voip/java/android/net/sip/SimpleSessionDescription.java - LeafOS-Project/android_frameworks_base - Gitiles

 /*
  * Copyright (C) 2010 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 package android.net.sip;

 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Locale;

 /**
  * An object used to manipulate messages of Session Description Protocol (SDP).
  * It is mainly designed for the uses of Session Initiation Protocol (SIP).
  * Therefore, it only handles connection addresses ("c="), bandwidth limits,
  * ("b="), encryption keys ("k="), and attribute fields ("a="). Currently this
  * implementation does not support multicast sessions.
  *
  * <p>Here is an example code to create a session description.</p>
  * <pre>
  * SimpleSessionDescription description = new SimpleSessionDescription(
  *     System.currentTimeMillis(), "1.2.3.4");
  * Media media = description.newMedia("audio", 56789, 1, "RTP/AVP");
  * media.setRtpPayload(0, "PCMU/8000", null);
  * media.setRtpPayload(8, "PCMA/8000", null);
  * media.setRtpPayload(127, "telephone-event/8000", "0-15");
  * media.setAttribute("sendrecv", "");
  * </pre>
  * <p>Invoking <code>description.encode()</code> will produce a result like the
  * one below.</p>
  * <pre>
  * v=0
  * o=- 1284970442706 1284970442709 IN IP4 1.2.3.4
  * s=-
  * c=IN IP4 1.2.3.4
  * t=0 0
  * m=audio 56789 RTP/AVP 0 8 127
  * a=rtpmap:0 PCMU/8000
  * a=rtpmap:8 PCMA/8000
  * a=rtpmap:127 telephone-event/8000
  * a=fmtp:127 0-15
  * a=sendrecv
  * </pre>
  * @hide
  */
 public class SimpleSessionDescription {
     private final Fields mFields = new Fields("voscbtka");
     private final ArrayList<Media> mMedia = new ArrayList<Media>();

     /**
      * Creates a minimal session description from the given session ID and
      * unicast address. The address is used in the origin field ("o=") and the
      * connection field ("c="). See {@link SimpleSessionDescription} for an
      * example of its usage.
      */
     public SimpleSessionDescription(long sessionId, String address) {
         address = (address.indexOf(':') < 0 ? "IN IP4 " : "IN IP6 ") + address;
         mFields.parse("v=0");
         mFields.parse(String.format(Locale.US, "o=- %d %d %s", sessionId,
                 System.currentTimeMillis(), address));
         mFields.parse("s=-");
         mFields.parse("t=0 0");
         mFields.parse("c=" + address);
     }

     /**
      * Creates a session description from the given message.
      *
      * @throws IllegalArgumentException if message is invalid.
      */
     public SimpleSessionDescription(String message) {
         String[] lines = message.trim().replaceAll(" +", " ").split("[\r\n]+");
         Fields fields = mFields;

         for (String line : lines) {
             try {
                 if (line.charAt(1) != '=') {
                     throw new IllegalArgumentException();
                 }
                 if (line.charAt(0) == 'm') {
                     String[] parts = line.substring(2).split(" ", 4);
                     String[] ports = parts[1].split("/", 2);
                     Media media = newMedia(parts[0], Integer.parseInt(ports[0]),
                             (ports.length < 2) ? 1 : Integer.parseInt(ports[1]),
                             parts[2]);
                     for (String format : parts[3].split(" ")) {
                         media.setFormat(format, null);
                     }
                     fields = media;
                 } else {
                     fields.parse(line);
                 }
             } catch (Exception e) {
                 throw new IllegalArgumentException("Invalid SDP: " + line);
             }
         }
     }

     /**
      * Creates a new media description in this session description.
      *
      * @param type The media type, e.g. {@code "audio"}.
      * @param port The first transport port used by this media.
      * @param portCount The number of contiguous ports used by this media.
      * @param protocol The transport protocol, e.g. {@code "RTP/AVP"}.
      */
     public Media newMedia(String type, int port, int portCount,
             String protocol) {
         Media media = new Media(type, port, portCount, protocol);
         mMedia.add(media);
         return media;
     }

