journal.bend source
journal.bend on the hub · documented module
# Append-only journal: checksummed frames, fsync'd appends, and crash recovery of the committed prefix. Source: https://github.com/paymog/bend-kit/tree/main/journalimport Base# bend-kit-bytes@0.3.0.0, the version bend-kit-hash@0.1.0.0 takes, so Hash.crc32 accepts these Bytes.import 0x49814d83de8f70993a43e1002be29ecd/bytes.bend as Bytesimport bend-kit-hash@0.1.0.0/hash.bend as Hash# A frame is one record and one commit: three u32 little-endian fields, then the payload.# len, then U32.not(len), then the CRC-32 of the payload, then len payload octets.# A frame is committed when all 12 + len of its octets are in the file.# Clean: the input ends on a frame boundary.# Torn: the input ends inside a frame. A crash cut the last append short.# Corrupt: a whole header or a whole frame fails its check. Recovery does not go past it.type Tail is Data: Clean{} Torn{} Corrupt{why: String}# One decoding step. Short, Bad, and End give the input back untouched, at the frame start.type Step<-P: Type, -S: Type> is Type: End{s: S} Short{s: S} Bad{why: String, s: S} Got{p: P, s: S}# The committed records in order, how the input ends, and the input from the first frame not taken.type Recovery<a, -P: Kind(a), -S: Type> is Type: Recovery{records: List<a, P>, tail: Tail, rest: S}# The state after every committed record, how the input ends, and the input from the first frame not taken.type Replay<-A: Type, -S: Type> is Type: Replay{acc: A, tail: Tail, rest: S}# The decoder is generic over the input S and the payload P. Bytes runs it; a list of octets proves it.# fits(s, at, n): n octets from at fit in s. u32(s, at): the field at at. cut(s, hs, len): a copy of# [hs, hs + len). skip(s, hs, len): s from hs + len. sum(p): the checksum of p.def next.verdict(~P: Type, ~S: Type, ~skip: S -> @+hs:U32 -> @+len:U32 -> S, ok: Bool, +len: U32, s: S, p: P) -> Step<P, S>: match ok: case True{}: Got{p, skip(s, 12, len)} case False{}: Bad{"checksum mismatch", s}def next.summed(~P: Type, ~S: Type, ~skip: S -> @+hs:U32 -> @+len:U32 -> S, +want: U32, +len: U32, s: S, r: P & U32) -> Step<P, S>: (p, +got) = r next.verdict(~P, ~S, ~skip, U32.is_eq(got, want), len, s, p)def next.cut(~P: Type, ~S: Type, ~skip: S -> @+hs:U32 -> @+len:U32 -> S, ~sum: P -> P & U32, +want: U32, +len: U32, r: S & P) -> Step<P, S>: (s, p) = r next.summed(~P, ~S, ~skip, want, len, s, sum(p))def next.want(~P: Type, ~S: Type, ~cut: S -> @+hs:U32 -> @+len:U32 -> S & P, ~skip: S -> @+hs:U32 -> @+len:U32 -> S, ~sum: P -> P & U32, +len: U32, r: S & U32) -> Step<P, S>: (s, +want) = r next.cut(~P, ~S, ~skip, ~sum, want, len, cut(s, 12, len))def next.body(~P: Type, ~S: Type, ~u32: S -> @+at:U32 -> S & U32, ~cut: S -> @+hs:U32 -> @+len:U32 -> S & P, ~skip: S -> @+hs:U32 -> @+len:U32 -> S, ~sum: P -> P & U32, +len: U32, r: S & Bool) -> Step<P, S>: (s, whole) = r match whole: case True{}: next.want(~P, ~S, ~cut, ~skip, ~sum, len, u32(s, 8)) case False{}: Short{s}def next.size(~P: Type, ~S: Type, ~fits: S -> @+at:U32 -> @+n:U32 -> S & Bool, ~u32: S -> @+at:U32 -> S & U32, ~cut: S -> @+hs:U32 -> @+len:U32 -> S & P, ~skip: S -> @+hs:U32 -> @+len:U32 -> S, ~sum: P -> P & U32, over: Bool, +len: U32, s: S) -> Step<P, S>: match over: case True{}: Bad{"length over max", s} case False{}: next.body(~P, ~S, ~u32, ~cut, ~skip, ~sum, len, fits(s, 12, len))def next.head(~P: Type, ~S: Type, ~fits: S -> @+at:U32 -> @+n:U32 -> S & Bool, ~u32: S -> @+at:U32 -> S & U32, ~cut: S -> @+hs:U32 -> @+len:U32 -> S & P, ~skip: S -> @+hs:U32 -> @+len:U32 -> S, ~sum: P -> P & U32, ok: Bool, +max: U32, +len: U32, s: S) -> Step<P, S>: match ok: case True{}: next.size(~P, ~S, ~fits, ~u32, ~cut, ~skip, ~sum, U32.is_gt(len, max), len, s) case False{}: Bad{"length check mismatch", s}def next.lenx(~P: Type, ~S: Type, ~fits: S -> @+at:U32 -> @+n:U32 -> S & Bool, ~u32: S -> @+at:U32 -> S & U32, ~cut: S -> @+hs:U32 -> @+len:U32 -> S & P, ~skip: S -> @+hs:U32 -> @+len:U32 -> S, ~sum: P -> P & U32, +max: U32, +len: U32, r: S & U32) -> Step<P, S>: (s, +lenx) = r next.head(~P, ~S, ~fits, ~u32, ~cut, ~skip, ~sum, U32.is_eq(lenx, U32.not(len)), max, len, s)def next.len(~P: Type, ~S: Type, ~fits: S -> @+at:U32 -> @+n:U32 -> S & Bool, ~u32: S -> @+at:U32 -> S & U32, ~cut: S -> @+hs:U32 -> @+len:U32 -> S & P, ~skip: S -> @+hs:U32 -> @+len:U32 -> S, ~sum: P -> P & U32, +max: U32, r: S & U32) -> Step<P, S>: (s, +len) = r next.lenx(~P, ~S, ~fits, ~u32, ~cut, ~skip, ~sum, max, len, u32(s, 4))# The two length fields are checked before the payload is waited for, so a damaged length is# Bad and never a Torn tail that hides the frames after it.def next.start(~P: Type, ~S: Type, ~fits: S -> @+at:U32 -> @+n:U32 -> S & Bool, ~u32: S -> @+at:U32 -> S & U32, ~cut: S -> @+hs:U32 -> @+len:U32 -> S & P, ~skip: S -> @+hs:U32 -> @+len:U32 -> S, ~sum: P -> P & U32, +max: U32, r: S & Bool) -> Step<P, S>: (s, both) = r match both: case True{}: next.len(~P, ~S, ~fits, ~u32, ~cut, ~skip, ~sum, max, u32(s, 0)) case False{}: Short{s}def next.any(~P: Type, ~S: Type, ~fits: S -> @+at:U32 -> @+n:U32 -> S & Bool, ~u32: S -> @+at:U32 -> S & U32, ~cut: S -> @+hs:U32 -> @+len:U32 -> S & P, ~skip: S -> @+hs:U32 -> @+len:U32 -> S, ~sum: P -> P & U32, +max: U32, r: S & Bool) -> Step<P, S>: (s, some) = r match some: case True{}: next.start(~P, ~S, ~fits, ~u32, ~cut, ~skip, ~sum, max, fits(s, 0, 8)) case False{}: End{s}# One frame from s. max caps a payload's length.def next(~P: Type, ~S: Type, ~fits: S -> @+at:U32 -> @+n:U32 -> S & Bool, ~u32: S -> @+at:U32 -> S & U32, ~cut: S -> @+hs:U32 -> @+len:U32 -> S & P, ~skip: S -> @+hs:U32 -> @+len:U32 -> S, ~sum: P -> P & U32, +max: U32, s: S) -> Step<P, S>: next.any(~P, ~S, ~fits, ~u32, ~cut, ~skip, ~sum, max, fits(s, 0, 1))def recover.con(~a: Quant, ~P: Kind(a), ~S: Type, p: P, r: Recovery<a, P, S>) -> Recovery<a, P, S>: Recovery{rs, t, s} = r Recovery{Con{p, rs}, t, s}# Every frame from st on. Once n frames are taken, the next one is the last: the tail is Corrupt,# and rest starts after it. Callers give n at least the frame count, so this never happens.def recover.go(~a: Quant, ~P: Kind(a), ~S: Type, ~fits: S -> @+at:U32 -> @+n:U32 -> S & Bool, ~u32: S -> @+at:U32 -> S & U32, ~cut: S -> @+hs:U32 -> @+len:U32 -> S & P, ~skip: S -> @+hs:U32 -> @+len:U32 -> S, ~sum: P -> P & U32, n: Nat, +max: U32, st: Step<P, S>) -> Recovery<a, P, S>: match n st: case 0n End{s}: Recovery{Nil{}, Clean{}, s} case 0n Short{s}: Recovery{Nil{}, Torn{}, s} case 0n Bad{why, s}: Recovery{Nil{}, Corrupt{why}, s} case 0n Got{p, s}: Recovery{Con{p, Nil{}}, Corrupt{"frame budget exhausted"}, s} case 1n+m End{s}: Recovery{Nil{}, Clean{}, s} case 1n+m Short{s}: Recovery{Nil{}, Torn{}, s} case 1n+m Bad{why, s}: Recovery{Nil{}, Corrupt{why}, s} case 1n+m Got{p, s}: recover.con(~a, ~P, ~S, p, recover.go(~a, ~P, ~S, ~fits, ~u32, ~cut, ~skip, ~sum, m, max, next(~P, ~S, ~fits, ~u32, ~cut, ~skip, ~sum, max, s)))# Every committed record of s, in order.def recover(~a: Quant, ~P: Kind(a), ~S: Type, ~fits: S -> @+at:U32 -> @+n:U32 -> S & Bool, ~u32: S -> @+at:U32 -> S & U32, ~cut: S -> @+hs:U32 -> @+len:U32 -> S & P, ~skip: S -> @+hs:U32 -> @+len:U32 -> S, ~sum: P -> P & U32, n: Nat, +max: U32, s: S) -> Recovery<a, P, S>: recover.go(~a, ~P, ~S, ~fits, ~u32, ~cut, ~skip, ~sum, n, max, next(~P, ~S, ~fits, ~u32, ~cut, ~skip, ~sum, max, s))# step folded over every frame from st on, without a list of the records. n as in recover.go.def replay.go(~P: Type, ~S: Type, ~A: Type, ~fits: S -> @+at:U32 -> @+n:U32 -> S & Bool, ~u32: S -> @+at:U32 -> S & U32, ~cut: S -> @+hs:U32 -> @+len:U32 -> S & P, ~skip: S -> @+hs:U32 -> @+len:U32 -> S, ~sum: P -> P & U32, ~step: A -> P -> A, n: Nat, +max: U32, st: Step<P, S>, acc: A) -> Replay<A, S>: match n st: case 0n End{s}: Replay{acc, Clean{}, s} case 0n Short{s}: Replay{acc, Torn{}, s} case 0n Bad{why, s}: Replay{acc, Corrupt{why}, s} case 0n Got{p, s}: Replay{step(acc, p), Corrupt{"frame budget exhausted"}, s} case 1n+m End{s}: Replay{acc, Clean{}, s} case 1n+m Short{s}: Replay{acc, Torn{}, s} case 1n+m Bad{why, s}: Replay{acc, Corrupt{why}, s} case 1n+m Got{p, s}: replay.go(~P, ~S, ~A, ~fits, ~u32, ~cut, ~skip, ~sum, ~step, m, max, next(~P, ~S, ~fits, ~u32, ~cut, ~skip, ~sum, max, s), step(acc, p))def replay(~P: Type, ~S: Type, ~A: Type, ~fits: S -> @+at:U32 -> @+n:U32 -> S & Bool, ~u32: S -> @+at:U32 -> S & U32, ~cut: S -> @+hs:U32 -> @+len:U32 -> S & P, ~skip: S -> @+hs:U32 -> @+len:U32 -> S, ~sum: P -> P & U32, ~step: A -> P -> A, n: Nat, +max: U32, s: S, acc: A) -> Replay<A, S>: replay.go(~P, ~S, ~A, ~fits, ~u32, ~cut, ~skip, ~sum, ~step, n, max, next(~P, ~S, ~fits, ~u32, ~cut, ~skip, ~sum, max, s), acc)# The model: a list of octets. The laws are stated over it.# A model field holds its value in the first of its four cells and 0 in the others. Bytes holds it# as four little-endian octets. Both take four cells, so offsets agree; check.bend tests the octets.def list.fits(xs: List<&2, U32>, +at: U32, +n: U32) -> List<&2, U32> & Bool: +ys = xs (ys, Nat.is_le(Nat.add(U32.to_nat(at), U32.to_nat(n)), List.length(&2, U32, ys)))def list.field(xs: List<&2, U32>) -> U32: match xs: case Con{x, t}: x case Nil{}: 0def list.u32(xs: List<&2, U32>, +at: U32) -> List<&2, U32> & U32: +ys = xs (ys, list.field(List.drop(&2, U32, ys, U32.to_nat(at))))def list.cut(xs: List<&2, U32>, +hs: U32, +len: U32) -> List<&2, U32> & List<&2, U32>: +ys = xs (ys, List.take(&2, U32, List.drop(&2, U32, ys, U32.to_nat(hs)), U32.to_nat(len)))def list.skip(xs: List<&2, U32>, +hs: U32, +len: U32) -> List<&2, U32>: List.drop(&2, U32, xs, Nat.add(U32.to_nat(hs), U32.to_nat(len)))def crc.bit(n: Nat, +c: U32) -> U32: match n: case 0n: c case 1n+m: crc.bit(m, Bool.pick(U32, U32.is_eq((c .