Improved detection and reporting of errors in the readfile() extension SQL

function.

FossilOrigin-Name: d2f0b5a483869d39f5c5814c9d6df3d3b8a46d582b4dcf0cf11e23b707c4213e

ext/misc/fileio.c

@@ -121,22 +121,47 @@ SQLITE_EXTENSION_INIT1
 
 /*
 ** Set the result stored by context ctx to a blob containing the 
-** contents of file zName.
+** contents of file zName.  Or, leave the result unchanged (NULL)
+** if the file does not exist or is unreadable.
+**
+** If the file exceeds the SQLite blob size limit, through an
+** SQLITE_TOOBIG error.
+**
+** Throw an SQLITE_IOERR if there are difficulties pulling the file
+** off of disk.
 */
 static void readFileContents(sqlite3_context *ctx, const char *zName){
   FILE *in;
-  long nIn;
+  sqlite3_int64 nIn;
   void *pBuf;
+  sqlite3 *db;
+  int mxBlob;
 
   in = fopen(zName, "rb");
-  if( in==0 ) return;
+  if( in==0 ){
+    /* File does not exist or is unreadable. Leave the result set to NULL. */
+    return;
+  }
   fseek(in, 0, SEEK_END);
   nIn = ftell(in);
   rewind(in);
+  db = sqlite3_context_db_handle(ctx);
+  mxBlob = sqlite3_limit(db, SQLITE_LIMIT_LENGTH, -1);
+  if( nIn>mxBlob ){
+    sqlite3_result_error_code(ctx, SQLITE_TOOBIG);
+    fclose(in);
+    return;
+  }
   pBuf = sqlite3_malloc( nIn );
-  if( pBuf && 1==fread(pBuf, nIn, 1, in) ){
+  if( pBuf==0 ){
+    sqlite3_result_error_nomem(ctx);
+    fclose(in);
+    return;
+  }
+  if( 1==fread(pBuf, nIn, 1, in) ){
     sqlite3_result_blob(ctx, pBuf, nIn, sqlite3_free);
   }else{
+    sqlite3_result_error_code(ctx, SQLITE_IOERR);
     sqlite3_free(pBuf);
   }
   fclose(in);