3.2.4.1.4 Sending Compounded Requests

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A nonzero value for the NextCommand field in the SMB2 header indicates a compound request. NextCommand in the SMB2 header of a request specifies an offset, in bytes, from the beginning of the SMB2 header under consideration to the start of the 8-byte aligned SMB2 header of the subsequent request. Such compounding can be used to append multiple requests up to the maximum size<107> that is supported by the transport. The client MUST choose one of two possible styles of message compounding specified in subsequent sections. These two styles MUST NOT be intermixed in the same transport send and, in such a case, the server SHOULD<108> fail the requests with STATUS_INVALID_PARAMETER. Compounded requests MUST be aligned on 8-byte boundaries; the last request of the compounded requests does not need to be padded to an 8-byte boundary.

Compounding Unrelated Requests

SMB2_FLAGS_RELATED_OPERATIONS MUST NOT be set in the Flags field of all SMB2 headers in the chain. The client MUST NOT expect the responses of unrelated requests to arrive in the same transport receive from the server, or even in the same order they were sent.<109>

Compounding Related Requests

SMB2_FLAGS_RELATED_OPERATIONS MUST be set in the Flags field of SMB2 headers on all requests except the first one. The client can choose to send multiple requests required to perform a desired action as a compounded send containing related operations. Two examples would be to open a file and read from it, or to write to a file and close it. This form of compounding MUST NOT be used in combination with compounding unrelated requests within a single send.<110>

To issue a compounded send of related requests, take the following steps:

  1. The client MUST construct the initial request as it would if sending the requests separately.

  2. It MUST set the NextCommand field in the SMB2 header of the initial request to the offset, in bytes, from the beginning of the SMB2 header to the beginning of the 8-byte aligned SMB2 header of the subsequent request. It MUST NOT set SMB2_FLAGS_RELATED_OPERATIONS in the Flags field of the SMB2 header for this request.

  3. The client MUST construct the subsequent request as it would do normally. For any subsequent requests the client MUST set SMB2_FLAGS_RELATED_OPERATIONS in the Flags field of the SMB2 header to indicate that it is using the SessionId, TreeId, and FileId supplied in the previous request (or generated by the server in processing that request). For an operation compounded with an SMB2 CREATE request, the FileId field SHOULD be set to { 0xFFFFFFFFFFFFFFFF, 0xFFFFFFFFFFFFFFFF }.