Slack: validate blocks input shape centrally

src/slack/blocks-input.test.ts

@@ -0,0 +1,41 @@
+import { describe, expect, it } from "vitest";
+import { parseSlackBlocksInput } from "./blocks-input.js";
+
+describe("parseSlackBlocksInput", () => {
+  it("returns undefined when blocks are missing", () => {
+    expect(parseSlackBlocksInput(undefined)).toBeUndefined();
+    expect(parseSlackBlocksInput(null)).toBeUndefined();
+  });
+
+  it("accepts blocks arrays", () => {
+    const parsed = parseSlackBlocksInput([{ type: "divider" }]);
+    expect(parsed).toEqual([{ type: "divider" }]);
+  });
+
+  it("accepts JSON blocks strings", () => {
+    const parsed = parseSlackBlocksInput(
+      '[{"type":"section","text":{"type":"mrkdwn","text":"hi"}}]',
+    );
+    expect(parsed).toEqual([{ type: "section", text: { type: "mrkdwn", text: "hi" } }]);
+  });
+
+  it("rejects invalid JSON", () => {
+    expect(() => parseSlackBlocksInput("{bad-json")).toThrow(/valid JSON/i);
+  });
+
+  it("rejects non-array payloads", () => {
+    expect(() => parseSlackBlocksInput({ type: "divider" })).toThrow(/must be an array/i);
+  });
+
+  it("rejects empty arrays", () => {
+    expect(() => parseSlackBlocksInput([])).toThrow(/at least one block/i);
+  });
+
+  it("rejects non-object blocks", () => {
+    expect(() => parseSlackBlocksInput(["not-a-block"])).toThrow(/must be an object/i);
+  });
+
+  it("rejects blocks without type", () => {
+    expect(() => parseSlackBlocksInput([{}])).toThrow(/non-empty string type/i);
+  });
+});

src/slack/blocks-input.ts

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+import type { Block, KnownBlock } from "@slack/web-api";
+
+const SLACK_MAX_BLOCKS = 50;
+
+function parseBlocksJson(raw: string) {
+  try {
+    return JSON.parse(raw);
+  } catch {
+    throw new Error("blocks must be valid JSON");
+  }
+}
+
+function assertBlocksArray(raw: unknown) {
+  if (!Array.isArray(raw)) {
+    throw new Error("blocks must be an array");
+  }
+  if (raw.length === 0) {
+    throw new Error("blocks must contain at least one block");
+  }
+  if (raw.length > SLACK_MAX_BLOCKS) {
+    throw new Error(`blocks cannot exceed ${SLACK_MAX_BLOCKS} items`);
+  }
+  for (const block of raw) {
+    if (!block || typeof block !== "object" || Array.isArray(block)) {
+      throw new Error("each block must be an object");
+    }
+    const type = (block as { type?: unknown }).type;
+    if (typeof type !== "string" || type.trim().length === 0) {
+      throw new Error("each block must include a non-empty string type");
+    }
+  }
+}
+
+export function parseSlackBlocksInput(raw: unknown): (Block | KnownBlock)[] | undefined {
+  if (raw == null) {
+    return undefined;
+  }
+  const parsed = typeof raw === "string" ? parseBlocksJson(raw) : raw;
+  assertBlocksArray(parsed);
+  return parsed as (Block | KnownBlock)[];
+}