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flagconfig.go
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flagconfig.go
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// Package flagconfig provides a flag to specifiy a config file which
// will in turn be used to read unspecified flag values.
package flagconfig
import (
"flag"
"fmt"
"io/ioutil"
"log"
"os"
"path/filepath"
"strings"
)
var configFile = flag.String(
"c", defaultConfig(), "Config file to read flags from.")
func Usage() {
Parse()
fmt.Fprintf(os.Stderr, "Usage of %s:\n", os.Args[0])
flag.VisitAll(func(f *flag.Flag) {
fmt.Fprintf(os.Stderr, " -%s=%s: %s\n", f.Name, f.Value.String(), f.Usage)
})
}
func defaultConfig() string {
home := os.Getenv("HOME")
basename := filepath.Base(os.Args[0])
path := filepath.Join(home, ".config", basename, "config")
_, err := os.Open(path)
if err == nil {
return path
}
path = filepath.Join("/", "etc", "conf.d", basename)
_, err = os.Open(path)
if err == nil {
return path
}
return ""
}
func contains(list []*flag.Flag, f *flag.Flag) bool {
for _, i := range list {
if i == f {
return true
}
}
return false
}
func readConfig() map[string]string {
bytes, err := ioutil.ReadFile(*configFile)
if err != nil {
log.Fatalf("Failed to read config file %s: %s", *configFile, err)
}
lines := strings.Split(string(bytes), "\n")
result := make(map[string]string, len(lines))
for _, line := range lines {
trimmed := strings.TrimSpace(line)
if trimmed == "" || trimmed[0] == '#' {
continue
}
parts := strings.Split(line, "=")
if len(parts) != 2 {
log.Fatalf("Invalid config line: %s", line)
}
result[strings.TrimSpace(parts[0])] = strings.TrimSpace(parts[1])
}
return result
}
func Parse() {
ParseSet(flag.CommandLine)
}
func ParseSet(set *flag.FlagSet) {
if *configFile == "" {
return
}
config := readConfig()
explicit := make([]*flag.Flag, 0)
all := make([]*flag.Flag, 0)
set.Visit(func(f *flag.Flag) {
explicit = append(explicit, f)
})
set.VisitAll(func(f *flag.Flag) {
all = append(all, f)
if !contains(explicit, f) {
val := config[f.Name]
if val != "" {
err := f.Value.Set(val)
if err != nil {
log.Fatalf("Failed to set flag %s with value %s", f.Name, val)
}
}
}
})
Outer:
for name, val := range config {
for _, f := range all {
if f.Name == name {
continue Outer
}
}
log.Fatalf("Unknown flag %s=%s in config file.", name, val)
}
}