数据帧

  Indicates that this is the final fragment in a message.  The first fragment MAY also be the final fragment.

RSV1, RSV2, RSV3: 1 bit each

  Defines the interpretation of the "Payload data".  If an unknown opcode is received, the receiving endpoint MUST _Fail the WebSocket Connection_.  The following values are defined.

  *  %x0 denotes a continuation frame

  *  %x1 denotes a text frame

  *  %x2 denotes a binary frame

  *  %x3-7 are reserved for further non-control frames

  *  %x8 denotes a connection close

  *  %x9 denotes a ping

  *  %xA denotes a pong

  *  %xB-F are reserved for further control frames

Mask: 1 bit

  Defines whether the "Payload data" is masked.  If set to 1, a
  masking key is present in masking-key, and this is used to unmask
  the "Payload data" as perSection 5.3.  All frames sent from
  client to server have this bit set to 1.

Payload length: 7 bits, 7+16 bits, or 7+64 bits

  The length of the "Payload data", in bytes: if 0-125, that is the
  payload length.  If 126, the following 2 bytes interpreted as a
  16-bit unsigned integer are the payload length.  If 127, the
  following 8 bytes interpreted as a 64-bit unsigned integer (the
  most significant bit MUST be 0) are the payload length.  Multibyte
  length quantities are expressed in network byte order.  Note that
  in all cases, the minimal number of bytes MUST be used to encode
  the length, for example, the length of a 124-byte-long string
  can't be encoded as the sequence 126, 0, 124.  The payload length
  is the length of the "Extension data" + the length of the
  "Application data".  The length of the "Extension data" may be
  zero, in which case the payload length is the length of the
  "Application data".

  All frames sent from the client to the server are masked by a
  32-bit value that is contained within the frame.  This field is
  present if the mask bit is set to 1 and is absent if the mask bit
  is set to 0.  SeeSection 5.3 for further information on client-
  to-server masking.

Payload data: (x+y) bytes

  The "Payload data" is defined as "Extension data" concatenated
  with "Application data".

Extension data: x bytes

  The "Extension data" is 0 bytes unless an extension has been
  negotiated.  Any extension MUST specify the length of the
  "Extension data", or how that length may be calculated, and how
  the extension use MUST be negotiated during the opening handshake.
  If present, the "Extension data" is included in the total payload
  length.

Application data: y bytes

  Arbitrary "Application data", taking up the remainder of the frame
  after any "Extension data".  The length of the "Application data"
  is equal to the payload length minus the length of the "Extension
  data&quot;.</div></div>
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