     /**
      * Returns all the media descriptions in this session description.
      */
     public Media[] getMedia() {
         return mMedia.toArray(new Media[mMedia.size()]);
     }

     /**
      * Encodes the session description and all its media descriptions in a
      * string. Note that the result might be incomplete if a required field
      * has never been added before.
      */
     public String encode() {
         StringBuilder buffer = new StringBuilder();
         mFields.write(buffer);
         for (Media media : mMedia) {
             media.write(buffer);
         }
         return buffer.toString();
     }

     /**
      * Returns the connection address or {@code null} if it is not present.
      */
     public String getAddress() {
         return mFields.getAddress();
     }

     /**
      * Sets the connection address. The field will be removed if the address
      * is {@code null}.
      */
     public void setAddress(String address) {
         mFields.setAddress(address);
     }

     /**
      * Returns the encryption method or {@code null} if it is not present.
      */
     public String getEncryptionMethod() {
         return mFields.getEncryptionMethod();
     }

     /**
      * Returns the encryption key or {@code null} if it is not present.
      */
     public String getEncryptionKey() {
         return mFields.getEncryptionKey();
     }

     /**
      * Sets the encryption method and the encryption key. The field will be
      * removed if the method is {@code null}.
      */
     public void setEncryption(String method, String key) {
         mFields.setEncryption(method, key);
     }

     /**
      * Returns the types of the bandwidth limits.
      */
     public String[] getBandwidthTypes() {
         return mFields.getBandwidthTypes();
     }

     /**
      * Returns the bandwidth limit of the given type or {@code -1} if it is not
      * present.
      */
     public int getBandwidth(String type) {
         return mFields.getBandwidth(type);
     }

     /**
      * Sets the bandwith limit for the given type. The field will be removed if
      * the value is negative.
      */
     public void setBandwidth(String type, int value) {
         mFields.setBandwidth(type, value);
     }

     /**
      * Returns the names of all the attributes.
      */
     public String[] getAttributeNames() {
         return mFields.getAttributeNames();
     }

     /**
      * Returns the attribute of the given name or {@code null} if it is not
      * present.
      */
     public String getAttribute(String name) {
         return mFields.getAttribute(name);
     }

     /**
      * Sets the attribute for the given name. The field will be removed if
      * the value is {@code null}. To set a binary attribute, use an empty
      * string as the value.
      */
     public void setAttribute(String name, String value) {
         mFields.setAttribute(name, value);
     }

     /**
      * This class represents a media description of a session description. It
      * can only be created by {@link SimpleSessionDescription#newMedia}. Since
      * the syntax is more restricted for RTP based protocols, two sets of access
      * methods are implemented. See {@link SimpleSessionDescription} for an
      * example of its usage.
      */
     public static class Media extends Fields {
         private final String mType;
         private final int mPort;
         private final int mPortCount;
         private final String mProtocol;
         private ArrayList<String> mFormats = new ArrayList<String>();

         private Media(String type, int port, int portCount, String protocol) {
             super("icbka");
             mType = type;
             mPort = port;
             mPortCount = portCount;
             mProtocol = protocol;
         }

         /**
          * Returns the media type.
          */
         public String getType() {
             return mType;
         }

         /**
          * Returns the first transport port used by this media.
          */
         public int getPort() {
             return mPort;
         }

         /**
          * Returns the number of contiguous ports used by this media.
          */
         public int getPortCount() {
             return mPortCount;
         }

         /**
          * Returns the transport protocol.
          */
         public String getProtocol() {
             return mProtocol;
         }

         /**
          * Returns the media formats.
          */
         public String[] getFormats() {
             return mFormats.toArray(new String[mFormats.size()]);
         }

         /**
          * Returns the {@code fmtp} attribute of the given format or
          * {@code null} if it is not present.
          */
         public String getFmtp(String format) {
             return super.get("a=fmtp:" + format, ' ');
         }

         /**
          * Sets a format and its {@code fmtp} attribute. If the attribute is
          * {@code null}, the corresponding field will be removed.
          */
         public void setFormat(String format, String fmtp) {
             mFormats.remove(format);
             mFormats.add(format);
             super.set("a=rtpmap:" + format, ' ', null);
             super.set("a=fmtp:" + format, ' ', fmtp);
         }

