B4X
B4X
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 B4X Downloads
Dim success As Boolean = False
' 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.
Dim sbJpgBase64 As ChilkatStringBuilder
sbJpgBase64.Initialize
sbJpgBase64.Append("/9j/4AAQSkZJRgABAQEASABIAAD//gAmRmlsZSB3cml0dGVuIGJ5IEFkb2JlIFBob3Rvc2hvcD8g" & Chr(13) & Chr(10))
sbJpgBase64.Append("NC4w/9sAQwAQCwwODAoQDg0OEhEQExgoGhgWFhgxIyUdKDozPTw5Mzg3QEhcTkBEV0U3OFBtUVdf" & Chr(13) & Chr(10))
sbJpgBase64.Append("YmdoZz5NcXlwZHhcZWdj/9sAQwEREhIYFRgvGhovY0I4QmNjY2NjY2NjY2NjY2NjY2NjY2NjY2Nj" & Chr(13) & Chr(10))
sbJpgBase64.Append("Y2NjY2NjY2NjY2NjY2NjY2NjY2NjY2NjY2Nj/8IAEQgAFAAUAwERAAIRAQMRAf/EABcAAAMBAAAA" & Chr(13) & Chr(10))
sbJpgBase64.Append("AAAAAAAAAAAAAAIDBAX/xAAYAQADAQEAAAAAAAAAAAAAAAABAgMEAP/aAAwDAQACEAMQAAAB2kZY" & Chr(13) & Chr(10))
sbJpgBase64.Append("NNEijWKddfTmLgALWH//xAAbEAACAgMBAAAAAAAAAAAAAAABAgMRAAQSE//aAAgBAQABBQL0XqN+" & Chr(13) & Chr(10))
sbJpgBase64.Append("pM2aqJGMiqFFCyg7z//EABwRAAICAgMAAAAAAAAAAAAAAAERAAIQIQMSUf/aAAgBAwEBPwHqU5aq" & Chr(13) & Chr(10))
sbJpgBase64.Append("Axx+y1tMQl4elj//xAAcEQEAAQUBAQAAAAAAAAAAAAABEQACEBIhA1H/2gAIAQIBAT8B3Bhqy7Zc" & Chr(13) & Chr(10))
sbJpgBase64.Append("enyiwmGgDhiOzj//xAAdEAABAwUBAAAAAAAAAAAAAAABAAIREBIhIkFR/9oACAEBAAY/ArZyn+Cg" & Chr(13) & Chr(10))
sbJpgBase64.Append("xtxWuJaoCnqDuin/xAAcEAABBAMBAAAAAAAAAAAAAAABABEhYRAxQVH/2gAIAQEAAT8hkEwPUUR9" & Chr(13) & Chr(10))
sbJpgBase64.Append("DYfE4nxtRpIkBTsayuALIiuY/9oADAMBAAIAAwAAABDWPTsf/8QAGhEAAwADAQAAAAAAAAAAAAAA" & Chr(13) & Chr(10))
sbJpgBase64.Append("AAEREDFBIf/aAAgBAwEBPxC0DVPcWm+Ce4OesrkE6bjH/8QAGBEBAQEBAQAAAAAAAAAAAAAAAREA" & Chr(13) & Chr(10))
sbJpgBase64.Append("QRD/2gAIAQIBAT8QahMiOc8YgSrnTY3ELclHXn//xAAcEAEBAAIDAQEAAAAAAAAAAAABEQAhMUFx" & Chr(13) & Chr(10))
sbJpgBase64.Append("EFH/2gAIAQEAAT8Qn3igmSZSj+c4N4zapMy9IjFV98wncN2iuLFsCEbDGxQkI6RO/n//2Q==" & Chr(13) & Chr(10))
Dim mime As ChilkatMime
mime.Initialize
mime.ContentType = "image/jpeg"
mime.SetBodyFromEncoded("base64", sbJpgBase64.GetAsString)
Log(mime.GetMime)
Log("-")
' 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.
Log(mime.GetMime)
Log("-")
' 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"
Dim jpgBase64 As String = mime.GetBodyEncoded
Log(jpgBase64)
Log("-")
' 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
Dim mimeStr As String = mime.GetMime
Log(mimeStr)
Log("-")