From 4f01edb9230f58ff84b0dd892c931ec8ac9aad55 Mon Sep 17 00:00:00 2001 From: Brian Picciano Date: Tue, 13 Sep 2022 12:56:08 +0200 Subject: move src out of srv, clean up default.nix and Makefile --- src/cfg/cfg.go | 255 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 255 insertions(+) create mode 100644 src/cfg/cfg.go (limited to 'src/cfg/cfg.go') diff --git a/src/cfg/cfg.go b/src/cfg/cfg.go new file mode 100644 index 0000000..d87c45b --- /dev/null +++ b/src/cfg/cfg.go @@ -0,0 +1,255 @@ +// Package cfg implements a simple wrapper around go's flag package, in order to +// implement initialization hooks. +package cfg + +import ( + "context" + "flag" + "fmt" + "os" + "strconv" + "strings" +) + +// Cfger is a component which can be used with Cfg to setup its initialization. +type Cfger interface { + SetupCfg(*Cfg) +} + +// Params are used to initialize a Cfg instance. +type Params struct { + + // Args are the command line arguments, excluding the command-name. + // + // Defaults to os.Args[1:] + Args []string + + // Env is the process's environment variables. + // + // Defaults to the real environment variables. + Env map[string]string + + // EnvPrefix indicates a string to prefix to all environment variable names + // that Cfg will read. Will be automatically suffixed with a "_" if given. + EnvPrefix string +} + +func (p Params) withDefaults() Params { + + if p.Args == nil { + p.Args = os.Args[1:] + } + + if p.Env == nil { + + p.Env = map[string]string{} + + for _, envVar := range os.Environ() { + + parts := strings.SplitN(envVar, "=", 2) + + if len(parts) < 2 { + panic(fmt.Sprintf("envVar %q returned from os.Environ() somehow", envVar)) + } + + p.Env[parts[0]] = parts[1] + } + } + + if p.EnvPrefix != "" { + p.EnvPrefix = strings.TrimSuffix(p.EnvPrefix, "_") + "_" + } + + return p +} + +// Cfg is a wrapper around the stdlib's FlagSet and a set of initialization +// hooks. +type Cfg struct { + params Params + flagSet *flag.FlagSet + + hooks []func(ctx context.Context) error +} + +// New initializes and returns a new instance of *Cfg. +func New(params Params) *Cfg { + + params = params.withDefaults() + + return &Cfg{ + params: params, + flagSet: flag.NewFlagSet("", flag.ExitOnError), + } +} + +// OnInit appends the given callback to the sequence of hooks which will run on +// a call to Init. +func (c *Cfg) OnInit(cb func(context.Context) error) { + c.hooks = append(c.hooks, cb) +} + +// Init runs all hooks registered using OnInit, in the same order OnInit was +// called. If one returns an error that error is returned and no further hooks +// are run. +func (c *Cfg) Init(ctx context.Context) error { + if err := c.flagSet.Parse(c.params.Args); err != nil { + return err + } + + for _, h := range c.hooks { + if err := h(ctx); err != nil { + return err + } + } + + return nil +} + +func (c *Cfg) envifyName(name string) string { + name = c.params.EnvPrefix + name + name = strings.Replace(name, "-", "_", -1) + name = strings.ToUpper(name) + return name +} + +func envifyUsage(envName, usage string) string { + return fmt.Sprintf("%s (overrides %s)", usage, envName) +} + +// StringVar is equivalent to flag.FlagSet's StringVar method, but will +// additionally set up an environment variable for the parameter. +func (c *Cfg) StringVar(p *string, name, value, usage string) { + + envName := c.envifyName(name) + + c.flagSet.StringVar(p, name, value, envifyUsage(envName, usage)) + + if val := c.params.Env[envName]; val != "" { + *p = val + } +} + +// Args returns a pointer which will be filled with the process's positional +// arguments after Init is called. The positional arguments are all CLI +// arguments starting with the first non-flag argument. +// +// The usage argument should describe what these arguments are, and its notation +// should indicate if they are optional or variadic. For example: +// +// // optional variadic +// "[names...]" +// +// // required single args +// " " +// +// // Mixed +// " [baz] [other...]" +// +func (c *Cfg) Args(usage string) *[]string { + + args := new([]string) + + c.flagSet.Usage = func() { + fmt.Fprintf(os.Stderr, "USAGE [flags...] %s\n", usage) + fmt.Fprintf(os.Stderr, "\nFLAGS\n\n") + c.flagSet.PrintDefaults() + } + + c.OnInit(func(ctx context.Context) error { + *args = c.flagSet.Args() + return nil + }) + + return args +} + +// String is equivalent to flag.FlagSet's String method, but will additionally +// set up an environment variable for the parameter. +func (c *Cfg) String(name, value, usage string) *string { + p := new(string) + c.StringVar(p, name, value, usage) + return p +} + +// IntVar is equivalent to flag.FlagSet's IntVar method, but will additionally +// set up an environment variable for the parameter. +func (c *Cfg) IntVar(p *int, name string, value int, usage string) { + + envName := c.envifyName(name) + + c.flagSet.IntVar(p, name, value, envifyUsage(envName, usage)) + + // if we can't parse the envvar now then just hold onto the error until + // Init, otherwise we'd have to panic here and that'd be ugly. + var err error + + if valStr := c.params.Env[envName]; valStr != "" { + + var val int + val, err = strconv.Atoi(valStr) + + if err != nil { + err = fmt.Errorf( + "parsing envvar %q with value %q: %w", + envName, valStr, err, + ) + + } else { + *p = val + } + } + + c.OnInit(func(context.Context) error { return err }) +} + +// Int is equivalent to flag.FlagSet's Int method, but will additionally set up +// an environment variable for the parameter. +func (c *Cfg) Int(name string, value int, usage string) *int { + p := new(int) + c.IntVar(p, name, value, usage) + return p +} + +// BoolVar is equivalent to flag.FlagSet's BoolVar method, but will additionally +// set up an environment variable for the parameter. +func (c *Cfg) BoolVar(p *bool, name string, value bool, usage string) { + + envName := c.envifyName(name) + + c.flagSet.BoolVar(p, name, value, envifyUsage(envName, usage)) + + if valStr := c.params.Env[envName]; valStr != "" { + *p = valStr != "" && valStr != "0" && valStr != "false" + } +} + +// Bool is equivalent to flag.FlagSet's Bool method, but will additionally set +// up an environment variable for the parameter. +func (c *Cfg) Bool(name string, value bool, usage string) *bool { + p := new(bool) + c.BoolVar(p, name, value, usage) + return p +} + +// SubCmd should be called _after_ Init. Init will have consumed all arguments +// up until the first non-flag argument. This non-flag argument is a +// sub-command, and is returned by this method. This method also resets Cfg's +// internal state so that new options can be added to it. +// +// If there is no sub-command following the initial set of flags then this will +// return empty string. +func (c *Cfg) SubCmd() string { + c.params.Args = c.flagSet.Args() + if len(c.params.Args) == 0 { + return "" + } + + subCmd := c.params.Args[0] + + c.flagSet = flag.NewFlagSet(subCmd, flag.ExitOnError) + c.hooks = nil + c.params.Args = c.params.Args[1:] + + return subCmd +} -- cgit v1.2.3