refactor(fstypes): use std::array for magic / SHA2 members

include/dwarfs/fstypes.h

@@ -21,11 +21,13 @@
 
 #pragma once
 
+#include <array>
 #include <cstddef>
 #include <cstdint>
 #include <iosfwd>
 #include <optional>
 #include <string>
+#include <string_view>
 #include <vector>
 
 #include <dwarfs/block_compressor.h> // TODO: or the other way round?
@@ -54,9 +56,13 @@ enum class section_type : uint16_t {
 };
 
 struct file_header {
-  char magic[6]; // "DWARFS"
-  uint8_t major; // major version
-  uint8_t minor; // minor version
+  std::array<char, 6> magic; // "DWARFS"
+  uint8_t major;             // major version
+  uint8_t minor;             // minor version
+
+  std::string_view magic_sv() const {
+    return std::string_view(magic.data(), magic.size());
+  }
 };
 
 struct section_header {
@@ -70,15 +76,16 @@ struct section_header {
 };
 
 struct section_header_v2 {
-  char magic[6];            //  [0] "DWARFS" / file_header no longer needed
-  uint8_t major;            //  [6] major version
-  uint8_t minor;            //  [7] minor version
-  uint8_t sha2_512_256[32]; //  [8] SHA2-512/256 starting from next field
-  uint64_t xxh3_64;         // [40] XXH3-64 starting from next field
-  uint32_t number;          // [48] section number
-  uint16_t type;            // [52] section type
-  uint16_t compression;     // [54] compression
-  uint64_t length;          // [56] length of section
+  std::array<char, 6> magic; //  [0] "DWARFS" / file_header no longer needed
+  uint8_t major;             //  [6] major version
+  uint8_t minor;             //  [7] minor version
+  std::array<uint8_t, 32>    //  [8] SHA2-512/256 starting from next field
+      sha2_512_256;          //
+  uint64_t xxh3_64;          // [40] XXH3-64 starting from next field
+  uint32_t number;           // [48] section number
+  uint16_t type;             // [52] section type
+  uint16_t compression;      // [54] compression
+  uint64_t length;           // [56] length of section
 
   std::string to_string() const;
   void dump(std::ostream& os) const;

src/internal/fs_section.cpp

@@ -204,8 +204,8 @@ class fs_section_v2 final : public fs_section::impl {
         sizeof(section_header_v2) - offsetof(section_header_v2, xxh3_64);
     return checksum::verify(checksum::algorithm::SHA2_512_256,
                             mm.as<void>(start_ - hdr_sha_len),
-                            hdr_.length + hdr_sha_len, &hdr_.sha2_512_256,
-                            sizeof(hdr_.sha2_512_256));
+                            hdr_.length + hdr_sha_len, hdr_.sha2_512_256.data(),
+                            hdr_.sha2_512_256.size());
   }
 
   std::span<uint8_t const> data(mmif const& mm) const override {
@@ -221,8 +221,8 @@ class fs_section_v2 final : public fs_section::impl {
   }
 
   std::optional<std::vector<uint8_t>> sha2_512_256_value() const override {
-    return std::vector<uint8_t>(hdr_.sha2_512_256,
-                                hdr_.sha2_512_256 + sizeof(hdr_.sha2_512_256));
+    return std::vector<uint8_t>(hdr_.sha2_512_256.begin(),
+                                hdr_.sha2_512_256.end());
   }
 
  private:

src/reader/internal/filesystem_parser.cpp

@@ -121,7 +121,7 @@ filesystem_parser::filesystem_parser(std::shared_ptr<mmif> mm,
 
   auto fh = mm_->as<file_header>(image_offset_);
 
-  if (::memcmp(&fh->magic[0], "DWARFS", 6) != 0) {
+  if (fh->magic_sv() != "DWARFS") {
     DWARFS_THROW(runtime_error, "magic not found");
   }
 

src/writer/filesystem_writer.cpp

@@ -500,7 +500,7 @@ void fsblock::build_section_header(section_header_v2& sh,
                                    std::optional<fs_section> const& sec) {
   auto range = fsb.data();
 
-  ::memcpy(&sh.magic[0], "DWARFS", 6);
+  ::memcpy(sh.magic.data(), "DWARFS", 6);
   sh.major = MAJOR_VERSION;
   sh.minor = MINOR_VERSION;
   sh.number = fsb.block_no();
@@ -520,9 +520,9 @@ void fsblock::build_section_header(section_header_v2& sh,
       auto xxh = sec->xxh3_64_value();
       auto sha = sec->sha2_512_256_value();
 
-      if (xxh && sha && sha->size() == sizeof(sh.sha2_512_256)) {
+      if (xxh && sha && sha->size() == sh.sha2_512_256.size()) {
         sh.xxh3_64 = xxh.value();
-        std::copy(sha->begin(), sha->end(), &sh.sha2_512_256[0]);
+        std::copy(sha->begin(), sha->end(), sh.sha2_512_256.data());
         return;
       }
     }
@@ -538,7 +538,8 @@ void fsblock::build_section_header(section_header_v2& sh,
   sha.update(&sh.xxh3_64,
              sizeof(section_header_v2) - offsetof(section_header_v2, xxh3_64));
   sha.update(range.data(), range.size());
-  DWARFS_CHECK(sha.finalize(&sh.sha2_512_256), "SHA512/256 checksum failed");
+  DWARFS_CHECK(sha.finalize(sh.sha2_512_256.data()),
+               "SHA512/256 checksum failed");
 }
 
 } // namespace

test/filesystem_test.cpp

@@ -207,7 +207,7 @@ std::string valid_v1_header() {
 std::string valid_v2_header(uint32_t section_number = 0) {
   section_header_v2 hdr;
   std::memset(&hdr, 0, sizeof(hdr));
-  std::memcpy(hdr.magic, "DWARFS", 6);
+  std::memcpy(hdr.magic.data(), "DWARFS", 6);
   hdr.major = 2;
   hdr.minor = 3;
   hdr.number = section_number;