diff --git a/srtcore/packet.cpp b/srtcore/packet.cpp
index aacc37f2c..813d07995 100644
--- a/srtcore/packet.cpp
+++ b/srtcore/packet.cpp
@@ -252,6 +252,13 @@ void srt::CPacket::setLength(size_t len)
     m_PacketVector[PV_DATA].setLength(len);
 }
 
+void srt::CPacket::setLength(size_t len, size_t cap)
+{
+   SRT_ASSERT(len <= cap);
+   setLength(len);
+   m_zCapacity = cap;
+}
+
 void srt::CPacket::pack(UDTMessageType pkttype, const int32_t* lparam, void* rparam, size_t size)
 {
     // Set (bit-0 = 1) and (bit-1~15 = type)
@@ -456,10 +463,15 @@ int32_t srt::CPacket::getMsgSeq(bool has_rexmit) const
 
 bool srt::CPacket::getRexmitFlag() const
 {
-    // return false; //
     return 0 != MSGNO_REXMIT::unwrap(m_nHeader[SRT_PH_MSGNO]);
 }
 
+void srt::CPacket::setRexmitFlag(bool bRexmit)
+{
+    const int32_t clr_msgno = m_nHeader[SRT_PH_MSGNO] & ~MSGNO_REXMIT::mask;
+    m_nHeader[SRT_PH_MSGNO] = clr_msgno | MSGNO_REXMIT::wrap(bRexmit? 1 : 0);
+}
+
 srt::EncryptionKeySpec srt::CPacket::getMsgCryptoFlags() const
 {
     return EncryptionKeySpec(MSGNO_ENCKEYSPEC::unwrap(m_nHeader[SRT_PH_MSGNO]));
diff --git a/srtcore/packet.h b/srtcore/packet.h
index a288caa52..e6d2516a9 100644
--- a/srtcore/packet.h
+++ b/srtcore/packet.h
@@ -236,6 +236,11 @@ class CPacket
     /// @param len [in] the payload or the control information field length.
     void setLength(size_t len);
 
+    /// Set the payload or the control information field length.
+    /// @param len [in] the payload or the control information field length.
+    /// @param cap [in] capacity (if known).
+    void setLength(size_t len, size_t cap);
+
     /// Pack a Control packet.
     /// @param pkttype [in] packet type filed.
     /// @param lparam [in] pointer to the first data structure, explained by the packet type.
@@ -286,6 +291,8 @@ class CPacket
     /// (because the peer will understand this bit as a part of MSGNO field).
     bool getRexmitFlag() const;
 
+    void setRexmitFlag(bool bRexmit);
+
     /// Read the message sequence number.
     /// @return packet header field [1]
     int32_t getMsgSeq(bool has_rexmit = true) const;
@@ -335,6 +342,7 @@ class CPacket
 
     int32_t m_extra_pad;
     bool    m_data_owned;
+    size_t  m_zCapacity;
 
 protected:
     CPacket& operator=(const CPacket&);
@@ -368,6 +376,8 @@ class CPacket
     char*       data() { return m_pcData; }
     const char* data() const { return m_pcData; }
     size_t      size() const { return getLength(); }
+    size_t      capacity() const { return m_zCapacity; }
+    void        setCapacity(size_t cap) { m_zCapacity = cap; }
     uint32_t    header(SrtPktHeaderFields field) const { return m_nHeader[field]; }
 
 #if ENABLE_LOGGING