         /**
          * Removes a format and its {@code fmtp} attribute.
          */
         public void removeFormat(String format) {
             mFormats.remove(format);
             super.set("a=rtpmap:" + format, ' ', null);
             super.set("a=fmtp:" + format, ' ', null);
         }

         /**
          * Returns the RTP payload types.
          */
         public int[] getRtpPayloadTypes() {
             int[] types = new int[mFormats.size()];
             int length = 0;
             for (String format : mFormats) {
                 try {
                     types[length] = Integer.parseInt(format);
                     ++length;
                 } catch (NumberFormatException e) { }
             }
             return Arrays.copyOf(types, length);
         }

         /**
          * Returns the {@code rtpmap} attribute of the given RTP payload type
          * or {@code null} if it is not present.
          */
         public String getRtpmap(int type) {
             return super.get("a=rtpmap:" + type, ' ');
         }

         /**
          * Returns the {@code fmtp} attribute of the given RTP payload type or
          * {@code null} if it is not present.
          */
         public String getFmtp(int type) {
             return super.get("a=fmtp:" + type, ' ');
         }

         /**
          * Sets a RTP payload type and its {@code rtpmap} and {@code fmtp}
          * attributes. If any of the attributes is {@code null}, the
          * corresponding field will be removed. See
          * {@link SimpleSessionDescription} for an example of its usage.
          */
         public void setRtpPayload(int type, String rtpmap, String fmtp) {
             String format = String.valueOf(type);
             mFormats.remove(format);
             mFormats.add(format);
             super.set("a=rtpmap:" + format, ' ', rtpmap);
             super.set("a=fmtp:" + format, ' ', fmtp);
         }

         /**
          * Removes a RTP payload and its {@code rtpmap} and {@code fmtp}
          * attributes.
          */
         public void removeRtpPayload(int type) {
             removeFormat(String.valueOf(type));
         }

         private void write(StringBuilder buffer) {
             buffer.append("m=").append(mType).append(' ').append(mPort);
             if (mPortCount != 1) {
                 buffer.append('/').append(mPortCount);
             }
             buffer.append(' ').append(mProtocol);
             for (String format : mFormats) {
                 buffer.append(' ').append(format);
             }
             buffer.append("\r\n");
             super.write(buffer);
         }
     }

     /**
      * This class acts as a set of fields, and the size of the set is expected
      * to be small. Therefore, it uses a simple list instead of maps. Each field
      * has three parts: a key, a delimiter, and a value. Delimiters are special
      * because they are not included in binary attributes. As a result, the
      * private methods, which are the building blocks of this class, all take
      * the delimiter as an argument.
      */
     private static class Fields {
         private final String mOrder;
         private final ArrayList<String> mLines = new ArrayList<String>();

         Fields(String order) {
             mOrder = order;
         }

         /**
          * Returns the connection address or {@code null} if it is not present.
          */
         public String getAddress() {
             String address = get("c", '=');
             if (address == null) {
                 return null;
             }
             String[] parts = address.split(" ");
             if (parts.length != 3) {
                 return null;
             }
             int slash = parts[2].indexOf('/');
             return (slash < 0) ? parts[2] : parts[2].substring(0, slash);
         }

         /**
          * Sets the connection address. The field will be removed if the address
          * is {@code null}.
          */
         public void setAddress(String address) {
             if (address != null) {
                 address = (address.indexOf(':') < 0 ? "IN IP4 " : "IN IP6 ") +
                         address;
             }
             set("c", '=', address);
         }

         /**
          * Returns the encryption method or {@code null} if it is not present.
          */
         public String getEncryptionMethod() {
             String encryption = get("k", '=');
             if (encryption == null) {
                 return null;
             }
             int colon = encryption.indexOf(':');
             return (colon == -1) ? encryption : encryption.substring(0, colon);
         }

         /**
          * Returns the encryption key or {@code null} if it is not present.
          */
         public String getEncryptionKey() {
             String encryption = get("k", '=');
             if (encryption == null) {
                 return null;
             }
             int colon = encryption.indexOf(':');
             return (colon == -1) ? null : encryption.substring(0, colon + 1);
         }

