fix: etag middleware corrupted binary stream responses

(see ringo/ringojs#439) to construct the etag md5 digest it copies the response body into an array of byte arrays/byte strings, but `Stream.forEach()` re-uses a single binary buffer [1], so if the streamed response exceeds 8192 bytes and thus be split up into multiple buffers the body created by etag middleware would essentially consist of different byte arrays all containing the same bytes. the fix is to use `Binary.prototype.slice()` to copy the body part - this is expensive and effectively thwarts the use of `response.stream()`, but it's what the etag middleware did before #409 too, and at least it doesn't corrupt binary responses anymore.

[1] https://github.com/ringo/ringojs/blob/master/modules/io.js#L48

lib/middleware/etag.js

@@ -2,7 +2,11 @@
  * @fileOverview Middleware for conditional HTTP GET request based on
  * response body message digests.
  *
- * The response body must implement a digest() method for this middleware to work.
+ * If the response body doesn't implement a `digest()` method this middleware
+ * creates a base 16 encoded MD5 digest of it. Note that for binary responses
+ * this is a memory expensive operation, as it needs to copy the body contents
+ * to create the digest. Especially for streamed JSGI responses the body should
+ * contain a `digest()` method.
  */
 
 const strings = require('ringo/utils/strings');
@@ -32,7 +36,7 @@ exports.middleware = function etag(next, app) {
         let {status, headers, body} = res;
 
         if (status === 200) {
-            let etags, etag;
+            let etags, etag, binBody;
             let header = request.headers["if-none-match"];
             if (header) {
                 etags = header.split(",").map(function(s) {return s.trim() });
@@ -43,9 +47,9 @@ exports.middleware = function etag(next, app) {
                 etag = body.digest();
             } else {
                 // we can't rely on body having map(), so we fake it with forEach()
-                const binBody = [];
+                binBody = [];
                 body.forEach(function(part) {
-                    binBody.push(binary.toByteString(part));
+                    binBody.push((part instanceof Binary) ? part.slice() : binary.toByteString(part));
                 });
                 etag = digest(binBody);
             }

test/middleware/etag_test.js

@@ -1,5 +1,9 @@
 const assert = require("assert");
 const {Headers} = require("ringo/utils/http");
+const fs = require("fs");
+const {Arrays} = java.util;
+const response = require("ringo/jsgi/response");
+const {MemoryStream} = require("io");
 
 const {Application} = require("../../lib/stick");
 
@@ -33,6 +37,27 @@ exports.testBasicMD5 = function() {
     assert.equal(headers.get("etag"), "1234567890");
 };
 
+exports.testBinaryStreamResponse = function() {
+    const file = module.resolve("./fixtures/ringo-drums.png");
+    const app = new Application();
+    app.configure("etag", "route");
+    app.get("/", function() {
+        return response.stream(fs.open(file, {binary: true}), "image/png");
+    });
+    const result = app({
+        method: 'GET',
+        headers: {},
+        env: {},
+        pathInfo: '/'
+    });
+    const headers = Headers(result.headers);
+    assert.equal(headers.get("content-type"), "image/png");
+    assert.equal(headers.get("etag"), "0C15DE3FBC9D7A7B936F98147CD7FDCB");
+    const body = new MemoryStream();
+    result.body.forEach(part => body.write(part));
+    assert.isTrue(Arrays.equals(body.content, fs.read(file, {binary: true})));
+};
+
 if (require.main === module) {
     require("system").exit(require("test").run(module.id));
 }