diff options
| -rw-r--r-- | doc/src/sgml/protocol.sgml | 5 | ||||
| -rw-r--r-- | src/interfaces/libpq/fe-cancel.c | 28 |
2 files changed, 32 insertions, 1 deletions
diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml index b115884acb3..e56eac8fd0f 100644 --- a/doc/src/sgml/protocol.sgml +++ b/doc/src/sgml/protocol.sgml @@ -537,6 +537,11 @@ The frontend should not respond to this message, but should continue listening for a ReadyForQuery message. </para> + <para> + The <productname>PostgreSQL</productname> server will always send this + message, but some third party backend implementations of the protocol + that don't support query cancellation are known not to. + </para> </listitem> </varlistentry> diff --git a/src/interfaces/libpq/fe-cancel.c b/src/interfaces/libpq/fe-cancel.c index 65517c5703b..c872a0267f0 100644 --- a/src/interfaces/libpq/fe-cancel.c +++ b/src/interfaces/libpq/fe-cancel.c @@ -379,7 +379,24 @@ PQgetCancel(PGconn *conn) /* Check that we have received a cancellation key */ if (conn->be_cancel_key_len == 0) - return NULL; + { + /* + * In case there is no cancel key, return an all-zero PGcancel object. + * Actually calling PQcancel on this will fail, but we allow creating + * the PGcancel object anyway. Arguably it would be better return NULL + * to indicate that cancellation is not possible, but there'd be no + * way for the caller to distinguish "out of memory" from "server did + * not send a cancel key". Also, this is how PGgetCancel() has always + * behaved, and if we changed it, some clients would stop working + * altogether with servers that don't support cancellation. (The + * modern PQcancelCreate() function returns a failed connection object + * instead.) + * + * The returned dummy object has cancel_pkt_len == 0; we check for + * that in PQcancel() to identify it as a dummy. + */ + return calloc(1, sizeof(PGcancel)); + } cancel_req_len = offsetof(CancelRequestPacket, cancelAuthCode) + conn->be_cancel_key_len; cancel = malloc(offsetof(PGcancel, cancel_req) + cancel_req_len); @@ -544,6 +561,15 @@ PQcancel(PGcancel *cancel, char *errbuf, int errbufsize) return false; } + if (cancel->cancel_pkt_len == 0) + { + /* This is a dummy PGcancel object, see PQgetCancel */ + strlcpy(errbuf, "PQcancel() -- no cancellation key received", errbufsize); + /* strlcpy probably doesn't change errno, but be paranoid */ + SOCK_ERRNO_SET(save_errno); + return false; + } + /* * We need to open a temporary connection to the postmaster. Do this with * only kernel calls. |