Added data URL support for node.js; (#4725)

* Added data URL support for node.js;
Added missed data URL protocol for the browser environment;
Optimized JSON parsing in the default response transformer;
Refactored project structure;
Added `cause` prop for AxiosError instance that refers to the original error if it was wrapped with `AxiosError.from` method;
Added fromDataURI helper;
Added test for handling data:url as an `arraybuffer|text|stream`;

* Added throwing of 405 HTTP error if the method is not GET;

test/unit/adapters/http.js

@@ -1442,4 +1442,47 @@ describe('supports http with nodejs', function () {
         }).catch(done);
     });
   });
+
+  describe('Data URL', function () {
+    it('should support requesting data URL as a Buffer', function (done) {
+      const buffer = Buffer.from('123');
+
+      const dataURI = 'data:application/octet-stream;base64,' + buffer.toString('base64');
+
+      axios.get(dataURI).then(({data})=> {
+        assert.deepStrictEqual(data, buffer);
+        done();
+      }).catch(done);
+    });
+
+    it('should support requesting data URL as a String (text)', function (done) {
+      const buffer = Buffer.from('123', 'utf-8');
+
+      const dataURI = 'data:application/octet-stream;base64,' + buffer.toString('base64');
+
+      axios.get(dataURI, {responseType: "text"}).then(({data})=> {
+        assert.deepStrictEqual(data, '123');
+        done();
+      }).catch(done);
+    });
+
+    it('should support requesting data URL as a Stream', function (done) {
+      const buffer = Buffer.from('123', 'utf-8');
+
+      const dataURI = 'data:application/octet-stream;base64,' + buffer.toString('base64');
+
+      axios.get(dataURI, {responseType: "stream"}).then(({data})=> {
+        var str = '';
+
+        data.on('data', function(response){
+          str += response.toString();
+        });
+
+        data.on('end', function(){
+          assert.strictEqual(str, '123');
+          done();
+        });
+      }).catch(done);
+    });
+  });
 });

test/unit/helpers/fromDataURI.js

@@ -0,0 +1,12 @@
+var assert = require('assert');
+var fromDataURI = require('../../../lib/helpers/fromDataURI');
+
+describe('helpers::fromDataURI', function () {
+  it('should return buffer from data uri', function () {
+    const buffer= Buffer.from('123');
+
+    const dataURI = 'data:application/octet-stream;base64,' + buffer.toString('base64');
+
+    assert.deepStrictEqual(fromDataURI(dataURI), buffer);
+  });
+});