Delphi ActiveX
Delphi ActiveX
MIME Content-Transfer-Encoding Header Field
See more MIME Examples
Explains the Content-Transfer-Encoding header field and how it affects how data is stored in the MIME.
Chilkat Delphi ActiveX Downloads
uses
Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, Chilkat_TLB;
...
procedure TForm1.Button1Click(Sender: TObject);
var
success: Integer;
sbJpgBase64: TChilkatStringBuilder;
mime: TChilkatMime;
mimeBytes: Array of Byte;
jpgBytes: Array of Byte;
jpgBase64: WideString;
mimeStr: WideString;
begin
success := 0;
// The Content-Transfer-Encoding header field is typically set to one of these values:
//
// base64
// quoted-printable
// binary
// 8bit
// 7bit
// If the encoding is base64 or quoted-printable, then the bytes of the content are encoded as such.
// The values "8bit", "7bit", and "binary" all imply that NO encoding has been performed.
// Here are some guidelines and hints:
//
// 1) "8bit", "7bit", and "binary" encodings (i.e. NO encoding) results in the smallest MIME.
// 2) A "binary" encoding implies non-text data. Binary MIME CANNOT be retrieved as a string. It can only be retrieved as a byte array.
// 3) "8bit" and "7bit" encodings imply text.
// 7bit implies that the text is us-ascii (all byte values less than or equal to 0x7F).
// 8bit implies that the text contains non-us-ascii chars.
// 4) Base64 is the best choice for encoding non-text data, such as PDF's, images, etc.
// 5) quoted-printable is the best choice for encoding text data where most chars are going to be us-ascii. This would typically
// include all Western European languages. For Asian, Arabic, Hebrew, etc. where most chars in the text are non-us-ascii,
// the most efficient encoding would be base64.
// Let's demonstrate with this small JPG image.
sbJpgBase64 := TChilkatStringBuilder.Create(Self);
sbJpgBase64.Append('/9j/4AAQSkZJRgABAQEASABIAAD//gAmRmlsZSB3cml0dGVuIGJ5IEFkb2JlIFBob3Rvc2hvcD8g' + #13#10);
sbJpgBase64.Append('NC4w/9sAQwAQCwwODAoQDg0OEhEQExgoGhgWFhgxIyUdKDozPTw5Mzg3QEhcTkBEV0U3OFBtUVdf' + #13#10);
sbJpgBase64.Append('YmdoZz5NcXlwZHhcZWdj/9sAQwEREhIYFRgvGhovY0I4QmNjY2NjY2NjY2NjY2NjY2NjY2NjY2Nj' + #13#10);
sbJpgBase64.Append('Y2NjY2NjY2NjY2NjY2NjY2NjY2NjY2NjY2Nj/8IAEQgAFAAUAwERAAIRAQMRAf/EABcAAAMBAAAA' + #13#10);
sbJpgBase64.Append('AAAAAAAAAAAAAAIDBAX/xAAYAQADAQEAAAAAAAAAAAAAAAABAgMEAP/aAAwDAQACEAMQAAAB2kZY' + #13#10);
sbJpgBase64.Append('NNEijWKddfTmLgALWH//xAAbEAACAgMBAAAAAAAAAAAAAAABAgMRAAQSE//aAAgBAQABBQL0XqN+' + #13#10);
sbJpgBase64.Append('pM2aqJGMiqFFCyg7z//EABwRAAICAgMAAAAAAAAAAAAAAAERAAIQIQMSUf/aAAgBAwEBPwHqU5aq' + #13#10);
sbJpgBase64.Append('Axx+y1tMQl4elj//xAAcEQEAAQUBAQAAAAAAAAAAAAABEQACEBIhA1H/2gAIAQIBAT8B3Bhqy7Zc' + #13#10);
sbJpgBase64.Append('enyiwmGgDhiOzj//xAAdEAABAwUBAAAAAAAAAAAAAAABAAIREBIhIkFR/9oACAEBAAY/ArZyn+Cg' + #13#10);
sbJpgBase64.Append('xtxWuJaoCnqDuin/xAAcEAABBAMBAAAAAAAAAAAAAAABABEhYRAxQVH/2gAIAQEAAT8hkEwPUUR9' + #13#10);
sbJpgBase64.Append('DYfE4nxtRpIkBTsayuALIiuY/9oADAMBAAIAAwAAABDWPTsf/8QAGhEAAwADAQAAAAAAAAAAAAAA' + #13#10);
sbJpgBase64.Append('AAEREDFBIf/aAAgBAwEBPxC0DVPcWm+Ce4OesrkE6bjH/8QAGBEBAQEBAQAAAAAAAAAAAAAAAREA' + #13#10);
sbJpgBase64.Append('QRD/2gAIAQIBAT8QahMiOc8YgSrnTY3ELclHXn//xAAcEAEBAAIDAQEAAAAAAAAAAAABEQAhMUFx' + #13#10);
