feat: make adding a custom codec possible

With this change it is possible to add a custom codec via `addCodec()`.

Example:

    const name = 'my-custom-codec'
    const code = Buffer.from('ffff', 'hex')
    multicodec.addCodec(name, code)

Author: vmx

src/index.js

@@ -77,3 +77,14 @@ exports.getCodeVarint = (codecName) => {
   }
   return code
 }
+
+/**
+ * Add a new codec
+ * @param {string} name Name of the codec
+ * @param {Buffer} code The code of the codec
+ * @returns {void}
+ */
+exports.addCodec = (name, code) => {
+  codecNameToCodeVarint[name] = util.varintBufferEncode(code)
+  codeToCodecName[code.toString('hex')] = name
+}

test/multicodec.spec.js

@@ -6,6 +6,7 @@ const dirtyChai = require('dirty-chai')
 const expect = chai.expect
 chai.use(dirtyChai)
 const multicodec = require('../src')
+const util = require('../src/util')
 
 describe('multicodec', () => {
   it('add prefix through multicodec (string)', () => {
@@ -34,6 +35,15 @@ describe('multicodec', () => {
     expect(code).to.eql(Buffer.from('1b', 'hex'))
   })
 
+  it('works with custom codec when getting the code', () => {
+    const name = 'my-custom-codec1'
+    const code = Buffer.from('ffff', 'hex')
+    multicodec.addCodec(name, code)
+
+    const codeVarint = multicodec.getCodeVarint(name)
+    expect(util.varintBufferDecode(codeVarint)).to.deep.eql(code)
+  })
+
   it('throws error on unknown codec name when getting the code', () => {
     expect(() => {
       multicodec.getCodeVarint('this-codec-doesnt-exist')
@@ -42,6 +52,27 @@ describe('multicodec', () => {
     )
   })
 
+  it('works with custom codec when getting the codec', () => {
+    const name = 'my-custom-codec2'
+    const code = Buffer.from('ffff', 'hex')
+    multicodec.addCodec(name, code)
+
+    const buf = Buffer.from('hey')
+    const prefixedBuf = multicodec.addPrefix(name, buf)
+    expect(multicodec.getCodec(prefixedBuf)).to.eql(name)
+  })
+
+  it('throws error on unknown codec when adding as prefix', () => {
+    const name = 'this-codec-doesnt-exist'
+
+    const buf = Buffer.from('hey')
+    expect(() => {
+      multicodec.addPrefix(name, buf)
+    }).to.throw(
+      'multicodec not recognized'
+    )
+  })
+
   it('throws error on unknown codec name when getting the codec', () => {
     const code = Buffer.from('ffee', 'hex')