From 13d37f875b25a78bbffb396a988751a9a2555d08 Mon Sep 17 00:00:00 2001
From: roger2hk <roger2hk@gmail.com>
Date: Wed, 10 Jul 2024 14:28:47 +0000
Subject: [PATCH] Only add the immutable `Cache-Control` header when the number
 of hash in the returned tile match the requested tile width

---
 cmd/example-mysql/main.go | 34 +++++++++++++++++++++++-----------
 1 file changed, 23 insertions(+), 11 deletions(-)

diff --git a/cmd/example-mysql/main.go b/cmd/example-mysql/main.go
index 202e59f1..51a1578e 100644
--- a/cmd/example-mysql/main.go
+++ b/cmd/example-mysql/main.go
@@ -73,10 +73,10 @@ func main() {
 	})
 
 	http.HandleFunc("GET /tile/{level}/{index...}", func(w http.ResponseWriter, r *http.Request) {
-		level, index, err := parseTileLevelIndex(r.PathValue("level"), r.PathValue("index"))
+		level, index, width, err := parseTileLevelIndexWidth(r.PathValue("level"), r.PathValue("index"))
 		if err != nil {
 			w.WriteHeader(http.StatusBadRequest)
-			if _, werr := w.Write([]byte(err.Error())); werr != nil {
+			if _, werr := w.Write([]byte(fmt.Sprintf("Malformed URL: %s", err.Error()))); werr != nil {
 				klog.Errorf("/tile/{level}/{index...}: %v", werr)
 			}
 			return
@@ -94,7 +94,12 @@ func main() {
 			return
 		}
 
-		w.Header().Set("Cache-Control", "public, max-age=31536000, immutable")
+		// Only add the immutable Cache-Control header when the number of hash in the returned tile match the requested tile width.
+		// This ensures the response will not be cached when returning a partial tile on a full tile request.
+		if len(tile)/32 == int(width) {
+			w.Header().Set("Cache-Control", "public, max-age=31536000, immutable")
+		}
+
 		if _, err := w.Write(tile); err != nil {
 			klog.Errorf("/tile/{level}/{index...}: %v", err)
 			return
@@ -120,19 +125,18 @@ func main() {
 	}
 }
 
-// parseTileLevelIndex takes level and index in string, validates and returns them in uint64.
-// Note that this doesn't return any of the partial tile component.
+// parseTileLevelWidthIndex takes level and index in string, validates and returns the level, index and width in uint64.
 //
 // Examples:
 // "/tile/0/x001/x234/067" means level 0 and index 1234067 of a full tile.
 // "/tile/0/x001/x234/067.p/8" means level 0, index 1234067 and width 8 of a partial tile.
-func parseTileLevelIndex(level, index string) (uint64, uint64, error) {
+func parseTileLevelIndexWidth(level, index string) (uint64, uint64, uint64, error) {
 	l, err := strconv.ParseUint(level, 10, 64)
 	if err != nil {
-		return 0, 0, fmt.Errorf("malformed URL: failed to parse tile level")
+		return 0, 0, 0, fmt.Errorf("failed to parse tile level")
 	}
 
-	var i uint64
+	var i, w uint64
 	switch indexPaths := strings.Split(index, "/"); len(indexPaths) {
 	// Full tile = 3
 	// Partial tile = 4
@@ -142,11 +146,19 @@ func parseTileLevelIndex(level, index string) (uint64, uint64, error) {
 		indexPath = strings.ReplaceAll(indexPath, ".p", "")
 		i, err = strconv.ParseUint(indexPath, 10, 64)
 		if err != nil {
-			return 0, 0, fmt.Errorf("malformed URL: failed to parse tile index")
+			return 0, 0, 0, fmt.Errorf("failed to parse tile index")
+		}
+
+		w = 256
+		if len(indexPaths) == 4 {
+			w, err = strconv.ParseUint(indexPaths[3], 10, 64)
+			if err != nil {
+				return 0, 0, 0, fmt.Errorf("failed to parse tile index")
+			}
 		}
 	default:
-		return 0, 0, fmt.Errorf("malformed URL: failed to parse tile index")
+		return 0, 0, 0, fmt.Errorf("failed to parse tile index")
 	}
 
-	return l, i, nil
+	return l, i, w, nil
 }