mirror of
https://github.com/Kpa-clawbot/meshcore-analyzer.git
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Alex BandClaude Opus 5.5
38ed9d6ce6
## Problem
`pathLen` is how `pickBestObservation` chooses each transmission's best
(longest-path) observation, so it runs for every observation on every
load and ingest, and again from the resolved-path index. It decoded the
path JSON into a `[]interface{}` only to take its length.
## Change
- `countStringArray` counts the usual array of plain hex strings in
place, with no allocation (helpers `skipJSONSpace` and
`skipPlainJSONString`).
- Anything else falls back to the decoder exactly as before: escapes,
non-string elements, `null`, or malformed input. So the result is always
what decoding gives, including 0 for invalid JSON.
## Perf justification (AGENTS.md rule 0)
- **Complexity.** O(len(path_json)), a single pass with no allocation.
The old version was also linear but went through reflection and
allocated per element.
- **Scale.** It runs once per observation on every load and ingest (400k
observations in a busy regional network's 7-day window), plus each time
the best observation is re-picked.
Throwaway benchmark (not committed), current master vs this branch:
| `path_json` | master | this PR |
|---|---|---|
| `[]` | 215 ns, 32 B, 2 allocs | 4 ns, 0 allocs |
| 6 hops, 1-byte | 1825 ns, 488 B, 18 allocs | 27 ns, 0 allocs |
| 10 hops, 3-byte | 2815 ns, 936 B, 27 allocs | 72 ns, 0 allocs |
On a copy of that 7-day window:
| | master | this PR |
|---|---|---|
| allocated over startup (the whole server) | 5.41 GB | 5.10 GB |
| server CPU over the run | 175.6 s | 169.2 s |
`pathLen` accounted for about 275 MB of the startup allocations.
## Tests
- `TestPathLenDoesNotAllocate`: zero allocations for typical paths. Red
commit first (2–11 allocations), then green.
- `TestPathLenMatchesDecoding` compares the result with `json.Unmarshal`
into `[]interface{}` on 27 edge cases and 20,000 random inputs built
from JSON punctuation, escapes, `null`, objects and numbers.
- `cd cmd/server && go test ./...` passes.
- SonarQube: quality gate passed, no issues on added lines.
Backend only: no UI, API shape or config change.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
https://claude.ai/code/session_01KaR4xu8gVykQBkH8yG8m6H
---------
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
58 lines
1.8 KiB
Go
58 lines
1.8 KiB
Go
package main
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import (
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"encoding/json"
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"math/rand"
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"strings"
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"testing"
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)
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func pathLenReference(pathJSON string) int {
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if pathJSON == "" {
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return 0
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}
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var hops []interface{}
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if json.Unmarshal([]byte(pathJSON), &hops) != nil {
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return 0
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}
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return len(hops)
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}
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// pathLen picks the best observation of every transmission, so it runs for
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// every observation on every load and ingest. Decoding the path into a
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// []interface{} just to count it allocated about 275MB over one startup on a
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// week of a busy network. A path is an array of hex strings: those are
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// counted without decoding.
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func TestPathLenDoesNotAllocate(t *testing.T) {
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for _, pj := range []string{`[]`, `["aa"]`, `["a1b2c3","d4e5f6","0708"]`, ` [ "aa" , "bb" ] `} {
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if n := testing.AllocsPerRun(100, func() { _ = pathLen(pj) }); n != 0 {
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t.Errorf("pathLen(%s) allocates %.0f times, want 0", pj, n)
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}
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}
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}
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// pathLen counts exactly what decoding would, including the odd cases it
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// hands to the decoder.
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func TestPathLenMatchesDecoding(t *testing.T) {
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cases := []string{
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"", "[]", "[ ]", `["aa"]`, `["aa","bb"]`, ` ["aa" ,"bb" ]`, "\t[\n\"aa\"\r]\n",
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`["aa",]`, `["aa"`, `["aa"]x`, `[,]`, `["a\"b","c"]`, `["é"]`, `["a\\"]`,
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`[1,2,3]`, `["aa",null]`, `[["aa"]]`, `{"a":1}`, `"aa"`, `null`, `[""]`, `["",""]`,
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"[\"a\x01\"]", `["aa" "bb"]`, `["aa",,"bb"]`, "[\"\xff\xfe\"]", `[ "aa" , ]`,
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}
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rng := rand.New(rand.NewSource(1))
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alphabet := []string{`[`, `]`, `"`, `,`, ` `, `a`, `1`, `\`, `n`, `{`, `}`, `:`}
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for i := 0; i < 20000; i++ {
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var b strings.Builder
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for j := rng.Intn(12); j >= 0; j-- {
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b.WriteString(alphabet[rng.Intn(len(alphabet))])
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}
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cases = append(cases, b.String())
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}
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for _, pj := range cases {
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if got, want := pathLen(pj), pathLenReference(pj); got != want {
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t.Fatalf("pathLen(%q) = %d, decoding gives %d", pj, got, want)
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}
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}
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}
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