51 lines
1.3 KiB
Go
51 lines
1.3 KiB
Go
package common
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import (
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"crypto/sha256"
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"encoding/hex"
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"reflect"
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"strings"
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)
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type digestAnchor struct{}
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func modulePath() string {
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return reflect.TypeFor[digestAnchor]().PkgPath()
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}
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var digestSeed = func() (s [sha256.Size]byte) {
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return sha256.Sum256([]byte(modulePath()))
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}()
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// ETagFor returns a weak ETag derived from the namespace and content.
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func ETagFor(namespace, content string) string {
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buf := make([]byte, 0, sha256.Size+1+len(namespace)+1+len(content))
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buf = append(buf, digestSeed[:]...)
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buf = append(buf, 0)
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buf = append(buf, namespace...)
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buf = append(buf, 0)
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buf = append(buf, content...)
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digest := sha256.Sum256(buf)
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return `W/"` + hex.EncodeToString(digest[:]) + `"`
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}
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// ETagMatches reports whether an If-None-Match header matches etag under weak
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// comparison (RFC 9110 §13.1.2): the W/ prefix is ignored on both sides, and
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// "*" matches everything.
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func ETagMatches(ifNoneMatch, etag string) bool {
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ifNoneMatch = strings.TrimSpace(ifNoneMatch)
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if ifNoneMatch == "" {
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return false
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}
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if ifNoneMatch == "*" {
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return true
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}
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etag = strings.TrimPrefix(etag, "W/")
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for candidate := range strings.SplitSeq(ifNoneMatch, ",") {
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if strings.TrimPrefix(strings.TrimSpace(candidate), "W/") == etag {
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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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