&. 1 : U32), 1), ((c >> 1n) .^. 3988292384 : U32), (c >> 1n : U32)))def crc.go(xs: List<&2, U32>, +c: U32) -> U32: match xs: case Nil{}: c case Con{+x, t}: crc.go(t, crc.bit(8n, (c .^. (x .&. 255 : U32) : U32)))# CRC-32 (ISO-HDLC, as zlib and Hash.crc32) of a list of octets, bit by bit.def list.crc(xs: List<&2, U32>) -> U32: U32.not(crc.go(xs, 4294967295))def list.sum(xs: List<&2, U32>) -> List<&2, U32> & U32: +ys = xs (ys, list.crc(ys))def list.next(+max: U32, xs: List<&2, U32>) -> Step<List<&2, U32>, List<&2, U32>>: next(~List<&2, U32>, ~List<&2, U32>, ~list.fits, ~list.u32, ~list.cut, ~list.skip, ~list.sum, max, xs)def list.recover(n: Nat, +max: U32, xs: List<&2, U32>) -> Recovery<&2, List<&2, U32>, List<&2, U32>>: recover(~&2, ~List<&2, U32>, ~List<&2, U32>, ~list.fits, ~list.u32, ~list.cut, ~list.skip, ~list.sum, n, max, xs)def list.replay(~A: Type, ~step: A -> List<&2, U32> -> A, n: Nat, +max: U32, xs: List<&2, U32>, acc: A) -> Replay<A, List<&2, U32>>: replay(~List<&2, U32>, ~List<&2, U32>, ~A, ~list.fits, ~list.u32, ~list.cut, ~list.skip, ~list.sum, ~step, n, max, xs, acc)def list.head(+len: U32, +sum: U32) -> List<&2, U32>: [len, 0, 0, 0, U32.not(len), 0, 0, 0, sum, 0, 0, 0]def list.frame(+p: List<&2, U32>) -> List<&2, U32>: List.append(&2, U32, list.head(U32.from_nat(List.length(&2, U32, p)), list.crc(p)), p)# The frames of rs, one after another: what appending each record writes.def list.log(rs: List<&2, List<&2, U32>>) -> List<&2, U32>: match rs: case Nil{}: Nil{} case Con{p, t}: List.append(&2, U32, list.frame(p), list.log(t))# The Bytes instance. A cursor reads b from pos; pos only moves forward, past whole frames.type Cur is Type: Cur{b: Bytes.Bytes, pos: U32}def cur.fits(c: Cur, +at: U32, +n: U32) -> Cur & Bool: Cur{Bytes.Bytes{+len, buf}, +pos} = c (Cur{Bytes.Bytes{len, buf}, pos}, Bytes.fits((len - pos : U32), at, n))def cur.field(m: Maybe<&2, U32>) -> U32: match m: case Some{x}: x case None{}: 0def cur.u32.fin(+pos: U32, r: Bytes.Bytes & Maybe<&2, U32>) -> Cur & U32: (b, m) = r (Cur{b, pos}, cur.field(m))def cur.u32(c: Cur, +at: U32) -> Cur & U32: Cur{b, +pos} = c cur.u32.fin(pos, Bytes.get.u32le(b, (pos + at : U32)))def cur.cut.fin(+pos: U32, r: Bytes.Bytes & Bytes.Bytes) -> Cur & Bytes.Bytes: (b, p) = r (Cur{b, pos}, p)def cur.cut(c: Cur, +hs: U32, +len: U32) -> Cur & Bytes.Bytes: Cur{b, +pos} = c cur.cut.fin(pos, Bytes.slice(b, (pos + hs : U32), len))def cur.skip(c: Cur, +hs: U32, +len: U32) -> Cur: Cur{b, +pos} = c Cur{b, (pos + hs + len : U32)}# ponytail: Hash.crc32 builds its 256-entry table per record; share one table if recovery gets hot.def cur.sum(p: Bytes.Bytes) -> Bytes.Bytes & U32: Hash.crc32(p)# Every frame of b holds at least 12 octets, so