Line data Source code
1 : /*-------------------------------------------------------------------------
2 : *
3 : * libpq-be-fe-helpers.h
4 : * Helper functions for using libpq in extensions
5 : *
6 : * Code built directly into the backend is not allowed to link to libpq
7 : * directly. Extension code is allowed to use libpq however. However, libpq
8 : * used in extensions has to be careful not to block inside libpq, otherwise
9 : * interrupts will not be processed, leading to issues like unresolvable
10 : * deadlocks. Backend code also needs to take care to acquire/release an
11 : * external fd for the connection, otherwise fd.c's accounting of fd's is
12 : * broken.
13 : *
14 : * This file provides helper functions to make it easier to comply with these
15 : * rules. It is a header only library as it needs to be linked into each
16 : * extension using libpq, and it seems too small to be worth adding a
17 : * dedicated static library for.
18 : *
19 : * TODO: For historical reasons the connections established here are not put
20 : * into non-blocking mode. That can lead to blocking even when only the async
21 : * libpq functions are used. This should be fixed.
22 : *
23 : * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
24 : * Portions Copyright (c) 1994, Regents of the University of California
25 : *
26 : * src/include/libpq/libpq-be-fe-helpers.h
27 : *
28 : *-------------------------------------------------------------------------
29 : */
30 : #ifndef LIBPQ_BE_FE_HELPERS_H
31 : #define LIBPQ_BE_FE_HELPERS_H
32 :
33 : #include "libpq/libpq-be-fe.h"
34 : #include "miscadmin.h"
35 : #include "storage/fd.h"
36 : #include "storage/latch.h"
37 : #include "utils/timestamp.h"
38 : #include "utils/wait_event.h"
39 :
40 :
41 : static inline void libpqsrv_connect_prepare(void);
42 : static inline void libpqsrv_connect_internal(PGconn *conn, uint32 wait_event_info);
43 : static inline PGresult *libpqsrv_get_result_last(PGconn *conn, uint32 wait_event_info);
44 : static inline PGresult *libpqsrv_get_result(PGconn *conn, uint32 wait_event_info);
45 :
46 :
47 : /*
48 : * PQconnectdb() wrapper that reserves a file descriptor and processes
49 : * interrupts during connection establishment.
50 : *
51 : * Throws an error if AcquireExternalFD() fails, but does not throw if
52 : * connection establishment itself fails. Callers need to use PQstatus() to
53 : * check if connection establishment succeeded.
54 : */
55 : static inline PGconn *
56 44 : libpqsrv_connect(const char *conninfo, uint32 wait_event_info)
57 : {
58 44 : PGconn *conn = NULL;
59 :
60 44 : libpqsrv_connect_prepare();
61 :
62 44 : conn = PQconnectStart(conninfo);
63 :
64 44 : libpqsrv_connect_internal(conn, wait_event_info);
65 :
66 44 : return conn;
67 : }
68 :
69 : /*
70 : * Like libpqsrv_connect(), except that this is a wrapper for
71 : * PQconnectdbParams().
72 : */
73 : static inline PGconn *
74 1928 : libpqsrv_connect_params(const char *const *keywords,
75 : const char *const *values,
76 : int expand_dbname,
77 : uint32 wait_event_info)
78 : {
79 1928 : PGconn *conn = NULL;
80 :
81 1928 : libpqsrv_connect_prepare();
82 :
83 1928 : conn = PQconnectStartParams(keywords, values, expand_dbname);
84 :
85 1928 : libpqsrv_connect_internal(conn, wait_event_info);
86 :
87 1926 : return conn;
88 : }
89 :
90 : /*
91 : * PQfinish() wrapper that additionally releases the reserved file descriptor.
92 : *
93 : * It is allowed to call this with a NULL pgconn iff NULL was returned by
94 : * libpqsrv_connect*.
95 : */
96 : static inline void
97 1954 : libpqsrv_disconnect(PGconn *conn)
98 : {
99 : /*
100 : * If no connection was established, we haven't reserved an FD for it (or
101 : * already released it). This rule makes it easier to write PG_CATCH()
102 : * handlers for this facility's users.
103 : *
104 : * See also libpqsrv_connect_internal().
105 : */
106 1954 : if (conn == NULL)
107 4 : return;
108 :
109 1950 : ReleaseExternalFD();
110 1950 : PQfinish(conn);
111 : }
112 :
113 :
114 : /* internal helper functions follow */
115 :
116 :
117 : /*
118 : * Helper function for all connection establishment functions.
