only allow body to be consumed once, add some tests

classes/response.js

@@ -7,22 +7,32 @@ class Response {
     this.cacheFilePath = cacheFilePath;
     this.headers = new Headers(raw.headers);
     this.fromCache = fromCache;
+    this.consumed = false;
 
     if (this.bodyBuffer.type === 'Buffer') {
       this.bodyBuffer = Buffer.from(this.bodyBuffer);
     }
   }
 
+  consumeBody() {
+    if (this.consumed) {
+      throw new Error('Error: body used already');
+    }
+
+    this.consumed = true;
+    return this.bodyBuffer;
+  }
+
   text() {
-    return this.bodyBuffer.toString();
+    return this.consumeBody().toString();
   }
 
   json() {
-    return JSON.parse(this.bodyBuffer.toString());
+    return JSON.parse(this.consumeBody().toString());
   }
 
   buffer() {
-    return this.bodyBuffer;
+    return this.consumeBody();
   }
 
   async ejectFromCache() {

index.js

@@ -3,7 +3,6 @@ const fs = require('fs');
 const { URLSearchParams } = require('url');
 const crypto = require('crypto');
 const path = require('path');
-
 const Response = require('./classes/response.js');
 
 const CACHE_VERSION = 2;
@@ -12,6 +11,9 @@ function md5(str) {
   return crypto.createHash('md5').update(str).digest('hex');
 }
 
+// Since the bounday in FormData is random,
+// we ignore it for purposes of calculating
+// the cache key.
 function getFormDataCacheKey(formData) {
   const cacheKey = { ...formData };
 

test/tests.js

@@ -7,11 +7,15 @@ const FetchCache = require('../index.js');
 const { URLSearchParams } = require('url');
 
 const CACHE_PATH = path.join(__dirname, '..', '.cache');
+const expectedPngBuffer = fs.readFileSync(path.join(__dirname, 'expected_png.png'));
 
 const TWO_HUNDRED_URL = 'https://httpbin.org/status/200';
 const FOUR_HUNDRED_URL = 'https://httpbin.org/status/400';
 const THREE_HUNDRED_TWO_URL = 'https://httpbin.org/status/302';
 const TEXT_BODY_URL = 'https://httpbin.org/robots.txt';
+const JSON_BODY_URL = 'https://httpbin.org/json';
+const PNG_BODY_URL = 'https://httpbin.org/image/png';
+
 const TEXT_BODY_EXPECTED = 'User-agent: *\nDisallow: /deny\n';
 
 let fetch;
@@ -195,13 +199,51 @@ describe('Cache tests', function() {
 }).timeout(10000);
 
 describe('Data tests', function() {
+  it('Refuses to consume body twice', async function() {
+    res = await fetch(TEXT_BODY_URL);
+    await res.text();
+
+    try {
+      await res.text();
+      throw new Error('The above line should have thrown.');
+    } catch (err) {
+      // It threw
+    }
+  });
+
   it('Can get text body', async function() {
     res = await fetch(TEXT_BODY_URL);
     body = await res.text();
     assert.strictEqual(body, TEXT_BODY_EXPECTED);
+    assert.strictEqual(res.fromCache, false);
 
     res = await fetch(TEXT_BODY_URL);
     body = await res.text();
     assert.strictEqual(body, TEXT_BODY_EXPECTED);
+    assert.strictEqual(res.fromCache, true);
+  });
+
+  it('Can get JSON body', async function() {
+    res = await fetch(JSON_BODY_URL);
+    body = await res.json();
+    assert(body.slideshow);
+    assert.strictEqual(res.fromCache, false);
+
+    res = await fetch(JSON_BODY_URL);
+    body = await res.json();
+    assert(body.slideshow);
+    assert.strictEqual(res.fromCache, true);
+  });
+
+  it('Can get PNG buffer body', async function() {
+    res = await fetch(PNG_BODY_URL);
+    body = await res.buffer();
+    assert.strictEqual(expectedPngBuffer.equals(body), true);
+    assert.strictEqual(res.fromCache, false);
+
+    res = await fetch(PNG_BODY_URL);
+    body = await res.buffer();
+    assert.strictEqual(expectedPngBuffer.equals(body), true);
+    assert.strictEqual(res.fromCache, true);
   });
 }).timeout(10000);