fix: use POST to fetch (#1)

packages/node/src/amplitude.ts

@@ -1,5 +1,4 @@
 import { ExperimentUser } from './types/user';
-import { base64Decode } from './util/encode';
 
 /**
  * This class provides utility functions for parsing and handling identity
@@ -28,7 +27,7 @@ export class AmplitudeCookie {
     let user_id = undefined;
     if (values[1]) {
       try {
-        user_id = base64Decode(values[1]);
+        user_id = Buffer.from(values[1], 'base64').toString('utf-8');
       } catch (e) {
         user_id = undefined;
       }

packages/node/src/client.ts

@@ -5,7 +5,6 @@ import { FetchHttpClient } from './transport/http';
 import { HttpClient } from './types/transport';
 import { ExperimentUser } from './types/user';
 import { Variant, Variants } from './types/variant';
-import { urlSafeBase64Encode } from './util/encode';
 import { performance } from './util/performance';
 import { sleep } from './util/time';
 
@@ -75,16 +74,23 @@ export class ExperimentClient {
   ): Promise<Variants> {
     const start = performance.now();
     const userContext = this.addContext(user || {});
-    const encodedContext = urlSafeBase64Encode(JSON.stringify(userContext));
-    const endpoint = `${this.config.serverUrl}/sdk/vardata/${encodedContext}`;
+    const endpoint = `${this.config.serverUrl}/sdk/vardata`;
     const headers = {
       Authorization: `Api-Key ${this.apiKey}`,
     };
+    const body = JSON.stringify(user);
+    // CDN can only cache requests where the body is < 8KB
+    if (body.length > 8000) {
+      console.warn(
+        `[Experiment] encoded user object length ${body.length} cannot be cached by CDN; must be < 8KB`,
+      );
+    }
+    this.debug('[Experiment] Fetch variants for user: ', userContext);
     const response = await this.httpClient.request(
       endpoint,
-      'GET',
+      'POST',
       headers,
-      null,
+      body,
       timeoutMillis,
     );
     if (response.status !== 200) {

packages/node/src/transport/http.ts

@@ -1,6 +1,5 @@
 import http from 'http';
 import https from 'https';
-import querystring, { ParsedUrlQueryInput } from 'querystring';
 import url from 'url';
 
 import { SimpleResponse, HttpClient } from '../types/transport';
@@ -16,19 +15,15 @@ const request: HttpClient['request'] = (
   requestUrl: string,
   method: string,
   headers: Record<string, string>,
-  data?: Record<string, string>,
+  data: string,
   timeoutMillis?: number,
 ): Promise<SimpleResponse> => {
   const urlParams = url.parse(requestUrl);
-  if (method === 'GET' && data) {
-    urlParams.path = `${urlParams.path}?${querystring.encode(
-      data as ParsedUrlQueryInput,
-    )}`;
-  }
   const options = {
     ...urlParams,
-    method,
-    headers,
+    method: method,
+    headers: headers,
+    body: data,
     // Adds timeout to the socket connection, not the response.
     timeout: timeoutMillis,
   };

packages/node/src/types/transport.ts

@@ -8,7 +8,7 @@ export interface HttpClient {
     requestUrl: string,
     method: string,
     headers: Record<string, string>,
-    data?: Record<string, string>,
+    body: string,
     timeoutMillis?: number,
   ): Promise<SimpleResponse>;
 }

packages/node/test/client.test.ts

@@ -0,0 +1,34 @@
+import { ExperimentClient } from 'src/client';
+import { ExperimentUser } from 'src/types/user';
+
+const API_KEY = 'client-DvWljIjiiuqLbyjqdvBaLFfEBrAvGuA3';
+
+const testUser: ExperimentUser = { user_id: 'test_user' };
+
+const testClient: ExperimentClient = new ExperimentClient(API_KEY, {});
+
+const testTimeoutNoRetriesClient = new ExperimentClient(API_KEY, {
+  fetchRetries: 0,
+  fetchTimeoutMillis: 1,
+});
+
+const testTimeoutRetrySuccessClient = new ExperimentClient(API_KEY, {
+  fetchTimeoutMillis: 1,
+});
+
+test('ExperimentClient.fetch, success', async () => {
+  const variants = await testClient.fetch(testUser);
+  const variant = variants['sdk-ci-test'];
+  expect(variant).toEqual({ value: 'on', payload: 'payload' });
+});
+
+test('ExperimentClient.fetch, no retries, timeout failure', async () => {
+  const variants = await testTimeoutNoRetriesClient.fetch(testUser);
+  expect(variants).toEqual({});
+});
+
+test('ExperimentClient.fetch, no retries, timeout failure', async () => {
+  const variants = await testTimeoutRetrySuccessClient.fetch(testUser);
+  const variant = variants['sdk-ci-test'];
+  expect(variant).toEqual({ value: 'on', payload: 'payload' });
+});