feat: add many_from_buffer_exact for strict buffer size validation

barretenberg/cpp/src/barretenberg/api/api_ultra_honk.cpp

@@ -121,14 +121,14 @@ bool UltraHonkAPI::verify(const Flags& flags,
     if (auto json = try_parse_json(public_inputs_content)) {
         public_inputs = PublicInputsJson::parse(*json);
     } else {
-        public_inputs = many_from_buffer<uint256_t>(public_inputs_content);
+        public_inputs = many_from_buffer_exact<uint256_t>(public_inputs_content, "UltraHonk public inputs file");
     }
 
     auto proof_content = read_file(proof_path);
     if (auto json = try_parse_json(proof_content)) {
         proof = ProofJson::parse(*json);
     } else {
-        proof = many_from_buffer<uint256_t>(proof_content);
+        proof = many_from_buffer_exact<uint256_t>(proof_content, "UltraHonk proof file");
     }
 
     auto vk_content = read_file(vk_path);

barretenberg/cpp/src/barretenberg/api/file_io.hpp

@@ -1,5 +1,6 @@
 #pragma once
 #include "barretenberg/common/log.hpp"
+#include "barretenberg/common/serialize.hpp"
 #include "barretenberg/common/try_catch_shim.hpp"
 #include "barretenberg/ecc/curves/bn254/fr.hpp"
 #include <cstdint>
@@ -9,6 +10,7 @@
 #include <fstream>
 #include <ios>
 #include <sstream>
+#include <string_view>
 #include <sys/stat.h>
 #include <unistd.h>
 #include <vector>
@@ -153,6 +155,16 @@ inline std::vector<uint8_t> read_vk_file(const std::filesystem::path& vk_path)
     }
 }
 
+template <typename T>
+inline std::vector<T> many_from_buffer_exact(const std::vector<uint8_t>& buffer, std::string_view object_name)
+{
+    if (buffer.size() % sizeof(T) != 0) {
+        THROW std::runtime_error(std::string(object_name) + " size must be a multiple of " + std::to_string(sizeof(T)) +
+                                 " bytes, got " + std::to_string(buffer.size()));
+    }
+    return ::many_from_buffer<T>(buffer);
+}
+
 // On Windows, std::filesystem::path uses wide strings (wchar_t) and doesn't implicitly convert
 // to std::string. On Linux/macOS (libstdc++), the conversion is implicit so these aren't needed.
 #ifdef _WIN32

barretenberg/cpp/src/barretenberg/api/file_io.test.cpp

@@ -0,0 +1,25 @@
+#include "barretenberg/api/file_io.hpp"
+#include "barretenberg/common/assert.hpp"
+#include "barretenberg/common/serialize.hpp"
+#include "barretenberg/numeric/uint256/uint256.hpp"
+#include <gtest/gtest.h>
+
+using namespace bb;
+
+TEST(APIFileIO, ManyFromBufferExactRejectsTrailingBytes)
+{
+    std::vector<uint8_t> bytes(sizeof(uint256_t) + 1, 0);
+
+    EXPECT_THROW_WITH_MESSAGE((many_from_buffer_exact<uint256_t>(bytes, "UltraHonk proof file")),
+                              "UltraHonk proof file size must be a multiple of 32 bytes, got 33");
+}
+
+TEST(APIFileIO, ManyFromBufferExactAcceptsAlignedBuffers)
+{
+    std::vector<uint256_t> expected{ uint256_t(1), uint256_t(2) };
+    auto bytes = to_buffer(expected);
+
+    auto parsed = many_from_buffer_exact<uint256_t>(bytes, "UltraHonk proof file");
+
+    EXPECT_EQ(parsed, expected);
+}