fix: restore 255 char limit iaw oci distribution spec

Previous image name parsing enforced a strict 255 character limit. This
commit restores a check on image name length that adhears to the
language in the OCI image distribution specification.

Author: d3vco

lib/image-reference.ts

@@ -44,6 +44,11 @@ export class ParsedImageReference {
   /**
    * Rebuilds the image reference string from repository, registry, tag, and digest.
    * Format: [registry/]repository[:tag][@digest]
+   *
+   * Note: This does not normalize the reference for pulling. Specifically, it does not
+   * add the default "library/" namespace or the "registry-1.docker.io" registry for
+   * Docker Hub images. To get the components for pulling, use `registryForPull`,
+   * `normalizedRepository`, and `tailReferenceForPull`.
    */
   public toString(): string {
     let ref = "";
@@ -149,12 +154,21 @@ export function parseImageReference(reference: string): ParsedImageReference {
     repository = repository.slice(registry.length + 1);
   }
 
-  return new ParsedImageReference({
+  const parsed = new ParsedImageReference({
     repository,
     registry,
     tag: tag ?? undefined,
     digest: digest ?? undefined,
   });
+
+  // According to the OCI distribution specification: "Many clients impose a limit of
+  // 255 characters on the length of the concatenation of the registry hostname
+  // (and optional port), `/`, and `<name>` value."
+  if (parsed.fullName.length > 255) {
+    throw new Error("image repository name is more than 255 characters");
+  }
+
+  return parsed;
 }
 
 /**

test/lib/image-reference.spec.ts

@@ -184,6 +184,33 @@ describe("image-reference", () => {
         );
       });
 
+      it("throws for registry and repository name exceeding 255 characters", () => {
+        const registry = "example.com/";
+        const longName = "a".repeat(256 - registry.length);
+        expect(() => parseImageReference(registry + longName)).toThrow(
+          "image repository name is more than 255 characters",
+        );
+      });
+
+      it("allows registry and repository name of exactly 255 characters", () => {
+        const registry = "example.com/";
+        const name = "a".repeat(255 - registry.length);
+        expect(parseImageReference(registry + name)).toMatchObject({
+          registry: "example.com",
+          repository: name,
+        });
+      });
+
+      it("allows registry and repository name of exactly 255 characters with a digest", () => {
+        const registry = "example.com/";
+        const name = "a".repeat(255 - registry.length);
+        const digest = "@" + validSha256;
+        expect(parseImageReference(registry + name + digest)).toMatchObject({
+          registry: "example.com",
+          repository: name,
+        });
+      });
+
       it("throws for invalid digest (too short)", () => {
         expect(() => parseImageReference("nginx@sha256:abc")).toThrow(
           "invalid image reference format",