feat(middlewares): etag path-based middleware

Signed-off-by: James Elliott <james-d-elliott@users.noreply.github.com>

internal/middlewares/etag.go

@@ -0,0 +1,66 @@
+package middlewares
+
+import (
+	"bytes"
+	"crypto/sha256"
+	"net/url"
+	"sync"
+
+	"github.com/valyala/fasthttp"
+)
+
+func NewPathETag() *PathETag {
+	return &PathETag{
+		lock: &sync.Mutex{},
+		tags: map[string][]byte{},
+	}
+}
+
+type PathETag struct {
+	lock *sync.Mutex
+	tags map[string][]byte
+}
+
+func (m *PathETag) Middleware(next RequestHandler) RequestHandler {
+	hash := sha256.New()
+
+	return func(ctx *AutheliaCtx) {
+		var (
+			found bool
+			furl  *url.URL
+			err   error
+		)
+
+		if furl, err = ctx.GetXForwardedURL(); err == nil {
+			m.lock.Lock()
+
+			defer m.lock.Unlock()
+
+			if etag, ok := m.tags[furl.String()]; ok {
+				found = true
+
+				ctx.Response.Header.SetBytesV(fasthttp.HeaderETag, etag)
+				ctx.Response.Header.SetBytesK(headerCacheControl, "public, max-age=0, must-revalidate")
+
+				if bytes.Equal(etag, ctx.Request.Header.Peek(fasthttp.HeaderIfNoneMatch)) {
+					ctx.SetStatusCode(fasthttp.StatusNotModified)
+
+					return
+				}
+			}
+		}
+
+		next(ctx)
+
+		if !found && furl != nil {
+			if _, err = hash.Write(ctx.Response.Body()); err != nil {
+				return
+			}
+
+			m.tags[furl.String()] = hash.Sum(nil)
+
+			hash.Reset()
+		}
+	}
+
+}