119 : */
120 : static inline void
121 1972 : libpqsrv_connect_prepare(void)
122 : {
123 : /*
124 : * We must obey fd.c's limit on non-virtual file descriptors. Assume that
125 : * a PGconn represents one long-lived FD. (Doing this here also ensures
126 : * that VFDs are closed if needed to make room.)
127 : */
128 1972 : if (!AcquireExternalFD())
129 : {
130 : #ifndef WIN32 /* can't write #if within ereport() macro */
131 0 : ereport(ERROR,
132 : (errcode(ERRCODE_SQLCLIENT_UNABLE_TO_ESTABLISH_SQLCONNECTION),
133 : errmsg("could not establish connection"),
134 : errdetail("There are too many open files on the local server."),
135 : errhint("Raise the server's \"max_files_per_process\" and/or \"ulimit -n\" limits.")));
136 : #else
137 : ereport(ERROR,
138 : (errcode(ERRCODE_SQLCLIENT_UNABLE_TO_ESTABLISH_SQLCONNECTION),
139 : errmsg("could not establish connection"),
140 : errdetail("There are too many open files on the local server."),
141 : errhint("Raise the server's \"max_files_per_process\" setting.")));
142 : #endif
143 : }
144 1972 : }
145 :
146 : /*
147 : * Helper function for all connection establishment functions.
148 : */
149 : static inline void
150 1972 : libpqsrv_connect_internal(PGconn *conn, uint32 wait_event_info)
151 : {
152 : /*
153 : * With conn == NULL libpqsrv_disconnect() wouldn't release the FD. So do
154 : * that here.
155 : */
156 1972 : if (conn == NULL)
157 : {
158 0 : ReleaseExternalFD();
159 0 : return;
160 : }
161 :
162 : /*
163 : * Can't wait without a socket. Note that we don't want to close the libpq
164 : * connection yet, so callers can emit a useful error.
165 : */
166 1972 : if (PQstatus(conn) == CONNECTION_BAD)
167 110 : return;
168 :
169 : /*
170 : * WaitLatchOrSocket() can conceivably fail, handle that case here instead
171 : * of requiring all callers to do so.
172 : */
173 1862 : PG_TRY();
174 : {
175 : PostgresPollingStatusType status;
176 :
177 : /*
178 : * Poll connection until we have OK or FAILED status.
179 : *
180 : * Per spec for PQconnectPoll, first wait till socket is write-ready.
181 : */
182 1862 : status = PGRES_POLLING_WRITING;
183 8802 : while (status != PGRES_POLLING_OK && status != PGRES_POLLING_FAILED)
184 : {
185 : int io_flag;
186 : int rc;
187 :
188 5080 : if (status == PGRES_POLLING_READING)
189 1890 : io_flag = WL_SOCKET_READABLE;
190 : #ifdef WIN32
191 :
192 : /*
193 : * Windows needs a different test while waiting for
194 : * connection-made
195 : */
196 : else if (PQstatus(conn) == CONNECTION_STARTED)
197 : io_flag = WL_SOCKET_CONNECTED;
198 : #endif
199 : else
200 3190 : io_flag = WL_SOCKET_WRITEABLE;
201 :
202 5080 : rc = WaitLatchOrSocket(MyLatch,
203 : WL_EXIT_ON_PM_DEATH | WL_LATCH_SET | io_flag,
204 : PQsocket(conn),
205 : 0,
206 : wait_event_info);
207 :
208 : /* Interrupted? */
209 5080 : if (rc & WL_LATCH_SET)
210 : {
211 1330 : ResetLatch(MyLatch);
212 1330 : CHECK_FOR_INTERRUPTS();
213 : }
214 :
215 : /* If socket is ready, advance the libpq state machine */
216 5078 : if (rc & io_flag)
217 3750 : status = PQconnectPoll(conn);
218 : }
219 : }
220 0 : PG_CATCH();
221 : {
222 : /*
223 : * If an error is thrown here, the callers won't call
224 : * libpqsrv_disconnect() with a conn, so release resources
225 : * immediately.
226 : */
227 0 : ReleaseExternalFD();
228 0 : PQfinish(conn);
229 :
230 0 : PG_RE_THROW();
231 : }
232 1860 : PG_END_TRY();
233 : }
234 :
235 : /*
236 : * PQexec() wrapper that processes interrupts.
