Message (beat-link 0.3.7 API)

java.lang.Object
- org.deepsymmetry.beatlink.dbserver.Message

```
public class Message
extends Object
```
Encapsulates a full dbserver message, made up of a list of Field objects, and having a particular structure, as described in the Packet Analysis paper.

Known message types are found in Message.KnownType. Many requests return a series of messages that represent menu items; the known versions of these are reflected in Message.MenuItemType.

Author:

James Elliott

Nested Class Summary

Nested Classes
Modifier and Type	Class and Description
`static class`	`Message.KnownType` Defines all the message types we know about, with any information we know about their arguments.
`static class`	`Message.MenuIdentifier` For many types of query messages, the first argument of the message is a 4-byte integer which we currently refer to as r:m:s:1, because the first byte is the player number of the player making the request, the second byte identifies the menu or destination for which information is being loaded, the third byte identifies the media slot (USB or SD) being asked about (as described in `CdjStatus.TrackSourceSlot`), and the fourth byte always seems to be 1 (Austin's libpdjl called it sourceAnalyzed).
`static class`	`Message.MenuItemType`

Field Summary

Fields
Modifier and Type	Field and Description
`NumberField`	`argumentCount` The 1-byte number field that specifies how many arguments the message has.
`List<Field>`	`arguments` The arguments being sent as part of this message.
`List<Field>`	`fields` The entire list of fields that make up the message.
`static Map<Long,Message.KnownType>`	`KNOWN_TYPE_MAP` Allows a known message type to be looked up by the message type number.
`Message.KnownType`	`knownType` The recognized type, if any, of this message.
`static Map<Byte,Message.MenuIdentifier>`	`MENU_IDENTIFIER_MAP` Allows a menu/destination to be looked up by the value seen in the second byte of the first argument of many request messages.
`static Map<Long,Message.MenuItemType>`	`MENU_ITEM_TYPE_MAP` Allows a menu item type to be looked up by the value seen in the seventh argument of a `Message.KnownType.MENU_ITEM` response.
`static NumberField`	`MESSAGE_START` The special field that marks the start of a new message.
`NumberField`	`messageType` The 2-byte number field that identifies what type of message this is, immediately following the transaction sequence number.
`static long`	`NO_MENU_RESULTS_AVAILABLE` The value returned by `getMenuResultsCount()` when there is no data available for the request that was made.
`NumberField`	`transaction` The 4-byte number field that provides the sequence number tying a query to its response messages, immediately following the message start field.

Constructor Summary

Constructors
Constructor and Description
`Message(long transaction, long messageType, Field... arguments)` Constructor for experimenting with new message types.
`Message(long transaction, Message.KnownType messageType, Field... arguments)` Constructor from code using known message types.
`Message(NumberField transaction, NumberField messageType, Field... arguments)` Constructor when being read from the network, so already have all the fields created.

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`Message.MenuItemType`	`getMenuItemType()` Extracts the menu item type from a `Message.KnownType.MENU_ITEM` response.
`long`	`getMenuResultsCount()` Extracts the result count from a `Message.KnownType.MENU_AVAILABLE` response.
`static Message`	`read(DataInputStream is)` Read the next message from the stream.
`String`	`toString()`
`void`	`write(WritableByteChannel channel)` Writes the message to the specified channel, for example when creating metadata cache files.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

