Merge pull request #114 from SenseUnit/cfg_file

Cfg file

Author: Snawoot

README.md

@@ -346,6 +346,37 @@ Supported proxy schemes are:
    * `url` - actual proxy URL. Note that just like any query string parameter this one has to be URL-encoded to be passed as query string value.
    * `ttl` - time to live for cache record. Examples: `15s`, `2m`, `1h`.
 
+## Configuration files
+
+Reading options from configuration file is now supported too! For example, command from one of examples above:
+
+```
+dumbproxy \
+    -bind-address 127.0.0.1:10443 \
+    -proxyproto \
+    -auth basicfile://?path=/etc/dumbproxy.htpasswd \
+    -cert=/etc/letsencrypt/live/proxy.example.com/fullchain.pem \
+    -key=/etc/letsencrypt/live/proxy.example.com/privkey.pem
+```
+
+becomes just
+
+```
+dumbproxy -config dp.cfg
+```
+
+having dp.cfg file with following content:
+
+```
+bind-address 127.0.0.1:10443
+proxyproto
+auth basicfile://?path=/etc/dumbproxy.htpasswd
+cert /etc/letsencrypt/live/proxy.example.com/fullchain.pem
+key /etc/letsencrypt/live/proxy.example.com/privkey.pem
+```
+
+Configuration format is [RFC 4180](https://www.rfc-editor.org/rfc/rfc4180.html) CSV with space character (`" "`) as a field separator instead of comma, `#` as a comment start character. Lines with only one field are treated as boolean flags, lines with two or more fields are treated as a key and its value, having extra fields joined with space.
+
 ## Synopsis
 
 ```
@@ -395,6 +426,8 @@ Usage of /home/user/go/bin/dumbproxy:
     	enable TLS and use certificate
   -ciphers string
     	colon-separated list of enabled ciphers
+  -config value
+    	read configuration from file with space-separated keys and values
   -curves string
     	colon-separated list of enabled key exchange curves
   -deny-dst-addr value

main.go

@@ -6,10 +6,12 @@ import (
 	"crypto/tls"
 	"encoding/base64"
 	"encoding/binary"
+	"encoding/csv"
 	"encoding/hex"
 	"errors"
 	"flag"
 	"fmt"
+	"io"
 	"log"
 	"net"
 	"net/http"
@@ -313,6 +315,7 @@ func parse_args() CLIArgs {
 		return nil
 	})
 	flag.BoolVar(&args.proxyproto, "proxyproto", false, "listen proxy protocol")
+	flag.Func("config", "read configuration from file with space-separated keys and values", readConfig)
 	flag.Parse()
 	args.positionalArgs = flag.Args()
 	return args
@@ -809,6 +812,50 @@ func prompt(prompt string, secure bool) (string, error) {
 	return input, nil
 }
 
+func readConfig(filename string) error {
+	f, err := os.Open(filename)
+	if err != nil {
+		return fmt.Errorf("unable to open config file %q: %w", filename, err)
+	}
+	defer f.Close()
+	r := csv.NewReader(f)
+	r.Comma = ' '
+	r.Comment = '#'
+	r.FieldsPerRecord = -1
+	r.TrimLeadingSpace = true
+	r.ReuseRecord = true
+	for {
+		record, err := r.Read()
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			return fmt.Errorf("configuration file parsing failed: %w", err)
+		}
+		switch len(record) {
+		case 0:
+			continue
+		case 1:
+			if err := flag.Set(record[0], "true"); err != nil {
+				line, _ := r.FieldPos(0)
+				return fmt.Errorf("error parsing config file %q at line %d: %w", filename, line, err)
+			}
+		case 2:
+			if err := flag.Set(record[0], record[1]); err != nil {
+				line, _ := r.FieldPos(0)
+				return fmt.Errorf("error parsing config file %q at line %d: %w", filename, line, err)
+			}
+		default:
+			unified := strings.Join(record[1:], " ")
+			if err := flag.Set(record[0], unified); err != nil {
+				line, _ := r.FieldPos(0)
+				return fmt.Errorf("error parsing config file %q at line %d: %w", filename, line, err)
+			}
+		}
+	}
+	return nil
+}
+
 func main() {
 	os.Exit(run())
 }