Allow permission MIME converter resolution for requests

Setting `config.permissive = true` for the mime interceptor will allow
requests with an unknown Content-Type to proceed. In this situation the
mime interceptor will leave the request entity untouched.

Fixes: #88

docs/interceptors.md

@@ -357,6 +357,12 @@ See the docs for the MIME registry for more information on available converters
   <td><em>default registry</em></td>
   <td>custom MIME registry</td>
 </tr>
+<tr>
+  <td>permissive</td>
+  <td>optional</td>
+  td><em>false</em></td>
+  <td>allow an unknown mime type for a request</td>
+</tr>
 </table>
 
 **Example**

interceptor/mime.js

@@ -10,14 +10,17 @@
 
 	define(function (require) {
 
-		var interceptor, mime, registry, plainText, when;
+		var interceptor, mime, registry, noopConverter, when;
 
 		interceptor = require('../interceptor');
 		mime = require('../mime');
 		registry = require('../mime/registry');
 		when = require('when');
 
-		plainText = registry.lookup('text/plain');
+		noopConverter = {
+			read: function (obj) { return obj; },
+			write: function (obj) { return obj; }
+		};
 
 		/**
 		 * MIME type support for request and response entities.  Entities are
@@ -36,6 +39,7 @@
 		 *   converter, defaults to the client originating the request
 		 * @param {Registry} [config.registry] MIME registry, defaults to the root
 		 *   registry
+		 * @param {boolean} [config.permissive] Allow an unkown request MIME type
 		 *
 		 * @returns {Client}
 		 */
@@ -55,7 +59,13 @@
 					return request;
 				}
 
-				return config.registry.lookup(type).then(function (converter) {
+				return config.registry.lookup(type).otherwise(function () {
+					// failed to resolve converter
+					if (config.permissive) {
+						return noopConverter;
+					}
+					throw 'mime-unknown';
+				}).then(function (converter) {
 					var client = config.client || request.originator;
 
 					return when.attempt(converter.write, request.entity, { client: client, request: request, mime: type, registry: config.registry })
@@ -66,8 +76,6 @@
 							request.entity = entity;
 							return request;
 						});
-				}, function () {
-					throw 'mime-unknown';
 				});
 			},
 			response: function (response, config) {
@@ -77,7 +85,7 @@
 
 				var type = mime.parse(response.headers['Content-Type']);
 
-				return config.registry.lookup(type).otherwise(function () { return plainText; }).then(function (converter) {
+				return config.registry.lookup(type).otherwise(function () { return noopConverter; }).then(function (converter) {
 					var client = config.client || response.request && response.request.originator;
 
 					return when.attempt(converter.read, response.entity, { client: client, response: response, mime: type, registry: config.registry })

test/interceptor/mime-test.js

@@ -96,6 +96,23 @@
 					})
 				);
 			},
+			'should error the request if unable to find a converter for the desired mime, unless in permissive mode': function () {
+				var client, entity, request;
+
+				client = mime(
+					function (request) {
+						return { request: request, headers: {} };
+					},
+					{ permissive: true }
+				);
+
+				entity = {};
+				request = { headers: { 'Content-Type': 'application/vnd.com.example' }, entity: entity };
+				return client(request).then(function (response) {
+					assert.same(entity, response.request.entity);
+					assert.equals('application/vnd.com.example', response.request.headers['Content-Type']);
+				}).otherwise(fail);
+			},
 			'should use text/plain converter for a response if unable to find a converter for the desired mime': function () {
 				var client;