libpq: Remove PQservice()

This routine has been introduced as a shortcut to be able to retrieve a
service name from an active connection, for psql.  Per discussion, and
as it is only used by psql, let's remove it to not clutter the libpq API
more than necessary.

The logic in psql is replaced by lookups of PQconninfoOption for the
active connection, instead, updated each time the variables are synced
by psql, the prompt shortcut relying on the variable synced.

Reported-by: Noah Misch <noah@leadboat.com>
Discussion: https://postgr.es/m/20250706161319.c1.nmisch@google.com
Backpatch-through: 18

1 files changed, 35 insertions, 0 deletions

diff --git a/src/bin/psql/common.c b/src/bin/psql/common.c
index d2c0a49c46c..cd329ade12b 100644
--- a/src/bin/psql/common.c
+++ b/src/bin/psql/common.c
@@ -2531,6 +2531,41 @@ session_username(void)
 		return PQuser(pset.db);
 }
 
+/*
+ * Return the value of option for keyword in the current connection.
+ *
+ * The caller is responsible for freeing the result value allocated.
+ */
+char *
+get_conninfo_value(const char *keyword)
+{
+	PQconninfoOption *opts;
+	PQconninfoOption *serviceopt = NULL;
+	char	   *res = NULL;
+
+	if (pset.db == NULL)
+		return NULL;
+
+	opts = PQconninfo(pset.db);
+	if (opts == NULL)
+		return NULL;
+
+	for (PQconninfoOption *opt = opts; opt->keyword != NULL; ++opt)
+	{
+		if (strcmp(opt->keyword, keyword) == 0)
+		{
+			serviceopt = opt;
+			break;
+		}
+	}
+
+	/* Take a copy of the value, as it is freed by PQconninfoFree(). */
+	if (serviceopt && serviceopt->val != NULL)
+		res = pg_strdup(serviceopt->val);
+	PQconninfoFree(opts);
+
+	return res;
+}
 
 /* expand_tilde
  *