Recovery3 item 1: a seat verb's chunks in mesh-sdk's one form, sent and received
The bus module sends snapshot-get's file in chunks and the recovery module receives them; both now use buscalls.SeatChunks (subjects, body, receive), so the form lives once in mesh-sdk. Builds: design 47 G §681, A-64, A-139 Claude-Session: https://claude.ai/code/session_01NcbgfGKaxw984XyAPfLm4h
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package buscalls
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import (
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"encoding/json"
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"errors"
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"fmt"
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"io"
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"strconv"
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"time"
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)
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// SeatChunks is the send of one seat verb's answer file in chunks (design 47 G §681, A-64, A-139), a verb whose seat
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// definition says `chunks: true`: the holder's process sends the nth chunk on mesh.seat.<seat>.chunk.<verb>.<call>.<n>,
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// and the caller acknowledges it on mesh.seat.<seat>.ack.<verb>.<call>.<n> within SeatAckWithin before the next is sent.
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// `call` is the 128 random bits the caller chose. The holder sends with it and the caller receives with it: one form.
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type SeatChunks struct {
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Seat, Verb, Call string
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}
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// SeatChunkBytes is at most what one chunk carries: 512 KiB.
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const SeatChunkBytes = 512 << 10
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// SeatAckWithin is how long the holder waits for a chunk's acknowledgement, and so how long a caller waits for the next chunk.
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const SeatAckWithin = 30 * time.Second
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// SeatChunk is the body of one chunk: its number from 1, how many there are, and its bytes.
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type SeatChunk struct {
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N int64 `json:"n"`
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Of int64 `json:"of"`
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Data []byte `json:"data"`
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}
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// Chunk is the subject of the nth chunk.
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func (c SeatChunks) Chunk(n int64) string {
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return "mesh.seat." + c.Seat + ".chunk." + c.Verb + "." + c.Call + "." + strconv.FormatInt(n, 10)
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}
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// Ack is the subject the nth chunk is acknowledged on.
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func (c SeatChunks) Ack(n int64) string {
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return "mesh.seat." + c.Seat + ".ack." + c.Verb + "." + c.Call + "." + strconv.FormatInt(n, 10)
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}
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// Chunks is every chunk subject of this call: what a caller subscribes to before it asks the verb.
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func (c SeatChunks) Chunks() string {
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return "mesh.seat." + c.Seat + ".chunk." + c.Verb + "." + c.Call + ".*"
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}
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// SeatAcks is every acknowledgement of a verb's sends: what the holder subscribes to.
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func SeatAcks(seat, verb string) string {
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return "mesh.seat." + seat + ".ack." + verb + ".*.*"
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}
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// ErrSeatChunkMissed is a chunk that did not come within its bound: the holder ended the send.
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var ErrSeatChunkMissed = errors.New("a chunk did not come within its bound, so the send ended")
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// Receive reads `of` chunks in order, writes each one's bytes to w and acknowledges it before the next is sent. next
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// yields the subject and body of the next chunk heard on Chunks(), or ErrSeatChunkMissed at its bound (SeatAckWithin);
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// ack publishes on a subject. A chunk out of order, of another count or on another subject ends the receive, and so the
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// send, since it is never acknowledged. It answers the bytes written.
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func (c SeatChunks) Receive(of int64, next func() (subject string, body []byte, err error), ack func(subject string) error, w io.Writer) (int64, error) {
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var written int64
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for n := int64(1); n <= of; n++ {
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subject, body, err := next()
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if err != nil {
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return written, fmt.Errorf("chunk %d of %d: %w", n, of, err)
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}
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if subject != c.Chunk(n) {
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return written, fmt.Errorf("chunk %d of %d came on %s, not %s", n, of, subject, c.Chunk(n))
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}
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var ch SeatChunk
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if err := json.Unmarshal(body, &ch); err != nil {
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return written, fmt.Errorf("chunk %d of %d does not read: %w", n, of, err)
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}
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if ch.N != n || ch.Of != of {
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return written, fmt.Errorf("chunk %d of %d says it is %d of %d", n, of, ch.N, ch.Of)
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}
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k, err := w.Write(ch.Data)
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written += int64(k)
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if err != nil {
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return written, fmt.Errorf("chunk %d of %d cannot be written: %w", n, of, err)
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}
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if err := ack(c.Ack(n)); err != nil {
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return written, fmt.Errorf("chunk %d of %d cannot be acknowledged: %w", n, of, err)
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}
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}
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return written, nil
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}
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@@ -0,0 +1,72 @@
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package buscalls
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import (
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"bytes"
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"encoding/json"
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"errors"
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"strings"
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"testing"
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)
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// TestSeatChunksReceive: the chunks of a send are written in order and each acknowledged before the next; a missed,
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// misplaced or miscounted chunk ends the receive unacknowledged (design 47 G §681, A-139).
