Ensure that when the source of a backup is a database that is zero bytes

in size, the final destination database consists of at least one page. 
Truncating it to zero bytes is equivalent to zeroing the schema cookie 
and change counter, which can cause problems for existing clients.

FossilOrigin-Name: ca86138bda26c5ac5a7e67351acbd19fbd39b0ae

manifest

@@ -1,5 +1,5 @@
-C Allow\sthe\sshowdb\stool\sto\sbe\scompiled\swith\sMSVC.
-D 2012-10-13T09:31:20.156
+C Ensure\sthat\swhen\sthe\ssource\sof\sa\sbackup\sis\sa\sdatabase\sthat\sis\szero\sbytes\s\nin\ssize,\sthe\sfinal\sdestination\sdatabase\sconsists\sof\sat\sleast\sone\spage.\s\nTruncating\sit\sto\szero\sbytes\sis\sequivalent\sto\szeroing\sthe\sschema\scookie\s\nand\schange\scounter,\swhich\scan\scause\sproblems\sfor\sexisting\sclients.
+D 2012-10-13T23:16:00.555
 F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
 F Makefile.in 5f4f26109f9d80829122e0e09f9cda008fa065fb
 F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@@ -118,11 +118,11 @@ F src/alter.c f8db986c03eb0bfb221523fc9bbb9d0b70de3168
 F src/analyze.c 7553068d21e32a57fc33ab6b2393fc8c1ba41410
 F src/attach.c 34c15ecd686e58f08e5bb1389e28a0b65c2c83db
 F src/auth.c 523da7fb4979469955d822ff9298352d6b31de34
-F src/backup.c afc067b9a9050ff48b9d46285c53d096c556a73d
+F src/backup.c cab40f2c1fe79d6eb93d3b4086c78c41ad2fa5d0
 F src/bitvec.c 26675fe8e431dc555e6f2d0e11e651d172234aa1
 F src/btmutex.c 976f45a12e37293e32cae0281b15a21d48a8aaa7
-F src/btree.c 14de53ebb334633ee632ab3c5b9262cfe7cbe455
-F src/btree.h 078f76b28c338ab6eb6dd7324d63ee54463aeb6c
+F src/btree.c 299377f0793038ad3ea322907fbda7fbea615094
+F src/btree.h 3ad7964d6c5b1c7bff569aab6adfa075f8bf06cd
 F src/btreeInt.h 4e5c2bd0f9b36b2a815a6d84f771a61a65830621
 F src/build.c f35dac52924a6e8e6346a90f0c195a84e28b6f21
 F src/callback.c d7e46f40c3cf53c43550b7da7a1d0479910b62cc
@@ -162,7 +162,7 @@ F src/os.h 027491c77d2404c0a678bb3fb06286f331eb9b57
 F src/os_common.h 92815ed65f805560b66166e3583470ff94478f04
 F src/os_unix.c 0d3a39dd576c9f384fd7772a2dadc67b144c6ce7
 F src/os_win.c 28bd027791252a4012dffd4d64355a1eb84d761c
-F src/pager.c 82f7182b3dbf5f5e776980aa76db2f591564b15e
+F src/pager.c 36642c0955c19840b5445e7e9da7b5b0d8235346
 F src/pager.h 1109a06578ec5574dc2c74cf8d9f69daf36fe3e0
 F src/parse.y f29df90bd3adc64b33114ab1de9fb7768fcf2099
 F src/pcache.c f8043b433a57aba85384a531e3937a804432a346
@@ -289,6 +289,7 @@ F test/avtrans.test 0252654f4295ddda3b2cce0e894812259e655a85
 F test/backcompat.test ecd841f3a3bfb81518721879cc56a760670e3198
 F test/backup.test c9cdd23a495864b9edf75a9fa66f5cb7e10fcf62
 F test/backup2.test 34986ef926ea522911a51dfdb2f8e99b7b75ebcf
+F test/backup4.test 3c3639d28f3cdb4a123694a0a7c5fa7bfe304e2a
 F test/backup_ioerr.test 40d208bc9224b666ee3ed423f49bc9062a36a9d0
 F test/backup_malloc.test 7162d604ec2b4683c4b3799a48657fb8b5e2d450
 F test/badutf.test d5360fc31f643d37a973ab0d8b4fb85799c3169f
@@ -637,7 +638,7 @@ F test/openv2.test 0d3040974bf402e19b7df4b783e447289d7ab394
 F test/orderby1.test ef4f7c40df81b9a4303a718433d34052f07db47d
 F test/orderby2.test bc11009f7cd99d96b1b11e57b199b00633eb5b04
 F test/oserror.test 50417780d0e0d7cd23cf12a8277bb44024765df3
-F test/pager1.test 2163c6ef119f497a71a84137c957c63763e640ab
+F test/pager1.test 07116f72a61960b882952e7472cc2846d161d6e2
 F test/pager2.test 745b911dde3d1f24ae0870bd433dfa83d7c658c1
 F test/pager3.test 3856d9c80839be0668efee1b74811b1b7f7fc95f
 F test/pagerfault.test 452f2cc23e3bfcfa935f4442aec1da4fe1dc0442
@@ -1019,7 +1020,7 @@ F tool/vdbe-compress.tcl f12c884766bd14277f4fcedcae07078011717381
 F tool/warnings-clang.sh f6aa929dc20ef1f856af04a730772f59283631d4
 F tool/warnings.sh fbc018d67fd7395f440c28f33ef0f94420226381
 F tool/win/sqlite.vsix 67d8a99aceb56384a81b3f30d6c71743146d2cc9
-P de784399ed1f0e27fc875e32719643d19819c8fb
-R eae4686c36e29e07358a0f64b1678cc7
-U mistachkin
-Z 3d1371a2f131ddfec977348963d5fb7d
+P dce391fc6302301e9ac53a5e4fc69f3bd7ba13a7 ae025cae2266a91d4226bbdb66f82b9d7714750a
+R 6411855ed00a2b0cd5f5a66552e9b1b4
+U drh
+Z 1d2efa01eaf44e38b73ed9ee9ed57fac