sbJpgBase64.Append('EFH/2gAIAQEAAT8Qn3igmSZSj+c4N4zapMy9IjFV98wncN2iuLFsCEbDGxQkI6RO/n//2Q==' + #13#10);
mime := TChilkatMime.Create(Self);
mime.ContentType := 'image/jpeg';
mime.SetBodyFromEncoded('base64',sbJpgBase64.GetAsString());
Memo1.Lines.Add(mime.GetMime());
Memo1.Lines.Add('-');
// The result:
//
// Content-Type: image/jpeg
// Content-Transfer-Encoding: base64
//
// /9j/4AAQSkZJRgABAQEASABIAAD//gAmRmlsZSB3cml0dGVuIGJ5IEFkb2JlIFBob3Rvc2hvcD8g
// NC4w/9sAQwAQCwwODAoQDg0OEhEQExgoGhgWFhgxIyUdKDozPTw5Mzg3QEhcTkBEV0U3OFBtUVdf
// YmdoZz5NcXlwZHhcZWdj/9sAQwEREhIYFRgvGhovY0I4QmNjY2NjY2NjY2NjY2NjY2NjY2NjY2Nj
// Y2NjY2NjY2NjY2NjY2NjY2NjY2NjY2NjY2Nj/8IAEQgAFAAUAwERAAIRAQMRAf/EABcAAAMBAAAA
// AAAAAAAAAAAAAAIDBAX/xAAYAQADAQEAAAAAAAAAAAAAAAABAgMEAP/aAAwDAQACEAMQAAAB2kZY
// NNEijWKddfTmLgALWH//xAAbEAACAgMBAAAAAAAAAAAAAAABAgMRAAQSE//aAAgBAQABBQL0XqN+
// pM2aqJGMiqFFCyg7z//EABwRAAICAgMAAAAAAAAAAAAAAAERAAIQIQMSUf/aAAgBAwEBPwHqU5aq
// Axx+y1tMQl4elj//xAAcEQEAAQUBAQAAAAAAAAAAAAABEQACEBIhA1H/2gAIAQIBAT8B3Bhqy7Zc
// enyiwmGgDhiOzj//xAAdEAABAwUBAAAAAAAAAAAAAAABAAIREBIhIkFR/9oACAEBAAY/ArZyn+Cg
// xtxWuJaoCnqDuin/xAAcEAABBAMBAAAAAAAAAAAAAAABABEhYRAxQVH/2gAIAQEAAT8hkEwPUUR9
// DYfE4nxtRpIkBTsayuALIiuY/9oADAMBAAIAAwAAABDWPTsf/8QAGhEAAwADAQAAAAAAAAAAAAAA
// AAEREDFBIf/aAAgBAwEBPxC0DVPcWm+Ce4OesrkE6bjH/8QAGBEBAQEBAQAAAAAAAAAAAAAAAREA
// QRD/2gAIAQIBAT8QahMiOc8YgSrnTY3ELclHXn//xAAcEAEBAAIDAQEAAAAAAAAAAAABEQAhMUFx
// EFH/2gAIAQEAAT8Qn3igmSZSj+c4N4zapMy9IjFV98wncN2iuLFsCEbDGxQkI6RO/n//2Q==
//
// Set the Content-Transfer-Encoding to "binary" by setting the Encoding property.
mime.Encoding := 'binary';
// Try to get the MIME string. This CANNOT be done. The bytes of the JPG image do not
// represent chars, and to return a string means that bytes must be interpreted according
// to some character encoding (such as utf-8). Non-text binary bytes can only be
// contained in a string IF encoded in some way. Encodings such as Base64, quoted-printable,
// URL, etc. exist to make it possible to represent binary data in string format.
Memo1.Lines.Add(mime.GetMime());
Memo1.Lines.Add('-');
// We CAN get the binary MIME as bytes..
mimeBytes := mime.GetMimeBytes();
// Regardless of the Content-Transfer-Encoding, the
// body content can always be retrieved and the body bytes
// decoded from whatever encoding is used..
jpgBytes := mime.GetBodyBinary();
// To get the body in base64 format, first make sure
// the Content-Transfer-Encoding is base64, then call GetBodyEncoded.
mime.Encoding := 'base64';
jpgBase64 := mime.GetBodyEncoded();
Memo1.Lines.Add(jpgBase64);
Memo1.Lines.Add('-');
// Let's go back to "binary" MIME..
mime.Encoding := 'binary';
// Let's say we have MIME, and it was loaded directly from a file, or from
// a byte array. (It was not loaded from the contents of a string variable.)
// We don't know whether the MIME contains binary or 8bit encodings, and thus
// we dont' know if the MIME is safe to get as a string.
// The Convert8Bit method can be called to recursively traverse the MIME and set
// all 8bit or binary encodings to "base64". This makes the MIME safe for storing in
// a string.
mime.Convert8Bit();
mimeStr := mime.GetMime();
Memo1.Lines.Add(mimeStr);
Memo1.Lines.Add('-');
end;