diff --git a/trunk/src/utest/srs_utest_protocol.cpp b/trunk/src/utest/srs_utest_protocol.cpp
index 1a6a7a6e3..645e53296 100644
--- a/trunk/src/utest/srs_utest_protocol.cpp
+++ b/trunk/src/utest/srs_utest_protocol.cpp
@@ -95,6 +95,7 @@ MockBufferIO::MockBufferIO()
 {
     rtm = stm = SRS_UTIME_NO_TIMEOUT;
     rbytes = sbytes = 0;
+    in_err = out_err = srs_success;
 }
 
 MockBufferIO::~MockBufferIO()
@@ -109,6 +110,10 @@ MockBufferIO* MockBufferIO::append(string data)
 
 srs_error_t MockBufferIO::read_fully(void* buf, size_t size, ssize_t* nread)
 {
+    if (in_err != srs_success) {
+        return srs_error_copy(in_err);
+    }
+
     if (in_buffer.length() < (int)size) {
         return srs_error_new(ERROR_SOCKET_READ, "read");
     }
@@ -124,6 +129,10 @@ srs_error_t MockBufferIO::read_fully(void* buf, size_t size, ssize_t* nread)
 
 srs_error_t MockBufferIO::write(void* buf, size_t size, ssize_t* nwrite)
 {
+    if (out_err != srs_success) {
+        return srs_error_copy(out_err);
+    }
+
     sbytes += size;
     if (nwrite) {
         *nwrite = size;
@@ -165,6 +174,10 @@ int64_t MockBufferIO::get_send_bytes()
 srs_error_t MockBufferIO::writev(const iovec *iov, int iov_size, ssize_t* nwrite)
 {
     srs_error_t err = srs_success;
+
+    if (out_err != srs_success) {
+        return srs_error_copy(out_err);
+    }
     
     ssize_t total = 0;
     for (int i = 0; i <iov_size; i++) {
@@ -187,6 +200,10 @@ srs_error_t MockBufferIO::writev(const iovec *iov, int iov_size, ssize_t* nwrite
 
 srs_error_t MockBufferIO::read(void* buf, size_t size, ssize_t* nread)
 {
+    if (in_err != srs_success) {
+        return srs_error_copy(in_err);
+    }
+
     if (in_buffer.length() <= 0) {
         return srs_error_new(ERROR_SOCKET_READ, "read");
     }
@@ -199,6 +216,7 @@ srs_error_t MockBufferIO::read(void* buf, size_t size, ssize_t* nread)
         *nread = available;
     }
     in_buffer.erase(available);
+
     return srs_success;
 }
 
diff --git a/trunk/src/utest/srs_utest_protocol.hpp b/trunk/src/utest/srs_utest_protocol.hpp
index a27d338db..f009e10e6 100644
--- a/trunk/src/utest/srs_utest_protocol.hpp
+++ b/trunk/src/utest/srs_utest_protocol.hpp
@@ -79,6 +79,10 @@ public:
     SrsSimpleStream in_buffer;
     // data buffer for socket send.
     SrsSimpleStream out_buffer;
+public:
+    // Mock error for io.
+    srs_error_t in_err;
+    srs_error_t out_err;
 public:
     MockBufferIO();
     virtual ~MockBufferIO();
diff --git a/trunk/src/utest/srs_utest_protostack.cpp b/trunk/src/utest/srs_utest_protostack.cpp
index fdb8c23ea..413af4d4e 100644
--- a/trunk/src/utest/srs_utest_protostack.cpp
+++ b/trunk/src/utest/srs_utest_protostack.cpp
@@ -38,19 +38,37 @@ CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 
 using namespace std;
 
-class MockErrorPacket : public SrsPacket
+class MockPacket : public SrsPacket
 {
+public:
+    int size;
+public:
+    MockPacket() {
+        size = 0;
+    }
+    virtual ~MockPacket() {
+    }
 protected:
     virtual int get_size() {
-        return 1024;
+        return size;
     }
 };
 
-class MockPayloadErrorPacket : public SrsPacket
+class MockPacket2 : public MockPacket
 {
-protected:
+public:
+    char* payload;
+public:
+    MockPacket2() {
+        payload = NULL;
+    }
+    virtual ~MockPacket2() {
+        srs_freep(payload);
+    }
     virtual srs_error_t encode(int& size, char*& payload) {
-        size = 1024;
+        size = this->size;
+        payload = this->payload;
+        this->payload = NULL;
         return srs_success;
     }
 };
@@ -63,12 +81,16 @@ VOID TEST(ProtoStackTest, PacketEncode)
     char* payload;
 
     if (true) {
-        MockErrorPacket pkt;
+        MockPacket pkt;
+        pkt.size = 1024;
+
         HELPER_EXPECT_FAILED(pkt.encode(size, payload));
     }
 
     if (true) {
-        MockErrorPacket pkt;
+        MockPacket pkt;
+        pkt.size = 1024;
+
         SrsBuffer b;
         HELPER_EXPECT_FAILED(pkt.decode(&b));
     }
@@ -81,7 +103,9 @@ VOID TEST(ProtoStackTest, PacketEncode)
     }
 
     if (true) {
-        MockErrorPacket pkt;
+        MockPacket pkt;
+        pkt.size = 1024;
+
         EXPECT_EQ(1024, pkt.get_size());
     }
 }
@@ -192,7 +216,8 @@ VOID TEST(ProtoStackTest, SendPacketsError)
         MockBufferIO io;
         SrsProtocol p(&io);
 
-        SrsPacket* pkt = new MockErrorPacket();
+        MockPacket* pkt = new MockPacket();
+        pkt->size = 1024;
         HELPER_EXPECT_FAILED(p.send_and_free_packet(pkt, 1));
     }
 
@@ -208,11 +233,39 @@ VOID TEST(ProtoStackTest, SendPacketsError)
         MockBufferIO io;
         SrsProtocol p(&io);
 
-        SrsPacket* pkt = new MockPayloadErrorPacket();
+        MockPacket2* pkt = new MockPacket2();
+        pkt->size = 1024;
         HELPER_EXPECT_SUCCESS(p.send_and_free_packet(pkt, 1));
     }
 }
 
+VOID TEST(ProtoStackTest, SendHugePacket)
+{
+    srs_error_t err;
+
+    if (true) {
+        MockBufferIO io;
+        SrsProtocol p(&io);
+
+        MockPacket2* pkt = new MockPacket2();
+        pkt->size = 1024;
+        pkt->payload = new char[1024];
+        HELPER_EXPECT_SUCCESS(p.send_and_free_packet(pkt, 1));
+    }
+
+    if (true) {
+        MockBufferIO io;
+        SrsProtocol p(&io);
+
+        MockPacket2* pkt = new MockPacket2();
+        pkt->size = 16;
+        pkt->payload = new char[16];
+
+        io.out_err = srs_error_new(1, "fail");
+        HELPER_EXPECT_FAILED(p.send_and_free_packet(pkt, 1));
+    }
+}
+
 VOID TEST(ProtoStackTest, SendZeroMessages)
 {
     srs_error_t err;