feat: disambiguate errors (#9)

Author: Alan Shaw

src/index.js

@@ -32,22 +32,37 @@ export const hashMap = new Map(
   ].map(hash => [hash.code, hash])
 )
 
+/** The multihash hasher is not supported by this library. */
+export class UnsupportedHashError extends Error {
+  /** @param {number} code */
+  constructor (code) {
+    super(`multihash code ${code} is not supported`)
+  }
+}
+
+/** The bytes did not hash to the same value as the passed multihash. */
+export class HashMismatchError extends Error {
+  constructor () {
+    super('CID hash does not match bytes')
+  }
+}
+
 /**
  * Validates IPLD block bytes.
  * @param {Block} block
  */
 export function validateBlock (block) {
   const hasher = hashMap.get(block.cid.multihash.code)
   if (!hasher) {
-    throw new Error(`multihash code ${block.cid.multihash.code} is not supported`)
+    throw new UnsupportedHashError(block.cid.multihash.code)
   }
 
   const result = hasher.digest(block.bytes)
 
   /** @param {import('multiformats/hashes/interface').MultihashDigest} h */
   const compareDigests = h => {
     if (!equals(h.digest, block.cid.multihash.digest)) {
-      throw new Error('CID hash does not match bytes')
+      throw new HashMismatchError()
     }
   }
 

test/test.spec.js

@@ -2,8 +2,9 @@ import test from 'ava'
 import * as pb from '@ipld/dag-pb'
 import { CID } from 'multiformats/cid'
 import { CarWriter, CarBlockIterator } from '@ipld/car'
+import { blake2b512 } from '@multiformats/blake2/blake2b'
 
-import { validateBlock, hashMap } from '../src/index.js'
+import { validateBlock, hashMap, HashMismatchError, UnsupportedHashError } from '../src/index.js'
 
 const bytes = pb.encode({ Data: new Uint8Array([1, 2, 3]), Links: [] })
 
@@ -37,7 +38,24 @@ for (const [code, hasher] of hashMap) {
     const reader = await CarBlockIterator.fromIterable(out)
 
     for await (const block of reader) {
-      t.throwsAsync(async () => validateBlock(block))
+      const err = await t.throwsAsync(async () => validateBlock(block))
+      t.true(err instanceof HashMismatchError)
     }
   })
 }
+
+test('throws when validating blocks with unsupported hashers', async (t) => {
+  const hash = await blake2b512.digest(bytes)
+  const cid = CID.create(1, pb.code, hash)
+
+  const { writer, out } = CarWriter.create([cid])
+  writer.put({ cid, bytes })
+  writer.close()
+
+  const reader = await CarBlockIterator.fromIterable(out)
+
+  for await (const block of reader) {
+    const err = await t.throwsAsync(async () => validateBlock(block))
+    t.true(err instanceof UnsupportedHashError)
+  }
+})