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  • // Package main provides a utility program to launch the Dex container process with an optional
    // templating step (provided by gomplate).
    //
    // This was originally written as a shell script, but we rewrote it as a Go program so that it could
    // run as a raw binary in a distroless container.
    package main
    
    import (
    	"fmt"
    	"os"
    	"os/exec"
    	"strings"
    	"syscall"
    )
    
    func main() {
    	// Note that this docker-entrypoint program is args[0], and it is provided with the true process
    	// args.
    	args := os.Args[1:]
    
    	if err := run(args, realExec, realWhich); err != nil {
    		fmt.Println("error:", err.Error())
    		os.Exit(1)
    	}
    }
    
    func realExec(fork bool, args ...string) error {
    	if fork {
    		if output, err := exec.Command(args[0], args[1:]...).CombinedOutput(); err != nil {
    			return fmt.Errorf("cannot fork/exec command %s: %w (output: %q)", args, err, string(output))
    		}
    		return nil
    	}
    
    	argv0, err := exec.LookPath(args[0])
    	if err != nil {
    		return fmt.Errorf("cannot lookup path for command %s: %w", args[0], err)
    	}
    
    	if err := syscall.Exec(argv0, args, os.Environ()); err != nil {
    		return fmt.Errorf("cannot exec command %s (%q): %w", args, argv0, err)
    	}
    
    	return nil
    }
    
    func realWhich(path string) string {
    	fullPath, err := exec.LookPath(path)
    	if err != nil {
    		return ""
    	}
    	return fullPath
    }
    
    func run(args []string, execFunc func(bool, ...string) error, whichFunc func(string) string) error {
    	if args[0] != "dex" && args[0] != whichFunc("dex") {
    		return execFunc(false, args...)
    	}
    
    	if args[1] != "serve" {
    		return execFunc(false, args...)
    	}
    
    	newArgs := []string{}
    	for _, tplCandidate := range args {
    		if hasSuffixes(tplCandidate, ".tpl", ".tmpl", ".yaml") {
    			tmpFile, err := os.CreateTemp("/tmp", "dex.config.yaml-*")
    			if err != nil {
    				return fmt.Errorf("cannot create temp file: %w", err)
    			}
    
    			if err := execFunc(true, "gomplate", "-f", tplCandidate, "-o", tmpFile.Name()); err != nil {
    				return err
    			}
    
    			newArgs = append(newArgs, tmpFile.Name())
    		} else {
    			newArgs = append(newArgs, tplCandidate)
    		}
    	}
    
    	return execFunc(false, newArgs...)
    }
    
    func hasSuffixes(s string, suffixes ...string) bool {
    	for _, suffix := range suffixes {
    		if strings.HasSuffix(s, suffix) {
    			return true
    		}
    	}
    	return false
    }