filer: derive a view-specific validator for format views

Views validated conditional requests against the media entry's ETag,
so re-ingesting identical bytes with a different sidecar changed the
playlist and segment boundaries while clients kept getting 304s. Fold
the encoded layout and the request's view parameters into the ETag the
view serves and checks.

weed/server/filer_server_format.go

@@ -2,6 +2,7 @@ package weed_server
 
 import (
 	"context"
+	"crypto/md5"
 	"errors"
 	"fmt"
 	"io"
@@ -400,7 +401,17 @@ func (fs *FilerServer) serveFormatView(ctx context.Context, w http.ResponseWrite
 		http.Error(w, "format layout is stale", http.StatusNotFound)
 		return
 	}
-	if checkPreconditions(w, r, entry) {
+
+	// The view's validator must change when the layout or the requested
+	// representation changes, even when the media bytes and their MD5 do not:
+	// re-ingesting with a different sidecar must invalidate cached views.
+	viewIdentity := md5.New()
+	viewIdentity.Write([]byte(filer.ETagEntry(entry)))
+	viewIdentity.Write(encoded)
+	viewIdentity.Write([]byte(r.URL.RawQuery))
+	viewEntry := *entry
+	viewEntry.Md5 = viewIdentity.Sum(nil)
+	if checkPreconditions(w, r, &viewEntry) {
 		return
 	}
 
@@ -425,7 +436,7 @@ func (fs *FilerServer) serveFormatView(ctx context.Context, w http.ResponseWrite
 	// view responses are whole documents or whole extents
 	w.Header().Set("Accept-Ranges", "none")
 	w.Header().Set("Content-Type", plan.ContentType)
-	SetEtag(w, filer.ETagEntry(entry))
+	SetEtag(w, filer.ETagEntry(&viewEntry))
 
 	if plan.Body != nil {
 		w.Header().Set("Content-Length", strconv.Itoa(len(plan.Body)))