Issue #55: Expand ${DC} to consul datacenter

Expand the ${DC} variable in a urlprefix to the
data center of the consul agent.

registry/consul/parse.go

@@ -2,13 +2,14 @@ package consul
 
 import (
 	"log"
+	"os"
 	"strings"
 )
 
 // parseURLPrefixTag expects an input in the form of 'tag-host/path'
 // and returns the lower cased host plus the path unaltered if the
 // prefix matches the tag.
-func parseURLPrefixTag(s, prefix string) (host, path string, ok bool) {
+func parseURLPrefixTag(s, prefix string, env map[string]string) (host, path string, ok bool) {
 	if !strings.HasPrefix(s, prefix) {
 		return "", "", false
 	}
@@ -20,6 +21,18 @@ func parseURLPrefixTag(s, prefix string) (host, path string, ok bool) {
 		return "", "", false
 	}
 
-	host, path = strings.ToLower(strings.TrimSpace(p[0])), "/"+strings.TrimSpace(p[1])
+	// expand $x or ${x} to env[x] or ""
+	expand := func(s string) string {
+		return os.Expand(s, func(x string) string {
+			if env == nil {
+				return ""
+			}
+			return env[x]
+		})
+	}
+
+	host = strings.ToLower(expand(strings.TrimSpace(p[0])))
+	path = "/" + expand(strings.TrimSpace(p[1]))
+
 	return host, path, true
 }

registry/consul/parse_test.go

@@ -5,35 +5,61 @@ import "testing"
 func TestParseTag(t *testing.T) {
 	prefix := "p-"
 	tests := []struct {
-		tag, host, path string
-		ok              bool
+		tag  string
+		env  map[string]string
+		host string
+		path string
+		ok   bool
 	}{
-		{"p", "", "", false},
-		{"p-", "", "", false},
-		{"p- ", "", "", false},
-		{"p-/", "", "/", true},
-		{"p-/ ", "", "/", true},
-		{"p- / ", "", "/", true},
-		{"p-/foo", "", "/foo", true},
-		{"p-bar/foo", "bar", "/foo", true},
-		{"p-bar/foo/foo", "bar", "/foo/foo", true},
-		{"p-www.bar.com/foo/foo", "www.bar.com", "/foo/foo", true},
-		{"p-WWW.BAR.COM/foo/foo", "www.bar.com", "/foo/foo", true},
+		{tag: "p", host: "", path: "", ok: false},
+		{tag: "p-", host: "", path: "", ok: false},
+		{tag: "p- ", host: "", path: "", ok: false},
+		{tag: "p-/", host: "", path: "/", ok: true},
+		{tag: "p-/ ", host: "", path: "/", ok: true},
+		{tag: "p- / ", host: "", path: "/", ok: true},
+		{tag: "p-/foo", host: "", path: "/foo", ok: true},
+		{tag: "p-bar/foo", host: "bar", path: "/foo", ok: true},
+		{tag: "p-bar/foo/foo", host: "bar", path: "/foo/foo", ok: true},
+		{tag: "p-www.bar.com/foo/foo", host: "www.bar.com", path: "/foo/foo", ok: true},
+		{tag: "p-WWW.BAR.COM/foo/foo", host: "www.bar.com", path: "/foo/foo", ok: true},
+
+		{
+			tag:  "p-$x/$y",
+			host: "", path: "/",
+			ok: true,
+		},
+		{
+			tag:  "p-${x}/${y}",
+			host: "", path: "/",
+			ok: true,
+		},
+		{
+			tag:  "p-$x/$Y",
+			env:  map[string]string{"x": "Xx", "Y": "Yy"},
+			host: "xx", path: "/Yy",
+			ok: true,
+		},
+		{
+			tag:  "p-${x}/${Y}",
+			env:  map[string]string{"x": "Xx", "Y": "Yy"},
+			host: "xx", path: "/Yy",
+			ok: true,
+		},
 	}
 
 	for i, tt := range tests {
-		host, path, ok := parseURLPrefixTag(tt.tag, prefix)
+		host, path, ok := parseURLPrefixTag(tt.tag, prefix, tt.env)
 		if got, want := ok, tt.ok; got != want {
 			t.Errorf("%d: got %v want %v", i, got, want)
 		}
 		if !ok {
 			continue
 		}
 		if got, want := host, tt.host; got != want {
-			t.Errorf("%d: got %s want %s", i, got, want)
+			t.Errorf("%d: got host %q want %q", i, got, want)
 		}
 		if got, want := path, tt.path; got != want {
-			t.Errorf("%d: got %s want %s", i, got, want)
+			t.Errorf("%d: got path %q want %q", i, got, want)
 		}
 	}
 }

registry/consul/service.go

@@ -63,13 +63,23 @@ func serviceConfig(client *api.Client, name string, passing map[string]bool, tag
 		return nil
 	}
 
+	dc, err := datacenter(client)
+	if err != nil {
+		log.Printf("[WARN] consul: Error getting datacenter. %s", err)
+		return nil
+	}
+
 	q := &api.QueryOptions{RequireConsistent: true}
 	svcs, _, err := client.Catalog().Service(name, "", q)
 	if err != nil {
 		log.Printf("[WARN] consul: Error getting catalog service %s. %v", name, err)
 		return nil
 	}
 
+	env := map[string]string{
+		"DC": dc,
+	}
+
 	for _, svc := range svcs {
 		// check if the instance is in the list of instances
 		// which passed the health check
@@ -78,7 +88,7 @@ func serviceConfig(client *api.Client, name string, passing map[string]bool, tag
 		}
 
 		for _, tag := range svc.ServiceTags {
-			if host, path, ok := parseURLPrefixTag(tag, tagPrefix); ok {
+			if host, path, ok := parseURLPrefixTag(tag, tagPrefix, env); ok {
 				name, addr, port := svc.ServiceName, svc.ServiceAddress, svc.ServicePort
 
 				// use consul node address if service address is not set