Add support for binary HTTP request bodies

[connorworley]

Relates to #78

Expected behavior

An HTTP request with a binary body is sent through a mountebank proxy (such as a multipart/form-data request to upload an image). The request is proxied and somehow saved to a stub if predicated on its body.

Actual behavior

The binary request body is mangled with unicode replacement characters, and the request fails.

---

In addition to fixing the proxying behavior, I'd like to introduce a new body:base64 predicate type to match base64-encoded binary request bodies. If that sounds good I'll submit a PR soon.

[connorworley]

Err, with further thinking body:base64 doesn't really make sense - a new comparison operator like base64Equals would make more sense.

[connorworley]

For starters, this diff seems to fix the mangling:

index 872ef420..04c85da1 100644
--- a/src/models/http/httpProxy.js
+++ b/src/models/http/httpProxy.js
@@ -79,12 +79,12 @@ function create (logger) {
         if (originalRequest.body &&
             !headersHelper.hasHeader('Transfer-Encoding', originalRequest.headers) &&
             !headersHelper.hasHeader('Content-Length', originalRequest.headers)) {
-            options.headers['Content-Length'] = Buffer.byteLength(originalRequest.body);
+            options.headers['Content-Length'] = Buffer.byteLength(originalRequest.body, 'binary');
         }
 
         const proxiedRequest = protocol.request(options);
         if (originalRequest.body) {
-            proxiedRequest.write(originalRequest.body);
+            proxiedRequest.write(originalRequest.body, 'binary');
         }
         return proxiedRequest;
     }
diff --git a/src/models/http/httpRequest.js b/src/models/http/httpRequest.js
index 65dd80c3..8a0084f8 100644
--- a/src/models/http/httpRequest.js
+++ b/src/models/http/httpRequest.js
@@ -54,7 +54,7 @@ function createFrom (request) {
     const Q = require('q'),
         deferred = Q.defer();
     request.body = '';
-    request.setEncoding('utf8');
+    request.setEncoding('binary');
     request.on('data', chunk => { request.body += chunk; });
     request.on('end', () => { deferred.resolve(transform(request)); });
     return deferred.promise;

[connorworley]

Thinking further, comparing multipart/form-data requests is probably going to be more complicated than comparing base64-encoded bodies as the boundary is subject to change between requests. I'll try an injection-based approach once #416 lands.

edit: I may not actually need to predicate against the multipart/form-data request body at all, but I believe I do need the above diff for my use case. Will keep updating here.

[connorworley]

Resolved via #418

[bbyars]

Reopening as previous fix broke cirillic character predicate matching.