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package static
import (
"hash/crc32"
"io"
"net/http"
"github.com/spiral/roadrunner/v2/utils"
)
const etag string = "Etag"
// weak Etag prefix
var weakPrefix = []byte(`W/`)
// CRC32 table
var crc32q = crc32.MakeTable(0x48D90782)
// SetEtag sets etag for the file
func SetEtag(weak bool, f http.File, name string, w http.ResponseWriter) {
// preallocate
calculatedEtag := make([]byte, 0, 64)
// write weak
if weak {
calculatedEtag = append(calculatedEtag, weakPrefix...)
calculatedEtag = append(calculatedEtag, '"')
calculatedEtag = appendUint(calculatedEtag, crc32.Checksum(utils.AsBytes(name), crc32q))
calculatedEtag = append(calculatedEtag, '"')
w.Header().Set(etag, utils.AsString(calculatedEtag))
return
}
// read the file content
body, err := io.ReadAll(f)
if err != nil {
return
}
// skip for 0 body
if len(body) == 0 {
return
}
calculatedEtag = append(calculatedEtag, '"')
calculatedEtag = appendUint(calculatedEtag, uint32(len(body)))
calculatedEtag = append(calculatedEtag, '-')
calculatedEtag = appendUint(calculatedEtag, crc32.Checksum(body, crc32q))
calculatedEtag = append(calculatedEtag, '"')
w.Header().Set(etag, utils.AsString(calculatedEtag))
}
// appendUint appends n to dst and returns the extended dst.
func appendUint(dst []byte, n uint32) []byte {
var b [20]byte
buf := b[:]
i := len(buf)
var q uint32
for n >= 10 {
i--
q = n / 10
buf[i] = '0' + byte(n-q*10)
n = q
}
i--
buf[i] = '0' + byte(n)
dst = append(dst, buf[i:]...)
return dst
}
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