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RPC_X_WRONG_PIPE_ORDER
Pipe order is an RPC contract
RPC_X_WRONG_PIPE_ORDER is about the order in which a single RPC call processes streamed parameters. It does not mean that IP packets arrived out of order. A pipe can cause the stubs to call application-supplied routines several times during one call, and those callbacks have an ordering rule defined by the IDL signature.
For an operation with several input or input-output pipes, the input side must be completely processed in parameter order before output pipes are filled. Output and input-output pipes are then processed in their declared order after the input pipes have been drained. Microsoft maps the underlying RPC pipe-order fault to this Win32 error.
Where the violation is usually introduced
- A server manager starts producing an output pipe before it has consumed an earlier input pipe.
- Code with more than one pipe parameter skips a callback path or resumes the next pipe before the current one reaches its terminal state.
- A reentrant helper calls into logic that touches another pipe associated with the same RPC invocation.
- The IDL order changed, but the manager implementation still follows the old parameter sequence.
How to diagnose it
Read the generated client and server stubs together with the exact IDL operation declaration. Add tracing that identifies the call, parameter ordinal, direction, callback name, element count, and terminal condition. The trace should show every input pipe becoming exhausted before the first output pipe is populated, and each later pipe starting only after the preceding one is complete.
Do not try to solve this by changing transport settings, increasing RPC timeouts, or reordering network writes. The corrective action is to restore the pipe callback sequence implied by the IDL operation, or to redesign the operation so that independent streams are sent in separate calls.
References
- The Open Group: pipe processing order in DCE RPC stubs
- Microsoft: MIDL pipe type and direction rules
- Microsoft: mapping RPC pipe-order faults to Win32 errors
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