src/tint/utils/text/base64.h

// Copyright 2023 The Dawn & Tint Authors
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#ifndef SRC_TINT_UTILS_TEXT_BASE64_H_
#define SRC_TINT_UTILS_TEXT_BASE64_H_

#include <cstdint>
#include <optional>
#include <string>

#include "src/tint/utils/containers/vector.h"
#include "src/tint/utils/result.h"

namespace tint {

// Note: that Decode and Encode are not guaranteed to be a perfect roundtrip, because the value
// calculated by Decode is based on all the comments in the WGSL file, and the intended usage of
// encode is to be used as part of emitting a single comment string.
// So for this sequence: multiple comments -> Encode -> binary -> Decode, you will get a single
// string to put in a comment. The data when parsed should be equivalent though, you are just not
// guaranteed to get the exact same text out.

/// Decodes a byte from a base64 encoded character
/// @param c the character to decode
/// @return the decoded value, or std::nullopt if the character is padding ('=') or an invalid
/// character.
inline std::optional<uint8_t> DecodeBase64(char c) {
    if (c >= 'A' && c <= 'Z') {
        return static_cast<uint8_t>(c - 'A');
    }
    if (c >= 'a' && c <= 'z') {
        return static_cast<uint8_t>(26 + c - 'a');
    }
    if (c >= '0' && c <= '9') {
        return static_cast<uint8_t>(52 + c - '0');
    }
    if (c == '+') {
        return 62;
    }
    if (c == '/') {
        return 63;
    }
    return std::nullopt;
}
/// DecodeBase64FromComments parses all the comments from the WGSL source string as a base64 byte
/// stream. Non-base64 characters are skipped
/// @param wgsl the WGSL source
/// @return the base64 decoded bytes
Vector<std::byte, 0> DecodeBase64FromComments(std::string_view wgsl);

/// EncodeBase64 encodes a byte stream as a base64 string
/// @param data the data to encode
/// @return the base64 encoded string, or Failure if a byte is not in the range [0, 63]
Result<std::string> EncodeBase64(std::span<const std::byte> data);

}  // namespace tint

#endif  // SRC_TINT_UTILS_TEXT_BASE64_H_