237 : *
238 : * Unless PQsetnonblocking(conn, 1) is in effect, this can't process
239 : * interrupts while pushing the query text to the server. Consider that
240 : * setting if query strings can be long relative to TCP buffer size.
241 : *
242 : * This has the preconditions of PQsendQuery(), not those of PQexec(). Most
243 : * notably, PQexec() would silently discard any prior query results.
244 : */
245 : static inline PGresult *
246 7626 : libpqsrv_exec(PGconn *conn, const char *query, uint32 wait_event_info)
247 : {
248 7626 : if (!PQsendQuery(conn, query))
249 0 : return NULL;
250 7626 : return libpqsrv_get_result_last(conn, wait_event_info);
251 : }
252 :
253 : /*
254 : * PQexecParams() wrapper that processes interrupts.
255 : *
256 : * See notes at libpqsrv_exec().
257 : */
258 : static inline PGresult *
259 : libpqsrv_exec_params(PGconn *conn,
260 : const char *command,
261 : int nParams,
262 : const Oid *paramTypes,
263 : const char *const *paramValues,
264 : const int *paramLengths,
265 : const int *paramFormats,
266 : int resultFormat,
267 : uint32 wait_event_info)
268 : {
269 : if (!PQsendQueryParams(conn, command, nParams, paramTypes, paramValues,
270 : paramLengths, paramFormats, resultFormat))
271 : return NULL;
272 : return libpqsrv_get_result_last(conn, wait_event_info);
273 : }
274 :
275 : /*
276 : * Like PQexec(), loop over PQgetResult() until it returns NULL or another
277 : * terminal state. Return the last non-NULL result or the terminal state.
278 : */
279 : static inline PGresult *
280 24042 : libpqsrv_get_result_last(PGconn *conn, uint32 wait_event_info)
281 : {
282 24042 : PGresult *lastResult = NULL;
283 :
284 : for (;;)
285 22624 : {
286 : /* Wait for, and collect, the next PGresult. */
287 : PGresult *result;
288 :
289 46666 : result = libpqsrv_get_result(conn, wait_event_info);
290 46664 : if (result == NULL)
291 22620 : break; /* query is complete, or failure */
292 :
293 : /*
294 : * Emulate PQexec()'s behavior of returning the last result when there
295 : * are many.
296 : */
297 24044 : PQclear(lastResult);
298 24044 : lastResult = result;
299 :
300 48088 : if (PQresultStatus(lastResult) == PGRES_COPY_IN ||
301 47706 : PQresultStatus(lastResult) == PGRES_COPY_OUT ||
302 46290 : PQresultStatus(lastResult) == PGRES_COPY_BOTH ||
303 22628 : PQstatus(conn) == CONNECTION_BAD)
304 : break;
305 : }
306 24040 : return lastResult;
307 : }
308 :
309 : /*
310 : * Perform the equivalent of PQgetResult(), but watch for interrupts.
311 : */
312 : static inline PGresult *
313 49166 : libpqsrv_get_result(PGconn *conn, uint32 wait_event_info)
314 : {
315 : /*
316 : * Collect data until PQgetResult is ready to get the result without
317 : * blocking.
318 : */
319 73120 : while (PQisBusy(conn))
320 : {
321 : int rc;
322 :
323 24030 : rc = WaitLatchOrSocket(MyLatch,
324 : WL_EXIT_ON_PM_DEATH | WL_LATCH_SET |
325 : WL_SOCKET_READABLE,
326 : PQsocket(conn),
327 : 0,
328 : wait_event_info);
329 :
330 : /* Interrupted? */
331 24030 : if (rc & WL_LATCH_SET)
332 : {
333 18 : ResetLatch(MyLatch);
334 18 : CHECK_FOR_INTERRUPTS();
335 : }
336 :
337 : /* Consume whatever data is available from the socket */
338 24028 : if (PQconsumeInput(conn) == 0)
339 : {
340 : /* trouble; expect PQgetResult() to return NULL */
341 74 : break;
342 : }
343 : }
344 :
345 : /* Now we can collect and return the next PGresult */
346 49164 : return PQgetResult(conn);
347 : }
348 :
349 : /*
350 : * Submit a cancel request to the given connection, waiting only until
351 : * the given time.
352 : *
353 : * We sleep interruptibly until we receive confirmation that the cancel
354 : * request has been accepted, and if it is, return NULL; if the cancel
355 : * request fails, return an error message string (which is not to be
356 : * freed).
