAcks lost: message numbers from 1 to 7 such as 2 5 (a number twice loses two), or none.\nacks lost> 2 5\nDeliveries:\n 1 message 1 k1 alice +30\n 2 message 2 k2 bob +20 ack lost\n 3 message 3 k3 alice -10\n 4 message 4 k2 bob +25\n 5 message 2 k2 bob +20 sent again\n 6 message 5 k4 carol +50 ack lost\n 7 message 6 k4 carol +50\n 8 message 7 k5 bob -5\n 9 message 5 k4 carol +50 sent again\nRight: alice 20, bob 15, carol 50; message 4 refused.\n add alice 20, bob 60, carol 150: 3 applied again; message 4 applied under message 2's key.\n replay alice 20, bob 15, carol 50: message 4 told done with message 2's answer.\n check alice 20, bob 15, carol 50: right, keeping 5 keys with their requests.\n window 2 alice 20, bob 15, carol 50: right, keeping 2 keys with their requests.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> 2\nAcks lost: message numbers from 1 to 7 such as 2 5 (a number twice loses two), or none.\nacks lost> 1\nDeliveries:\n 1 message 1 k1 alice +30 ack lost\n 2 message 2 k2 bob +20\n 3 message 3 k3 alice -10\n 4 message 1 k1 alice +30 sent again\n 5 message 4 k2 bob +25\n 6 message 5 k4 carol +50\n 7 message 6 k4 carol +50\n 8 message 7 k5 bob -5\nRight: alice 20, bob 15, carol 50; message 4 refused.\n add alice 50, bob 40, carol 100: 2 applied again; message 4 applied under message 2's key.\n replay alice 20, bob 15, carol 50: message 4 told done with message 2's answer.\n check alice 20, bob 15, carol 50: right, keeping 5 keys with their requests.\n window 2 alice 50, bob 40, carol 50: 1 applied again; message 4 applied under message 2's key.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> 2\nAcks lost: message numbers from 1 to 7 such as 2 5 (a number twice loses two), or none.\nacks lost> none\nDeliveries:\n 1 message 1 k1 alice +30\n 2 message 2 k2 bob +20\n 3 message 3 k3 alice -10\n 4 message 4 k2 bob +25\n 5 message 5 k4 carol +50\n 6 message 6 k4 carol +50\n 7 message 7 k5 bob -5\nRight: alice 20, bob 15, carol 50; message 4 refused.\n add alice 20, bob 40, carol 100: 1 applied again; message 4 applied under message 2's key.\n replay alice 20, bob 15, carol 50: message 4 told done with message 2's answer.\n check alice 20, bob 15, carol 50: right, keeping 5 keys with their requests.\n window 2 alice 20, bob 15, carol 50: right, keeping 2 keys with their requests.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> 3\nEvery choice of which messages lose their first ack: 128 runs, each lost one sent again 3 deliveries later, or sooner at the end.\n handler right applied twice reuse mishandled keys kept\n add 0 128 128 0\n replay 0 0 128 5\n check 128 0 0 5\n window 1 0 124 120 1\n window 2 40 74 64 2\n window 3 128 0 0 3\n applied twice: some request was applied more than once.\n reuse mishandled: a key reused for another request was not refused, or a message was wrongly refused.\nThe first window right on every run keeps 3 keys; check keeps 5. How small a window can be depends on how late a message comes back.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> 5\nsent again after (1 to 9 deliveries)> 6\nA message whose ack is lost is now sent again 6 deliveries later.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> 3\nEvery choice of which messages lose their first ack: 128 runs, each lost one sent again 6 deliveries later, or sooner at the end.\n handler right applied twice reuse mishandled keys kept\n add 0 128 128 0\n replay 0 0 128 5\n check 128 0 0 5\n window 1 0 126 128 1\n window 2 8 118 32 2\n window 3 16 96 32 3\n window 4 128 0 0 4\n applied twice: some request was applied more than once.\n reuse mishandled: a key reused for another request was not refused, or a message was wrongly refused.\nThe first window right on every run keeps 4 keys; check keeps 5. How small a window can be depends on how late a message comes back.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> 6\nwindow (1 to 9 keys)> 4\nThe window now keeps 4 keys.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> 2\nAcks lost: message numbers from 1 to 7 such as 2 5 (a number twice loses two), or none.\nacks lost> 1 2 2\nDeliveries:\n 1 message 1 k1 alice +30 ack lost\n 2 message 2 k2 bob +20 ack lost\n 3 message 3 k3 alice -10\n 4 message 4 k2 bob +25\n 5 message 5 k4 carol +50\n 6 message 6 k4 carol +50\n 7 message 1 k1 alice +30 sent again\n 8 message 2 k2 bob +20 sent again, ack lost\n 9 message 7 k5 bob -5\n 10 message 2 k2 bob +20 sent again\nRight: alice 20, bob 15, carol 50; message 4 refused.\n add alice 50, bob 80, carol 100: 4 applied again; message 4 applied under message 2's key.\n replay alice 20, bob 15, carol 50: message 4 told done with message 2's answer.\n check alice 20, bob 15, carol 50: right, keeping 5 keys with their requests.\n window 4 alice 20, bob 15, carol 50: right, keeping 4 keys with their requests.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> 4\nkey (up to 8 letters and digits)> k1\naccount (up to 10 lowercase letters)> alice\namount (a whole number from -999 to 999, not 0)> 30\nAdded message 8: k1 alice +30, a retry of message 1.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> 1\nMessages (a message whose ack is lost is sent again 6 deliveries later; the window keeps 4 keys):\n 1 k1 alice +30\n 2 k2 bob +20\n 3 k3 alice -10\n 4 k2 bob +25 the key of message 2, for another request\n 5 k4 carol +50\n 6 k4 carol +50 a retry of message 5\n 7 k5 bob -5\n 8 k1 alice +30 a retry of message 1\nRight: alice 20, bob 15, carol 50; message 4 refused.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> 3\nEvery choice of which messages lose their first ack: 256 runs, each lost one sent again 6 deliveries later, or sooner at the end.\n handler right applied twice reuse mishandled keys kept\n add 0 256 256 0\n replay 0 0 256 5\n check 256 0 0 5\n window 1 0 256 256 1\n window 2 0 256 64 2\n window 3 0 256 64 3\n window 4 0 256 64 4\n window 5 256 0 0 5\n applied twice: some request was applied more than once.\n reuse mishandled: a key reused for another request was not refused, or a message was wrongly refused.\nThe first window right on every run keeps 5 keys; check keeps 5. How small a window can be depends on how late a message comes back.\n\n1) messages 2) deliver 3) every lost ack 4) add a message 5) redelivery 6) window 7) quit\nchoice> 7\nBye.\n", "interpreter": "equal" } ], "builtOn": [ { "slug": "at-least-once-delivery", "caseId": "215-at-least-once-delivery", "title": "Duplicates are a property of the handler" }, { "slug": "idempotency-key-reuse", "caseId": "281-idempotency-key-reuse", "title": "Idempotency key reuse — the key says retry and the body says otherwise" } ], "updated": "2026-10-16" }