Improve error serialization to walk the chain of `.cause()` errors

from the likes of `WError` or `VError` error classes from
[verror](https://github.com/davepacheco/node-verror) and
[restify v2.0](https://github.com/mcavage/node-restify).

CHANGES.md

@@ -2,7 +2,10 @@
 
 ## bunyan 0.14.3 (not yet released)
 
-(nothing yet)
+- Improve error serialization to walk the chain of `.cause()` errors
+  from the likes of `WError` or `VError` error classes from the likes of
+  [verror](https://github.com/davepacheco/node-verror) and
+  [restify v2.0](https://github.com/mcavage/node-restify).
 
 
 ## bunyan 0.14.2

lib/bunyan.js

@@ -987,6 +987,24 @@ Logger.stdSerializers.res = function res(res) {
   }
 };
 
+
+/*
+ * This function dumps long stack traces for exceptions having a cause()
+ * method. The error classes from
+ * [verror](https://github.com/davepacheco/node-verror) and
+ * [restify v2.0](https://github.com/mcavage/node-restify) are examples.
+ *
+ * Based on `dumpException` in
+ * https://github.com/davepacheco/node-extsprintf/blob/master/lib/extsprintf.js
+ */
+function getFullErrorStack(ex)
+{
+  var ret = ex.stack || ex.toString();
+  if (ex.cause && typeof(ex.cause) === 'function')
+    ret += '\nCaused by: ' + getFullErrorStack(ex);
+  return (ret);
+}
+
 // Serialize an Error object
 // (Core error properties are enumerable in node 0.4, not in 0.6).
 var errSerializer = Logger.stdSerializers.err = function err(err) {
@@ -995,7 +1013,7 @@ var errSerializer = Logger.stdSerializers.err = function err(err) {
   var obj = {
     message: err.message,
     name: err.name,
-    stack: err.stack
+    stack: getFullErrorStack(err)
   }
   Object.keys(err).forEach(function (k) {
     if (err[k] !== undefined) {
@@ -1005,6 +1023,7 @@ var errSerializer = Logger.stdSerializers.err = function err(err) {
   return obj;
 };
 
+
 // A JSON stringifier that handles cycles safely.
 // Usage: JSON.stringify(obj, safeCycles())
 function safeCycles() {