Verify downloaded file against content-md5 response header

wxdata/source/scwx/util/digest.cpp

@@ -0,0 +1,82 @@
+#include <scwx/util/digest.hpp>
+#include <scwx/util/logger.hpp>
+
+namespace scwx
+{
+namespace util
+{
+
+static const std::string logPrefix_ = "scwx::util::digest";
+static const auto        logger_    = scwx::util::Logger::Create(logPrefix_);
+
+bool ComputeDigest(const EVP_MD*              mdtype,
+                   std::istream&              is,
+                   std::vector<std::uint8_t>& digest)
+{
+   int         mdsize;
+   EVP_MD_CTX* mdctx = nullptr;
+
+   digest.clear();
+
+   if ((mdsize = EVP_MD_get_size(mdtype)) < 1)
+   {
+      logger_->error("Invalid digest");
+      return false;
+   }
+
+   if ((mdctx = EVP_MD_CTX_new()) == nullptr)
+   {
+      logger_->error("Error allocating a digest context");
+      return false;
+   }
+
+   if (!EVP_DigestInit_ex(mdctx, mdtype, nullptr))
+   {
+      logger_->error("Message digest initialization failed");
+      EVP_MD_CTX_free(mdctx);
+      return false;
+   }
+
+   is.seekg(0, std::ios_base::end);
+   const std::size_t streamSize = is.tellg();
+   is.seekg(0, std::ios_base::beg);
+
+   std::size_t bytesRead = 0;
+   std::size_t chunkSize = 4096;
+   std::string fileData;
+   fileData.resize(chunkSize);
+
+   while (bytesRead < streamSize)
+   {
+      const std::size_t bytesRemaining = streamSize - bytesRead;
+      const std::size_t readSize       = std::min(chunkSize, bytesRemaining);
+
+      is.read(fileData.data(), readSize);
+
+      if (!is.good() || !EVP_DigestUpdate(mdctx, fileData.data(), readSize))
+      {
+         logger_->error("Message digest update failed");
+         EVP_MD_CTX_free(mdctx);
+         return false;
+      }
+
+      bytesRead += readSize;
+   }
+
+   digest.resize(mdsize);
+
+   if (!EVP_DigestFinal_ex(mdctx, digest.data(), nullptr))
+   {
+      logger_->error("Message digest finalization failed");
+      EVP_MD_CTX_free(mdctx);
+      digest.clear();
+      return false;
+   }
+
+   EVP_MD_CTX_free(mdctx);
+
+   return true;
+}
+
+} // namespace util
+} // namespace scwx