WebServer HTTP Response Header

Question

When adding header data to the response. We accept what the user is telling us and do no conversion of the data.

But: The Response object (and its stream) is going to handle the encoding/ transport. So we filter out content-length: and transport-encoding headers from outgoing requests as this will be added manually by the Response object.

HeaderResponse.h

#ifndef THORSANVIL_NISSE_NISSEHTTP_HEADER_RESPONSE_H
#define THORSANVIL_NISSE_NISSEHTTP_HEADER_RESPONSE_H

#include "NisseHTTPConfig.h"
#include <string_view>
#include <string>
#include <map>
#include <iostream>

namespace ThorsAnvil::Nisse::NisseHTTP
{

inline bool ichar_equals(char a, char b)
{
    return std::tolower(static_cast<unsigned char>(a)) ==
           std::tolower(static_cast<unsigned char>(b));
}

class HeaderResponse
{
    std::map<std::string, std::string>  headers;
    public:
        bool    empty() const;
        void    add(std::string_view header, std::string_view value);

    friend std::ostream& operator<<(std::ostream& stream, HeaderResponse const& headersBlock)
    {
        for (auto header: headersBlock.headers)
        {
            if (std::ranges::equal(std::string_view(header.first), std::string_view("content-length"), ichar_equals)) {
                continue;
            }
            if (std::ranges::equal(std::string_view(header.first), std::string_view("transfer-encoding"), ichar_equals)) {
                continue;
            }
            stream << header.first << ": " << header.second << "\r\n";
        }
        return stream;
    }
};

}

#endif

HeaderResponse.cpp

#include "HeaderResponse.h"

using namespace ThorsAnvil::Nisse::NisseHTTP;

bool HeaderResponse::empty() const
{
    return headers.empty();
}

void HeaderResponse::add(std::string_view header, std::string_view value)
{
    headers.emplace(header, value);
}

Answer 1

1. Better to keep all implementation logic in source file including operator<< and the inline function. You may replace the inline function with a lambda function like:

   auto ignore_case_char_compare = [](const char a, const char b)
                                   {
                                       return 
                                         std::tolower(static_cast<unsigned char>(a)) ==
                                         std::tolower(static_cast<unsigned char>(b));
                                   };
   

2. for (auto header: headersBlock.headers), here you can use structured bindings to separate header key and value, like:

   for (const auto& [headerKey, headerValue] : headersBlock.headers)
   

3. You can combine two if statements inside the loop into one using || operator.