         /**
          * Sets the encryption method and the encryption key. The field will be
          * removed if the method is {@code null}.
          */
         public void setEncryption(String method, String key) {
             set("k", '=', (method == null || key == null) ?
                     method : method + ':' + key);
         }

         /**
          * Returns the types of the bandwidth limits.
          */
         public String[] getBandwidthTypes() {
             return cut("b=", ':');
         }

         /**
          * Returns the bandwidth limit of the given type or {@code -1} if it is
          * not present.
          */
         public int getBandwidth(String type) {
             String value = get("b=" + type, ':');
             if (value != null) {
                 try {
                     return Integer.parseInt(value);
                 } catch (NumberFormatException e) { }
                 setBandwidth(type, -1);
             }
             return -1;
         }

         /**
          * Sets the bandwith limit for the given type. The field will be removed
          * if the value is negative.
          */
         public void setBandwidth(String type, int value) {
             set("b=" + type, ':', (value < 0) ? null : String.valueOf(value));
         }

         /**
          * Returns the names of all the attributes.
          */
         public String[] getAttributeNames() {
             return cut("a=", ':');
         }

         /**
          * Returns the attribute of the given name or {@code null} if it is not
          * present.
          */
         public String getAttribute(String name) {
             return get("a=" + name, ':');
         }

         /**
          * Sets the attribute for the given name. The field will be removed if
          * the value is {@code null}. To set a binary attribute, use an empty
          * string as the value.
          */
         public void setAttribute(String name, String value) {
             set("a=" + name, ':', value);
         }

         private void write(StringBuilder buffer) {
             for (int i = 0; i < mOrder.length(); ++i) {
                 char type = mOrder.charAt(i);
                 for (String line : mLines) {
                     if (line.charAt(0) == type) {
                         buffer.append(line).append("\r\n");
                     }
                 }
             }
         }

         /**
          * Invokes {@link #set} after splitting the line into three parts.
          */
         private void parse(String line) {
             char type = line.charAt(0);
             if (mOrder.indexOf(type) == -1) {
                 return;
             }
             char delimiter = '=';
             if (line.startsWith("a=rtpmap:") || line.startsWith("a=fmtp:")) {
                 delimiter = ' ';
             } else if (type == 'b' || type == 'a') {
                 delimiter = ':';
             }
             int i = line.indexOf(delimiter);
             if (i == -1) {
                 set(line, delimiter, "");
             } else {
                 set(line.substring(0, i), delimiter, line.substring(i + 1));
             }
         }

         /**
          * Finds the key with the given prefix and returns its suffix.
          */
         private String[] cut(String prefix, char delimiter) {
             String[] names = new String[mLines.size()];
             int length = 0;
             for (String line : mLines) {
                 if (line.startsWith(prefix)) {
                     int i = line.indexOf(delimiter);
                     if (i == -1) {
                         i = line.length();
                     }
                     names[length] = line.substring(prefix.length(), i);
                     ++length;
                 }
             }
             return Arrays.copyOf(names, length);
         }

         /**
          * Returns the index of the key.
          */
         private int find(String key, char delimiter) {
             int length = key.length();
             for (int i = mLines.size() - 1; i >= 0; --i) {
                 String line = mLines.get(i);
                 if (line.startsWith(key) && (line.length() == length ||
                         line.charAt(length) == delimiter)) {
                     return i;
                 }
             }
             return -1;
         }

         /**
          * Sets the key with the value or removes the key if the value is
          * {@code null}.
          */
         private void set(String key, char delimiter, String value) {
             int index = find(key, delimiter);
             if (value != null) {
                 if (value.length() != 0) {
                     key = key + delimiter + value;
                 }
                 if (index == -1) {
                     mLines.add(key);
                 } else {
                     mLines.set(index, key);
                 }
             } else if (index != -1) {
                 mLines.remove(index);
             }
         }

         /**
          * Returns the value of the key.
          */
         private String get(String key, char delimiter) {
             int index = find(key, delimiter);
             if (index == -1) {
                 return null;
             }
             String line = mLines.get(index);
             int length = key.length();
             return (line.length() == length) ? "" : line.substring(length + 1);
         }
     }
 }
	/*
	* Copyright (C) 2010 The Android Open Source Project
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	package android.net.sip;

	import java.util.ArrayList;
	import java.util.Arrays;
	import java.util.Locale;

