Start assets component image signature tests

src/assets/image_format.cpp

@@ -0,0 +1,94 @@
+#include "assets/image_format.h"
+
+#include <array>
+#include <cstdint>
+
+namespace pp::assets {
+
+namespace {
+
+constexpr std::array png_signature {
+    std::byte { 0x89 },
+    std::byte { 0x50 },
+    std::byte { 0x4e },
+    std::byte { 0x47 },
+    std::byte { 0x0d },
+    std::byte { 0x0a },
+    std::byte { 0x1a },
+    std::byte { 0x0a },
+};
+
+[[nodiscard]] bool starts_with(std::span<const std::byte> bytes, std::span<const std::byte> prefix) noexcept
+{
+    if (bytes.size() < prefix.size()) {
+        return false;
+    }
+
+    for (std::size_t i = 0; i < prefix.size(); ++i) {
+        if (bytes[i] != prefix[i]) {
+            return false;
+        }
+    }
+
+    return true;
+}
+
+[[nodiscard]] bool is_prefix_of(std::span<const std::byte> bytes, std::span<const std::byte> signature) noexcept
+{
+    if (bytes.size() >= signature.size()) {
+        return false;
+    }
+
+    for (std::size_t i = 0; i < bytes.size(); ++i) {
+        if (bytes[i] != signature[i]) {
+            return false;
+        }
+    }
+
+    return true;
+}
+
+}
+
+pp::foundation::Result<ImageFormat> detect_image_format(std::span<const std::byte> bytes) noexcept
+{
+    if (bytes.empty()) {
+        return pp::foundation::Result<ImageFormat>::failure(
+            pp::foundation::Status::invalid_argument("image data must not be empty"));
+    }
+
+    if (starts_with(bytes, png_signature)) {
+        return pp::foundation::Result<ImageFormat>::success(ImageFormat::png);
+    }
+
+    if (is_prefix_of(bytes, png_signature)) {
+        return pp::foundation::Result<ImageFormat>::failure(
+            pp::foundation::Status::out_of_range("image data is a truncated PNG signature"));
+    }
+
+    if (bytes.size() < 3U) {
+        return pp::foundation::Result<ImageFormat>::failure(
+            pp::foundation::Status::out_of_range("image data is too short to identify"));
+    }
+
+    if (bytes[0] == std::byte { 0xff } && bytes[1] == std::byte { 0xd8 } && bytes[2] == std::byte { 0xff }) {
+        return pp::foundation::Result<ImageFormat>::success(ImageFormat::jpeg);
+    }
+
+    return pp::foundation::Result<ImageFormat>::failure(
+        pp::foundation::Status::invalid_argument("unsupported image signature"));
+}
+
+const char* image_format_name(ImageFormat format) noexcept
+{
+    switch (format) {
+    case ImageFormat::png:
+        return "png";
+    case ImageFormat::jpeg:
+        return "jpeg";
+    }
+
+    return "unknown";
+}
+
+}

src/assets/image_format.h

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+#pragma once
+
+#include "foundation/result.h"
+
+#include <cstddef>
+#include <span>
+
+namespace pp::assets {
+
+enum class ImageFormat {
+    png,
+    jpeg,
+};
+
+[[nodiscard]] pp::foundation::Result<ImageFormat> detect_image_format(
+    std::span<const std::byte> bytes) noexcept;
+
+[[nodiscard]] const char* image_format_name(ImageFormat format) noexcept;
+
+}