PRIORITY / PRIORITY帧

The PRIORITY frame (type=0x2) specifies the sender-advised priority of a stream (Section 5.3). It can be sent in any stream state, including idle or closed streams.

+-+-------------------------------------------------------------+
|E|                  Stream Dependency (31)                     |
+-+-------------+-----------------------------------------------+
|   Weight (8)  |
+-+-------------+
                Figure 8: PRIORITY Frame Payload

PRIORITY帧(type=0x2)指定了发送者建议的流优先级( 5.3节 )。可以在任何流状态下发送PRIORITY帧，包括空闲(idle)的 和 关闭(closed) 的流。

+-+-------------------------------------------------------------+
|E|                  Stream Dependency (31)                     |
+-+-------------+-----------------------------------------------+
|   Weight (8)  |
+-+-------------+
                        图 8: PRIORITY帧载荷

The payload of a PRIORITY frame contains the following fields:

• E: A single-bit flag indicating that the stream dependency is exclusive (see Section 5.3).
• Stream Dependency: A 31-bit stream identifier for the stream that this stream depends on (see Section 5.3).
• Weight: An unsigned 8-bit integer representing a priority weight for the stream (see Section 5.3). Add one to the value to obtain a weight between 1 and 256.

PRIORITY帧的载荷包含以下域：

• E标识(E): 1bit标识，指明流依赖(Stream Dependency)是否是专用的(参见 5.3节 )。
• 流依赖(Stream Dependency): 该流所依赖的流(参见 5.3节 )的31bit标识符。
• 权重(Weight): 一个8bit的无符号整数，表示该流的优先级权重(参见 5.3节 )。范围是1到255。

The PRIORITY frame does not define any flags.

PRIORITY帧没有定义任何标识。

The PRIORITY frame always identifies a stream. If a PRIORITY frame is received with a stream identifier of 0x0, the recipient MUST respond with a connection error (Section 5.4.1) of type PROTOCOL_ERROR.

PRIORITY帧总是标识出了某一个流。如果收到一个流标识符为0x0的PRIORITY帧，接收方必须响应一个 PROTOCOL_ERROR 类型的连接错误( 5.4.1节 )。

The PRIORITY frame can be sent on a stream in any state, though it cannot be sent between consecutive frames that comprise a single header block (Section 4.3). Note that this frame could arrive after processing or frame sending has completed, which would cause it to have no effect on the identified stream. For a stream that is in the "half-closed (remote)" or "closed" state, this frame can only affect processing of the identified stream and its dependent streams; it does not affect frame transmission on that stream.

可以在处于任意状态的流上发送PRIORITY帧，但却不能在包含同一个首部块4.3节的连续帧之间发送。需要注意的是，PRIORITY帧可能会在处理或发送帧完成后到达，这会导致PRIORITY帧在特定的流上不起作用。对处于 半关闭(远端)(half-closed (remote)) 或者 关闭(closed) 状态的流来说，PRIORITY帧只能影响对该特定流及其从属流的处理，而不会影响在该流上的帧传送。

The PRIORITY frame can be sent for a stream in the "idle" or "closed" state. This allows for the reprioritization of a group of dependent streams by altering the priority of an unused or closed parent stream.

可以在处于 空闲(idle) 或者 关闭(closed) 状态的流上发送PRIORITY帧，从而可以通过改变一个未使用的或者关闭的母流的优先级，来改变其从属流的优先级顺序。

A PRIORITY frame with a length other than 5 octets MUST be treated as a stream error (Section 5.4.2) of type FRAME_SIZE_ERROR.

必须将不是5字节长度的PRIORITY帧当做一个类型为 FRAME_SIZE_ERROR 的流错误 5.4.2节。