len / 12 + 1 steps reach the end.def fuel(+len: U32) -> Nat: U32.to_nat((len / 12 + 1 : U32))# step folded over every committed record of b, in order. rest.pos is where the committed prefix ends.def replay.bytes(~A: Type, ~step: A -> Bytes.Bytes -> A, +max: U32, b: Bytes.Bytes, acc: A) -> Replay<A, Cur>: Bytes.Bytes{+len, buf} = b replay(~Bytes.Bytes, ~Cur, ~A, ~cur.fits, ~cur.u32, ~cur.cut, ~cur.skip, ~cur.sum, ~step, fuel(len), max, Cur{Bytes.Bytes{len, buf}, 0}, acc)def frame.of(+len: U32, r: Bytes.Bytes & U32) -> Bytes.Bytes: (p, +sum) = r Bytes.append(Bytes.set.u32le(Bytes.set.u32le(Bytes.set.u32le(Bytes.new(12), 0, len), 4, U32.not(len)), 8, sum), p)# The frame that appending p writes.def frame(p: Bytes.Bytes) -> Bytes.Bytes: Bytes.Bytes{+len, buf} = p frame.of(len, Hash.crc32(Bytes.Bytes{len, buf}))# Effects. Each one finishes its write with fsync (F_FULLFSYNC on macOS in C) before it answers.# Opens path for reading and appending, creating it, and fsyncs its directory. Answers the file and# its whole contents. Fails with EFBIG when the file holds more than limit octets.def open.words(path: String, limit: U32) -> IO(Result<&1, &1, U32 & String, File & U32 & Array<U32>>): import "./effs/journal.c" import "./effs/journal.js"# Writes len octets of words at the end of file, then fsyncs it.def append.words(file: File, len: U32, words: Array<U32>) -> IO(File & Result<&1, &1, U32 & String, Unit>): import "./effs/journal.c" import "./effs/journal.js"# Cuts file to len octets, then fsyncs it.def truncate(file: File, len: U32) -> IO(File & Result<&1, &1, U32 & String, Unit>): import "./effs/journal.c" import "./effs/journal.js"# An open journal. max caps a record's length. end is the file's length. ok turns False when an# append fails: what reached the disk is then unknown, so appends stop until the journal is reopened.type Journal is Type: Journal{file: File, max: U32, end: U32, ok: Bool}def open.cut(r: File & Result<&1, &1, U32 & String, Unit>, +max: U32, +end: U32, -A: Type, acc: A) -> IO(Result<&1, &1, U32 & String, Journal & A>): match r: case (file, Fail{e}): do IO<Result<&1, &1, U32 & String, Journal & A>>: File.close(file) return Fail{e} case (file, Done{u}): do IO<Result<&1, &1, U32 & String, Journal & A>>: return Done{(Journal{file, max, end, True{}}, acc)}def open.tail(t: Tail, file: File, +max: U32, +pos: U32, -A: Type, acc: A) -> IO(Result<&1, &1, U32 & String, Journal & A>): match t: case Clean{}: do IO<Result<&1, &1, U32 & String, Journal & A>>: return Done{(Journal{file, max, pos, True{}}, acc)} case Torn{}: do IO<Result<&1, &1, U32 & String, Journal & A>>: r : File & Result<&1, &1, U32 & String, Unit> <- truncate(file, pos) open.cut(r, max, pos, A, acc) case Corrupt{why}: do IO<Result<&1, &1, U32 & String, Journal & A>>: File.close(file) return Fail{(22, "journal: corrupt frame at offset " ++ U32.show(pos) ++ ": " ++ why)}def open.replayed(file: File, +max: U32, -A: Type, r: Replay<A, Cur>) -> IO(Result<&1, &1, U32 & String, Journal & A>): Replay{acc, t, rest} = r Cur{b, +pos} = rest open.tail(t, file, max, pos, A, acc)def open.read(~A: Type, ~step: A -> Bytes.Bytes -> A, r: Result<&1, &1, U32 & String, File & U32 & Array<U32>>, +max: U32, acc: A) -> IO(Result<&1, &1, U32 & String, Journal & A>): match r: case Fail{e}: do IO<Result<&1, &1, U32 & String, Journal & A>>: return Fail{e} case Done{(file, (len, words))}: open.replayed(file, max, A, replay.bytes(~A, ~step, max, Bytes.Bytes{len, words}, acc))# Opens the journal at path and folds step over its committed records, from acc.