👷 Add etag middleware

middleware/etag/etag.go

@@ -0,0 +1,121 @@
+package etag
+
+import (
+	"bytes"
+	"hash/crc32"
+
+	"github.com/gofiber/fiber/v2"
+	"github.com/gofiber/fiber/v2/internal/bytebufferpool"
+)
+
+// Config defines the config for middleware.
+type Config struct {
+	// Weak
+	Weak bool
+
+	// Next defines a function to skip this middleware when returned true.
+	//
+	// Optional. Default: nil
+	Next func(c *fiber.Ctx) bool
+}
+
+// ConfigDefault is the default config
+var ConfigDefault = Config{}
+
+var normalizedHeaderETag = []byte("Etag")
+var weakPrefix = []byte("W/")
+
+// New creates a new middleware handler
+func New(config ...Config) fiber.Handler {
+	// Set default config
+	cfg := ConfigDefault
+
+	// Override config if provided
+	if len(config) > 0 {
+		cfg = config[0]
+	}
+
+	// Return new handler
+	return func(c *fiber.Ctx) (err error) {
+		// Don't execute middleware if Next returns true
+		if cfg.Next != nil && cfg.Next(c) {
+			return c.Next()
+		}
+
+		// Return err if next handler returns one
+		if err = c.Next(); err != nil {
+			return
+		}
+
+		// Don't generate ETags for invalid responses
+		if c.Response().StatusCode() != fiber.StatusOK {
+			return
+		}
+		body := c.Response().Body()
+		// Skips ETag if no response body is present
+		if len(body) <= 0 {
+			return
+		}
+		// Get ETag header from request
+		clientEtag := c.Request().Header.Peek(fiber.HeaderIfNoneMatch)
+
+		// Generate ETag for response
+		crc32q := crc32.MakeTable(0xD5828281)
+
+		bb := bytebufferpool.Get()
+		defer bytebufferpool.Put(bb)
+
+		// Enable weak tag
+		if cfg.Weak {
+			_, _ = bb.Write(weakPrefix)
+		}
+
+		_ = bb.WriteByte('"')
+		appendUint(bb.Bytes(), uint32(len(body)))
+		_ = bb.WriteByte('-')
+		appendUint(bb.Bytes(), crc32.Checksum(body, crc32q))
+		_ = bb.WriteByte('"')
+		etag := bb.Bytes()
+
+		// Check if client's ETag is weak
+		if bytes.HasPrefix(clientEtag, weakPrefix) {
+			// Check if server's ETag is weak
+			if bytes.Equal(clientEtag[2:], etag) || bytes.Equal(clientEtag[2:], etag[2:]) {
+				// W/1 == 1 || W/1 == W/1
+				c.Context().ResetBody()
+				return c.SendStatus(fiber.StatusNotModified)
+			}
+			// W/1 != W/2 || W/1 != 2
+			c.Response().Header.SetCanonical(normalizedHeaderETag, etag)
+			return
+		}
+		if bytes.Contains(clientEtag, etag) {
+			// 1 == 1
+			c.Context().ResetBody()
+			return c.SendStatus(fiber.StatusNotModified)
+		}
+		// 1 != 2
+		c.Response().Header.SetCanonical(normalizedHeaderETag, etag)
+
+		return
+	}
+}
+
+// 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
+}

middleware/etag/etag_test.go

@@ -0,0 +1,32 @@
+package etag
+
+import (
+	"net/http/httptest"
+	"testing"
+
+	"github.com/valyala/fasthttp"
+
+	"github.com/gofiber/fiber/v2"
+	"github.com/gofiber/fiber/v2/utils"
+)
+
+// go test -run Test_ETag
+func Test_ETag(t *testing.T) {
+	i := 1<<32 - 1
+
+	t.Logf("%d, %d, %s", int32(i), uint32(i), fasthttp.AppendUint(nil, i))
+}
+
+// go test -run Test_ETag_Next
+func Test_ETag_Next(t *testing.T) {
+	app := fiber.New()
+	app.Use(New(Config{
+		Next: func(_ *fiber.Ctx) bool {
+			return true
+		},
+	}))
+
+	resp, err := app.Test(httptest.NewRequest("GET", "/", nil))
+	utils.AssertEqual(t, nil, err)
+	utils.AssertEqual(t, fiber.StatusNotFound, resp.StatusCode)
+}