FrameDescriptor (Aeron Message Transport)

java.lang.Object
- io.aeron.logbuffer.FrameDescriptor

public class FrameDescriptor
extends Object

Description of the structure for message framing in a log buffer.

All messages are logged in frames that have a minimum header layout as follows plus a reserve then the encoded message follows:

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |R|                       Frame Length                          |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-------------------------------+
  |  Version      |B|E| Flags     |             Type              |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-------------------------------+
  |R|                       Term Offset                           |
  +-+-------------------------------------------------------------+
  |                      Additional Fields                       ...
 ...                                                              |
  +---------------------------------------------------------------+
  |                        Encoded Message                       ...
 ...                                                              |
  +---------------------------------------------------------------+

The (B)egin and (E)nd flags are used for message fragmentation. R is for reserved bit. Both (B)egin and (E)nd flags are set for a message that does not span frames.

Field Summary

Fields
Modifier and Type	Field and Description
`static byte`	`BEGIN_FRAG_FLAG` Beginning fragment of a frame.
`static byte`	`END_FRAG_FLAG` End fragment of a frame.
`static int`	`FLAGS_OFFSET` Offset within a frame at which the flags field begins
`static int`	`FRAME_ALIGNMENT` Alignment as a multiple of bytes for each frame.
`static int`	`MAX_MESSAGE_LENGTH` Set a pragmatic maximum message length regardless of term length to encourage better design.
`static int`	`PADDING_FRAME_TYPE` Padding frame type to indicate the message should be ignored.
`static int`	`SESSION_ID_OFFSET` Offset within a frame at which the session id field begins
`static int`	`TERM_ID_OFFSET` Offset within a frame at which the term id field begins
`static int`	`TERM_OFFSET` Offset within a frame at which the term offset field begins
`static int`	`TYPE_OFFSET` Offset within a frame at which the type field begins
`static byte`	`UNFRAGMENTED` End fragment of a frame.
`static int`	`VERSION_OFFSET` Offset within a frame at which the version field begins

Constructor Summary

Constructors
Constructor and Description

FrameDescriptor()

Constructors
Constructor and Description
`FrameDescriptor()`

Method Summary

All Methods Static Methods Concrete Methods
Modifier and Type	Method and Description
`static int`	`computeMaxMessageLength(int termLength)` Compute the maximum supported message length for a buffer of given termLength.
`static int`	`flagsOffset(int termOffset)` The buffer offset at which the flags field begins.
`static byte`	`frameFlags(UnsafeBuffer buffer, int termOffset)` Get the flags field for a frame.
`static void`	`frameFlags(UnsafeBuffer buffer, int termOffset, byte flags)` Write the flags field for a frame.
`static int`	`frameLength(UnsafeBuffer buffer, int termOffset)` Get the length of a frame from the header.
`static void`	`frameLengthOrdered(UnsafeBuffer buffer, int termOffset, int frameLength)` Write the length header for a frame in a memory ordered fashion.
`static int`	`frameLengthVolatile(UnsafeBuffer buffer, int termOffset)` Get the length of a frame from the header as a volatile read.
`static int`	`frameSessionId(UnsafeBuffer buffer, int termOffset)` Get the session id of a frame from the header.
`static void`	`frameSessionId(UnsafeBuffer buffer, int termOffset, int sessionId)` Write the session id field for a frame.
`static int`	`frameTermId(UnsafeBuffer buffer, int termOffset)` Get the term id of a frame from the header.
`static void`	`frameTermId(UnsafeBuffer buffer, int termOffset, int termId)` Write the term id field for a frame.
`static void`	`frameTermOffset(UnsafeBuffer buffer, int termOffset)` Write the term offset field for a frame.
`static int`	`frameType(UnsafeBuffer buffer, int termOffset)` Read the type of the frame from header.
`static void`	`frameType(UnsafeBuffer buffer, int termOffset, int type)` Write the type field for a frame.
`static int`	`frameVersion(UnsafeBuffer buffer, int termOffset)` Read the type of the frame from header.
`static boolean`	`isPaddingFrame(UnsafeBuffer buffer, int termOffset)` Is the frame starting at the termOffset a padding frame at the end of a buffer?
`static int`	`lengthOffset(int termOffset)` The buffer offset at which the length field begins.
`static int`	`sessionIdOffset(int termOffset)` The buffer offset at which the session id field begins.
`static int`	`termIdOffset(int termOffset)` The buffer offset at which the term id field begins.
`static int`	`termOffsetOffset(int termOffset)` The buffer offset at which the term offset field begins.
`static int`	`typeOffset(int termOffset)` The buffer offset at which the type field begins.
`static int`	`versionOffset(int termOffset)` The buffer offset at which the version field begins.

