Prevent write operations on large objects in read-only transactions

Attempting such an operation would already fail, but in various and
confusing ways.  For example, while in recovery, some elog() messages
would be reported, but these should never be user-facing.  This commit
restricts any write operations done on large objects in a read-only
context, so as the errors generated are more user-friendly.  This is per
the discussion done with Tom Lane and Robert Haas.

Some regression tests are added to check the case of all the SQL
functions working on large objects (including an update of the test's
alternate output).

Author: Yugo Nagata
Discussion: https://postgr.es/m/[email protected]

1 files changed, 21 insertions, 0 deletions

diff --git a/src/backend/libpq/be-fsstubs.c b/src/backend/libpq/be-fsstubs.c
index 5804532881e..3e5cada7eb5 100644
--- a/src/backend/libpq/be-fsstubs.c
+++ b/src/backend/libpq/be-fsstubs.c
@@ -93,6 +93,9 @@ be_lo_open(PG_FUNCTION_ARGS)
 	elog(DEBUG4, "lo_open(%u,%d)", lobjId, mode);
 #endif
 
+	if (mode & INV_WRITE)
+		PreventCommandIfReadOnly("lo_open(INV_WRITE)");
+
 	/*
 	 * Allocate a large object descriptor first.  This will also create
 	 * 'fscxt' if this is the first LO opened in this transaction.
@@ -245,6 +248,8 @@ be_lo_creat(PG_FUNCTION_ARGS)
 {
 	Oid			lobjId;
 
+	PreventCommandIfReadOnly("lo_creat()");
+
 	lo_cleanup_needed = true;
 	lobjId = inv_create(InvalidOid);
 
@@ -256,6 +261,8 @@ be_lo_create(PG_FUNCTION_ARGS)
 {
 	Oid			lobjId = PG_GETARG_OID(0);
 
+	PreventCommandIfReadOnly("lo_create()");
+
 	lo_cleanup_needed = true;
 	lobjId = inv_create(lobjId);
 
@@ -306,6 +313,8 @@ be_lo_unlink(PG_FUNCTION_ARGS)
 {
 	Oid			lobjId = PG_GETARG_OID(0);
 
+	PreventCommandIfReadOnly("lo_unlink()");
+
 	/*
 	 * Must be owner of the large object.  It would be cleaner to check this
 	 * in inv_drop(), but we want to throw the error before not after closing
@@ -368,6 +377,8 @@ be_lowrite(PG_FUNCTION_ARGS)
 	int			bytestowrite;
 	int			totalwritten;
 
+	PreventCommandIfReadOnly("lowrite()");
+
 	bytestowrite = VARSIZE_ANY_EXHDR(wbuf);
 	totalwritten = lo_write(fd, VARDATA_ANY(wbuf), bytestowrite);
 	PG_RETURN_INT32(totalwritten);
@@ -413,6 +424,8 @@ lo_import_internal(text *filename, Oid lobjOid)
 	LargeObjectDesc *lobj;
 	Oid			oid;
 
+	PreventCommandIfReadOnly("lo_import()");
+
 	/*
 	 * open the file to be read in
 	 */
@@ -561,6 +574,8 @@ be_lo_truncate(PG_FUNCTION_ARGS)
 	int32		fd = PG_GETARG_INT32(0);
 	int32		len = PG_GETARG_INT32(1);
 
+	PreventCommandIfReadOnly("lo_truncate()");
+
 	lo_truncate_internal(fd, len);
 	PG_RETURN_INT32(0);
 }
@@ -571,6 +586,8 @@ be_lo_truncate64(PG_FUNCTION_ARGS)
 	int32		fd = PG_GETARG_INT32(0);
 	int64		len = PG_GETARG_INT64(1);
 
+	PreventCommandIfReadOnly("lo_truncate64()");
+
 	lo_truncate_internal(fd, len);
 	PG_RETURN_INT32(0);
 }
@@ -815,6 +832,8 @@ be_lo_from_bytea(PG_FUNCTION_ARGS)
 	LargeObjectDesc *loDesc;
 	int			written PG_USED_FOR_ASSERTS_ONLY;
 
+	PreventCommandIfReadOnly("lo_from_bytea()");
+
 	lo_cleanup_needed = true;
 	loOid = inv_create(loOid);
 	loDesc = inv_open(loOid, INV_WRITE, CurrentMemoryContext);
@@ -837,6 +856,8 @@ be_lo_put(PG_FUNCTION_ARGS)
 	LargeObjectDesc *loDesc;
 	int			written PG_USED_FOR_ASSERTS_ONLY;
 
+	PreventCommandIfReadOnly("lo_put()");
+
 	lo_cleanup_needed = true;
 	loDesc = inv_open(loOid, INV_WRITE, CurrentMemoryContext);