	/**
	* An object used to manipulate messages of Session Description Protocol (SDP).
	* It is mainly designed for the uses of Session Initiation Protocol (SIP).
	* Therefore, it only handles connection addresses ("c="), bandwidth limits,
	* ("b="), encryption keys ("k="), and attribute fields ("a="). Currently this
	* implementation does not support multicast sessions.
	*
	* <p>Here is an example code to create a session description.</p>
	* <pre>
	* SimpleSessionDescription description = new SimpleSessionDescription(
	* System.currentTimeMillis(), "1.2.3.4");
	* Media media = description.newMedia("audio", 56789, 1, "RTP/AVP");
	* media.setRtpPayload(0, "PCMU/8000", null);
	* media.setRtpPayload(8, "PCMA/8000", null);
	* media.setRtpPayload(127, "telephone-event/8000", "0-15");
	* media.setAttribute("sendrecv", "");
	* </pre>
	* <p>Invoking <code>description.encode()</code> will produce a result like the
	* one below.</p>
	* <pre>
	* v=0
	* o=- 1284970442706 1284970442709 IN IP4 1.2.3.4
	* s=-
	* c=IN IP4 1.2.3.4
	* t=0 0
	* m=audio 56789 RTP/AVP 0 8 127
	* a=rtpmap:0 PCMU/8000
	* a=rtpmap:8 PCMA/8000
	* a=rtpmap:127 telephone-event/8000
	* a=fmtp:127 0-15
	* a=sendrecv
	* </pre>
	* @hide
	*/
	public class SimpleSessionDescription {
	private final Fields mFields = new Fields("voscbtka");
	private final ArrayList<Media> mMedia = new ArrayList<Media>();

	/**
	* Creates a minimal session description from the given session ID and
	* unicast address. The address is used in the origin field ("o=") and the
	* connection field ("c="). See {@link SimpleSessionDescription} for an
	* example of its usage.
	*/
	public SimpleSessionDescription(long sessionId, String address) {
	address = (address.indexOf(':') < 0 ? "IN IP4 " : "IN IP6 ") + address;
	mFields.parse("v=0");
	mFields.parse(String.format(Locale.US, "o=- %d %d %s", sessionId,
	System.currentTimeMillis(), address));
	mFields.parse("s=-");
	mFields.parse("t=0 0");
	mFields.parse("c=" + address);
	}

	/**
	* Creates a session description from the given message.
	*
	* @throws IllegalArgumentException if message is invalid.
	*/
	public SimpleSessionDescription(String message) {
	String[] lines = message.trim().replaceAll(" +", " ").split("[\r\n]+");
	Fields fields = mFields;

	for (String line : lines) {
	try {
	if (line.charAt(1) != '=') {
	throw new IllegalArgumentException();
	}
	if (line.charAt(0) == 'm') {
	String[] parts = line.substring(2).split(" ", 4);
	String[] ports = parts[1].split("/", 2);
	Media media = newMedia(parts[0], Integer.parseInt(ports[0]),
	(ports.length < 2) ? 1 : Integer.parseInt(ports[1]),
	parts[2]);
	for (String format : parts[3].split(" ")) {
	media.setFormat(format, null);
	}
	fields = media;
	} else {
	fields.parse(line);
	}
	} catch (Exception e) {
	throw new IllegalArgumentException("Invalid SDP: " + line);
	}
	}
	}

	/**
	* Creates a new media description in this session description.
	*
	* @param type The media type, e.g. {@code "audio"}.
	* @param port The first transport port used by this media.
	* @param portCount The number of contiguous ports used by this media.
	* @param protocol The transport protocol, e.g. {@code "RTP/AVP"}.
	*/
	public Media newMedia(String type, int port, int portCount,
	String protocol) {
	Media media = new Media(type, port, portCount, protocol);
	mMedia.add(media);
	return media;
	}

	/**
	* Returns all the media descriptions in this session description.
	*/
	public Media[] getMedia() {
	return mMedia.toArray(new Media[mMedia.size()]);
	}