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

- Field Detail
  - MAX_MESSAGE_LENGTH
```
public static final int MAX_MESSAGE_LENGTH
```
    Set a pragmatic maximum message length regardless of term length to encourage better design. Messages larger than half the cache size should be broken up into chunks and streamed.
    
    See Also:
    
    Constant Field Values
  - FRAME_ALIGNMENT
```
public static final int FRAME_ALIGNMENT
```
    Alignment as a multiple of bytes for each frame. The length field will store the unaligned length in bytes.
    
    See Also:
    
    Constant Field Values
  - BEGIN_FRAG_FLAG
```
public static final byte BEGIN_FRAG_FLAG
```
    Beginning fragment of a frame.
    
    See Also:
    
    Constant Field Values
  - END_FRAG_FLAG
```
public static final byte END_FRAG_FLAG
```
    End fragment of a frame.
    
    See Also:
    
    Constant Field Values
  - UNFRAGMENTED
```
public static final byte UNFRAGMENTED
```
    End fragment of a frame.
    
    See Also:
    
    Constant Field Values
  - VERSION_OFFSET
```
public static final int VERSION_OFFSET
```
    Offset within a frame at which the version field begins
    
    See Also:
    
    Constant Field Values
  - FLAGS_OFFSET
```
public static final int FLAGS_OFFSET
```
    Offset within a frame at which the flags field begins
    
    See Also:
    
    Constant Field Values
  - TYPE_OFFSET
```
public static final int TYPE_OFFSET
```
    Offset within a frame at which the type field begins
    
    See Also:
    
    Constant Field Values
  - TERM_OFFSET
```
public static final int TERM_OFFSET
```
    Offset within a frame at which the term offset field begins
    
    See Also:
    
    Constant Field Values
  - TERM_ID_OFFSET
```
public static final int TERM_ID_OFFSET
```
    Offset within a frame at which the term id field begins
    
    See Also:
    
    Constant Field Values
  - SESSION_ID_OFFSET
```
public static final int SESSION_ID_OFFSET
```
    Offset within a frame at which the session id field begins
    
    See Also:
    
    Constant Field Values
  - PADDING_FRAME_TYPE
```
public static final int PADDING_FRAME_TYPE
```
    Padding frame type to indicate the message should be ignored.
    
    See Also:
    
    Constant Field Values
- Constructor Detail
  - FrameDescriptor
```
public FrameDescriptor()
```
- Method Detail
  - computeMaxMessageLength
```
public static int computeMaxMessageLength(int termLength)
```
    Compute the maximum supported message length for a buffer of given termLength.
    
    Parameters:
    
    termLength - of the log buffer.
    
    Returns:
    
    the maximum supported length for a message.
  - lengthOffset
```
public static int lengthOffset(int termOffset)
```
    The buffer offset at which the length field begins.
    
    Parameters:
    
    termOffset - at which the frame begins.
    
    Returns:
    
    the offset at which the length field begins.
  - versionOffset
```
public static int versionOffset(int termOffset)
```
    The buffer offset at which the version field begins.
    
    Parameters:
    
    termOffset - at which the frame begins.
    
    Returns:
    
    the offset at which the version field begins.
  - flagsOffset
```
public static int flagsOffset(int termOffset)
```
    The buffer offset at which the flags field begins.
    
    Parameters:
    
    termOffset - at which the frame begins.
    
    Returns:
    
    the offset at which the flags field begins.
  - typeOffset
```
public static int typeOffset(int termOffset)
```
    The buffer offset at which the type field begins.
    
    Parameters:
    
    termOffset - at which the frame begins.
    
    Returns:
    
    the offset at which the type field begins.
  - termOffsetOffset
```
public static int termOffsetOffset(int termOffset)
```
    The buffer offset at which the term offset field begins.
    
    Parameters:
    
    termOffset - at which the frame begins.
    
    Returns:
    
    the offset at which the term offset field begins.
  - termIdOffset
```
public static int termIdOffset(int termOffset)
```
    The buffer offset at which the term id field begins.
    
    Parameters:
    
    termOffset - at which the frame begins.
    
    Returns:
    
    the offset at which the term id field begins.
  - sessionIdOffset
```
public static int sessionIdOffset(int termOffset)
```
    The buffer offset at which the session id field begins.
    
    Parameters:
    
    termOffset - at which the frame begins.
    
    Returns:
    
    the offset at which the session id field begins.
  - frameVersion
```
public static int frameVersion(UnsafeBuffer buffer,
                               int termOffset)
```
    Read the type of the frame from header.
    
    Parameters:
    
    buffer - containing the frame.
    
    termOffset - at which a frame begins.
    
    Returns:
    
    the value of the frame type header.
  - frameFlags
```
public static byte frameFlags(UnsafeBuffer buffer,
                              int termOffset)
```
    Get the flags field for a frame.
    
