bpo-43296: Handle sqlite3_value_blob() errors (GH-24674)

3 files changed, 24 insertions, 7 deletions

diff --git a/Lib/sqlite3/test/userfunctions.py b/Lib/sqlite3/test/userfunctions.py
index 749ea049c8..148d9f596a 100644
--- a/Lib/sqlite3/test/userfunctions.py
+++ b/Lib/sqlite3/test/userfunctions.py
@@ -276,6 +276,10 @@ class FunctionTests(unittest.TestCase):
         val = cur.fetchone()[0]
         self.assertEqual(val, 2)
 
+    def test_empty_blob(self):
+        cur = self.con.execute("select isblob(x'')")
+        self.assertTrue(cur.fetchone()[0])
+
     # Regarding deterministic functions:
     #
     # Between 3.8.3 and 3.15.0, deterministic functions were only used to
diff --git a/Misc/NEWS.d/next/Library/2021-03-01-13-01-33.bpo-43296.p_gU6T.rst b/Misc/NEWS.d/next/Library/2021-03-01-13-01-33.bpo-43296.p_gU6T.rst
new file mode 100644
index 0000000000..741dfcd705
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2021-03-01-13-01-33.bpo-43296.p_gU6T.rst
@@ -0,0 +1,3 @@
+Improve :mod:`sqlite3` error handling: ``sqlite3_value_blob()`` errors that
+set ``SQLITE_NOMEM`` now raise :exc:`MemoryError`. Patch by Erlend E.
+Aasland.
diff --git a/Modules/_sqlite/connection.c b/Modules/_sqlite/connection.c
index 6d3ccb9b94..93365495f5 100644
--- a/Modules/_sqlite/connection.c
+++ b/Modules/_sqlite/connection.c
@@ -546,7 +546,6 @@ _pysqlite_build_py_params(sqlite3_context *context, int argc,
     sqlite3_value* cur_value;
     PyObject* cur_py_value;
     const char* val_str;
-    Py_ssize_t buflen;
 
     args = PyTuple_New(argc);
     if (!args) {
@@ -571,19 +570,26 @@ _pysqlite_build_py_params(sqlite3_context *context, int argc,
                     cur_py_value = Py_NewRef(Py_None);
                 }
                 break;
-            case SQLITE_BLOB:
-                buflen = sqlite3_value_bytes(cur_value);
-                cur_py_value = PyBytes_FromStringAndSize(
-                    sqlite3_value_blob(cur_value), buflen);
+            case SQLITE_BLOB: {
+                sqlite3 *db = sqlite3_context_db_handle(context);
+                const void *blob = sqlite3_value_blob(cur_value);
+
+                if (blob == NULL && sqlite3_errcode(db) == SQLITE_NOMEM) {
+                    PyErr_NoMemory();
+                    goto error;
+                }
+
+                Py_ssize_t size = sqlite3_value_bytes(cur_value);
+                cur_py_value = PyBytes_FromStringAndSize(blob, size);
                 break;
+            }
             case SQLITE_NULL:
             default:
                 cur_py_value = Py_NewRef(Py_None);
         }
 
         if (!cur_py_value) {
-            Py_DECREF(args);
-            return NULL;
+            goto error;
         }
 
         PyTuple_SetItem(args, i, cur_py_value);
@@ -591,6 +597,10 @@ _pysqlite_build_py_params(sqlite3_context *context, int argc,
     }
 
     return args;
+
+error:
+    Py_DECREF(args);
+    return NULL;
 }
 
 static void