Fix libpq to not require user's home directory to exist.

tglsfdc · tglsfdc · commit ee02c1c897ee · 2017-10-25T19:32:24.000-04:00
Some people like to run libpq-using applications in environments where there's no home directory. We've broken that scenario before (cf commits 5b40677 and bd58d9d), and commit ba005f1 broke it again, by making it a hard error if we fail to get the home directory name while looking for ~/.pgpass. The previous precedent is that if we can't get the home directory name, we should just silently act as though the file we hoped to find there doesn't exist. Rearrange the new code to honor that. Looking around, the service-file code added by commit 41a4e45 had the same disease. Apparently, that escaped notice because it only runs when a service name has been specified, which I guess the people who use this scenario don't do. Nonetheless, it's wrong too, so fix that case as well. Add a comment about this policy to pqGetHomeDirectory, in the probably vain hope of forestalling the same error in future. And upgrade the rather miserable commenting in parseServiceInfo, too. In passing, also back off parseServiceInfo's assumption that only ENOENT is an ignorable error from stat() when checking a service file. We would need to ignore at least ENOTDIR as well (cf 5b40677), and seeing that the far-better-tested code for ~/.pgpass treats all stat() failures alike, I think this code ought to as well. Per bug #14872 from Dan Watson. Back-patch the .pgpass change to v10 where ba005f1 came in. The service-file bugs are far older, so back-patch the other changes to all supported branches. Discussion: https://postgr.es/m/20171025200457.1471.34504@wrigleys.postgresql.org
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
@@ -3905,6 +3905,16 @@ ldapServiceLookup(const char *purl, PQconninfoOption *options,
 
 #define MAXBUFSIZE 256
 
+/*
+ * parseServiceInfo: if a service name has been given, look it up and absorb
+ * connection options from it into *options.
+ *
+ * Returns 0 on success, nonzero on failure.  On failure, if errorMessage
+ * isn't null, also store an error message there.  (Note: the only reason
+ * this function and related ones don't dump core on errorMessage == NULL
+ * is the undocumented fact that printfPQExpBuffer does nothing when passed
+ * a null PQExpBuffer pointer.)
+ */
 static int
 parseServiceInfo(PQconninfoOption *options, PQExpBuffer errorMessage)
 {
@@ -3923,23 +3933,24 @@ parseServiceInfo(PQconninfoOption *options, PQExpBuffer errorMessage)
 	if (service == NULL)
 		service = getenv("PGSERVICE");
 
+	/* If no service name given, nothing to do */
 	if (service == NULL)
 		return 0;
 
+	/*
+	 * Try PGSERVICEFILE if specified, else try ~/.pg_service.conf (if that
+	 * exists).
+	 */
 	if ((env = getenv("PGSERVICEFILE")) != NULL)
 		strlcpy(serviceFile, env, sizeof(serviceFile));
 	else
 	{
 		char		homedir[MAXPGPATH];
 
 		if (!pqGetHomeDirectory(homedir, sizeof(homedir)))
-		{
-			printfPQExpBuffer(errorMessage, libpq_gettext("could not get home directory to locate service definition file"));
-			return 1;
-		}
+			goto next_file;
 		snprintf(serviceFile, MAXPGPATH, "%s/%s", homedir, ".pg_service.conf");
-		errno = 0;
-		if (stat(serviceFile, &stat_buf) != 0 && errno == ENOENT)
+		if (stat(serviceFile, &stat_buf) != 0)
 			goto next_file;
 	}
 
@@ -3955,8 +3966,7 @@ parseServiceInfo(PQconninfoOption *options, PQExpBuffer errorMessage)
 	 */
 	snprintf(serviceFile, MAXPGPATH, "%s/pg_service.conf",
 			 getenv("PGSYSCONFDIR") ? getenv("PGSYSCONFDIR") : SYSCONFDIR);
-	errno = 0;
-	if (stat(serviceFile, &stat_buf) != 0 && errno == ENOENT)
+	if (stat(serviceFile, &stat_buf) != 0)
 		goto last_file;
 
 	status = parseServiceFile(serviceFile, service, options, errorMessage, &group_found);
@@ -5906,7 +5916,15 @@ dot_pg_pass_warning(PGconn *conn)
  *
  * This is essentially the same as get_home_path(), but we don't use that
  * because we don't want to pull path.c into libpq (it pollutes application
- * namespace)
+ * namespace).
+ *
+ * Returns true on success, false on failure to obtain the directory name.
+ *
+ * CAUTION: although in most situations failure is unexpected, there are users
+ * who like to run applications in a home-directory-less environment.  On
+ * failure, you almost certainly DO NOT want to report an error.  Just act as
+ * though whatever file you were hoping to find in the home directory isn't
+ * there (which it isn't).
  */
 bool
 pqGetHomeDirectory(char *buf, int bufsize)
