From 6964f5f9f2f83db92d94287c0f0d380db7006585 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Luis=20D=C3=ADaz=20M=C3=A1s?= <piponazo@gmail.com>
Date: Wed, 13 Apr 2022 13:25:50 +0200
Subject: [PATCH] DataBuf::c_data() returns nullptr when empty + avoid
 duplication

After the previous commit, I realized that std::vector::data() also
returns nullptr when the vector is empty. So I decided to emulate this
behavior in DataBuf::c_data().

Anyways, the changes done in the previous commit are valid and allow us
to avoid some processing when the DataBuf is empty.
---
 include/exiv2/types.hpp  |  2 +-
 src/types.cpp            | 15 ++++-----------
 unitTests/test_types.cpp |  3 ++-
 3 files changed, 7 insertions(+), 13 deletions(-)

diff --git a/include/exiv2/types.hpp b/include/exiv2/types.hpp
index 03419f0f..05268dac 100644
--- a/include/exiv2/types.hpp
+++ b/include/exiv2/types.hpp
@@ -201,7 +201,7 @@ struct EXIV2API DataBuf {
   int cmpBytes(size_t offset, const void* buf, size_t bufsize) const;
 
   //! Returns a data pointer.
-  byte* data(size_t offset = 0);
+  [[nodiscard]] byte* data(size_t offset = 0);
 
   //! Returns a (read-only) data pointer.
   [[nodiscard]] const byte* c_data(size_t offset = 0) const;
diff --git a/src/types.cpp b/src/types.cpp
index 1d03c8b4..a3f691e9 100644
--- a/src/types.cpp
+++ b/src/types.cpp
@@ -172,21 +172,14 @@ int Exiv2::DataBuf::cmpBytes(size_t offset, const void* buf, size_t bufsize) con
 }
 
 byte* Exiv2::DataBuf::data(size_t offset) {
-  if (offset >= pData_.size()) {
-    throw std::out_of_range("Overflow in Exiv2::DataBuf::c_data");
-  }
-  if (pData_.empty() || pData_.size() == offset) {
-    return nullptr;
-  }
-  return &pData_[offset];
+  return const_cast<byte*>(c_data(offset));
 }
 
 const byte* Exiv2::DataBuf::c_data(size_t offset) const {
-  if (offset >= pData_.size()) {
-    throw std::out_of_range("Overflow in Exiv2::DataBuf::c_data");
-  }
-  if (pData_.empty() || pData_.size() == offset) {
+  if (pData_.empty()) {
     return nullptr;
+  } else if (offset >= pData_.size()) {
+    throw std::out_of_range("Overflow in Exiv2::DataBuf::c_data");
   }
   return &pData_[offset];
 }
diff --git a/unitTests/test_types.cpp b/unitTests/test_types.cpp
index 227a345e..ba77a11c 100644
--- a/unitTests/test_types.cpp
+++ b/unitTests/test_types.cpp
@@ -48,7 +48,8 @@ TEST(DataBuf, canBeConstructedFromExistingData) {
 TEST(DataBuf, tryingToAccessTooFarElementThrows) {
   const std::array<byte, 4> data {'h', 'o', 'l', 'a'};
   DataBuf instance(data.data(), data.size());
-  ASSERT_THROW(instance.data(4), std::out_of_range);
+  ASSERT_THROW([[maybe_unused]] auto d = instance.data(4), std::out_of_range);
+  ASSERT_THROW([[maybe_unused]] auto d = instance.c_data(4), std::out_of_range);
 }
 
 // Test methods like DataBuf::read_uint32 and DataBuf::write_uint32.