Libautoupdate

Cross-platform C library that enables your application to auto-update itself in place.

API

There is only one public API, i.e. autoupdate().

int autoupdate(argc, argv, host, port, path, current)

It accepts the following arguments:

• the 1st and 2nd arguments are the same as those passed to main()
• host is the host name of the update server to communicate with
• port is the port of the server, which is a string on Windows and a 16-bit integer on macOS / Linux
• path is the paramater passed to the HTTP/1.0 HEAD request of the Round 1
• current is the current version string to be compared with what is returned from the server
  • a new version is considered detected if this string is not a substring of the server's reply

It never returns if a new version was detected and auto-update was successfully performed. Otherwise, it returns one of the following integers to indicate the situation:

Return Value	Indication
0	Latest version confirmed. No need to update
1	Auto-update shall not proceed due to environment variable CI being set
2	Auto-update process failed prematurely and detailed errors are printed to stderr
3	Failed to restart after replacing itself with the new version
4	Auto-update shall not proceed due to being already checked in the last 24 hours

Communication

Round 1

Libautoupdate first makes a HTTP/1.0 HEAD request to the server, in order to peek the latest version string.

Libautoupdate -- HTTP/1.0 HEAD request --> Server

The server is expected to repond with HTTP 302 Found and provide a Location header.

It then compares the content of Location header with the current version string. It proceeds to Round 2 if the current version string is NOT a sub-string of the Location header.

Round 2

Libautoupdate makes a full HTTP/1.0 GET request to the Location header of the last round.

Libautoupdate -- HTTP/1.0 GET request --> Server

The server is expected to respond with 200 OK transferring the new release itself.

Based on the Content-Type header received, an addtional inflation operation might be performed:

• Content-Type: application/x-gzip: Gzip Inflation is performed
• Content-Type: application/zip: Deflate compression is assumed and the first file is inflated and used

Self-replacing

After 2 rounds of communication with the server, libautoupdate will then proceeds with a self-replacing process, i.e. the program replaces itself in-place with the help of the system temporary directory, after which it restarts itself with the new release.

Examples

Just call autoupdate() at the beginning of your main(), before all actual logic of your application. See the following code for examples.

Windows

#include <autoupdate.h>

int wmain(int argc, wchar_t *wargv[])
{
	int autoupdate_result;

	autoupdate_result = autoupdate(
		argc,
		wargv,
		"enclose.io",
		"80",
		"/nodec/nodec-x64.exe"
		"v1.1.0"
	);

	/* 
		actual logic of your application
		...
	*/
}

macOS / Linux

#include <autoupdate.h>

int main(int argc, char *argv[])
{
	int autoupdate_result;

	autoupdate_result = autoupdate(
		argc,
		argv,
		"enclose.io",
		80,
		"/nodec/nodec-darwin-x64"
		"v1.1.0"
	);

	/* 
		actual logic of your application
		...
	*/
}

Hints

• Set environment variable CI=true will prevent auto-updating
• Remove the file ~/.libautoupdate will remove the once-per-24-hours check limit

To-do

• Cater to bad network connection situations
• Print more information about the new version
• Use better error messages when the user did not have permissions to move the new version into the destination directory
• Move the old binary to the system temporary directory, yet not deleting it.
  • The Operating System will delete it when restarted/tmpdir-full
  • Add facility to restore/rollback to the old file once the new version went wrong

Authors

Minqi Pan et al.

License

MIT

See Also

• Node.js Packer: Packing your Node.js application into a single executable.
• Ruby Packer: Packing your Ruby application into a single executable.