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@ -5,7 +5,10 @@ package cfg |
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import ( |
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"context" |
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"flag" |
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"fmt" |
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"os" |
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"strconv" |
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"strings" |
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) |
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// Cfger is a component which can be used with Cfg to setup its initialization.
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@ -13,20 +16,70 @@ type Cfger interface { |
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SetupCfg(*Cfg) |
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} |
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// Params are used to initialize a Cfg instance.
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type Params struct { |
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// Args are the command line arguments, excluding the command-name.
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//
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// Defaults to os.Args[1:]
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Args []string |
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// Env is the process's environment variables.
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//
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// Defaults to the real environment variables.
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Env map[string]string |
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// EnvPrefix indicates a string to prefix to all environment variable names
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// that Cfg will read. Will be automatically suffixed with a "_" if given.
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EnvPrefix string |
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} |
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func (p Params) withDefaults() Params { |
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if p.Args == nil { |
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p.Args = os.Args[1:] |
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} |
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if p.Env == nil { |
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p.Env = map[string]string{} |
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for _, envVar := range os.Environ() { |
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parts := strings.SplitN(envVar, "=", 2) |
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if len(parts) < 2 { |
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panic(fmt.Sprintf("envVar %q returned from os.Environ() somehow", envVar)) |
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} |
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p.Env[parts[0]] = parts[1] |
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} |
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} |
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if p.EnvPrefix != "" { |
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p.EnvPrefix = strings.TrimSuffix(p.EnvPrefix, "_") + "_" |
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} |
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return p |
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} |
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// Cfg is a wrapper around the stdlib's FlagSet and a set of initialization
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// hooks.
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type Cfg struct { |
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*flag.FlagSet |
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params Params |
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flagSet *flag.FlagSet |
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hooks []func(ctx context.Context) error |
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args []string |
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} |
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// New initializes and returns a new instance of *Cfg.
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func New() *Cfg { |
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func New(params Params) *Cfg { |
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params = params.withDefaults() |
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return &Cfg{ |
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FlagSet: flag.NewFlagSet("", flag.ExitOnError), |
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args: os.Args[1:], |
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params: params, |
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flagSet: flag.NewFlagSet("", flag.ExitOnError), |
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} |
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} |
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@ -40,7 +93,7 @@ func (c *Cfg) OnInit(cb func(context.Context) error) { |
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// called. If one returns an error that error is returned and no further hooks
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// are run.
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func (c *Cfg) Init(ctx context.Context) error { |
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if err := c.FlagSet.Parse(c.args); err != nil { |
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if err := c.flagSet.Parse(c.params.Args); err != nil { |
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return err |
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} |
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@ -53,6 +106,77 @@ func (c *Cfg) Init(ctx context.Context) error { |
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return nil |
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} |
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func (c *Cfg) envifyName(name string) string { |
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name = c.params.EnvPrefix + name |
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name = strings.Replace(name, "-", "_", -1) |
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name = strings.ToUpper(name) |
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return name |
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} |
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func envifyUsage(envName, usage string) string { |
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return fmt.Sprintf("%s (overrides %s)", usage, envName) |
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} |
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// StringVar is equivalent to flag.FlagSet's StringVar method, but will
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// additionally set up an environment variable for the parameter.
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func (c *Cfg) StringVar(p *string, name, value, usage string) { |
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envName := c.envifyName(name) |
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c.flagSet.StringVar(p, name, value, envifyUsage(envName, usage)) |
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if val := c.params.Env[envName]; val != "" { |
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*p = val |
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} |
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} |
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// String is equivalent to flag.FlagSet's String method, but will additionally
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// set up an environment variable for the parameter.
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func (c *Cfg) String(name, value, usage string) *string { |
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p := new(string) |
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c.StringVar(p, name, value, usage) |
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return p |
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} |
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// IntVar is equivalent to flag.FlagSet's IntVar method, but will additionally
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// set up an environment variable for the parameter.
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func (c *Cfg) IntVar(p *int, name string, value int, usage string) { |
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envName := c.envifyName(name) |
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c.flagSet.IntVar(p, name, value, envifyUsage(envName, usage)) |
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// if we can't parse the envvar now then just hold onto the error until
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// Init, otherwise we'd have to panic here and that'd be ugly.
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var err error |
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if valStr := c.params.Env[envName]; valStr != "" { |
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var val int |
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val, err = strconv.Atoi(valStr) |
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if err != nil { |
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err = fmt.Errorf( |
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"parsing envvar %q with value %q: %w", |
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envName, valStr, err, |
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) |
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} else { |
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*p = val |
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} |
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} |
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c.OnInit(func(context.Context) error { return err }) |
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} |
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// Int is equivalent to flag.FlagSet's Int method, but will additionally set up
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// an environment variable for the parameter.
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func (c *Cfg) Int(name string, value int, usage string) *int { |
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p := new(int) |
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c.IntVar(p, name, value, usage) |
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return p |
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} |
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// SubCmd should be called _after_ Init. Init will have consumed all arguments
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// up until the first non-flag argument. This non-flag argument is a
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// sub-command, and is returned by this method. This method also resets Cfg's
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@ -61,16 +185,16 @@ func (c *Cfg) Init(ctx context.Context) error { |
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// If there is no sub-command following the initial set of flags then this will
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// return empty string.
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func (c *Cfg) SubCmd() string { |
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c.args = c.FlagSet.Args() |
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if len(c.args) == 0 { |
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c.params.Args = c.flagSet.Args() |
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if len(c.params.Args) == 0 { |
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return "" |
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} |
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subCmd := c.args[0] |
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subCmd := c.params.Args[0] |
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c.FlagSet = flag.NewFlagSet(subCmd, flag.ExitOnError) |
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c.flagSet = flag.NewFlagSet(subCmd, flag.ExitOnError) |
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c.hooks = nil |
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c.args = c.args[1:] |
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c.params.Args = c.params.Args[1:] |
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return subCmd |
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} |
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