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cfgfile.go
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cfgfile.go
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package cfgfile
import (
"flag"
"fmt"
"io/ioutil"
"os"
"path/filepath"
"strings"
"github.com/elastic/beats/libbeat/logp"
"gopkg.in/yaml.v2"
)
// Command line flags
var configfile *string
var testConfig *bool
func init() {
// The default config cannot include the beat name as it is not initialised when this
// function is called, but see ChangeDefaultCfgfileFlag
configfile = flag.String("c", "beat.yml", "Configuration file")
testConfig = flag.Bool("configtest", false, "Test configuration and exit.")
}
// ChangeDefaultCfgfileFlag replaces the value and default value for the `-c` flag so that
// it reflects the beat name.
func ChangeDefaultCfgfileFlag(beatName string) error {
cliflag := flag.Lookup("c")
if cliflag == nil {
return fmt.Errorf("Flag -c not found")
}
path, err := filepath.Abs(filepath.Dir(os.Args[0]))
if err != nil {
return fmt.Errorf("Failed to set default config file location because "+
"the absolute path to %s could not be obtained. %v",
os.Args[0], err)
}
cliflag.DefValue = filepath.Join(path, beatName+".yml")
return cliflag.Value.Set(cliflag.DefValue)
}
// Read reads the configuration from a yaml file into the given interface structure.
// In case path is not set this method reads from the default configuration file for the beat.
func Read(out interface{}, path string) error {
if path == "" {
path = *configfile
}
filecontent, err := ioutil.ReadFile(path)
if err != nil {
return fmt.Errorf("Failed to read %s: %v. Exiting.", path, err)
}
filecontent = expandEnv(filecontent)
if err = yaml.Unmarshal(filecontent, out); err != nil {
return fmt.Errorf("YAML config parsing failed on %s: %v. Exiting.", path, err)
}
return nil
}
func IsTestConfig() bool {
return *testConfig
}
// expandEnv replaces ${var} in config according to the values of the current
// environment variables. The replacement is case-sensitive. References to
// undefined variables are replaced by the empty string. A default value can be
// given by using the form ${var:default value}.
func expandEnv(config []byte) []byte {
return []byte(expand(string(config), func(key string) string {
keyAndDefault := strings.SplitN(key, ":", 2)
key = keyAndDefault[0]
v := os.Getenv(key)
if v == "" && len(keyAndDefault) == 2 {
// Set value to the default.
v = keyAndDefault[1]
logp.Info("Replacing config environment variable '${%s}' with "+
"default '%s'", key, keyAndDefault[1])
} else {
logp.Info("Replacing config environment variable '${%s}' with '%s'",
key, v)
}
return v
}))
}
// The following methods were copied from the os package of the stdlib. The
// expand method was modified to only expand variables defined with braces and
// ignore $var.
// Expand replaces ${var} in the string based on the mapping function.
func expand(s string, mapping func(string) string) string {
buf := make([]byte, 0, 2*len(s))
// ${} is all ASCII, so bytes are fine for this operation.
i := 0
for j := 0; j < len(s); j++ {
if s[j] == '$' && j+2 < len(s) && s[j+1] == '{' {
buf = append(buf, s[i:j]...)
name, w := getShellName(s[j+1:])
buf = append(buf, mapping(name)...)
j += w
i = j + 1
}
}
return string(buf) + s[i:]
}
// isShellSpecialVar reports whether the character identifies a special
// shell variable such as $*.
func isShellSpecialVar(c uint8) bool {
switch c {
case '*', '#', '$', '@', '!', '?', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
return true
}
return false
}
// isAlphaNum reports whether the byte is an ASCII letter, number, or underscore
func isAlphaNum(c uint8) bool {
return c == '_' || '0' <= c && c <= '9' || 'a' <= c && c <= 'z' || 'A' <= c && c <= 'Z'
}
// getShellName returns the name that begins the string and the number of bytes
// consumed to extract it. If the name is enclosed in {}, it's part of a ${}
// expansion and two more bytes are needed than the length of the name.
func getShellName(s string) (string, int) {
switch {
case s[0] == '{':
if len(s) > 2 && isShellSpecialVar(s[1]) && s[2] == '}' {
return s[1:2], 3
}
// Scan to closing brace
for i := 1; i < len(s); i++ {
if s[i] == '}' {
return s[1:i], i + 1
}
}
return "", 1 // Bad syntax; just eat the brace.
case isShellSpecialVar(s[0]):
return s[0:1], 1
}
// Scan alphanumerics.
var i int
for i = 0; i < len(s) && isAlphaNum(s[i]); i++ {
}
return s[:i], i
}