ENG 09 1 File Handler

File parsing is extracting the file (or files) from a multipart-data POST request to an HttpFile object through MultiPartParser, here is some information about:

MultiPartParser Object

Summary:

It is the object that you will use to extract and temporarily store the request files.

• parse(const std::shared_ptr<HttpRequest> &req)

  Summary:

  Receives the request object as a parameter, reads and identifies the files (if heard) and transfers it to the MultiPartParser variable.

  Example:

    #include "mycontroller.h"
  
    using namespace drogon;
  
    void mycontroller::postfile(const HttpRequestPtr &req, std::function<void (const HttpResponsePtr &)> &&callback) {
        // Only Post Requests (File Form)
  
        MultiPartParser fileParser;
        fileParser.parse(req);
    }

• getFiles()

  Summary

  Must be called after parse(), returns files of request in the format std::vector&ltHttpFile&gt.

  Example:

    #include "mycontroller.h"
  
    using namespace drogon;
  
    void mycontroller::postfile(const HttpRequestPtr &req, std::function<void (const HttpResponsePtr &)> &&callback) {
        // Only Post Requests (File Form)
  
        MultiPartParser fileParser;
        fileParser.parse(req);
  
        // Check if have files
        if (fileParser.getFiles().empty()) {
            // No files found
        }
  
        size_t num_of_files = fileParser.getFiles().size();
    }

• getParameters()

  Summary

  Must be called after parse(), returns the list of other parts from the MultiPartData form.

  Returns:

  std::unordered_map&ltstd::basic_string&ltchar&gt&gt (key, value)

  Example:

    #include "mycontroller.h"
  
    using namespace drogon;
  
    void mycontroller::postfile(const HttpRequestPtr &req, std::function<void (const HttpResponsePtr &)> &&callback) {
        // Only Post Requests (File Form)
  
        MultiPartParser fileParser;
        fileParser.parse(req);
  
        if (!fileParser.getFiles().empty()) {
            for (const auto &header : fileParser.getParameters()){
                header.first // Key form
                header.second // Value from key form
            }
        }
    }

• getParameter<Typename T>(const std::string &key)

  Summary

  Must be called after parse(), individual version of getParameters().

  Inputs:

  The type of the expected object (will be converted automatically), the key value of the parameter.

  Returns:

  The content of the parameter corresponding to the key in the informed format, if it does not exist, will return the default value of the T Object.

  Example:

    #include "mycontroller.h"
  
    using namespace drogon;
  
    void mycontroller::postfile(const HttpRequestPtr &req, std::function<void (const HttpResponsePtr &)> &&callback) {
        // Only Post Requests (File Form)
  
        MultiPartParser fileParser;
        fileParser.parse(req);
  
        std::string email = fileParser.getParameter<std::string>("email_form");
  
        // Default type of string is ""
        if (email.empty()) {
            // email_form not found
        }
    }

HttpFile Object

Summary:

It is the object that represents a file in memory, used by MultiPartParser.

• getFileName()

  Summary

  Self-explanatory name, gets the original name of the file that was received.

  Returns:

  std::string.

  Example:

    #include "mycontroller.h"
  
    using namespace drogon;
  
    void mycontroller::postfile(const HttpRequestPtr &req, std::function<void (const HttpResponsePtr &)> &&callback) {
        // Only Post Requests (File Form)
  
        MultiPartParser fileParser;
        fileParser.parse(req);
  
        std::string filename = fileParser.getFiles()[0].getFileName();
    }

• fileLength()

  Summary

  Gets the file size.

  Returns:

  size_t

  Example:

    #include "mycontroller.h"
  
    using namespace drogon;
  
    void mycontroller::postfile(const HttpRequestPtr &req, std::function<void (const HttpResponsePtr &)> &&callback) {
        // Only Post Requests (File Form)
  
        MultiPartParser fileParser;
        fileParser.parse(req);
  
        size_t filesize = fileParser.getFiles()[0].fileLength();
    }

• getFileExtension()

  Summary

  Gets the file extension.

  Returns:

  std::string

  Example:

    #include "mycontroller.h"
  
    using namespace drogon;
  
    void mycontroller::postfile(const HttpRequestPtr &req, std::function<void (const HttpResponsePtr &)> &&callback) {
        // Only Post Requests (File Form)
  
        MultiPartParser fileParser;
        fileParser.parse(req);
  
        std::string file_extension = fileParser.getFiles()[0].getFileExtension();
    }

• getMd5()

  Summary

  Get MD5 hash of file to check integrity.

  Returns:

  std::string

• save()

  Summary

  Save the file to the file system. The folder saving the file is UploadPath configured in config.json (or equivalent). The full path is

  drogon::app().getUploadPath()+"/"+this->getFileName()

  Or to simplify, it is saved as: UploadPath/filename

• save(const std::string &path)

  Summary

  Version if parameter is not omitted, uses the &path parameter instead of UploadPath.

  Example:

    #include "mycontroller.h"
  
    using namespace drogon;
  
    void mycontroller::postfile(const HttpRequestPtr &req, std::function<void (const HttpResponsePtr &)> &&callback) {
        // Only Post Requests (File Form)
  
        MultiPartParser fileParser;
        fileParser.parse(req);
  
        // Relative path
        fileParser.getFiles()[0].save("./"); // Writes the file to the same directory on the server, with the original name
  
        // Absolute path
        fileParser.getFiles()[0].save("/home/user/downloads/"); // Writes the file in the indicated directory, with the original name
    }

• saveAs(const std::string &path)

  Summary

  Writes the file to the path parameter with a new name (ignores the original name).

  Example:

    #include "mycontroller.h"
  
    using namespace drogon;
  
    void mycontroller::postfile(const HttpRequestPtr &req, std::function<void (const HttpResponsePtr &)> &&callback) {
        // Only Post Requests (File Form)
  
        MultiPartParser fileParser;
        fileParser.parse(req);
  
        // Relative path
        fileParser.getFiles()[0].saveAs("./image.png"); // Same path of server
        /* Just example, Don't do this, you would overwrite the file format without checking if it really is png */
  
        // Absolute path
        fileParser.getFiles()[0].save("/home/user/downloads/anyname." + fileParser.getFiles()[0].getFileExtension());
    }

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