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());
  }

MultiPartParser Object

Summary:

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

Summary:

Example:

getFiles()

Summary

Example:

getParameters()

Summary

Returns:

Example:

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

Summary

Inputs:

Returns:

Example:

HttpFile Object

Summary:

getFileName()

Summary

Returns:

Example:

fileLength()

Summary

Returns:

Example:

getFileExtension()

Summary

Returns:

Example:

getMd5()

Summary

Returns:

save()

Summary

save(const std::string &path)

Summary

Example:

saveAs(const std::string &path)

Summary

Example:

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`MultiPartParser` Object

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

`getFiles()`

`getParameters()`

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

`HttpFile` Object

`getFileName()`

`fileLength()`

`getFileExtension()`

`getMd5()`

`save()`

`save(const std::string &path)`

`saveAs(const std::string &path)`