Fix appendvfs bug exposed with bigger files, and add tests for such conditions.

FossilOrigin-Name: 19b1f53a1c0a14440ae8ac71660a2595d37a4a5b201055c19366c7dca75d6660

1 files changed, 35 insertions, 23 deletions

diff --git a/ext/misc/appendvfs.c b/ext/misc/appendvfs.c
index 3fff9a10f..970bb282c 100644
--- a/ext/misc/appendvfs.c
+++ b/ext/misc/appendvfs.c
@@ -122,6 +122,10 @@ struct ApndFile {
   sqlite3_int64 iPgOne;
   /* File offset of written append-mark, or -1 if unwritten */
   sqlite3_int64 iMark;
+  /* Whenever file is open and .iMark >= 0, and file size changes are
+   * not in progress, .iMark + sizeof(append mark) == base file size,
+   * and append file size == .iMark - .iPgOne .
+   */
 };
 
 /*
@@ -217,6 +221,7 @@ static const sqlite3_io_methods apnd_io_methods = {
 ** Close an apnd-file.
 */
 static int apndClose(sqlite3_file *pFile){
+  assert((ApndFile *pFile)pFile == ORIGFILE(pFile));
   pFile = ORIGFILE(pFile);
   return pFile->pMethods->xClose(pFile);
 }
@@ -250,6 +255,7 @@ static int apndWriteMark(
   int i = APND_MARK_FOS_SZ;
   int rc;
   assert(pFile == ORIGFILE(paf));
+  /* assert(pFile == paf->base); */
   memcpy(a, APND_MARK_PREFIX, APND_MARK_PREFIX_SZ);
   while (--i >= 0) {
     a[APND_MARK_PREFIX_SZ+i] = (unsigned char)(iPgOne & 0xff);
@@ -276,6 +282,7 @@ static int apndWrite(
   sqlite_int64 iWriteEnd = iOfst + iAmt;
   if( iWriteEnd>=APND_MAX_SIZE ) return SQLITE_FULL;
   pFile = ORIGFILE(pFile);
+  /* assert(pFile == paf->base); */
   /* If append-mark is absent or will be overwritten, write it. */
   if( paf->iMark < 0 || paf->iPgOne + iWriteEnd > paf->iMark ){
     int rc = apndWriteMark(paf, pFile, iWriteEnd);
@@ -499,55 +506,60 @@ static int apndIsOrdinaryDatabaseFile(sqlite3_int64 sz, sqlite3_file *pFile){
 ** Open an apnd file handle.
 */
 static int apndOpen(
-  sqlite3_vfs *pVfs,
+  sqlite3_vfs *pApndVfs,
   const char *zName,
   sqlite3_file *pFile,
   int flags,
   int *pOutFlags
 ){
-  ApndFile *p;
-  sqlite3_file *pSubFile;
-  sqlite3_vfs *pSubVfs;
+  ApndFile *pApndFile = (ApndFile*)pFile;
+  sqlite3_file *pBaseFile = ORIGFILE(pFile);
+  sqlite3_vfs *pBaseVfs = ORIGVFS(pApndVfs);
   int rc;
   sqlite3_int64 sz;
-  pSubVfs = ORIGVFS(pVfs);
   if( (flags & SQLITE_OPEN_MAIN_DB)==0 ){
-    /* The appendvfs is not to be used for transient or temporary databases. */
-    return pSubVfs->xOpen(pSubVfs, zName, pFile, flags, pOutFlags);
+    /* The appendvfs is not to be used for transient or temporary databases.
+     * Just use the base VFS open to initialize the given file object and
+     * open the underlying file. (Appendvfs is then unused for this file.)
+     */
+    return pBaseVfs->xOpen(pBaseVfs, zName, pFile, flags, pOutFlags);
   }
-  p = (ApndFile*)pFile;
-  memset(p, 0, sizeof(*p));
-  pSubFile = ORIGFILE(pFile);
+  memset(pApndFile, 0, sizeof(ApndFile));
   pFile->pMethods = &apnd_io_methods;
-  rc = pSubVfs->xOpen(pSubVfs, zName, pSubFile, flags, pOutFlags);
+  /* Record that append mark has not been written until seen otherwise. */
+  pApndFile->iMark = -1;
+
+  rc = pBaseVfs->xOpen(pBaseVfs, zName, pBaseFile, flags, pOutFlags);
   if( rc ) goto apnd_open_done;
-  rc = pSubFile->pMethods->xFileSize(pSubFile, &sz);
+  rc = pBaseFile->pMethods->xFileSize(pBaseFile, &sz);
   if( rc ){
-    pSubFile->pMethods->xClose(pSubFile);
+    pBaseFile->pMethods->xClose(pBaseFile);
     goto apnd_open_done;
   }
-  if( apndIsOrdinaryDatabaseFile(sz, pSubFile) ){
-    memmove(pFile, pSubFile, pSubVfs->szOsFile);
+  if( apndIsOrdinaryDatabaseFile(sz, pBaseFile) ){
+    /* The file being opened appears to be just an ordinary DB. Copy
+     * the base dispatch-table so this instance mimics the base VFS. 
+     */
+    memmove(pApndFile, pBaseFile, pBaseVfs->szOsFile);
     return SQLITE_OK;
   }
-  /* Record that append mark has not been written until seen otherwise. */
-  p->iMark = -1;
-  p->iPgOne = apndReadMark(sz, pFile);
-  if( p->iPgOne>=0 ){
+  pApndFile->iPgOne = apndReadMark(sz, pFile);
+  if( pApndFile->iPgOne>=0 ){
     /* Append mark was found, infer its offset */
-    p->iMark = sz - p->iPgOne - APND_MARK_SIZE;
+    pApndFile->iMark = sz - APND_MARK_SIZE;
+    /* pApndFile->base = pBaseFile; */
     return SQLITE_OK;
   }
   if( (flags & SQLITE_OPEN_CREATE)==0 ){
-    pSubFile->pMethods->xClose(pSubFile);
+    pBaseFile->pMethods->xClose(pBaseFile);
     rc = SQLITE_CANTOPEN;
   }
   /* Round newly added appendvfs location to #define'd page boundary. 
    * Note that nothing has yet been written to the underlying file.
    * The append mark will be written along with first content write.
-   * Until then, the p->iMark value indicates it is not yet written.
+   * Until then, paf->iMark value indicates it is not yet written.
    */
-  p->iPgOne = APND_START_ROUNDUP(sz, APND_ROUNDUP_BITS);
+  pApndFile->iPgOne = APND_START_ROUNDUP(sz, APND_ROUNDUP_BITS);
 apnd_open_done:
   if( rc ) pFile->pMethods = 0;
   return rc;