manifest.uuid

@@ -1 +1 @@
-dce391fc6302301e9ac53a5e4fc69f3bd7ba13a7
+ca86138bda26c5ac5a7e67351acbd19fbd39b0ae

src/backup.c

@@ -413,7 +413,13 @@ int sqlite3_backup_step(sqlite3_backup *p, int nPage){
     ** same schema version.
     */
     if( rc==SQLITE_DONE ){
-      rc = sqlite3BtreeUpdateMeta(p->pDest,1,p->iDestSchema+1);
+      if( nSrcPage==0 ){
+        rc = sqlite3BtreeNewDb(p->pDest);
+        nSrcPage = 1;
+      }
+      if( rc==SQLITE_OK || rc==SQLITE_DONE ){
+        rc = sqlite3BtreeUpdateMeta(p->pDest,1,p->iDestSchema+1);
+      }
       if( rc==SQLITE_OK ){
         if( p->pDestDb ){
           sqlite3ResetAllSchemasOfConnection(p->pDestDb);
@@ -447,6 +453,7 @@ int sqlite3_backup_step(sqlite3_backup *p, int nPage){
         }else{
           nDestTruncate = nSrcPage * (pgszSrc/pgszDest);
         }
+        assert( nDestTruncate>0 );
         sqlite3PagerTruncateImage(pDestPager, nDestTruncate);
 
         if( pgszSrc<pgszDest ){
@@ -465,7 +472,8 @@ int sqlite3_backup_step(sqlite3_backup *p, int nPage){
           i64 iEnd;
 
           assert( pFile );
-          assert( (i64)nDestTruncate*(i64)pgszDest >= iSize || (
+          assert( nDestTruncate==0 
+              || (i64)nDestTruncate*(i64)pgszDest >= iSize || (
                 nDestTruncate==(int)(PENDING_BYTE_PAGE(p->pDest->pBt)-1)
              && iSize>=PENDING_BYTE && iSize<=PENDING_BYTE+pgszDest
           ));

src/btree.c

@@ -2531,6 +2531,20 @@ static int newDatabase(BtShared *pBt){
   return SQLITE_OK;
 }
 
+/*
+** Initialize the first page of the database file (creating a database
+** consisting of a single page and no schema objects). Return SQLITE_OK
+** if successful, or an SQLite error code otherwise.
+*/
+int sqlite3BtreeNewDb(Btree *p){
+  int rc;
+  sqlite3BtreeEnter(p);
+  p->pBt->nPage = 0;
+  rc = newDatabase(p->pBt);
+  sqlite3BtreeLeave(p);
+  return rc;
+}
+
 /*
 ** Attempt to start a new transaction. A write-transaction
 ** is started if the second argument is nonzero, otherwise a read-

src/btree.h

@@ -117,6 +117,8 @@ void sqlite3BtreeTripAllCursors(Btree*, int);
 void sqlite3BtreeGetMeta(Btree *pBtree, int idx, u32 *pValue);
 int sqlite3BtreeUpdateMeta(Btree*, int idx, u32 value);
 
