Changed implementation of issue #304 fix

It no longer uses regular expressions.
It supports both the Unix `{$ENV_VAR}` _and_ the Windows `{%ENV_VAR%}`
syntax.
Added test for both Unix and Windows env. syntax.

caddy/parse/parsing.go

@@ -4,14 +4,9 @@ import (
 	"net"
 	"os"
 	"path/filepath"
-	"regexp"
 	"strings"
 )
 
-var (
-	envRegEx = regexp.MustCompile("{\\$[^}]+}")
-)
-
 type parser struct {
 	Dispenser
 	block           serverBlock // current server block being parsed
@@ -337,10 +332,23 @@ func (sb serverBlock) HostList() []string {
 }
 
 func getValFromEnv(s string) string {
-	envRefs := envRegEx.FindAllString(s, -1)
+	s = replaceEnvReferences(s, "{$", "}")
+	s = replaceEnvReferences(s, "{%", "%}")
+	return s
+}
+
+func replaceEnvReferences(s, refStart, refEnd string) string {
+	index := strings.Index(s, refStart)
+	for index != -1 {
+		endIndex := strings.Index(s, refEnd)
+		if endIndex != -1 {
+			ref := s[index : endIndex+len(refEnd)]
+			s = strings.Replace(s, ref, os.Getenv(ref[len(refStart):len(ref)-len(refEnd)]), -1)
+		} else {
+			return s
+		}
 
-	for _, ref := range envRefs {
-		s = strings.Replace(s, ref, os.Getenv(ref[2:len(ref)-1]), -1)
+		index = strings.Index(s, refStart)
 	}
 
 	return s

caddy/parse/parsing_test.go

@@ -391,6 +391,22 @@ func TestEnvironmentReplacement(t *testing.T) {
 			[]address{{"127.0.0.1", "1234"}},
 			[]address{{"localhost", "8080"}},
 		}},
+
+		{`{%MY_ADDRESS%}`, [][]address{
+			{{"servername.com", ""}},
+		}},
+
+		{`{%MY_ADDRESS%}:{%MY_PORT%}`, [][]address{
+			[]address{{"servername.com", "8080"}},
+		}},
+
+		{`{%MY_ADDRESS2%}:1234 {
+		  }
+		  localhost:{%MY_PORT%} {
+		  }`, [][]address{
+			[]address{{"127.0.0.1", "1234"}},
+			[]address{{"localhost", "8080"}},
+		}},
 	} {
 		p := testParser(test.input)
 		blocks, err := p.parseAll()