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74 lines
2.3 KiB
Go
74 lines
2.3 KiB
Go
package envflag
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import (
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"flag"
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"log"
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"os"
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"strings"
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"github.com/VictoriaMetrics/VictoriaMetrics/lib/envtemplate"
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)
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var (
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enable = flag.Bool("envflag.enable", false, "Whether to enable reading flags from environment variables additionally to command line. "+
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"Command line flag values have priority over values from environment vars. "+
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"Flags are read only from command line if this flag isn't set. See https://docs.victoriametrics.com/#environment-variables for more details")
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prefix = flag.String("envflag.prefix", "", "Prefix for environment variables if -envflag.enable is set")
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)
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// Parse parses environment vars and command-line flags.
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//
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// Flags set via command-line override flags set via environment vars.
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//
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// This function must be called instead of flag.Parse() before using any flags in the program.
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func Parse() {
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// Substitute %{ENV_VAR} inside args with the corresponding environment variable values
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args := os.Args[1:]
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dstArgs := args[:0]
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for _, arg := range args {
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s, err := envtemplate.ReplaceString(arg)
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if err != nil {
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// Do not use lib/logger here, since it is uninitialized yet.
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log.Fatalf("cannot process arg %q: %s", arg, err)
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}
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if len(s) > 0 {
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dstArgs = append(dstArgs, s)
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}
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}
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os.Args = os.Args[:1+len(dstArgs)]
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// Parse flags
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flag.Parse()
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if !*enable {
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return
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}
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// Remember explicitly set command-line flags.
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flagsSet := make(map[string]bool)
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flag.Visit(func(f *flag.Flag) {
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flagsSet[f.Name] = true
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})
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// Obtain the remaining flag values from environment vars.
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flag.VisitAll(func(f *flag.Flag) {
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if flagsSet[f.Name] {
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// The flag is explicitly set via command-line.
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return
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}
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// Get flag value from environment var.
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fname := getEnvFlagName(f.Name)
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if v, ok := envtemplate.LookupEnv(fname); ok {
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if err := flag.Set(f.Name, v); err != nil {
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// Do not use lib/logger here, since it is uninitialized yet.
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log.Fatalf("cannot set flag %s to %q, which is read from environment variable %q: %s", f.Name, v, fname, err)
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}
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}
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})
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}
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func getEnvFlagName(s string) string {
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// Substitute dots with underscores, since env var names cannot contain dots.
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// See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/311#issuecomment-586354129 for details.
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s = strings.ReplaceAll(s, ".", "_")
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return *prefix + s
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}
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