feat: cache string represntation

store the string form of the CID as a non-enumerable property where
an instance is constructed from a valid string, or after the first
call to toBaseEncodedString where the supplied base matches the
default base.

adds tests for string caching, and some missing test cases.

License: MIT
Signed-off-by: Oli Evans <[email protected]>

Author: olizilla

src/index.js

@@ -88,6 +88,7 @@ class CID {
         this.multibaseName = 'base58btc'
       }
       CID.validateCID(this)
+      Object.defineProperty(this, 'string', { value: version })
       return
     }
 
@@ -221,18 +222,25 @@ class CID {
    * @returns {string}
    */
   toBaseEncodedString (base = this.multibaseName) {
-    switch (this.version) {
-      case 0: {
-        if (base !== 'base58btc') {
-          throw new Error('not supported with CIDv0, to support different bases, please migrate the instance do CIDv1, you can do that through cid.toV1()')
-        }
-        return mh.toB58String(this.multihash)
+    if (this.string && base === this.multibaseName) {
+      return this.string
+    }
+    let str = null
+    if (this.version === 0) {
+      if (base !== 'base58btc') {
+        throw new Error('not supported with CIDv0, to support different bases, please migrate the instance do CIDv1, you can do that through cid.toV1()')
       }
-      case 1:
-        return multibase.encode(base, this.buffer).toString()
-      default:
-        throw new Error('Unsupported version')
+      str = mh.toB58String(this.multihash)
+    } else if (this.version === 1) {
+      str = multibase.encode(base, this.buffer).toString()
+    } else {
+      throw new Error('unsupported version')
+    }
+    if (base === this.multibaseName) {
+      // cache the string value
+      Object.defineProperty(this, 'string', { value: str })
     }
+    return str
   }
 
   toString (base) {

test/index.spec.js

@@ -266,6 +266,11 @@ describe('CID', () => {
     invalid.forEach((i) => it(`new CID(1, 'dag-pb', ${Buffer.isBuffer(i) ? 'buffer' : 'string'}<${i.toString()}>)`, () => {
       expect(() => new CID(1, 'dag-pb', i)).to.throw()
     }))
+
+    const invalidVersions = [-1, 2]
+    invalidVersions.forEach((i) => it(`new CID(${i}, 'dag-pb', buffer)`, () => {
+      expect(() => new CID(i, 'dag-pb', hash)).to.throw()
+    }))
   })
 
   describe('idempotence', () => {
@@ -326,14 +331,44 @@ describe('CID', () => {
     })
   })
 
-  describe('buffer reuse', () => {
+  describe('caching', () => {
     it('should cache CID as buffer', done => {
       multihashing(Buffer.from(`TEST${Date.now()}`), 'sha2-256', (err, hash) => {
         if (err) return done(err)
         const cid = new CID(1, 'dag-pb', hash)
         expect(cid.buffer).to.equal(cid.buffer)
+        expect(Object.hasOwnProperty('buffer')).to.be.false()
         done()
       })
     })
+    it('should cache string representation when it matches the multibaseName it was constructed with', () => {
+      // not string to cache yet
+      const cid = new CID(1, 'dag-pb', hash, 'base32')
+      expect(cid.string).to.be.undefined()
+
+      // we dont cache alternate base encodings yet.
+      expect(cid.toBaseEncodedString('base64')).to.equal('mAXASILp4Fr+PAc/qQUFA3l2uIiOwA2Gjlhd6nLQQ/2HyABWt')
+      expect(cid.string).to.be.undefined()
+
+      const base32String = 'bafybeif2pall7dybz7vecqka3zo24irdwabwdi4wc55jznaq75q7eaavvu'
+      expect(cid.toBaseEncodedString()).to.equal(base32String)
+
+      // it cached!
+      expect(cid.string).to.equal(base32String)
+      expect(Object.hasOwnProperty('_string')).to.be.false()
+      expect(cid.toBaseEncodedString()).to.equal(base32String)
+      expect(cid.toBaseEncodedString('base64')).to.equal('mAXASILp4Fr+PAc/qQUFA3l2uIiOwA2Gjlhd6nLQQ/2HyABWt')
+
+      // alternate base not cached!
+      expect(cid.string).to.equal(base32String)
+    })
+    it('should cache string representation when constructed with one', () => {
+      const base32String = 'bafybeif2pall7dybz7vecqka3zo24irdwabwdi4wc55jznaq75q7eaavvu'
+      const cid = new CID(base32String)
+      expect(cid.string).to.equal(base32String)
+      expect(cid.toBaseEncodedString('base64')).to.equal('mAXASILp4Fr+PAc/qQUFA3l2uIiOwA2Gjlhd6nLQQ/2HyABWt')
+      expect(cid.string).to.equal(base32String)
+      expect(cid.toBaseEncodedString()).to.equal(base32String)
+    })
   })
 })