From f0aaec98f3221d6b8cbdc594a977e8a079314511 Mon Sep 17 00:00:00 2001
From: Matias Fontanini <matias.fontanini@gmail.com>
Date: Sun, 14 May 2017 09:04:51 -0700
Subject: [PATCH] Calculate IPv6 headers size on demand

---
 include/tins/ipv6.h |  2 +-
 src/ipv6.cpp        | 17 ++++++++++++-----
 2 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/include/tins/ipv6.h b/include/tins/ipv6.h
index 013581d..ba19222 100644
--- a/include/tins/ipv6.h
+++ b/include/tins/ipv6.h
@@ -320,6 +320,7 @@ public:
 private:
     void write_serialization(uint8_t* buffer, uint32_t total_sz);
     void set_last_next_header(uint8_t value);
+    uint32_t calculate_headers_size() const;
     static void write_header(const ext_header& header, Memory::OutputMemoryStream& stream);
     static bool is_extension_header(uint8_t header_id);
 
@@ -345,7 +346,6 @@ private:
 
     ipv6_header header_;
     headers_type ext_headers_;
-    uint32_t headers_size_;
 };
 }
 
diff --git a/src/ipv6.cpp b/src/ipv6.cpp
index 07170bf..03901fc 100644
--- a/src/ipv6.cpp
+++ b/src/ipv6.cpp
@@ -70,14 +70,13 @@ PDU::metadata IPv6::extract_metadata(const uint8_t *buffer, uint32_t total_sz) {
 }
 
 IPv6::IPv6(address_type ip_dst, address_type ip_src, PDU* /*child*/)
-: header_(), headers_size_(0) {
+: header_() {
     version(6);
     dst_addr(ip_dst);
     src_addr(ip_src);
 }
 
-IPv6::IPv6(const uint8_t* buffer, uint32_t total_sz) 
-: headers_size_(0) {
+IPv6::IPv6(const uint8_t* buffer, uint32_t total_sz) {
     InputMemoryStream stream(buffer, total_sz);
     stream.read(header_);
     uint8_t current_header = header_.next_header;
@@ -208,7 +207,7 @@ void IPv6::dst_addr(const address_type& new_dst_addr) {
 }
 
 uint32_t IPv6::header_size() const {
-    return sizeof(header_) + headers_size_;
+    return sizeof(header_) + calculate_headers_size();
 }
 
 bool IPv6::matches_response(const uint8_t* ptr, uint32_t total_sz) const {
@@ -282,7 +281,6 @@ void IPv6::send(PacketSender& sender, const NetworkInterface &) {
 
 void IPv6::add_ext_header(const ext_header& header) {
     ext_headers_.push_back(header);
-    headers_size_ += static_cast<uint32_t>(header.data_size() + sizeof(uint8_t) * 2);
 }
 
 const IPv6::ext_header* IPv6::search_header(ExtensionHeader id) const {
@@ -307,6 +305,15 @@ void IPv6::set_last_next_header(uint8_t value) {
     }
 }
 
+uint32_t IPv6::calculate_headers_size() const {
+    typedef headers_type::const_iterator const_iterator;
+    uint32_t output = 0;
+    for (const_iterator iter = ext_headers_.begin(); iter != ext_headers_.end(); ++iter) {
+        output += static_cast<uint32_t>(iter->data_size() + sizeof(uint8_t) * 2);
+    }
+    return output;
+}
+
 void IPv6::write_header(const ext_header& header, OutputMemoryStream& stream) {
     const uint8_t length = header.length_field() / 8;
     stream.write(header.option());