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In libpq, always append new error messages to conn->errorMessage.

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Previously, we had an undisciplined mish-mash of printfPQExpBuffer and
appendPQExpBuffer calls to report errors within libpq.  This commit
establishes a uniform rule that appendPQExpBuffer[Str] should be used.
conn->errorMessage is reset only at the start of an application request,
and then accumulates messages till we're done.  We can remove no less
than three different ad-hoc mechanisms that were used to get the effect
of concatenation of error messages within a sequence of operations.

Although this makes things quite a bit cleaner conceptually, the main
reason to do it is to make the world safer for the multiple-target-host
feature that was added awhile back.  Previously, there were many cases
in which an error occurring during an individual host connection attempt
would wipe out the record of what had happened during previous attempts.
(The reporting is still inadequate, in that it can be hard to tell which
host got the failure, but that seems like a matter for a separate commit.)

Currently, lo_import and lo_export contain exceptions to the "never
use printfPQExpBuffer" rule.  If we changed them, we'd risk reporting
an incidental lo_close failure before the actual read or write
failure, which would be confusing, not least because lo_close happened
after the main failure.  We could improve this by inventing an
internal version of lo_close that doesn't reset the errorMessage; but
we'd also need a version of PQfn() that does that, and it didn't quite
seem worth the trouble for now.

Discussion: https://postgr.es/m/BN6PR05MB3492948E4FD76C156E747E8BC9160@BN6PR05MB3492.namprd05.prod.outlook.com
This commit is contained in:
Tom Lane
2021-01-11 13:12:09 -05:00
parent ce6a71fa53
commit ffa2e46701
14 changed files with 699 additions and 774 deletions
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18
src/interfaces/libpq/libpq-int.h
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@@ -522,7 +522,11 @@ struct pg_conn
* connection */
#endif
/* Buffer for current error message */
/*
* Buffer for current error message. This is cleared at the start of any
* connection attempt or query cycle; after that, all code should append
* messages to it, never overwrite.
*/
PQExpBufferData errorMessage; /* expansible string */
/* Buffer for receiving various parts of messages */
@@ -600,7 +604,6 @@ extern pgthreadlock_t pg_g_threadlock;
/* === in fe-exec.c === */
extern void pqSetResultError(PGresult *res, const char *msg);
extern void pqCatenateResultError(PGresult *res, const char *msg);
extern void *pqResultAlloc(PGresult *res, size_t nBytes, bool isBinary);
extern char *pqResultStrdup(PGresult *res, const char *str);
extern void pqClearAsyncResult(PGconn *conn);
@@ -612,6 +615,7 @@ extern void pqSaveMessageField(PGresult *res, char code,
extern void pqSaveParameterStatus(PGconn *conn, const char *name,
const char *value);
extern int pqRowProcessor(PGconn *conn, const char **errmsgp);
extern int PQsendQueryContinue(PGconn *conn, const char *query);
/* === in fe-protocol2.c === */
@@ -708,7 +712,7 @@ extern void pgtls_init_library(bool do_ssl, int do_crypto);
* The conn parameter is only used to be able to pass back an error
* message - no connection-local setup is made here.
*
* Returns 0 if OK, -1 on failure (with a message in conn->errorMessage).
* Returns 0 if OK, -1 on failure (adding a message to conn->errorMessage).
*/
extern int pgtls_init(PGconn *conn);
@@ -725,8 +729,8 @@ extern void pgtls_close(PGconn *conn);
/*
* Read data from a secure connection.
*
* On failure, this function is responsible for putting a suitable message
* into conn->errorMessage. The caller must still inspect errno, but only
* On failure, this function is responsible for appending a suitable message
* to conn->errorMessage. The caller must still inspect errno, but only
* to determine whether to continue/retry after error.
*/
extern ssize_t pgtls_read(PGconn *conn, void *ptr, size_t len);
@@ -739,8 +743,8 @@ extern bool pgtls_read_pending(PGconn *conn);
/*
* Write data to a secure connection.
*
* On failure, this function is responsible for putting a suitable message
* into conn->errorMessage. The caller must still inspect errno, but only
* On failure, this function is responsible for appending a suitable message
* to conn->errorMessage. The caller must still inspect errno, but only
* to determine whether to continue/retry after error.
*/
extern ssize_t pgtls_write(PGconn *conn, const void *ptr, size_t len);