multipart.h

#pragma once
 
#include <string>
#include <vector>
#include <sstream>
 
#include "crow/http_request.h"
#include "crow/returnable.h"
 
namespace crow
{
    ///Encapsulates anything related to processing and organizing `multipart/xyz` messages
    namespace multipart
    {
        const std::string dd = "--";
        const std::string crlf = "\r\n";
 
        ///The first part in a section, contains metadata about the part
        struct header
        {
                std::pair<std::string, std::string> value; ///< The first part of the header, usually `Content-Type` or `Content-Disposition`
                std::unordered_map<std::string, std::string> params; ///< The parameters of the header, come after the `value`
        };
 
        ///One part of the multipart message
 
        ///It is usually separated from other sections by a `boundary`
        ///
        struct part
        {
            std::vector<header> headers; ///< (optional) The first part before the data, Contains information regarding the type of data and encoding
            std::string body; ///< The actual data in the part
        };
 
        ///The parsed multipart request/response
        struct message : public returnable
        {
            ci_map headers;
            std::string boundary; ///< The text boundary that separates different `parts`
            std::vector<part> parts; ///< The individual parts of the message
 
            const std::string& get_header_value(const std::string& key) const
            {
                return crow::get_header_value(headers, key);
            }
 
            ///Represent all parts as a string (**does not include message headers**)
            std::string dump() const override
            {
                std::stringstream str;
                std::string delimiter = dd + boundary;
 
                for (unsigned i=0 ; i<parts.size(); i++)
                {
                    str << delimiter << crlf;
                    str << dump(i);
                }
                str << delimiter << dd << crlf;
                return str.str();
            }
 
            ///Represent an individual part as a string
            std::string dump(int part_) const
            {
                std::stringstream str;
                part item = parts[part_];
                for (header item_h: item.headers)
                {
                    str << item_h.value.first << ": " << item_h.value.second;
                    for (auto& it: item_h.params)
                    {
                        str << "; " << it.first << '=' << pad(it.second);
                    }
                    str << crlf;
                }
                str << crlf;
                str << item.body << crlf;
                return str.str();
            }
 
            ///Default constructor using default values
            message(const ci_map& headers, const std::string& boundary, const std::vector<part>& sections)
              : returnable("multipart/form-data"), headers(headers), boundary(boundary), parts(sections){}
 
            ///Create a multipart message from a request data
            message(const request& req)
              : returnable("multipart/form-data"),
                headers(req.headers),
                boundary(get_boundary(get_header_value("Content-Type"))),
                parts(parse_body(req.body))
            {}
 
          private:
 
            std::string get_boundary(const std::string& header) const
            {
                size_t found = header.find("boundary=");
                if (found)
                    return header.substr(found+9);
                return std::string();
            }
 
            std::vector<part> parse_body(std::string body)
            {
 
                  std::vector<part> sections;
 
                  std::string delimiter = dd + boundary;
 
                  while(body != (crlf))
                  {
                      size_t found = body.find(delimiter);
                      std::string section = body.substr(0, found);
 
                      //+2 is the CRLF
                      //We don't check it and delete it so that the same delimiter can be used for
                      //the last delimiter (--delimiter--CRLF).
                      body.erase(0, found + delimiter.length() + 2);
                      if (!section.empty())
                      {
                          sections.emplace_back(parse_section(section));
                      }
                  }
                  return sections;
            }
 
            part parse_section(std::string& section)
            {
                struct part to_return;
 
                size_t found = section.find(crlf+crlf);
                std::string head_line = section.substr(0, found+2);
                section.erase(0, found + 4);
 
                parse_section_head(head_line, to_return);
                to_return.body = section.substr(0, section.length()-2);
                return to_return;
            }
 
            void parse_section_head(std::string& lines, part& part)
            {
                while (!lines.empty())
                {
                    header to_add;
 
                    size_t found = lines.find(crlf);
                    std::string line = lines.substr(0, found);
                    lines.erase(0, found+2);
                    //add the header if available
                    if (!line.empty())
                    {
                        size_t found = line.find("; ");
                        std::string header = line.substr(0, found);
                        if (found != std::string::npos)
                            line.erase(0, found+2);
                        else
                            line = std::string();
 
                        size_t header_split = header.find(": ");
 
                        to_add.value = std::pair<std::string, std::string>(header.substr(0, header_split), header.substr(header_split+2));
                    }
 
                    //add the parameters
                    while (!line.empty())
                    {
                        size_t found = line.find("; ");
                        std::string param = line.substr(0, found);
                        if (found != std::string::npos)
                            line.erase(0, found+2);
                        else
                            line = std::string();
 
                        size_t param_split = param.find('=');
 
                        std::string value = param.substr(param_split+1);
 
                        to_add.params.emplace(param.substr(0, param_split), trim(value));
                    }
                    part.headers.emplace_back(to_add);
                }
            }
 
            inline std::string trim (std::string& string, const char& excess = '"') const
            {
                if (string.length() > 1 && string[0] == excess && string[string.length()-1] == excess)
                    return string.substr(1, string.length()-2);
                return string;
            }
 
            inline std::string pad (std::string& string, const char& padding = '"') const
            {
                    return (padding + string + padding);
            }
 
        };
    }
}