fix: better error for missing web crypto

This PR simply detects missing web crypto and throws an error with an appropriate message.

This is a stepping stone that will help users understand the problem until we have time to do a refactor of this module and of all the modules that use it to enable optionally passing your own crypto implementation.

refs https://github.com/libp2p/js-libp2p-crypto/pull/149
refs https://github.com/libp2p/js-libp2p-crypto/pull/150
refs https://github.com/libp2p/js-libp2p-crypto/issues/105
refs https://github.com/ipfs/js-ipfs/issues/2153
refs https://github.com/ipfs/js-ipfs/issues/2017

License: MIT
Signed-off-by: Alan Shaw <alan@tableflip.io>

test/browser.js

@@ -0,0 +1,61 @@
+/* eslint-env mocha */
+'use strict'
+
+const chai = require('chai')
+const dirtyChai = require('dirty-chai')
+const expect = chai.expect
+chai.use(dirtyChai)
+const crypto = require('../')
+const webcrypto = require('../src/webcrypto')
+
+async function expectMissingWebCrypto (fn) {
+  try {
+    await fn()
+  } catch (err) {
+    expect(err.code).to.equal('ERR_MISSING_WEB_CRYPTO')
+    return
+  }
+  throw new Error('Expected missing web crypto error')
+}
+
+describe('Missing web crypto', () => {
+  let webcryptoGet
+  let rsaPrivateKey
+
+  before(async () => {
+    rsaPrivateKey = await crypto.keys.generateKeyPair('RSA', 512)
+  })
+
+  before(() => {
+    webcryptoGet = webcrypto.get
+    webcrypto.get = () => webcryptoGet({})
+  })
+
+  after(() => {
+    webcrypto.get = webcryptoGet
+  })
+
+  it('should error for hmac create when web crypto is missing', () => {
+    return expectMissingWebCrypto(() => crypto.hmac.create('SHA256', Buffer.from('secret')))
+  })
+
+  it('should error for generate ephemeral key pair when web crypto is missing', () => {
+    return expectMissingWebCrypto(() => crypto.keys.generateEphemeralKeyPair('P-256'))
+  })
+
+  it('should error for generate rsa key pair when web crypto is missing', () => {
+    return expectMissingWebCrypto(() => crypto.keys.generateKeyPair('rsa', 256))
+  })
+
+  it('should error for unmarshal RSA private key when web crypto is missing', () => {
+    return expectMissingWebCrypto(() => crypto.keys.unmarshalPrivateKey(crypto.keys.marshalPrivateKey(rsaPrivateKey)))
+  })
+
+  it('should error for sign RSA private key when web crypto is missing', () => {
+    return expectMissingWebCrypto(() => rsaPrivateKey.sign(Buffer.from('test')))
+  })
+
+  it('should error for verify RSA public key when web crypto is missing', () => {
+    return expectMissingWebCrypto(() => rsaPrivateKey.public.verify(Buffer.from('test'), Buffer.from('test')))
+  })
+})