357 : *
358 : * For other problems (to wit: OOM when strdup'ing an error message from
359 : * libpq), this function can ereport(ERROR).
360 : *
361 : * Note: this function leaks a string's worth of memory when reporting
362 : * libpq errors. Make sure to call it in a transient memory context.
363 : */
364 : static inline const char *
365 4 : libpqsrv_cancel(PGconn *conn, TimestampTz endtime)
366 : {
367 : PGcancelConn *cancel_conn;
368 4 : const char *error = NULL;
369 :
370 4 : cancel_conn = PQcancelCreate(conn);
371 4 : if (cancel_conn == NULL)
372 0 : return "out of memory";
373 :
374 : /* In what follows, do not leak any PGcancelConn on any errors. */
375 :
376 4 : PG_TRY();
377 : {
378 4 : if (!PQcancelStart(cancel_conn))
379 : {
380 0 : error = pchomp(PQcancelErrorMessage(cancel_conn));
381 0 : goto exit;
382 : }
383 :
384 : for (;;)
385 4 : {
386 : PostgresPollingStatusType pollres;
387 : TimestampTz now;
388 : long cur_timeout;
389 8 : int waitEvents = WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH;
390 :
391 8 : pollres = PQcancelPoll(cancel_conn);
392 8 : if (pollres == PGRES_POLLING_OK)
393 4 : break; /* success! */
394 :
395 : /* If timeout has expired, give up, else get sleep time. */
396 4 : now = GetCurrentTimestamp();
397 4 : cur_timeout = TimestampDifferenceMilliseconds(now, endtime);
398 4 : if (cur_timeout <= 0)
399 : {
400 0 : error = "cancel request timed out";
401 0 : break;
402 : }
403 :
404 4 : switch (pollres)
405 : {
406 4 : case PGRES_POLLING_READING:
407 4 : waitEvents |= WL_SOCKET_READABLE;
408 4 : break;
409 0 : case PGRES_POLLING_WRITING:
410 0 : waitEvents |= WL_SOCKET_WRITEABLE;
411 0 : break;
412 0 : default:
413 0 : error = pchomp(PQcancelErrorMessage(cancel_conn));
414 0 : goto exit;
415 : }
416 :
417 : /* Sleep until there's something to do */
418 4 : WaitLatchOrSocket(MyLatch, waitEvents, PQcancelSocket(cancel_conn),
419 : cur_timeout, PG_WAIT_CLIENT);
420 :
421 4 : ResetLatch(MyLatch);
422 :
423 4 : CHECK_FOR_INTERRUPTS();
424 : }
425 4 : exit: ;
426 : }
427 0 : PG_FINALLY();
428 : {
429 4 : PQcancelFinish(cancel_conn);
430 : }
431 4 : PG_END_TRY();
432 :
433 4 : return error;
434 : }
435 :
436 : /*
437 : * libpqsrv_notice_receiver
438 : *
439 : * Custom notice receiver for libpq connections.
440 : *
441 : * This function is intended to be set via PQsetNoticeReceiver() so that
442 : * NOTICE, WARNING, and similar messages from the connection are reported via
443 : * ereport(), instead of being printed to stderr.
444 : *
445 : * Because this will be called from libpq with a "real" (not wrapped)
446 : * PGresult, we need to temporarily ignore libpq-be-fe.h's wrapper macros
447 : * for PGresult and also PQresultErrorMessage, and put back the wrappers
448 : * afterwards. That's not pretty, but there seems no better alternative.
449 : */
450 : #undef PGresult
451 : #undef PQresultErrorMessage
452 :
453 : static inline void
454 16 : libpqsrv_notice_receiver(void *arg, const PGresult *res)
455 : {
456 : const char *message;
457 : int len;
458 16 : const char *prefix = (const char *) arg;
459 :
460 : /*
461 : * Trim the trailing newline from the message text returned from
462 : * PQresultErrorMessage(), as it always includes one, to produce cleaner
463 : * log output.
464 : */
465 16 : message = PQresultErrorMessage(res);
466 16 : len = strlen(message);
467 16 : if (len > 0 && message[len - 1] == '\n')
468 16 : len--;
469 :
470 16 : ereport(LOG,
471 : errmsg_internal("%s: %.*s", prefix, len, message));
472 16 : }
473 :
474 : #define PGresult libpqsrv_PGresult
475 : #define PQresultErrorMessage libpqsrv_PQresultErrorMessage
476 :
477 : #endif /* LIBPQ_BE_FE_HELPERS_H */
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