(Android™) MIME Body vs. Sub-Parts

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.

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// Important: Don't forget to include the call to System.loadLibrary
// as shown at the bottom of this code sample.
package com.test;

import android.app.Activity;
import com.chilkatsoft.*;

import android.widget.TextView;
import android.os.Bundle;

public class SimpleActivity extends Activity {

  private static final String TAG = "Chilkat";

  // Called when the activity is first created.
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

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

    CkMime mime = new CkMime();

    // Create a multipart/mixed MIME message with two sub-parts.
    // We'll use the Base64 encoding for the 2nd sub-part.
    CkMime part1 = new CkMime();
    boolean success = part1.SetBodyFromPlainText("This is part 1");

    CkMime part2 = new CkMime();
    success = part2.SetBodyFromPlainText("This is part 2");
    part2.put_Encoding("base64");

    success = mime.NewMultipartMixed();
    mime.put_UseMmDescription(false);
    success = mime.AppendPart(part1);
    success = mime.AppendPart(part2);

    // Show the MIME message:
    Log.i(TAG, 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.get_NumParts();
    Log.i(TAG, "Num Parts = " + String.valueOf(n));
    Log.i(TAG, "Body = " + mime.getBodyDecoded());

    // The GetEntireBody retrieves the entire content after
    // the header.  (Perhaps GetEntireBody should've been named
    // GetEntireContent to make it less confusing...)
    Log.i(TAG, "---- EntireBody:");
    Log.i(TAG, mime.getEntireBody());
    Log.i(TAG, "********");

    // 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:
    CkMime part;
    // index 0 is the 1st part, index 1 is the 2nd part.
    part = mime.GetPart(1);
    Log.i(TAG, "Decoded Body:");
    Log.i(TAG, part.getBodyDecoded());
    Log.i(TAG, "Encoded Body:");
    Log.i(TAG, part.getBodyEncoded());


  }

  static {
      System.loadLibrary("chilkat");

      // Note: If the incorrect library name is passed to System.loadLibrary,
      // then you will see the following error message at application startup:
      //"The application <your-application-name> has stopped unexpectedly. Please try again."
  }
}