diff --git a/trunk/src/core/srs_core_amf0.cpp b/trunk/src/core/srs_core_amf0.cpp
index 8a2e07ad2..dbcd93bc7 100755
--- a/trunk/src/core/srs_core_amf0.cpp
+++ b/trunk/src/core/srs_core_amf0.cpp
@@ -55,22 +55,28 @@ std::string srs_amf0_read_string(SrsStream* stream)
 	
 	// marker
 	if (!stream->require(1)) {
+		srs_warn("amf0 read string marker failed");
 		return str;
 	}
 	
 	char marker = stream->read_char();
 	if (marker != RTMP_AMF0_String) {
+		srs_warn("amf0 check string marker failed. marker=%#x, required=%#x", marker, RTMP_AMF0_String);
 		return str;
 	}
+	srs_verbose("amf0 read string marker success");
 	
 	// len
 	if (!stream->require(2)) {
+		srs_warn("amf0 read string length failed");
 		return str;
 	}
 	int16_t len = stream->read_2bytes();
+	srs_verbose("amf0 read string length success. len=%d", len);
 	
 	// data
 	if (!stream->require(len)) {
+		srs_warn("amf0 read string data failed");
 		return str;
 	}
 	str = stream->read_string(len);
@@ -85,6 +91,7 @@ std::string srs_amf0_read_string(SrsStream* stream)
 			return "";
 		}
 	}
+	srs_verbose("amf0 read string data success. str=%s", str.c_str());
 	
 	return str;
 }
diff --git a/trunk/src/core/srs_core_stream.hpp b/trunk/src/core/srs_core_stream.hpp
index 9b5787dee..aa6ed92fa 100755
--- a/trunk/src/core/srs_core_stream.hpp
+++ b/trunk/src/core/srs_core_stream.hpp
@@ -66,8 +66,17 @@ public:
 	*/
 	virtual bool require(int required_size);
 public:
+	/**
+	* get 1bytes char from stream.
+	*/
 	virtual char read_char();
+	/**
+	* get 2bytes int from stream.
+	*/
 	virtual int16_t read_2bytes();
+	/**
+	* get string from stream, length specifies by param len.
+	*/
 	virtual std::string read_string(int len);
 };