Use a hook for getting the walreceiver password

The hook will be defined in the neon extension. Using a hook limits the
amount of Postgres changes.

Signed-off-by: Tristan Partin <tristan.partin@databricks.com>

Author: tristan957

src/backend/replication/libpqwalreceiver/libpqwalreceiver.c

@@ -128,6 +128,7 @@ libpqrcv_connect(const char *conninfo, bool logical, const char *appname,
 	WalReceiverConn *conn;
 	PostgresPollingStatusType status;
 /* BEGIN_NEON */
+	char	   *password = NULL;
 	const char *keys[7];
 	const char *vals[7];
 /* END_NEON */
@@ -142,16 +143,17 @@ libpqrcv_connect(const char *conninfo, bool logical, const char *appname,
 
 /* BEGIN_NEON */
 	/*
-	 * We use neon_storage_token for the password because conninfo strings are
-	 * limited to MAXCONNINFO in length. Our tokens encode Unity Catalog
-	 * permissions, so they can be quite lengthy.
+	 * We use the output GetWalRcvPassword_hook for the password because
+	 * conninfo strings are limited to MAXCONNINFO in length. Our tokens can
+	 * make the connection info larger than the limit.
 	 */
-	if (pg_strcasecmp(appname, "walreceiver") == 0)
+	if (pg_strcasecmp(appname, "walreceiver") == 0 && GetWalRcvPassword_hook)
 	{
-		if (neon_storage_token && neon_storage_token[0] != '\0')
+		password = GetWalRcvPassword_hook();
+		if (password && password[0] != '\0')
 		{
 			keys[++i] = "password";
-			vals[i] = neon_storage_token;
+			vals[i] = password;
 		}
 	}
 /* END_NEON */
@@ -182,6 +184,8 @@ libpqrcv_connect(const char *conninfo, bool logical, const char *appname,
 	conn = palloc0(sizeof(WalReceiverConn));
 	conn->streamConn = PQconnectStartParams(keys, vals,
 											 /* expand_dbname = */ true);
+	if (password)
+		pfree(password);
 	if (PQstatus(conn->streamConn) == CONNECTION_BAD)
 		goto bad_connection_errmsg;
 

src/backend/replication/walreceiver.c

@@ -89,12 +89,13 @@
 int			wal_receiver_status_interval;
 int			wal_receiver_timeout;
 bool		hot_standby_feedback;
-char	   *neon_storage_token;
 
 /* libpqwalreceiver connection */
 static WalReceiverConn *wrconn = NULL;
 WalReceiverFunctionsType *WalReceiverFunctions = NULL;
 
+GetWalRcvPassword_hook_type GetWalRcvPassword_hook = NULL;
+
 #define NAPTIME_PER_CYCLE 100	/* max sleep time between cycles (100ms) */
 
 /*

src/include/replication/walreceiver.h

@@ -24,11 +24,13 @@
 #include "storage/spin.h"
 #include "utils/tuplestore.h"
 
+typedef char *(*GetWalRcvPassword_hook_type) (void);
+extern PGDLLIMPORT GetWalRcvPassword_hook_type GetWalRcvPassword_hook;
+
 /* user-settable parameters */
 extern int	wal_receiver_status_interval;
 extern int	wal_receiver_timeout;
 extern bool hot_standby_feedback;
-extern PGDLLIMPORT char *neon_storage_token;
 
 /*
  * MAXCONNINFO: maximum size of a connection string.