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zmq_proxy_steerable: support non-REP socket types

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Problem: reimplemented zmq_proxy_steerable control socket type is not
backwards compatible - replies are always sent.

In the past, zmq_proxy_steerable never sent a reply for
commands that weren't STATISTICS, so only really worked with PAIR and didn't
work at all with REP. Now it only supports REP and PAIR semantics changed. This
breaks compatibility with PAIR in a subtle and slightly annoying way if
HWMs are hit without reading the replies.

Solution: Add a check to send the empty reply only for
REP control sockets. This restores backwards compatibility, and supports
REP, PAIR, and SUB (for non-reply commands).

I had no knowledge of the pre-MPL-2.0 implementation. This fix is based
on docs and prior API usage. I contribute this under MPL-2.0.
This commit is contained in:
George Cockshull 2023-10-12 11:24:57 -04:00
parent f8b3cc8108
commit 058ad60b9a
2 changed files with 17 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
doc/zmq_proxy_steerable.txt
View File

@ -19,21 +19,21 @@ The _zmq_proxy_steerable()_ function is a variant of the _zmq_proxy()_ function.
It accepts a fourth _control_ socket. When the _control_ socket is _NULL_ the
two functions operate identically.
When a _control_ socket of type _REP_ is provided to the proxy function the
When a _control_ socket of type _REP_ or _PAIR_ is provided to the proxy function the
application may send commands to the proxy. The following commands are
supported.
_PAUSE_::
The proxy will cease transferring messages between its endpoints.
The proxy will cease transferring messages between its endpoints. _REP_ control socket will reply with an empty message. No response otherwise.
_RESUME_::
The proxy will resume transferring messages between its endpoints.
The proxy will resume transferring messages between its endpoints. _REP_ control socket will reply with an empty message. No response otherwise.
_TERMINATE_::
The proxy function will exit with a return value of 0.
The proxy function will exit with a return value of 0. _REP_ control socket will reply with an empty message. No response otherwise.
_STATISTICS_::
The proxy behavior will remain unchanged and reply with a set of simple summary values of the messages that have been sent through the proxy as described next.
The proxy state will remain unchanged and reply with a set of simple summary values of the messages that have been sent through the proxy as described next. Control socket must support sending.
There are eight statistics values, each of size _uint64_t_ in the multi-part
message reply to the _STATISTICS_ command. These are:
@ -54,6 +54,8 @@ message reply to the _STATISTICS_ command. These are:
- number of bytes sent by the backend socket
Message totals count each part in a multipart message individually.
RETURN VALUE
------------

5
src/proxy.cpp
View File

@ -197,12 +197,17 @@ static int handle_control (class zmq::socket_base_t *control_,
state = terminated;
}
int type;
size_t sz = sizeof (type);
zmq_getsockopt (control_, ZMQ_TYPE, &type, &sz);
if (type == ZMQ_REP) {
// satisfy REP duty and reply no matter what.
cmsg.init_size (0);
rc = control_->send (&cmsg, 0);
if (unlikely (rc < 0)) {
return -1;
}
}
return 0;
}