From 84547fa6d408bdda1685f6d5972232bb19d97a7d Mon Sep 17 00:00:00 2001
From: Pieter Wuille <pieter.wuille@gmail.com>
Date: Wed, 18 Jul 2018 17:52:43 -0700
Subject: [PATCH] Avoid creating a temporary vector for size-prefixed elements

---
 src/script/sign.h | 18 ++++++++----------
 src/serialize.h   |  8 ++++++++
 2 files changed, 16 insertions(+), 10 deletions(-)

diff --git a/src/script/sign.h b/src/script/sign.h
index e3a6196b2..250b63703 100644
--- a/src/script/sign.h
+++ b/src/script/sign.h
@@ -116,26 +116,24 @@ static constexpr uint8_t PSBT_OUT_BIP32_DERIVATION = 0x02;
 // as a 0 length key which indicates that this is the separator. The separator has no value.
 static constexpr uint8_t PSBT_SEPARATOR = 0x00;
 
-// Takes a stream and multiple arguments and serializes them into a vector and then into the stream
+// Takes a stream and multiple arguments and serializes them as if first serialized into a vector and then into the stream
 // The resulting output into the stream has the total serialized length of all of the objects followed by all objects concatenated with each other.
 template<typename Stream, typename... X>
 void SerializeToVector(Stream& s, const X&... args)
 {
-    std::vector<unsigned char> ret;
-    CVectorWriter ss(SER_NETWORK, PROTOCOL_VERSION, ret, 0);
-    SerializeMany(ss, args...);
-    s << ret;
+    WriteCompactSize(s, GetSerializeSizeMany(s, args...));
+    SerializeMany(s, args...);
 }
 
 // Takes a stream and multiple arguments and unserializes them first as a vector then each object individually in the order provided in the arguments
 template<typename Stream, typename... X>
 void UnserializeFromVector(Stream& s, X&... args)
 {
-    std::vector<unsigned char> data;
-    s >> data;
-    CDataStream ss(data, SER_NETWORK, PROTOCOL_VERSION);
-    UnserializeMany(ss, args...);
-    if (!ss.eof()) {
+    size_t expected_size = ReadCompactSize(s);
+    size_t remaining_before = s.size();
+    UnserializeMany(s, args...);
+    size_t remaining_after = s.size();
+    if (remaining_after + expected_size != remaining_before) {
         throw std::ios_base::failure("Size of value was not the stated size");
     }
 }
diff --git a/src/serialize.h b/src/serialize.h
index df3b47ba8..627225b6e 100644
--- a/src/serialize.h
+++ b/src/serialize.h
@@ -991,4 +991,12 @@ size_t GetSerializeSize(const S& s, const T& t)
     return (CSizeComputer(s.GetType(), s.GetVersion()) << t).size();
 }
 
+template <typename S, typename... T>
+size_t GetSerializeSizeMany(const S& s, const T&... t)
+{
+    CSizeComputer sc(s.GetType(), s.GetVersion());
+    SerializeMany(sc, t...);
+    return sc.size();
+}
+
 #endif // BITCOIN_SERIALIZE_H