perf: cache latest semvers resolved from remote (#42)

lib/x/async.ts

@@ -0,0 +1 @@
+export { Mutex } from "https://deno.land/x/[email protected]/mutex.ts";

src/dependency.ts

@@ -1,6 +1,8 @@
 import type { Maybe } from "../lib/types.ts";
+import { Mutex } from "../lib/x/async.ts";
 import type { Path, SemVerString } from "./types.ts";
-import { parseSemVer } from "./semver.ts";
+import { parseSemVer, SEMVER_REGEXP } from "./semver.ts";
+import { assertExists } from "../lib/std/assert.ts";
 
 export interface Dependency {
   name: string;
@@ -31,6 +33,23 @@ function parseProps(
 async function resolveLatestSemVer(
   url: URL,
 ): Promise<Maybe<SemVerString>> {
+  await LatestSemverCache.lock(url);
+  const result = await _resolve(url);
+  LatestSemverCache.unlock(url);
+  return result;
+}
+
+async function _resolve(
+  url: URL,
+): Promise<Maybe<SemVerString>> {
+  const cached = LatestSemverCache.get(url);
+  if (cached) {
+    return cached;
+  }
+  if (cached === null) {
+    // The dependency is already found to be up to date.
+    return;
+  }
   const props = parseProps(url);
   if (!props) {
     // The specifier is does not contain a semver.
@@ -42,7 +61,9 @@ async function resolveLatestSemVer(
         `https://registry.npmjs.org/${props.name}`,
       );
       if (!response.ok) {
-        throw new Error(`Failed to fetch npm registry: ${response.statusText}`);
+        throw new Error(
+          `Failed to fetch npm registry: ${response.statusText}`,
+        );
       }
       const json = await response.json();
       if (!json["dist-tags"]?.latest) {
@@ -53,9 +74,10 @@ async function resolveLatestSemVer(
       const latestSemVer: string = json["dist-tags"].latest;
       if (latestSemVer === props.version) {
         // The dependency is up to date
+        LatestSemverCache.set(url, null);
         return;
       }
-      return latestSemVer as SemVerString;
+      return LatestSemverCache.set(url, latestSemVer as SemVerString);
     }
     case "http:":
     case "https:": {
@@ -66,14 +88,19 @@ async function resolveLatestSemVer(
       await response.arrayBuffer();
       if (!response.redirected) {
         // The host did not redirect to a url with semver
+        LatestSemverCache.set(url, null);
         return;
       }
       const specifierWithLatestSemVer = response.url;
       if (specifierWithLatestSemVer === url.href) {
         // The dependency is up to date
+        LatestSemverCache.set(url, null);
         return;
       }
-      return parseSemVer(specifierWithLatestSemVer);
+      return LatestSemverCache.set(
+        url,
+        parseSemVer(specifierWithLatestSemVer) as SemVerString,
+      );
     }
     case "node:":
     case "file:":
@@ -83,3 +110,40 @@ async function resolveLatestSemVer(
       return;
   }
 }
+
+class LatestSemverCache {
+  static #mutex = new Map<string, Mutex>();
+  static #cache = new Map<string, SemVerString | null>();
+
+  static lock(url: URL): Promise<void> {
+    const key = this.getKey(url);
+    const mutex = this.#mutex.get(key) ??
+      this.#mutex.set(key, new Mutex()).get(key)!;
+    return mutex.acquire();
+  }
+
+  static unlock(url: URL): void {
+    const key = this.getKey(url);
+    const mutex = this.#mutex.get(key);
+    assertExists(mutex);
+    mutex.release();
+  }
+
+  static get(url: URL): SemVerString | null | undefined {
+    const key = this.getKey(url);
+    return this.#cache.get(key);
+  }
+
+  static set<T extends SemVerString | null>(
+    url: URL,
+    semver: T,
+  ): T {
+    const key = this.getKey(url);
+    this.#cache.set(key, semver);
+    return semver;
+  }
+
+  static getKey(url: URL): string {
+    return url.href.split(SEMVER_REGEXP)[0];
+  }
+}

src/semver.ts

@@ -2,7 +2,7 @@ import type { Maybe } from "../lib/types.ts";
 import type { SemVerString } from "./types.ts";
 
 // Ref: https://semver.org/#is-there-a-suggested-regular-expression-regex-to-check-a-semver-string
-const SEMVER_REGEXP =
+export const SEMVER_REGEXP =
   /@v?(0|[1-9]\d*)\.(0|[1-9]\d*)\.(0|[1-9]\d*)(?:-((?:0|[1-9]\d*|\d*[a-zA-Z-][0-9a-zA-Z-]*)(?:\.(?:0|[1-9]\d*|\d*[a-zA-Z-][0-9a-zA-Z-]*))*))?(?:\+([0-9a-zA-Z-]+(?:\.[0-9a-zA-Z-]+)*))?/g;
 
 export function parseSemVer(