DosPeekNmPipe

This call reads pipe without removing the read data from the pipe.

DosPeekNmPipe

(Handle, Buffer, BufferLen, BytesRead, BytesAvail, PipeState)

Handle (HPIPE) - input

Handle of the named pipe, returned by DosMakeNmPipe or DosOpen.
Buffer (PBYTE) - output
Address of the output buffer.
BufferLen (USHORT) - input
Number of bytes to be read.
BytesRead (PUSHORT) - output
Address of the number of bytes read.
BytesAvail (PUSHORT) - output
Address of the 4-byte buffer where the system returns the number of bytes that were available. The buffer structure is:
• Bytes
  Bytes buffered in pipe (including message header bytes and bytes peeked).
  2 Bytes
  Bytes in current message (zero for a byte stream pipe).
  PipeState (PUSHORT) - output
  Address of a value representing the state of the named pipe.

  Value

  Definition
  1
  Disconnected
  2
  Listening
  3
  Connected
  4
  Closing
  The pipe is in a disconnected state immediately after:

  o

  A DosMakeNmPipe but before the first DosConnectNmPipe, or
  o
  A DosDisConnectNmPipe but before the next DosConnectNmPipe. A disconnected pipe has no client end and cannot accept a DosOpen. The serving end must issue DosConnectNmPipe, so an open can be accepted.

  The pipe is in a listening state after a DosConnectNmPipe. A listening pipe is ready to accept a DosOpen request. If the pipe is not in a listening state, DosOpen returns ERROR_PIPE_BUSY.

  The pipe is in a connected state after a successful DosOpen to the listening pipe. The connected pipe allows the serving and client ends to perform I/O, provided both have valid handles.

  The pipe is in a closing state after the last DosClose to the pipe from either the client or server end.

  After DosClose has been issued for the client handle and any duplicates, and the serving end has read all buffered data, the serving end is returned ERROR_EOF for reads and ERROR_BROKEN_PIPE for writes. The serving end must acknowledge the closing of the client end by issuing either DosDisConnectNmPipe or DosClose. Issuing DosClose deallocates the pipe.

  rc (USHORT) - return
  Return code descriptions are:
  • NO_ERROR 230
    ERROR_BAD_PIPE
    231
    ERROR_PIPE_BUSY
    233
    ERROR_PIPE_NOT_CONNECTED
    Remarks

    DosPeekNmPipe is similar to a DosRead, except the bytes read from the pipe are not removed. In addition, a DosPeekNmPipe never blocks, regardless of the blocking mode set. If the pipe cannot be accessed immediately, ERROR_PIPE_BUSY is returned. Because the peek cannot block, it returns only what is currently in the pipe. Thus, a portion of a message may be returned, even though the size of the peek can accommodate the entire message.

    The value returned in PipeState can be used by the client or the server end to determine the current state of the pipe and take appropriate action.

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