From 4e5a54ce49848252c7bef038286f7d5939974387 Mon Sep 17 00:00:00 2001
From: Lee Rhodes <leerho@users.noreply.github.com>
Date: Thu, 29 Oct 2026 15:33:30 -0700
Subject: [PATCH] Include the header in the tdigest serialize buffer size

tdigest::serialize(header_size_bytes, with_buffer) sized the vector by
get_serialized_size_bytes() alone but wrote the sketch starting at
header_size_bytes, so a non-zero header wrote past the end of the
vector. The size now includes the header, as in the other sketches.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 tdigest/include/tdigest_impl.hpp |  2 +-
 tdigest/test/tdigest_test.cpp    | 22 ++++++++++++++++++++++
 2 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/tdigest/include/tdigest_impl.hpp b/tdigest/include/tdigest_impl.hpp
index 958c8c40..ab9da04c 100644
--- a/tdigest/include/tdigest_impl.hpp
+++ b/tdigest/include/tdigest_impl.hpp
@@ -378,7 +378,7 @@ size_t tdigest<T, A>::get_serialized_size_bytes(bool with_buffer) const {
 template<typename T, typename A>
 auto tdigest<T, A>::serialize(unsigned header_size_bytes, bool with_buffer) const -> vector_bytes {
   if (!with_buffer) const_cast<tdigest*>(this)->compress(); // side effect
-  vector_bytes bytes(get_serialized_size_bytes(with_buffer), 0, buffer_.get_allocator());
+  vector_bytes bytes(header_size_bytes + get_serialized_size_bytes(with_buffer), 0, buffer_.get_allocator());
   uint8_t* ptr = bytes.data() + header_size_bytes;
   *ptr++ = get_preamble_longs();
   *ptr++ = SERIAL_VERSION;
diff --git a/tdigest/test/tdigest_test.cpp b/tdigest/test/tdigest_test.cpp
index 30b1fc1a..8c8535ad 100644
--- a/tdigest/test/tdigest_test.cpp
+++ b/tdigest/test/tdigest_test.cpp
@@ -18,6 +18,7 @@
  */
 
 #include <catch2/catch.hpp>
+#include <algorithm>
 #include <cmath>
 #include <cstdint>
 #include <cstring>
@@ -347,6 +348,27 @@ TEST_CASE("serialize deserialize bytes many values with buffer", "[tdigest]") {
   REQUIRE(td.get_quantile(0.5) == deserialized_td.get_quantile(0.5));
 }
 
+TEST_CASE("serialize bytes with header", "[tdigest]") {
+  const unsigned header_size_bytes = 7;
+  auto check = [header_size_bytes](const tdigest<double>& td, bool with_buffer) {
+    auto bytes = td.serialize(header_size_bytes, with_buffer);
+    auto bytes_no_header = td.serialize(0, with_buffer);
+    REQUIRE(bytes.size() == header_size_bytes + bytes_no_header.size());
+    REQUIRE(bytes.size() == header_size_bytes + td.get_serialized_size_bytes(with_buffer));
+    REQUIRE(std::equal(bytes_no_header.begin(), bytes_no_header.end(), bytes.begin() + header_size_bytes));
+    auto deserialized_td = tdigest<double>::deserialize(bytes.data() + header_size_bytes, bytes.size() - header_size_bytes);
+    REQUIRE(td.get_total_weight() == deserialized_td.get_total_weight());
+  };
+  tdigest<double> td(100);
+  check(td, false);
+  td.update(123);
+  check(td, false);
+  check(td, true);
+  for (int i = 0; i < 10000; ++i) td.update(i);
+  check(td, true);
+  check(td, false);
+}
+
 TEST_CASE("serialize deserialize steam and bytes equivalence empty", "[tdigest]") {
   tdigest<double> td(100);
   std::stringstream s(std::ios::in | std::ios::out | std::ios::binary);