	/**
	* Encodes the session description and all its media descriptions in a
	* string. Note that the result might be incomplete if a required field
	* has never been added before.
	*/
	public String encode() {
	StringBuilder buffer = new StringBuilder();
	mFields.write(buffer);
	for (Media media : mMedia) {
	media.write(buffer);
	}
	return buffer.toString();
	}

	/**
	* Returns the connection address or {@code null} if it is not present.
	*/
	public String getAddress() {
	return mFields.getAddress();
	}

	/**
	* Sets the connection address. The field will be removed if the address
	* is {@code null}.
	*/
	public void setAddress(String address) {
	mFields.setAddress(address);
	}

	/**
	* Returns the encryption method or {@code null} if it is not present.
	*/
	public String getEncryptionMethod() {
	return mFields.getEncryptionMethod();
	}

	/**
	* Returns the encryption key or {@code null} if it is not present.
	*/
	public String getEncryptionKey() {
	return mFields.getEncryptionKey();
	}

	/**
	* Sets the encryption method and the encryption key. The field will be
	* removed if the method is {@code null}.
	*/
	public void setEncryption(String method, String key) {
	mFields.setEncryption(method, key);
	}

	/**
	* Returns the types of the bandwidth limits.
	*/
	public String[] getBandwidthTypes() {
	return mFields.getBandwidthTypes();
	}

	/**
	* Returns the bandwidth limit of the given type or {@code -1} if it is not
	* present.
	*/
	public int getBandwidth(String type) {
	return mFields.getBandwidth(type);
	}

	/**
	* Sets the bandwith limit for the given type. The field will be removed if
	* the value is negative.
	*/
	public void setBandwidth(String type, int value) {
	mFields.setBandwidth(type, value);
	}

	/**
	* Returns the names of all the attributes.
	*/
	public String[] getAttributeNames() {
	return mFields.getAttributeNames();
	}

	/**
	* Returns the attribute of the given name or {@code null} if it is not
	* present.
	*/
	public String getAttribute(String name) {
	return mFields.getAttribute(name);
	}

	/**
	* Sets the attribute for the given name. The field will be removed if
	* the value is {@code null}. To set a binary attribute, use an empty
	* string as the value.
	*/
	public void setAttribute(String name, String value) {
	mFields.setAttribute(name, value);
	}

	/**
	* This class represents a media description of a session description. It
	* can only be created by {@link SimpleSessionDescription#newMedia}. Since
	* the syntax is more restricted for RTP based protocols, two sets of access
	* methods are implemented. See {@link SimpleSessionDescription} for an
	* example of its usage.
	*/
	public static class Media extends Fields {
	private final String mType;
	private final int mPort;
	private final int mPortCount;
	private final String mProtocol;
	private ArrayList<String> mFormats = new ArrayList<String>();

	private Media(String type, int port, int portCount, String protocol) {
	super("icbka");
	mType = type;
	mPort = port;
	mPortCount = portCount;
	mProtocol = protocol;
	}

	/**
	* Returns the media type.
	*/
	public String getType() {
	return mType;
	}

	/**
	* Returns the first transport port used by this media.
	*/
	public int getPort() {
	return mPort;
	}

	/**
	* Returns the number of contiguous ports used by this media.
	*/
	public int getPortCount() {
	return mPortCount;
	}

	/**
	* Returns the transport protocol.
	*/
	public String getProtocol() {
	return mProtocol;
	}

	/**
	* Returns the media formats.
	*/
	public String[] getFormats() {
	return mFormats.toArray(new String[mFormats.size()]);
	}

	/**
	* Returns the {@code fmtp} attribute of the given format or
	* {@code null} if it is not present.
	*/
	public String getFmtp(String format) {
	return super.get("a=fmtp:" + format, ' ');
	}

	/**
	* Sets a format and its {@code fmtp} attribute. If the attribute is
	* {@code null}, the corresponding field will be removed.
	*/
	public void setFormat(String format, String fmtp) {
	mFormats.remove(format);
	mFormats.add(format);
	super.set("a=rtpmap:" + format, ' ', null);
	super.set("a=fmtp:" + format, ' ', fmtp);
	}

