Awesome

Idea

This was an attempt to make a privately hosted file storage, similar to Dropbox.
The idea was to build a native application, able to handle filesystem events and synchronize files via a server.
It's not finished, and never will be. I'm hosting it here for demonstration purposes only.

Implementation

During synchronization only difference between file versions is transfered over the network.
Files are hashed into parts, which are stored on the server in trees, just like in a Git repository.
Thus, it's possible to see the whole history of a node, and rollback any changes.

The code is cross-platform (compiles on Linux, OSX, and Windows). It's written in C, and source files are preprocessed with PerlPP. This preprocessor turned out to be very helpful as it's much more flexible than the standard C-preprocessor.

Code Generation

For example, it's very important and difficult to correctly manage memory in C programs.
In the code below, pay attention to <<<<<<<<<<<<<<<<<<<<<<<. Cleanup actions $onCleanup are placed near the code, where this memory is allocated. However, all of the cleanup will be done at the very end $cleanup. The cleanup will be executed even if any internal $call fails.

static bbb_result_t
_ProcessEntry( const char* const path, const size_t skip, const char* const name, @_t* const ss ) {

  /* ... */
  
	$call bbb_util_Malloc( ( void** )&entry, sizeof( @_entry_t ) + pathMem );
	$onCleanup              // <<<<<<<<<<<<<<<<<<<<<<<
		if ( BBB_FAILED( result ) ) {
			free( entry );
		}
	$$                      // <<<<<<<<<<<<<<<<<<<<<<<

	$call bbb_util_Malloc( ( void** )&fullPath, pathMem + skip + 1 );
	$onCleanup              // <<<<<<<<<<<<<<<<<<<<<<<
		free( fullPath );
	$$                      // <<<<<<<<<<<<<<<<<<<<<<<

	if ( stat( fullPath, &entryInfo ) ) {
		BBB_ERR( BBB_ERROR_FILESYSTEMIO, "Cannot get info about %s: %s", fullPath, strerror( errno ) );
		result = BBB_ERROR_FILESYSTEMIO;
		$gotoCleanup;         // <<<<<<<<<<<<<<<<<<<<<<<
	}

  /* ... */
  
	if ( S_ISDIR( entryInfo.st_mode ) ) {
		entry->status |= @^ENTRY_STATUS_DIR;
		$call _AddToSnapshot( entry, ss );
		$call _ProcessDir( fullPath, skip, ss );
	} else if ( S_ISREG( entryInfo.st_mode ) ) {
		entry->status &= ~@^ENTRY_STATUS_DIR;
		$call _AddToSnapshot( entry, ss );
	} else {
		BBB_LOG( "Skipping irregular file: %s", fullPath );
		$gotoCleanup;         // <<<<<<<<<<<<<<<<<<<<<<<
	}

	$cleanup;               // <<<<<<<<<<<<<<<<<<<<<<<
	return result;
}

The final C-code looks like this:

static bbb_result_t
_ProcessEntry( const char* const path, const size_t skip, const char* const name, bbb_sshot_t* const ss ) {
       /* ... */
       
       pathMem = ( strlen( path ) - skip + strlen( name ) + 1 + BBB_WORD_SIZE ) & ~( BBB_WORD_SIZE - 1 );

       if ( BBB_FAILED( result =  bbb_util_Malloc( ( void** )&entry, sizeof( bbb_sshot_entry_t ) + pathMem )  ) ) { 
           goto L_cleanup_0;
       }   

       if ( BBB_FAILED( result =  bbb_util_Malloc( ( void** )&fullPath, pathMem + skip + 1 )  ) ) { 
           goto L_cleanup_1;
       }
       
       /* ... */
       
L_cleanup_2:
       free( fullPath );

L_cleanup_1:
       if ( BBB_FAILED( result ) ) {
           free( entry );
       }

L_cleanup_0:
       return result;
}