--- /dev/null
+var stream = require('stream')
+
+
+function isStream (obj) {
+ return obj instanceof stream.Stream
+}
+
+
+function isReadable (obj) {
+ return isStream(obj) && typeof obj._read == 'function' && typeof obj._readableState == 'object'
+}
+
+
+function isWritable (obj) {
+ return isStream(obj) && typeof obj._write == 'function' && typeof obj._writableState == 'object'
+}
+
+
+function isDuplex (obj) {
+ return isReadable(obj) && isWritable(obj)
+}
+
+
+module.exports = isStream
+module.exports.isReadable = isReadable
+module.exports.isWritable = isWritable
+module.exports.isDuplex = isDuplex