New header_rewrite set-body-from operator could hypothetically lock up Transaction State Machine

[ywkaras]

The execution of the set-body-operator initiates an internal URL fetch:

trafficserver/plugins/header_rewrite/operators.cc

Line 1353 in 0d8a6ac

TSFetchUrl(static_cast<const char *>(req_buf), req_buf_size, reinterpret_cast<struct sockaddr const *>(&addr), fetchCont,

This execution function runs in the READ_RESPONSE_HDR Txn hook. The operator then runs a continuation on the SEND_RESPONSE_HDR Txn hook, that does not call TSHttpTxnReenable(). The intent is that the hook processing is reenabled once the internal URL fetch completes, here:

trafficserver/plugins/header_rewrite/operators.cc

Line 66 in 0d8a6ac

TSHttpTxnReenable(http_txn, TS_EVENT_HTTP_ERROR);

But, it is not clear there is a mechanism that will prevent the internal fetch from being completed before the operator's continuation runs on the SEND_RESPONSE_HDR. Also, if other continuations on a Txn hook also uses indirect reenabling, the reenable for the fetch completing could effectively reenable the wrong continuation.