fix(cli): attach file path and role to SBOM load errors

src/__tests__/cli.test.ts

@@ -1,5 +1,8 @@
 import { describe, it, expect } from 'vitest';
-import { parseArgs } from '../cli.js';
+import { mkdtemp, writeFile, rm } from 'node:fs/promises';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
+import { parseArgs, loadSbom } from '../cli.js';
 
 describe('parseArgs', () => {
   it('defaults to text format when no flag is given', () => {
@@ -38,3 +41,39 @@ describe('parseArgs', () => {
     expect(() => parseArgs(['old.json', 'new.json', '--bogus'])).toThrow(/Unknown option/);
   });
 });
+
+describe('loadSbom', () => {
+  it('wraps a missing file with its path and role', async () => {
+    await expect(loadSbom('/no/such/sbom-diff-missing.json', 'old')).rejects.toThrowError(
+      "Failed to read old SBOM '/no/such/sbom-diff-missing.json'",
+    );
+  });
+
+  it('wraps malformed JSON with its path and role', async () => {
+    const dir = await mkdtemp(join(tmpdir(), 'sbom-diff-'));
+    const path = join(dir, 'bad.json');
+    await writeFile(path, '{ not valid json');
+    try {
+      await expect(loadSbom(path, 'new')).rejects.toThrowError(
+        `Failed to parse new SBOM '${path}'`,
+      );
+    } finally {
+      await rm(dir, { recursive: true, force: true });
+    }
+  });
+
+  it('parses a valid SBOM file', async () => {
+    const dir = await mkdtemp(join(tmpdir(), 'sbom-diff-'));
+    const path = join(dir, 'good.json');
+    await writeFile(
+      path,
+      JSON.stringify({ bomFormat: 'CycloneDX', specVersion: '1.5', components: [] }),
+    );
+    try {
+      const sbom = await loadSbom(path, 'old');
+      expect(sbom.format).toBe('cyclonedx');
+    } finally {
+      await rm(dir, { recursive: true, force: true });
+    }
+  });
+});

src/cli.ts

@@ -11,7 +11,7 @@ import { pathToFileURL } from 'node:url';
 import { parse } from './parser.js';
 import { diff } from './diff.js';
 import { renderReport } from './reporter.js';
-import type { ReportFormat } from './types.js';
+import type { ReportFormat, SBOM } from './types.js';
 
 const USAGE = 'Usage: sbom-diff <old.json> <new.json> [--format text|json|markdown]';
 const VALID_FORMATS: ReportFormat[] = ['text', 'json', 'markdown'];
@@ -58,6 +58,36 @@ function assertFormat(value: string | undefined): ReportFormat {
   );
 }
 
+function errorMessage(err: unknown): string {
+  return err instanceof Error ? err.message : String(err);
+}
+
+/**
+ * Read and parse an SBOM file, attaching the file path and role to any failure.
+ *
+ * The underlying `readFile`/`JSON.parse` errors (e.g. `ENOENT` or
+ * `Expected property name or '}' in JSON at position 2`) don't say which of the
+ * two inputs failed or that the SBOM-load step is where it broke. In a CI gate a
+ * wrong or corrupt artifact is a common misconfiguration, so surface the path and
+ * whether the read or the parse failed instead of a bare low-level message.
+ *
+ * @param label human-readable role of the file, e.g. `old` or `new`.
+ * @throws if the file cannot be read or is not valid JSON / SBOM.
+ */
+export async function loadSbom(path: string, label: string): Promise<SBOM> {
+  let raw: string;
+  try {
+    raw = await readFile(path, 'utf-8');
+  } catch (err) {
+    throw new Error(`Failed to read ${label} SBOM '${path}': ${errorMessage(err)}`);
+  }
+  try {
+    return parse(raw);
+  } catch (err) {
+    throw new Error(`Failed to parse ${label} SBOM '${path}': ${errorMessage(err)}`);
+  }
+}
+
 async function main(): Promise<void> {
   const { positional, format } = parseArgs(process.argv.slice(2));
 
@@ -68,13 +98,11 @@ async function main(): Promise<void> {
 
   const [oldPath, newPath] = positional;
 
-  const [oldRaw, newRaw] = await Promise.all([
-    readFile(oldPath, 'utf-8'),
-    readFile(newPath, 'utf-8'),
+  const [oldSBOM, newSBOM] = await Promise.all([
+    loadSbom(oldPath, 'old'),
+    loadSbom(newPath, 'new'),
   ]);
 
-  const oldSBOM = parse(oldRaw);
-  const newSBOM = parse(newRaw);
   const report = diff(oldSBOM, newSBOM);
 
   console.log(renderReport(report, format));