headers.hpp

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#pragma once
 
/// @file userver/kafka/headers.hpp
/// @brief Kafka message header views and readers
 
#include <cstddef>
#include <iterator>
#include <string_view>
 
#include <userver/utils/span.hpp>
#include <userver/utils/zstring_view.hpp>
 
struct rd_kafka_headers_s;
 
USERVER_NAMESPACE_BEGIN
 
namespace kafka {
 
/// @brief Wrapper for Kafka header.
/// Header `name` must be valid null-terminated string.
/// Header `value` is treated as a binary data by Kafka.
struct HeaderView final {
    utils::zstring_view name;
    std::string_view value;
 
    bool operator==(const HeaderView&) const;
};
 
/// @brief Owning wrapper for Kafka header.
class OwningHeader final {
public:
    explicit OwningHeader(HeaderView header);
 
    OwningHeader(std::string name, std::string value);
 
    const std::string& GetName() const noexcept;
 
    std::string_view GetValue() const noexcept;
 
private:
    std::string name_;
    std::string value_;
};
 
bool operator==(const HeaderView& lhs, const OwningHeader& rhs);
bool operator==(const OwningHeader& lhs, const HeaderView& rhs);
 
/// @brief Ordered list of HeaderView.
/// Duplicated keys are supported.
/// Keys order is preserved.
using HeaderViews = utils::span<const HeaderView>;
 
/// @brief Header views iterator.
class HeadersIterator {
public:
    using iterator_category = std::forward_iterator_tag;
    using difference_type = std::ptrdiff_t;
    using value_type = HeaderView;
    using reference = HeaderView;
    using pointer = reference*;
 
    HeadersIterator() = default;
    HeadersIterator(const rd_kafka_headers_s* headers, std::size_t index);
 
    HeadersIterator operator++(int);
    HeadersIterator& operator++();
 
    reference operator*() const;
 
    bool operator==(const HeadersIterator&) const;
 
private:
    const rd_kafka_headers_s* headers_{nullptr};
    std::size_t index_{0};
};
 
static_assert(std::forward_iterator<HeadersIterator>);
 
/// @brief Class to read all message's headers.
class HeadersReader {
public:
    /// @note if `name` passed, only headers with matching name are read.
    HeadersReader(const rd_kafka_headers_s*);
 
    HeadersIterator begin() const;
    HeadersIterator end() const;
 
    std::size_t size() const noexcept;
 
private:
    const rd_kafka_headers_s* headers_{nullptr};
    std::size_t size_;
};
 
}  // namespace kafka
 
USERVER_NAMESPACE_END