mirror of
https://github.com/MeshTender/MeshTender.git
synced 2026-09-02 10:03:43 +00:00
63 lines
1.9 KiB
Go
63 lines
1.9 KiB
Go
package web
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import (
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"crypto/sha256"
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"encoding/hex"
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"encoding/json"
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"net/http"
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"strconv"
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"strings"
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"time"
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)
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// ServeJSONCached marshals v to JSON and serves it with a short public cache
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// window plus a content-derived ETag, replying 304 Not Modified when the
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// client's If-None-Match already matches. It is for small, public, infrequently
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// changing payloads (e.g. the org map's repeater points): the ETag lets repeat
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// visitors and CDNs revalidate cheaply instead of re-downloading, and max-age
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// caps how stale a change can be.
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//
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// It returns any marshal error before writing a status so the caller can log it
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// via ServerError; once headers/body are written it returns nil.
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func ServeJSONCached(w http.ResponseWriter, r *http.Request, maxAge time.Duration, v any) error {
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b, err := json.Marshal(v)
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if err != nil {
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return err
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}
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sum := sha256.Sum256(b)
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// A strong, quoted ETag over the exact bytes served (RFC 7232). 128 bits of
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// the digest is ample to make collisions irrelevant here.
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etag := `"` + hex.EncodeToString(sum[:16]) + `"`
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h := w.Header()
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h.Set("Content-Type", "application/json; charset=utf-8")
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h.Set("Cache-Control", "public, max-age="+strconv.Itoa(int(maxAge.Seconds())))
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h.Set("ETag", etag)
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if matchesETag(r.Header.Get("If-None-Match"), etag) {
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w.WriteHeader(http.StatusNotModified)
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return nil
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}
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_, _ = w.Write(b)
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return nil
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}
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// matchesETag reports whether the If-None-Match header (a comma-separated list,
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// possibly "*" or weak "W/"-prefixed validators) matches etag. We compare
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// ignoring the weak prefix, which is safe for a cache-revalidation check.
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func matchesETag(ifNoneMatch, etag string) bool {
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if ifNoneMatch == "" {
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return false
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}
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if strings.TrimSpace(ifNoneMatch) == "*" {
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return true
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}
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want := strings.TrimPrefix(etag, "W/")
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for _, part := range strings.Split(ifNoneMatch, ",") {
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if strings.TrimPrefix(strings.TrimSpace(part), "W/") == want {
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return true
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}
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}
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return false
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}
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