Feat(dag): DAG api (#568)

* Implement dag.get

* Handle dag put response, enable CIDs for dag get and fix dag get request param

src/dag/dag.js

@@ -66,12 +66,53 @@ module.exports = (send) => {
           if (err) {
             return callback(err)
           }
-          // TODO handle the result
+          if (result.Cid) {
+            return callback(null, new CID(result.Cid['/']))
+          } else {
+            return callback(result)
+          }
         })
       }
     }),
     get: promisify((cid, path, options, callback) => {
-      // TODO
+      if (typeof path === 'function') {
+        callback = path
+        path = undefined
+      }
+
+      if (typeof options === 'function') {
+        callback = options
+        options = {}
+      }
+
+      options = options || {}
+
+      if (CID.isCID(cid)) {
+        cid = cid.toBaseEncodedString()
+      }
+
+      if (typeof cid === 'string') {
+        const split = cid.split('/')
+        cid = split[0]
+        split.shift()
+
+        if (split.length > 0) {
+          path = split.join('/')
+        } else {
+          path = '/'
+        }
+      }
+
+      send({
+        path: 'dag/get',
+        args: cid + '/' + path,
+        qs: options
+      }, (err, result) => {
+        if (err) {
+          return callback(err)
+        }
+        callback(undefined, {value: result})
+      })
     })
   }