	/**
	* Removes a format and its {@code fmtp} attribute.
	*/
	public void removeFormat(String format) {
	mFormats.remove(format);
	super.set("a=rtpmap:" + format, ' ', null);
	super.set("a=fmtp:" + format, ' ', null);
	}

	/**
	* Returns the RTP payload types.
	*/
	public int[] getRtpPayloadTypes() {
	int[] types = new int[mFormats.size()];
	int length = 0;
	for (String format : mFormats) {
	try {
	types[length] = Integer.parseInt(format);
	++length;
	} catch (NumberFormatException e) { }
	}
	return Arrays.copyOf(types, length);
	}

	/**
	* Returns the {@code rtpmap} attribute of the given RTP payload type
	* or {@code null} if it is not present.
	*/
	public String getRtpmap(int type) {
	return super.get("a=rtpmap:" + type, ' ');
	}

	/**
	* Returns the {@code fmtp} attribute of the given RTP payload type or
	* {@code null} if it is not present.
	*/
	public String getFmtp(int type) {
	return super.get("a=fmtp:" + type, ' ');
	}

	/**
	* Sets a RTP payload type and its {@code rtpmap} and {@code fmtp}
	* attributes. If any of the attributes is {@code null}, the
	* corresponding field will be removed. See
	* {@link SimpleSessionDescription} for an example of its usage.
	*/
	public void setRtpPayload(int type, String rtpmap, String fmtp) {
	String format = String.valueOf(type);
	mFormats.remove(format);
	mFormats.add(format);
	super.set("a=rtpmap:" + format, ' ', rtpmap);
	super.set("a=fmtp:" + format, ' ', fmtp);
	}

	/**
	* Removes a RTP payload and its {@code rtpmap} and {@code fmtp}
	* attributes.
	*/
	public void removeRtpPayload(int type) {
	removeFormat(String.valueOf(type));
	}

	private void write(StringBuilder buffer) {
	buffer.append("m=").append(mType).append(' ').append(mPort);
	if (mPortCount != 1) {
	buffer.append('/').append(mPortCount);
	}
	buffer.append(' ').append(mProtocol);
	for (String format : mFormats) {
	buffer.append(' ').append(format);
	}
	buffer.append("\r\n");
	super.write(buffer);
	}
	}

	/**
	* This class acts as a set of fields, and the size of the set is expected
	* to be small. Therefore, it uses a simple list instead of maps. Each field
	* has three parts: a key, a delimiter, and a value. Delimiters are special
	* because they are not included in binary attributes. As a result, the
	* private methods, which are the building blocks of this class, all take
	* the delimiter as an argument.
	*/
	private static class Fields {
	private final String mOrder;
	private final ArrayList<String> mLines = new ArrayList<String>();

	Fields(String order) {
	mOrder = order;
	}

	/**
	* Returns the connection address or {@code null} if it is not present.
	*/
	public String getAddress() {
	String address = get("c", '=');
	if (address == null) {
	return null;
	}
	String[] parts = address.split(" ");
	if (parts.length != 3) {
	return null;
	}
	int slash = parts[2].indexOf('/');
	return (slash < 0) ? parts[2] : parts[2].substring(0, slash);
	}

	/**
	* Sets the connection address. The field will be removed if the address
	* is {@code null}.
	*/
	public void setAddress(String address) {
	if (address != null) {
	address = (address.indexOf(':') < 0 ? "IN IP4 " : "IN IP6 ") +
	address;
	}
	set("c", '=', address);
	}

	/**
	* Returns the encryption method or {@code null} if it is not present.
	*/
	public String getEncryptionMethod() {
	String encryption = get("k", '=');
	if (encryption == null) {
	return null;
	}
	int colon = encryption.indexOf(':');
	return (colon == -1) ? encryption : encryption.substring(0, colon);
	}

	/**
	* Returns the encryption key or {@code null} if it is not present.
	*/
	public String getEncryptionKey() {
	String encryption = get("k", '=');
	if (encryption == null) {
	return null;
	}
	int colon = encryption.indexOf(':');
	return (colon == -1) ? null : encryption.substring(0, colon + 1);
	}