# A torn tail is cut off and fsynced before open answers. A corrupt frame fails with EINVAL and# its offset; the file is left as it is. max caps a record's length; limit caps the file's size.def open(~A: Type, ~step: A -> Bytes.Bytes -> A, path: String, +max: U32, limit: U32, acc: A) -> IO(Result<&1, &1, U32 & String, Journal & A>): do IO<Result<&1, &1, U32 & String, Journal & A>>: r : Result<&1, &1, U32 & String, File & U32 & Array<U32>> <- open.words(path, limit) open.read(~A, ~step, r, max, acc)def append.back(+max: U32, +end: U32, +len: U32, r: File & Result<&1, &1, U32 & String, Unit>) -> Journal & Result<&1, &1, U32 & String, Unit>: match r: case (file, Done{u}): (Journal{file, max, (end + len : U32), True{}}, Done{u}) case (file, Fail{e}): (Journal{file, max, end, False{}}, Fail{e})def append.write(file: File, +max: U32, +end: U32, f: Bytes.Bytes) -> IO(Journal & Result<&1, &1, U32 & String, Unit>): Bytes.Bytes{+len, words} = f do IO<Journal & Result<&1, &1, U32 & String, Unit>>: r : File & Result<&1, &1, U32 & String, Unit> <- append.words(file, len, words) return append.back(max, end, len, r)def append.refuse(file: File, +max: U32, +end: U32, +ok: Bool, e: U32 & String) -> IO(Journal & Result<&1, &1, U32 & String, Unit>): do IO<Journal & Result<&1, &1, U32 & String, Unit>>: return (Journal{file, max, end, ok}, Fail{e})# The file stays under 4 GiB, so every offset and the next open's read fit a U32.def append.size(over: Bool, big: Bool, file: File, +max: U32, +end: U32, p: Bytes.Bytes) -> IO(Journal & Result<&1, &1, U32 & String, Unit>): match over big: case True{} _: append.refuse(file, max, end, True{}, (22, "journal: record over max")) case False{} True{}: append.refuse(file, max, end, True{}, (27, "journal: file would reach 4 GiB")) case False{} False{}: append.write(file, max, end, frame(p))def append.ok(ok: Bool, file: File, +max: U32, +end: U32, p: Bytes.Bytes) -> IO(Journal & Result<&1, &1, U32 & String, Unit>): match ok: case False{}: append.refuse(file, max, end, False{}, (5, "journal: an append failed; reopen the journal")) case True{}: Bytes.Bytes{+len, buf} = p append.size(U32.is_gt(len, max), Bool.or(U32.is_gt(end, 4294967283), U32.is_lt((4294967283 - end : U32), len)), file, max, end, Bytes.Bytes{len, buf})# Appends p as one frame and answers once it is fsynced: Done means durable, under the trust# assumptions in README.md. After a Fail the record may or may not survive a reopen.def append(j: Journal, p: Bytes.Bytes) -> IO(Journal & Result<&1, &1, U32 & String, Unit>): Journal{file, +max, +end, ok} = j append.ok(ok, file, max, end, p)def close(j: Journal) -> IO(Unit): Journal{file, max, end, ok} = j File.close(file)