    Parameters:
    
    buffer - containing the frame.
    
    termOffset - at which a frame begins.
    
    Returns:
    
    the value of the flags.
  - frameType
```
public static int frameType(UnsafeBuffer buffer,
                            int termOffset)
```
    Read the type of the frame from header.
    
    Parameters:
    
    buffer - containing the frame.
    
    termOffset - at which a frame begins.
    
    Returns:
    
    the value of the frame type header.
  - isPaddingFrame
```
public static boolean isPaddingFrame(UnsafeBuffer buffer,
                                     int termOffset)
```
    Is the frame starting at the termOffset a padding frame at the end of a buffer?
    
    Parameters:
    
    buffer - containing the frame.
    
    termOffset - at which a frame begins.
    
    Returns:
    
    true if the frame is a padding frame otherwise false.
  - frameLength
```
public static int frameLength(UnsafeBuffer buffer,
                              int termOffset)
```
    Get the length of a frame from the header.
    
    Parameters:
    
    buffer - containing the frame.
    
    termOffset - at which a frame begins.
    
    Returns:
    
    the value for the frame length.
  - frameTermId
```
public static int frameTermId(UnsafeBuffer buffer,
                              int termOffset)
```
    Get the term id of a frame from the header.
    
    Parameters:
    
    buffer - containing the frame.
    
    termOffset - at which a frame begins.
    
    Returns:
    
    the value for the term id field.
  - frameSessionId
```
public static int frameSessionId(UnsafeBuffer buffer,
                                 int termOffset)
```
    Get the session id of a frame from the header.
    
    Parameters:
    
    buffer - containing the frame.
    
    termOffset - at which a frame begins.
    
    Returns:
    
    the value for the session id field.
  - frameLengthVolatile
```
public static int frameLengthVolatile(UnsafeBuffer buffer,
                                      int termOffset)
```
    Get the length of a frame from the header as a volatile read.
    
    Parameters:
    
    buffer - containing the frame.
    
    termOffset - at which a frame begins.
    
    Returns:
    
    the value for the frame length.
  - frameLengthOrdered
```
public static void frameLengthOrdered(UnsafeBuffer buffer,
                                      int termOffset,
                                      int frameLength)
```
    Write the length header for a frame in a memory ordered fashion.
    
    Parameters:
    
    buffer - containing the frame.
    
    termOffset - at which a frame begins.
    
    frameLength - field to be set for the frame.
  - frameType
```
public static void frameType(UnsafeBuffer buffer,
                             int termOffset,
                             int type)
```
    Write the type field for a frame.
    
    Parameters:
    
    buffer - containing the frame.
    
    termOffset - at which a frame begins.
    
    type - type value for the frame.
  - frameFlags
```
public static void frameFlags(UnsafeBuffer buffer,
                              int termOffset,
                              byte flags)
```
    Write the flags field for a frame.
    
    Parameters:
    
    buffer - containing the frame.
    
    termOffset - at which a frame begins.
    
    flags - value for the frame.
  - frameTermOffset
```
public static void frameTermOffset(UnsafeBuffer buffer,
                                   int termOffset)
```
    Write the term offset field for a frame.
    
    Parameters:
    
    buffer - containing the frame.
    
    termOffset - at which a frame begins.
  - frameTermId
```
public static void frameTermId(UnsafeBuffer buffer,
                               int termOffset,
                               int termId)
```
    Write the term id field for a frame.
    
    Parameters:
    
    buffer - containing the frame.
    
    termOffset - at which a frame begins.
    
    termId - value for the frame.
  - frameSessionId
```
public static void frameSessionId(UnsafeBuffer buffer,
                                  int termOffset,
                                  int sessionId)
```
    Write the session id field for a frame.
    
    Parameters:
    
    buffer - containing the frame.
    
    termOffset - at which a frame begins.
    
    sessionId - value for the frame.

Class FrameDescriptor

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

MAX_MESSAGE_LENGTH

FRAME_ALIGNMENT

BEGIN_FRAG_FLAG

END_FRAG_FLAG

UNFRAGMENTED

VERSION_OFFSET

FLAGS_OFFSET

TYPE_OFFSET

TERM_OFFSET

TERM_ID_OFFSET

SESSION_ID_OFFSET

PADDING_FRAME_TYPE

Constructor Detail

FrameDescriptor

Method Detail

computeMaxMessageLength

lengthOffset

versionOffset

flagsOffset

typeOffset

termOffsetOffset

termIdOffset

sessionIdOffset

frameVersion

frameFlags

frameType

isPaddingFrame

frameLength

frameTermId

frameSessionId

frameLengthVolatile

frameLengthOrdered

frameType

frameFlags

frameTermOffset

frameTermId

frameSessionId