mirror of https://github.com/gofiber/fiber.git
124 lines
2.6 KiB
Go
124 lines
2.6 KiB
Go
package etag
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import (
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"bytes"
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"hash/crc32"
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"math"
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"github.com/gofiber/fiber/v3"
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"github.com/valyala/bytebufferpool"
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)
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// New creates a new middleware handler
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func New(config ...Config) fiber.Handler {
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// Set default config
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cfg := configDefault(config...)
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var (
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normalizedHeaderETag = []byte("Etag")
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weakPrefix = []byte("W/")
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)
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const crcPol = 0xD5828281
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crc32q := crc32.MakeTable(crcPol)
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// Return new handler
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return func(c fiber.Ctx) error {
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// Don't execute middleware if Next returns true
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if cfg.Next != nil && cfg.Next(c) {
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return c.Next()
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}
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// Return err if next handler returns one
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if err := c.Next(); err != nil {
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return err
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}
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// Don't generate ETags for invalid responses
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if c.Response().StatusCode() != fiber.StatusOK {
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return nil
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}
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body := c.Response().Body()
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// Skips ETag if no response body is present
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if len(body) == 0 {
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return nil
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}
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// Skip ETag if header is already present
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if c.Response().Header.PeekBytes(normalizedHeaderETag) != nil {
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return nil
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}
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// Generate ETag for response
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bb := bytebufferpool.Get()
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defer bytebufferpool.Put(bb)
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// Enable weak tag
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if cfg.Weak {
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bb.Write(weakPrefix)
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}
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// Write ETag
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bb.WriteByte('"')
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bodyLength := len(body)
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if bodyLength > math.MaxUint32 {
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return c.SendStatus(fiber.StatusRequestEntityTooLarge)
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}
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bb.B = appendUint(bb.Bytes(), uint32(bodyLength))
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bb.WriteByte('-')
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bb.B = appendUint(bb.Bytes(), crc32.Checksum(body, crc32q))
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bb.WriteByte('"')
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etag := bb.Bytes()
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// Get ETag header from request
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clientEtag := c.Request().Header.Peek(fiber.HeaderIfNoneMatch)
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// Check if client's ETag is weak
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if bytes.HasPrefix(clientEtag, weakPrefix) {
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// Check if server's ETag is weak
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if bytes.Equal(clientEtag[2:], etag) || bytes.Equal(clientEtag[2:], etag[2:]) {
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// W/1 == 1 || W/1 == W/1
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c.Context().ResetBody()
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return c.SendStatus(fiber.StatusNotModified)
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}
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// W/1 != W/2 || W/1 != 2
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c.Response().Header.SetCanonical(normalizedHeaderETag, etag)
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return nil
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}
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if bytes.Contains(clientEtag, etag) {
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// 1 == 1
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c.Context().ResetBody()
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return c.SendStatus(fiber.StatusNotModified)
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}
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// 1 != 2
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c.Response().Header.SetCanonical(normalizedHeaderETag, etag)
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return nil
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}
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}
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// appendUint appends n to dst and returns the extended dst.
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func appendUint(dst []byte, n uint32) []byte {
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var b [20]byte
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buf := b[:]
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i := len(buf)
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var q uint32
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for n >= 10 {
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i--
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q = n / 10
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buf[i] = '0' + byte(n-q*10)
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n = q
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}
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i--
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buf[i] = '0' + byte(n)
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dst = append(dst, buf[i:]...)
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return dst
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}
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