+int sqlite3BtreeNewDb(Btree *p);
+
 /*
 ** The second parameter to sqlite3BtreeGetMeta or sqlite3BtreeUpdateMeta
 ** should be one of the following values. The integer values are assigned 

src/pager.c

@@ -5665,7 +5665,7 @@ static int pager_incr_changecounter(Pager *pPager, int isDirectMode){
 # define DIRECT_MODE isDirectMode
 #endif
 
-  if( !pPager->changeCountDone && pPager->dbSize>0 ){
+  if( !pPager->changeCountDone && ALWAYS(pPager->dbSize>0) ){
     PgHdr *pPgHdr;                /* Reference to page 1 */
 
     assert( !pPager->tempFile && isOpen(pPager->fd) );

test/backup4.test

@@ -0,0 +1,106 @@
+# 2012 October 13
+#
+# The author disclaims copyright to this source code.  In place of
+# a legal notice, here is a blessing:
+#
+#    May you do good and not evil.
+#    May you find forgiveness for yourself and forgive others.
+#    May you share freely, never taking more than you give.
+#
+#***********************************************************************
+#
+# The tests in this file verify that if an empty database (zero bytes in 
+# size) is used as the source of a backup operation, the final destination
+# database is one page in size.
+#
+# The destination must consist of at least one page as truncating a 
+# database file to zero bytes is equivalent to resetting the database
+# schema cookie and change counter. Doing that could cause other clients
+# to become confused and continue using out-of-date cache data.
+#
+
+set testdir [file dirname $argv0]
+source $testdir/tester.tcl
+set testprefix backup4
+
+#-------------------------------------------------------------------------
+# At one point this test was failing because [db] was using an out of
+# date schema in test case 1.2.
+#
+do_execsql_test 1.0 {
+  CREATE TABLE t1(x, y, UNIQUE(x, y));
+  INSERT INTO t1 VALUES('one', 'two');
+  SELECT * FROM t1 WHERE x='one';
+  PRAGMA integrity_check;
+} {one two ok}
+
+do_test 1.1 {
+  sqlite3 db1 :memory:
+  db1 backup test.db
+  sqlite3 db1 test.db
+  db1 eval {
+    CREATE TABLE t1(x, y);
+    INSERT INTO t1 VALUES('one', 'two');
+  }
+  db1 close
+} {}
+
+do_execsql_test 1.2 {
+  SELECT * FROM t1 WHERE x='one';
+  PRAGMA integrity_check;
+} {one two ok}
+
+db close
+forcedelete test.db
+forcedelete test.db2
+sqlite3 db test.db
+
+#-------------------------------------------------------------------------
+# Test that if the source is zero bytes, the destination database 
+# consists of a single page only.
+#
+do_execsql_test 2.1 {
+  CREATE TABLE t1(a, b);
+  CREATE INDEX i1 ON t1(a, b);
+}
+
+do_test 2.2 { file size test.db } 3072
+
+do_test 2.3 {
+  sqlite3 db1 test.db2
+  db1 backup test.db
+  db1 close
+  file size test.db
+} {1024}
+
+do_test 2.4 { file size test.db2 } 0
+
+db close
+forcedelete test.db
+forcedelete test.db2
+sqlite3 db test.db
+
+#-------------------------------------------------------------------------
+# Test that if the destination has a page-size larger than the implicit
+# page-size of the source, the final destination database still consists
+# of a single page.
+#
+do_execsql_test 3.1 {
+  PRAGMA page_size = 4096;
+  CREATE TABLE t1(a, b);
+  CREATE INDEX i1 ON t1(a, b);
+}
+
+do_test 3.2 { file size test.db } 12288
+
+do_test 3.3 {
+  sqlite3 db1 test.db2
+  db1 backup test.db
+  db1 close
+  file size test.db
+} {1024}
+
+do_test 3.4 { file size test.db2 } 0
+
+finish_test
+

test/pager1.test

@@ -1365,7 +1365,7 @@ do_test pager1-9.4.1 {
 } {SQLITE_DONE SQLITE_OK}
 do_test pager1-9.4.2 {
   list [file size test.db2] [file size test.db]
-} {0 0}
+} {1024 0}
 db2 close
 
 #-------------------------------------------------------------------------