Fix thinko in PQisBusy().

In commit 1f39a1c06 I made PQisBusy consider conn->write_failed, but
that is now looking like complete brain fade.  In the first place, the
logic is quite wrong: it ought to be like "and not" rather than "or".
This meant that once we'd gotten into a write_failed state, PQisBusy
would always return true, probably causing the calling application to
iterate its loop until PQconsumeInput returns a hard failure thanks
to connection loss.  That's not what we want: the intended behavior
is to return an error PGresult, which the application probably has
much cleaner support for.

But in the second place, checking write_failed here seems like the
wrong thing anyway.  The idea of the write_failed mechanism is to
postpone handling of a write failure until we've read all we can from
the server; so that flag should not interfere with input-processing
behavior.  (Compare 7247e243a.)  What we *should* check for is
status = CONNECTION_BAD, ie, socket already closed.  (Most places that
close the socket don't touch asyncStatus, but they do reset status.)
This primarily ensures that if PQisBusy() returns true then there is
an open socket, which is assumed by several call sites in our own
code, and probably other applications too.

While at it, fix a nearby thinko in libpq's my_sock_write: we should
only consult errno for res < 0, not res == 0.  This is harmless since
pqsecure_raw_write would force errno to zero in such a case, but it
still could confuse readers.

Noted by Andres Freund.  Backpatch to v12 where 1f39a1c06 came in.

Discussion: https://postgr.es/m/20220211011025[email protected]

diff --git a/src/interfaces/libpq/fe-exec.c b/src/interfaces/libpq/fe-exec.c
index eea0237c3a5c5ac1007af89c531ff941d94aa3e8..9c465b1f967c2e4cfa6828d74af16ca22550c630 100644 (file)
--- a/src/interfaces/libpq/fe-exec.c
+++ b/src/interfaces/libpq/fe-exec.c
@@ -1760,10 +1760,14 @@ PQisBusy(PGconn *conn)
    parseInput(conn);
 
    /*
-    * PQgetResult will return immediately in all states except BUSY, or if we
-    * had a write failure.
+    * PQgetResult will return immediately in all states except BUSY.  Also,
+    * if we've detected read EOF and dropped the connection, we can expect
+    * that PQgetResult will fail immediately.  Note that we do *not* check
+    * conn->write_failed here --- once that's become set, we know we have
+    * trouble, but we need to keep trying to read until we have a complete
+    * server message or detect read EOF.
     */
-   return conn->asyncStatus == PGASYNC_BUSY || conn->write_failed;
+   return conn->asyncStatus == PGASYNC_BUSY && conn->status != CONNECTION_BAD;
 }
 
 

diff --git a/src/interfaces/libpq/fe-secure-openssl.c b/src/interfaces/libpq/fe-secure-openssl.c
index 01e825b322fe59a910c3d63c83e491b13e117839..987fe02419c3a66e4c6bdde997a800b556473168 100644 (file)
--- a/src/interfaces/libpq/fe-secure-openssl.c
+++ b/src/interfaces/libpq/fe-secure-openssl.c
@@ -1607,7 +1607,7 @@ my_sock_write(BIO *h, const char *buf, int size)
 
    res = pqsecure_raw_write((PGconn *) BIO_get_data(h), buf, size);
    BIO_clear_retry_flags(h);
-   if (res <= 0)
+   if (res < 0)
    {
        /* If we were interrupted, tell caller to retry */
        switch (SOCK_ERRNO)