ARI: Add duplicate channel ID checking for channel creation.

This is similar to what is done for origination, but for the 14 and up
channel creation method. When attempting to create a channel, if a
channel ID is specified and a channel already exists with that ID, then
a 409 is returned.

Change-Id: I77f9253278c6947939c418073b6b31065489187c

res/ari/resource_channels.c

@@ -1828,7 +1828,12 @@ void ast_ari_channels_create(struct ast_variable *headers,
 	ao2_cleanup(request_cap);
 
 	if (!chan_data->chan) {
-		ast_ari_response_alloc_failed(response);
+		if (ast_channel_errno() == AST_CHANNEL_ERROR_ID_EXISTS) {
+			ast_ari_response_error(response, 409, "Conflict",
+				"Channel with given unique ID already exists");
+		} else {
+			ast_ari_response_alloc_failed(response);
+		}
 		ast_channel_cleanup(originator);
 		chan_data_destroy(chan_data);
 		return;

res/res_ari_channels.c

@@ -386,6 +386,7 @@ static void ast_ari_channels_create_cb(
 		break;
 	case 500: /* Internal Server Error */
 	case 501: /* Not Implemented */
+	case 409: /* Channel with given unique ID already exists. */
 		is_valid = 1;
 		break;
 	default:

rest-api/api-docs/channels.json

@@ -217,6 +217,12 @@
 							"allowMultiple": false,
 							"dataType": "string"
 						}
+					],
+					"errorResponses": [
+						{
+							"code": 409,
+							"reason": "Channel with given unique ID already exists."
+						}
 					]
 				}
 			]