From 87e9b31f4b2fb61178506b17b04dca094b4a559f Mon Sep 17 00:00:00 2001
From: Edoardo Cavazza <edoardo.cavazza@chialab.it>
Date: Tue, 15 Jul 2025 11:36:34 +0200
Subject: [PATCH] Add `child` method to `S3` cache adapter.

---
 .changeset/odd-candles-knock.md           |  5 +++++
 packages/utils/src/lib/server/cache/s3.ts | 23 ++++++++++++++++++++++-
 2 files changed, 27 insertions(+), 1 deletion(-)
 create mode 100644 .changeset/odd-candles-knock.md

diff --git a/.changeset/odd-candles-knock.md b/.changeset/odd-candles-knock.md
new file mode 100644
index 0000000..db5b131
--- /dev/null
+++ b/.changeset/odd-candles-knock.md
@@ -0,0 +1,5 @@
+---
+"@chialab/sveltekit-utils": patch
+---
+
+Add `child` method to `S3` cache adapter.
diff --git a/packages/utils/src/lib/server/cache/s3.ts b/packages/utils/src/lib/server/cache/s3.ts
index 5bcbab5..bc8c125 100644
--- a/packages/utils/src/lib/server/cache/s3.ts
+++ b/packages/utils/src/lib/server/cache/s3.ts
@@ -18,6 +18,13 @@ type S3CacheOptions = {
 	defaultJitter?: JitterMode | JitterFn;
 };
 
+function joinParts(...prefixes: string[]): string {
+	return prefixes
+		.filter((p) => p && p.length > 0)
+		.map((p) => p.replace(/\/+$/, '').replace(/^\/+/, ''))
+		.join('/');
+}
+
 export class S3Cache<V extends Uint8Array = Uint8Array> extends BaseCache<V> {
 	readonly #options: S3CacheOptions;
 	readonly #client: S3;
@@ -39,7 +46,21 @@ export class S3Cache<V extends Uint8Array = Uint8Array> extends BaseCache<V> {
 	}
 
 	#buildKey(key: string): string {
-		return `${this.#options.keyPrefix ?? ''}${key}`;
+		return joinParts(this.#options.keyPrefix ?? '', key);
+	}
+
+	public child<V2 extends V>(
+		keyPrefix: string,
+		options?: Partial<Omit<S3CacheOptions, 'bucket' | 'keyPrefix'>>,
+	): S3Cache<V2> {
+		return new S3Cache<V2>(
+			{
+				...this.#options,
+				...options,
+				keyPrefix: joinParts(this.#options.keyPrefix ?? '', keyPrefix),
+			},
+			this.#client,
+		);
 	}
 
 	public async get(key: string): Promise<V | undefined> {