From 94ca0ab79e8ed53d854b6c6debaea2942d610b51 Mon Sep 17 00:00:00 2001
From: Jan <jan@laupetin.net>
Date: Thu, 23 Jan 2025 21:17:30 +0000
Subject: [PATCH] fix: loading of base64 data from gltf files

---
 src/Crypto/Impl/Base64.cpp                    | 25 +++++++++++++++++--
 src/Crypto/Impl/Base64.h                      |  1 +
 .../XModel/Gltf/Internal/GltfBuffer.cpp       |  5 ++--
 3 files changed, 27 insertions(+), 4 deletions(-)

diff --git a/src/Crypto/Impl/Base64.cpp b/src/Crypto/Impl/Base64.cpp
index f4400d6a..77d1717f 100644
--- a/src/Crypto/Impl/Base64.cpp
+++ b/src/Crypto/Impl/Base64.cpp
@@ -32,7 +32,8 @@ namespace base64
 
     size_t DecodeBase64(const void* base64Data, const size_t inputLength, void* outputBuffer, const size_t outputBufferSize)
     {
-        unsigned long outLength = GetBase64DecodeOutputLength(inputLength);
+        unsigned long outLength = GetBase64DecodeOutputLength(base64Data, inputLength);
+        assert(outLength <= outputBufferSize);
         if (outLength > outputBufferSize)
             return 0u;
 
@@ -42,8 +43,28 @@ namespace base64
         return static_cast<size_t>(outLength);
     }
 
+    size_t GetBase64DecodeOutputLength(const void* base64Data, const size_t inputLength)
+    {
+        assert(base64Data);
+        assert(inputLength);
+
+        if (!base64Data || inputLength == 0u)
+            return 0u;
+
+        auto padding = 0u;
+        if (inputLength >= 1 && static_cast<const char*>(base64Data)[inputLength - 1] == '=')
+        {
+            if (inputLength >= 2 && static_cast<const char*>(base64Data)[inputLength - 2] == '=')
+                padding = 2u;
+            else
+                padding = 1u;
+        }
+
+        return ((inputLength / 4u) * 3u) - padding;
+    }
+
     size_t GetBase64DecodeOutputLength(const size_t inputLength)
     {
-        return inputLength / 4u;
+        return (inputLength / 4u) * 3u;
     }
 } // namespace base64
diff --git a/src/Crypto/Impl/Base64.h b/src/Crypto/Impl/Base64.h
index 1e1ec51d..8264a8c3 100644
--- a/src/Crypto/Impl/Base64.h
+++ b/src/Crypto/Impl/Base64.h
@@ -8,5 +8,6 @@ namespace base64
     size_t GetBase64EncodeOutputLength(size_t inputLength);
 
     size_t DecodeBase64(const void* base64Data, size_t inputLength, void* outputBuffer, size_t outputBufferSize);
+    size_t GetBase64DecodeOutputLength(const void* base64Data, const size_t inputLength);
     size_t GetBase64DecodeOutputLength(size_t inputLength);
 } // namespace base64
diff --git a/src/ObjLoading/XModel/Gltf/Internal/GltfBuffer.cpp b/src/ObjLoading/XModel/Gltf/Internal/GltfBuffer.cpp
index a0edf7f0..fcca640b 100644
--- a/src/ObjLoading/XModel/Gltf/Internal/GltfBuffer.cpp
+++ b/src/ObjLoading/XModel/Gltf/Internal/GltfBuffer.cpp
@@ -48,11 +48,12 @@ bool DataUriBuffer::ReadDataFromUri(const std::string& uri)
     if (!IsDataUri(uri))
         return false;
 
+    const auto base64Data = &uri[URI_PREFIX_LENGTH];
     const auto base64DataLength = uri.size() - URI_PREFIX_LENGTH;
-    m_data_size = base64::GetBase64DecodeOutputLength(base64DataLength);
+    m_data_size = base64::GetBase64DecodeOutputLength(base64Data, base64DataLength);
     m_data = std::make_unique<uint8_t[]>(m_data_size);
 
-    m_data_size = base64::DecodeBase64(&uri[URI_PREFIX_LENGTH], base64DataLength, m_data.get(), m_data_size);
+    m_data_size = base64::DecodeBase64(base64Data, base64DataLength, m_data.get(), m_data_size);
 
     return m_data_size > 0;
 }