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(Unicode C) MIME Content-Transfer-Encoding Header FieldExplains the Content-Transfer-Encoding header field and how it affects how data is stored in the MIME.
#include <C_CkStringBuilderW.h> #include <C_CkMimeW.h> #include <C_CkByteData.h> void ChilkatSample(void) { BOOL success; HCkStringBuilderW sbJpgBase64; HCkMimeW mime; HCkByteData mimeBytes; HCkByteData jpgBytes; const wchar_t *jpgBase64; const wchar_t *mimeStr; // 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 = CkStringBuilderW_Create(); CkStringBuilderW_Append(sbJpgBase64,L"/9j/4AAQSkZJRgABAQEASABIAAD//gAmRmlsZSB3cml0dGVuIGJ5IEFkb2JlIFBob3Rvc2hvcD8g\r\n"); CkStringBuilderW_Append(sbJpgBase64,L"NC4w/9sAQwAQCwwODAoQDg0OEhEQExgoGhgWFhgxIyUdKDozPTw5Mzg3QEhcTkBEV0U3OFBtUVdf\r\n"); CkStringBuilderW_Append(sbJpgBase64,L"YmdoZz5NcXlwZHhcZWdj/9sAQwEREhIYFRgvGhovY0I4QmNjY2NjY2NjY2NjY2NjY2NjY2NjY2Nj\r\n"); CkStringBuilderW_Append(sbJpgBase64,L"Y2NjY2NjY2NjY2NjY2NjY2NjY2NjY2NjY2Nj/8IAEQgAFAAUAwERAAIRAQMRAf/EABcAAAMBAAAA\r\n"); CkStringBuilderW_Append(sbJpgBase64,L"AAAAAAAAAAAAAAIDBAX/xAAYAQADAQEAAAAAAAAAAAAAAAABAgMEAP/aAAwDAQACEAMQAAAB2kZY\r\n"); CkStringBuilderW_Append(sbJpgBase64,L"NNEijWKddfTmLgALWH//xAAbEAACAgMBAAAAAAAAAAAAAAABAgMRAAQSE//aAAgBAQABBQL0XqN+\r\n"); CkStringBuilderW_Append(sbJpgBase64,L"pM2aqJGMiqFFCyg7z//EABwRAAICAgMAAAAAAAAAAAAAAAERAAIQIQMSUf/aAAgBAwEBPwHqU5aq\r\n"); CkStringBuilderW_Append(sbJpgBase64,L"Axx+y1tMQl4elj//xAAcEQEAAQUBAQAAAAAAAAAAAAABEQACEBIhA1H/2gAIAQIBAT8B3Bhqy7Zc\r\n"); CkStringBuilderW_Append(sbJpgBase64,L"enyiwmGgDhiOzj//xAAdEAABAwUBAAAAAAAAAAAAAAABAAIREBIhIkFR/9oACAEBAAY/ArZyn+Cg\r\n"); CkStringBuilderW_Append(sbJpgBase64,L"xtxWuJaoCnqDuin/xAAcEAABBAMBAAAAAAAAAAAAAAABABEhYRAxQVH/2gAIAQEAAT8hkEwPUUR9\r\n"); CkStringBuilderW_Append(sbJpgBase64,L"DYfE4nxtRpIkBTsayuALIiuY/9oADAMBAAIAAwAAABDWPTsf/8QAGhEAAwADAQAAAAAAAAAAAAAA\r\n"); CkStringBuilderW_Append(sbJpgBase64,L"AAEREDFBIf/aAAgBAwEBPxC0DVPcWm+Ce4OesrkE6bjH/8QAGBEBAQEBAQAAAAAAAAAAAAAAAREA\r\n"); CkStringBuilderW_Append(sbJpgBase64,L"QRD/2gAIAQIBAT8QahMiOc8YgSrnTY3ELclHXn//xAAcEAEBAAIDAQEAAAAAAAAAAAABEQAhMUFx\r\n"); CkStringBuilderW_Append(sbJpgBase64,L"EFH/2gAIAQEAAT8Qn3igmSZSj+c4N4zapMy9IjFV98wncN2iuLFsCEbDGxQkI6RO/n//2Q==\r\n"); mime = CkMimeW_Create(); CkMimeW_putContentType(mime,L"image/jpeg"); CkMimeW_SetBodyFromEncoded(mime,L"base64",CkStringBuilderW_getAsString(sbJpgBase64)); wprintf(L"%s\n",CkMimeW_getMime(mime)); wprintf(L"-\n"); // 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. CkMimeW_putEncoding(mime,L"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. wprintf(L"%s\n",CkMimeW_getMime(mime)); wprintf(L"-\n"); // We CAN get the binary MIME as bytes.. mimeBytes = CkByteData_Create(); success = CkMimeW_GetMimeBytes(mime,mimeBytes); // Regardless of the Content-Transfer-Encoding, the // body content can always be retrieved and the body bytes // decoded from whatever encoding is used.. jpgBytes = CkByteData_Create(); success = CkMimeW_GetBodyBinary(mime,jpgBytes); // To get the body in base64 format, first make sure // the Content-Transfer-Encoding is base64, then call GetBodyEncoded. CkMimeW_putEncoding(mime,L"base64"); jpgBase64 = CkMimeW_getBodyEncoded(mime); wprintf(L"%s\n",jpgBase64); wprintf(L"-\n"); // Let's go back to "binary" MIME.. CkMimeW_putEncoding(mime,L"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. CkMimeW_Convert8Bit(mime); mimeStr = CkMimeW_getMime(mime); wprintf(L"%s\n",mimeStr); wprintf(L"-\n"); CkStringBuilderW_Dispose(sbJpgBase64); CkMimeW_Dispose(mime); CkByteData_Dispose(mimeBytes); CkByteData_Dispose(jpgBytes); } |
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