Allow to copy the database to either an external file or to another C…

…onnection
berkerpeksag · Mar 10, 2018 · Jul 28, 2016 · Jul 28, 2016 · Mar 1, 2017 · Mar 1, 2017
commit 960303f9eb394e2ba91d10e5e674997a48811ac2
diff --git a/Doc/library/sqlite3.rst b/Doc/library/sqlite3.rst
@@ -521,11 +521,12 @@ Connection Objects
                  f.write('%s\n' % line)
 
 
-   .. method:: backup(filename, *, pages=0, progress=None, name="main", sleep=250)
+   .. method:: backup(target, *, pages=0, progress=None, name="main", sleep=250)
 
       This method makes a backup of a SQLite database into the mandatory argument
-      *filename*, even while it's being accessed by other clients, or concurrently by
-      the same connection.
+      *target*, even while it's being accessed by other clients, or concurrently by
+      the same connection. The *target* can be either a string, the path to the file
+      where the backup will be written, or another :class:`Connection` instance.
 
       By default, or when *pages* is either ``0`` or a negative integer, the entire
       database is copied in a single step; otherwise the method performs a loop
@@ -544,9 +545,8 @@ Connection Objects
       The *sleep* argument specifies the number of milliseconds to sleep by between
       successive attempts to backup remaining pages.
 
-      Example::
+      Example 1, copy an existing database into another file::
 
-         # Copy an existing database into another file
          import sqlite3
 
          def progress(status, remaining, total):
@@ -555,6 +555,14 @@ Connection Objects
          con = sqlite3.connect('existing_db.db')
          con.backup('copy_of_existing_db.db', 1, progress)
 
+      Example 2, copy an existing database into a transient copy::
+
+         import sqlite3
+
+         source = sqlite3.connect('existing_db.db')
+         dest = sqlite3.connect(':memory')
+         source.backup(dest)
+
       .. note:: This is available only when the underlying SQLite library is at
                 version 3.6.11 or higher.
 

diff --git a/Lib/sqlite3/test/backup.py b/Lib/sqlite3/test/backup.py
@@ -20,6 +20,10 @@ def testBackup(self, bckfn):
         self.assertEqual(result[0][0], 3)
         self.assertEqual(result[1][0], 4)
 
+    def CheckBadTarget(self):
+        with self.assertRaises(TypeError):
+            self.cx.backup(None)
+
     def CheckKeywordOnlyArgs(self):
         with self.assertRaises(TypeError):
             self.cx.backup('foo', 1)
@@ -124,6 +128,13 @@ def CheckDatabaseSourceName(self):
             self.cx.backup(bckfn.name, name='attached_db')
             self.testBackup(bckfn.name)
 
+    def CheckBackupToOtherConnection(self):
+        dx = sqlite.connect(':memory:')
+        self.cx.backup(dx)
+        result = dx.execute("SELECT key FROM foo ORDER BY key").fetchall()
+        self.assertEqual(result[0][0], 3)
+        self.assertEqual(result[1][0], 4)
+
 def suite():
     return unittest.TestSuite(unittest.makeSuite(BackupTests, "Check"))
 

diff --git a/Modules/_sqlite/connection.c b/Modules/_sqlite/connection.c
@@ -1456,7 +1456,8 @@ pysqlite_connection_iterdump(pysqlite_Connection* self, PyObject* args)
 static PyObject *
 pysqlite_connection_backup(pysqlite_Connection* self, PyObject* args, PyObject* kwds)
 {
-    char* filename;
+    PyObject* target = NULL;
+    const char* filename;
     int pages = -1;
     PyObject* progress = Py_None;
     char* name = "main";
@@ -1466,10 +1467,16 @@ pysqlite_connection_backup(pysqlite_Connection* self, PyObject* args, PyObject*
     int sleep = 250;
     sqlite3 *bckconn;
     sqlite3_backup *bckhandle;
-    static char *keywords[] = {"filename", "pages", "progress", "name", "sleep", NULL};
+    static char *keywords[] = {"target", "pages", "progress", "name", "sleep", NULL};
 
-    if (!PyArg_ParseTupleAndKeywords(args, kwds, "s|$iOsi:backup", keywords,
-                                     &filename, &pages, &progress, &name, &sleep)) {
+    if (!PyArg_ParseTupleAndKeywords(args, kwds, "O|$iOsi:backup", keywords,
+                                     &target, &pages, &progress, &name, &sleep)) {
+        goto finally;
+    }
+
+    if (!PyUnicode_Check(target) && !PyObject_TypeCheck(target, &pysqlite_ConnectionType)) {
+        PyErr_SetString(PyExc_TypeError,
+                        "target argument must be either a string or a Connection instance");
         goto finally;
     }
 
@@ -1482,12 +1489,27 @@ pysqlite_connection_backup(pysqlite_Connection* self, PyObject* args, PyObject*
         pages = -1;
     }
 
-    Py_BEGIN_ALLOW_THREADS
-    rc = sqlite3_open(filename, &bckconn);
-    Py_END_ALLOW_THREADS
+    if (PyUnicode_Check(target)) {
+        filename = PyUnicode_AsUTF8(target);
+        if (filename == NULL) {
+            goto finally;
+        }
 
-    if (rc != SQLITE_OK) {
-        goto finally;
+        Py_BEGIN_ALLOW_THREADS
+        rc = sqlite3_open(filename, &bckconn);
+        Py_END_ALLOW_THREADS
+
+        if (rc != SQLITE_OK) {
+            goto finally;
+        }
+    }
+    else {
+        if ((pysqlite_Connection*)target == self) {
+            PyErr_SetString(PyExc_ValueError, "target cannot be the same connection instance");
+            goto finally;
+        }
+        filename = NULL;
+        bckconn = ((pysqlite_Connection*)target)->db;
     }
 
     Py_BEGIN_ALLOW_THREADS
@@ -1538,16 +1560,18 @@ pysqlite_connection_backup(pysqlite_Connection* self, PyObject* args, PyObject*
         }
     }
 
-    Py_BEGIN_ALLOW_THREADS
-    sqlite3_close(bckconn);
-    Py_END_ALLOW_THREADS
+    if (filename != NULL) {
+        Py_BEGIN_ALLOW_THREADS
+        sqlite3_close(bckconn);
+        Py_END_ALLOW_THREADS
+    }
 
     if (cberr == 0 && rc == SQLITE_OK) {
         Py_INCREF(Py_None);
         retval = Py_None;
     } else {
         /* Remove the probably incomplete/invalid backup */
-        if (unlink(filename) < 0) {
+        if (filename != NULL && unlink(filename) < 0) {
             /* FIXME: this should probably be chained to the outstanding
                exception */
             return PyErr_SetFromErrno(PyExc_OSError);