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func TestSeatChunksReceive(t *testing.T) {
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c := SeatChunks{Seat: "mesh-broker", Verb: "snapshot-get", Call: "0123456789abcdef0123456789abcdef"}
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if c.Chunk(2) != "mesh.seat.mesh-broker.chunk.snapshot-get.0123456789abcdef0123456789abcdef.2" ||
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c.Ack(2) != "mesh.seat.mesh-broker.ack.snapshot-get.0123456789abcdef0123456789abcdef.2" ||
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c.Chunks() != "mesh.seat.mesh-broker.chunk.snapshot-get.0123456789abcdef0123456789abcdef.*" ||
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SeatAcks("mesh-broker", "snapshot-get") != "mesh.seat.mesh-broker.ack.snapshot-get.*.*" {
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t.Fatalf("subjects: %s %s %s", c.Chunk(2), c.Ack(2), c.Chunks())
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}
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type sent struct {
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subject string
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body SeatChunk
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missed bool
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}
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good := []sent{{subject: c.Chunk(1), body: SeatChunk{N: 1, Of: 3, Data: []byte("ab")}},
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{subject: c.Chunk(2), body: SeatChunk{N: 2, Of: 3, Data: []byte("cd")}},
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{subject: c.Chunk(3), body: SeatChunk{N: 3, Of: 3, Data: []byte("e")}}}
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for _, tc := range []struct {
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name string
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sends []sent
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want string
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acks int
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err string
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}{
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{name: "three chunks", sends: good, want: "abcde", acks: 3},
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{name: "a missed chunk", sends: append(good[:1:1], sent{missed: true}), want: "ab", acks: 1, err: "chunk 2 of 3"},
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{name: "out of order", sends: []sent{good[1]}, acks: 0, err: "came on"},
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{name: "another count", sends: []sent{{subject: c.Chunk(1), body: SeatChunk{N: 1, Of: 2, Data: []byte("x")}}}, err: "says it is 1 of 2"},
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} {
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t.Run(tc.name, func(t *testing.T) {
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i, acks := 0, 0
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next := func() (string, []byte, error) {
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if i >= len(tc.sends) || tc.sends[i].missed {
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return "", nil, ErrSeatChunkMissed
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}
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s := tc.sends[i]
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i++
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body, _ := json.Marshal(s.body)
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return s.subject, body, nil
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}
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ack := func(subject string) error {
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acks++
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if subject != c.Ack(int64(acks)) {
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t.Fatalf("ack %d on %s", acks, subject)
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}
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return nil
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}
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var out bytes.Buffer
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n, err := c.Receive(3, next, ack, &out)
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if tc.err == "" && err != nil || tc.err != "" && (err == nil || !strings.Contains(err.Error(), tc.err)) {
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t.Fatalf("err %v, want %q", err, tc.err)
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}
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if tc.name == "a missed chunk" && !errors.Is(err, ErrSeatChunkMissed) {
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t.Fatalf("a missed chunk is not ErrSeatChunkMissed: %v", err)
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}
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if out.String() != tc.want || n != int64(len(tc.want)) || acks != tc.acks {
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t.Fatalf("wrote %q (%d), %d acks; want %q, %d acks", out.String(), n, acks, tc.want, tc.acks)
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}
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})
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}
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}
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