add strongestHashAlgorithms getter

src/index.ts

@@ -183,6 +183,14 @@ export class IntegrityMetadataSet {
     return this.#set.length;
   }
 
+  get strongestHashAlgorithms(): ReadonlyArray<HashAlgorithm> {
+    const strongestHashAlgorithms = this.strongest
+      .map(({ alg }) => alg as HashAlgorithm)
+      .filter(Boolean);
+
+    return [...new Set(strongestHashAlgorithms)];
+  }
+
   join(separator = " "): string {
     return this.#set.map(String).join(separator);
   }

test/integrity-metadata-set/strongest-hash-algorithms.js

@@ -0,0 +1,39 @@
+import assert from "node:assert";
+import { test } from "node:test";
+import { IntegrityMetadataSet } from "../../dist/index.js";
+
+test("pick the strongest hash algorithms", function () {
+  const integrityMetadataSet = new IntegrityMetadataSet(`
+sha256-MV9b23bQeMQ7isAGTkoBZGErH853yGk0W/yUx1iU7dM=
+sha384-VbxVaw0v4Pzlgrpf4Huq//A1ZTY4x6wNVJTCpkwL6hzFczHHwSpFzbyn9MNKCJ7r
+sha512-wVJ82JPBJHc9gRkRlwyP5uhX1t9dySJr2KFgYUwM2WOk3eorlLt9NgIe+dhl1c6ilKgt1JoLsmn1H256V/eUIQ==
+`);
+
+  assert.deepEqual(integrityMetadataSet.strongestHashAlgorithms, ["sha512"]);
+});
+
+test("if there are no supported algorithms, return the empty set", function () {
+  const integrityMetadataSet = new IntegrityMetadataSet(`
+sha1-lDpwLQbzRZmu4fjajvn3KWAx1pk=
+md5-bNNVbesNpUvKBgtMOUeYOQ==
+`);
+
+  assert.deepEqual(integrityMetadataSet.strongestHashAlgorithms, []);
+});
+
+test("custom getPrioritizedHashAlgorithm function can be used", function () {
+  const integrityMetadataSet = new IntegrityMetadataSet(
+    `
+sha256-MV9b23bQeMQ7isAGTkoBZGErH853yGk0W/yUx1iU7dM=
+sha384-VbxVaw0v4Pzlgrpf4Huq//A1ZTY4x6wNVJTCpkwL6hzFczHHwSpFzbyn9MNKCJ7r
+sha512-wVJ82JPBJHc9gRkRlwyP5uhX1t9dySJr2KFgYUwM2WOk3eorlLt9NgIe+dhl1c6ilKgt1JoLsmn1H256V/eUIQ==
+`,
+    {
+      getPrioritizedHashAlgorithm() {
+        return "sha384";
+      },
+    },
+  );
+
+  assert.deepEqual(integrityMetadataSet.strongestHashAlgorithms, ["sha384"]);
+});