- Field Detail
  - MESSAGE_START
```
public static final NumberField MESSAGE_START
```
    The special field that marks the start of a new message.
  - KNOWN_TYPE_MAP
```
public static final Map<Long,Message.KnownType> KNOWN_TYPE_MAP
```
    Allows a known message type to be looked up by the message type number.
  - MENU_ITEM_TYPE_MAP
```
public static final Map<Long,Message.MenuItemType> MENU_ITEM_TYPE_MAP
```
    Allows a menu item type to be looked up by the value seen in the seventh argument of a Message.KnownType.MENU_ITEM response.
  - transaction
```
public final NumberField transaction
```
    The 4-byte number field that provides the sequence number tying a query to its response messages, immediately following the message start field.
  - messageType
```
public final NumberField messageType
```
    The 2-byte number field that identifies what type of message this is, immediately following the transaction sequence number.
  - knownType
```
public final Message.KnownType knownType
```
    The recognized type, if any, of this message.
  - argumentCount
```
public final NumberField argumentCount
```
    The 1-byte number field that specifies how many arguments the message has.
  - arguments
```
public final List<Field> arguments
```
    The arguments being sent as part of this message.
  - fields
```
public final List<Field> fields
```
    The entire list of fields that make up the message.
  - MENU_IDENTIFIER_MAP
```
public static final Map<Byte,Message.MenuIdentifier> MENU_IDENTIFIER_MAP
```
    Allows a menu/destination to be looked up by the value seen in the second byte of the first argument of many request messages.
  - NO_MENU_RESULTS_AVAILABLE
```
public static final long NO_MENU_RESULTS_AVAILABLE
```
    The value returned by getMenuResultsCount() when there is no data available for the request that was made.
    
    See Also:
    
    Constant Field Values
- Constructor Detail
  - Message
```
public Message(long transaction,
               long messageType,
               Field... arguments)
```
    Constructor for experimenting with new message types.
    
    Parameters:
    
    transaction - the transaction ID (sequence number) that ties a message to its responses
    
    messageType - identifies the purpose and structure of the message
    
    arguments - the arguments to send with the message
  - Message
```
public Message(long transaction,
               Message.KnownType messageType,
               Field... arguments)
```
    Constructor from code using known message types.
    
    Parameters:
    
    transaction - the transaction ID (sequence number) that ties a message to its responses
    
    messageType - identifies the purpose and structure of the message
    
    arguments - the arguments to send with the message
  - Message
```
public Message(NumberField transaction,
               NumberField messageType,
               Field... arguments)
```
    Constructor when being read from the network, so already have all the fields created.
    
    Parameters:
    
    transaction - the transaction ID (sequence number) that ties a message to its responses
    
    messageType - identifies the purpose and structure of the message
    
    arguments - the arguments to send with the message
- Method Detail
  - read
```
public static Message read(DataInputStream is)
                    throws IOException
```
    Read the next message from the stream.
    
    Parameters:
    
    is - a stream connected to a dbserver which is expected to be sending a message.
    
    Returns:
    
    the next full message found on the stream.
    
    Throws:
    
    IOException - if there is a problem reading the message.
  - toString
```
public String toString()
```
    Overrides:
    
    toString in class Object
  - getMenuResultsCount
```
public long getMenuResultsCount()
```
    Extracts the result count from a Message.KnownType.MENU_AVAILABLE response.
    
    Returns:
    
    the reported count of available results
    
    Throws:
    
    IllegalArgumentException - if this is not a Message.KnownType.MENU_AVAILABLE response.
  - getMenuItemType
```
public Message.MenuItemType getMenuItemType()
```
    Extracts the menu item type from a Message.KnownType.MENU_ITEM response.
    
    Returns:
    
    the reported type of this menu item
    
    Throws:
    
    IllegalArgumentException - if this is not a Message.KnownType.MENU_ITEM response.
  - write
```
public void write(WritableByteChannel channel)
           throws IOException
```
    Writes the message to the specified channel, for example when creating metadata cache files.
    
    Parameters:
    
    channel - the channel to which it should be written
    
    Throws:
    
    IOException - if there is a problem writing to the channel

Class Message

Nested Class Summary

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

MESSAGE_START

KNOWN_TYPE_MAP

MENU_ITEM_TYPE_MAP

transaction

messageType

knownType

argumentCount

arguments

fields

MENU_IDENTIFIER_MAP

NO_MENU_RESULTS_AVAILABLE

Constructor Detail

Message

Message

Message

Method Detail

read

toString

getMenuResultsCount

getMenuItemType

write