	/**
	* Sets the encryption method and the encryption key. The field will be
	* removed if the method is {@code null}.
	*/
	public void setEncryption(String method, String key) {
	set("k", '=', (method == null \|\| key == null) ?
	method : method + ':' + key);
	}

	/**
	* Returns the types of the bandwidth limits.
	*/
	public String[] getBandwidthTypes() {
	return cut("b=", ':');
	}

	/**
	* Returns the bandwidth limit of the given type or {@code -1} if it is
	* not present.
	*/
	public int getBandwidth(String type) {
	String value = get("b=" + type, ':');
	if (value != null) {
	try {
	return Integer.parseInt(value);
	} catch (NumberFormatException e) { }
	setBandwidth(type, -1);
	}
	return -1;
	}

	/**
	* Sets the bandwith limit for the given type. The field will be removed
	* if the value is negative.
	*/
	public void setBandwidth(String type, int value) {
	set("b=" + type, ':', (value < 0) ? null : String.valueOf(value));
	}

	/**
	* Returns the names of all the attributes.
	*/
	public String[] getAttributeNames() {
	return cut("a=", ':');
	}

	/**
	* Returns the attribute of the given name or {@code null} if it is not
	* present.
	*/
	public String getAttribute(String name) {
	return get("a=" + name, ':');
	}

	/**
	* Sets the attribute for the given name. The field will be removed if
	* the value is {@code null}. To set a binary attribute, use an empty
	* string as the value.
	*/
	public void setAttribute(String name, String value) {
	set("a=" + name, ':', value);
	}

	private void write(StringBuilder buffer) {
	for (int i = 0; i < mOrder.length(); ++i) {
	char type = mOrder.charAt(i);
	for (String line : mLines) {
	if (line.charAt(0) == type) {
	buffer.append(line).append("\r\n");
	}
	}
	}
	}

	/**
	* Invokes {@link #set} after splitting the line into three parts.
	*/
	private void parse(String line) {
	char type = line.charAt(0);
	if (mOrder.indexOf(type) == -1) {
	return;
	}
	char delimiter = '=';
	if (line.startsWith("a=rtpmap:") \|\| line.startsWith("a=fmtp:")) {
	delimiter = ' ';
	} else if (type == 'b' \|\| type == 'a') {
	delimiter = ':';
	}
	int i = line.indexOf(delimiter);
	if (i == -1) {
	set(line, delimiter, "");
	} else {
	set(line.substring(0, i), delimiter, line.substring(i + 1));
	}
	}

	/**
	* Finds the key with the given prefix and returns its suffix.
	*/
	private String[] cut(String prefix, char delimiter) {
	String[] names = new String[mLines.size()];
	int length = 0;
	for (String line : mLines) {
	if (line.startsWith(prefix)) {
	int i = line.indexOf(delimiter);
	if (i == -1) {
	i = line.length();
	}
	names[length] = line.substring(prefix.length(), i);
	++length;
	}
	}
	return Arrays.copyOf(names, length);
	}

	/**
	* Returns the index of the key.
	*/
	private int find(String key, char delimiter) {
	int length = key.length();
	for (int i = mLines.size() - 1; i >= 0; --i) {
	String line = mLines.get(i);
	if (line.startsWith(key) && (line.length() == length \|\|
	line.charAt(length) == delimiter)) {
	return i;
	}
	}
	return -1;
	}

	/**
	* Sets the key with the value or removes the key if the value is
	* {@code null}.
	*/
	private void set(String key, char delimiter, String value) {
	int index = find(key, delimiter);
	if (value != null) {
	if (value.length() != 0) {
	key = key + delimiter + value;
	}
	if (index == -1) {
	mLines.add(key);
	} else {
	mLines.set(index, key);
	}
	} else if (index != -1) {
	mLines.remove(index);
	}
	}

	/**
	* Returns the value of the key.
	*/
	private String get(String key, char delimiter) {
	int index = find(key, delimiter);
	if (index == -1) {
	return null;
	}
	String line = mLines.get(index);
	int length = key.length();
	return (line.length() == length) ? "" : line.substring(length + 1);
	}
	}
	}