jschoubben
a8be5acd80
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
88 lines
3.5 KiB
Go
88 lines
3.5 KiB
Go
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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