Objective-C

MIME Body vs. Sub-Parts

See more MIME Examples

Explains the difference between sub-parts and body.

MIME documents (i.e. messages) can have a nested structure. The simplest MIME message contains a header followed by content (possibly encoded). The header is delimited from the content by two consecutive CRLF's.

A MIME message may be multipart. If so, then the Content-Type header field indicates "multipart" and the content the follows the header is itself a MIME message, which may also be multipart, etc. You can see how MIME messages effectively have a tree structure. The non-leaf nodes have Content-Types that are "multipart/" and the leaf nodes have non-multipart Content-Types.

The Chilkat MIME component/library uses two terms that need to be understood in order to effectively use the API. These are "body" and "sub-part". A multipart node has 1 or more sub-parts, but its body is empty. A leaf node (i.e. non-multipart node) has no sub-parts, but the body is (usually) non-empty.

This example creates a multipart MIME message and shows the results of getting the sub-parts and body of each node.

Objective-C

#import <CkoMime.h>

BOOL success = NO;

// This example assumes the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

CkoMime *mime = [[CkoMime alloc] init];

// Create a multipart/mixed MIME message with two sub-parts.
// We'll use the Base64 encoding for the 2nd sub-part.
CkoMime *part1 = [[CkoMime alloc] init];
success = [part1 SetBodyFromPlainText: @"This is part 1"];

CkoMime *part2 = [[CkoMime alloc] init];
success = [part2 SetBodyFromPlainText: @"This is part 2"];
part2.Encoding = @"base64";

success = [mime NewMultipartMixed];
mime.UseMmDescription = NO;
success = [mime AppendPart: part1];
success = [mime AppendPart: part2];

// Show the MIME message:
NSLog(@"%@",[mime GetMime]);

// Here's the MIME:
// Content-Type: multipart/mixed;
// 	boundary="------------040605030407000302060008"
// 
// --------------040605030407000302060008
// Content-Type: text/plain;
// 	 charset="us-ascii"
// Content-Transfer-Encoding: 7bit
// 
// This is part 1
// --------------040605030407000302060008
// Content-Type: text/plain;
// 	 charset="us-ascii"
// Content-Transfer-Encoding: base64
// 
// VGhpcyBpcyBwYXJ0IDI=
// 
// --------------040605030407000302060008--

// If we examine the root node of the MIME message, 
// we see that it has 2 sub-parts and the body is empty (as expected)
int n = [mime.NumParts intValue];
NSLog(@"%@%d",@"Num Parts = ",n);
NSLog(@"%@%@",@"Body = ",[mime GetBodyDecoded]);

// The GetEntireBody retrieves the entire content after
// the header.  (Perhaps GetEntireBody should've been named
// GetEntireContent to make it less confusing...)
NSLog(@"%@",@"---- EntireBody:");
NSLog(@"%@",[mime GetEntireBody]);
NSLog(@"%@",@"********");

// Now examine the 2nd sub-part.  It has a body encoded
// using base64.  Get the contents of the body in both
// decoded and encoded forms:

// index 0 is the 1st part, index 1 is the 2nd part.
CkoMime *part = [[CkoMime alloc] init];
[mime PartAt: [NSNumber numberWithInt: 1] subPart: part];

NSLog(@"%@",@"Decoded Body:");
NSLog(@"%@",[part GetBodyDecoded]);
NSLog(@"%@",@"Encoded Body:");
NSLog(@"%@",[part GetBodyEncoded]);