add Header proxy policy

caddyhttp/proxy/policy.go

@@ -18,12 +18,13 @@ type Policy interface {
 }
 
 func init() {
-	RegisterPolicy("random", func() Policy { return &Random{} })
-	RegisterPolicy("least_conn", func() Policy { return &LeastConn{} })
-	RegisterPolicy("round_robin", func() Policy { return &RoundRobin{} })
-	RegisterPolicy("ip_hash", func() Policy { return &IPHash{} })
-	RegisterPolicy("first", func() Policy { return &First{} })
-	RegisterPolicy("uri_hash", func() Policy { return &URIHash{} })
+	RegisterPolicy("random", func(arg string) Policy { return &Random{} })
+	RegisterPolicy("least_conn", func(arg string) Policy { return &LeastConn{} })
+	RegisterPolicy("round_robin", func(arg string) Policy { return &RoundRobin{} })
+	RegisterPolicy("ip_hash", func(arg string) Policy { return &IPHash{} })
+	RegisterPolicy("first", func(arg string) Policy { return &First{} })
+	RegisterPolicy("uri_hash", func(arg string) Policy { return &URIHash{} })
+	RegisterPolicy("header", func(arg string) Policy { return &Header{arg} })
 }
 
 // Random is a policy that selects up hosts from a pool at random.
@@ -160,3 +161,22 @@ func (r *First) Select(pool HostPool, request *http.Request) *UpstreamHost {
 	}
 	return nil
 }
+
+// Header is a policy that selects based on a hash of the given header
+type Header struct {
+	// The name of the request header, the value of which will determine
+	// how the request is routed
+	Name string
+}
+
+// Select selects the host based on hashing the header value
+func (r *Header) Select(pool HostPool, request *http.Request) *UpstreamHost {
+	if r.Name == "" {
+		return nil
+	}
+	val := request.Header.Get(r.Name)
+	if val == "" {
+		return nil
+	}
+	return hostByHashing(pool, val)
+}

caddyhttp/proxy/policy_test.go

@@ -302,3 +302,42 @@ func TestUriPolicy(t *testing.T) {
 		t.Error("Expected uri policy policy host to be nil.")
 	}
 }
+
+func TestHeaderPolicy(t *testing.T) {
+	pool := testPool()
+	tests := []struct {
+		Policy             *Header
+		RequestHeaderName  string
+		RequestHeaderValue string
+		NilHost            bool
+		HostIndex          int
+	}{
+		{&Header{""}, "", "", true, 0},
+		{&Header{""}, "Affinity", "somevalue", true, 0},
+		{&Header{""}, "Affinity", "", true, 0},
+
+		{&Header{"Affinity"}, "", "", true, 0},
+		{&Header{"Affinity"}, "Affinity", "somevalue", false, 1},
+		{&Header{"Affinity"}, "Affinity", "somevalue2", false, 0},
+		{&Header{"Affinity"}, "Affinity", "somevalue3", false, 2},
+		{&Header{"Affinity"}, "Affinity", "", true, 0},
+	}
+
+	for idx, test := range tests {
+		request, _ := http.NewRequest("GET", "/", nil)
+		if test.RequestHeaderName != "" {
+			request.Header.Add(test.RequestHeaderName, test.RequestHeaderValue)
+		}
+
+		host := test.Policy.Select(pool, request)
+		if test.NilHost && host != nil {
+			t.Errorf("%d: Expected host to be nil", idx)
+		}
+		if !test.NilHost && host == nil {
+			t.Errorf("%d: Did not expect host to be nil", idx)
+		}
+		if !test.NilHost && host != pool[test.HostIndex] {
+			t.Errorf("%d: Expected Header policy to be host %d", idx, test.HostIndex)
+		}
+	}
+}

caddyhttp/proxy/upstream.go

@@ -22,7 +22,7 @@ import (
 )
 
 var (
-	supportedPolicies = make(map[string]func() Policy)
+	supportedPolicies = make(map[string]func(string) Policy)
 )
 
 type staticUpstream struct {
@@ -243,7 +243,11 @@ func parseBlock(c *caddyfile.Dispenser, u *staticUpstream) error {
 		if !ok {
 			return c.ArgErr()
 		}
-		u.Policy = policyCreateFunc()
+		arg := ""
+		if c.NextArg() {
+			arg = c.Val()
+		}
+		u.Policy = policyCreateFunc(arg)
 	case "fail_timeout":
 		if !c.NextArg() {
 			return c.ArgErr()
@@ -523,7 +527,7 @@ func (u *staticUpstream) Stop() error {
 }
 
 // RegisterPolicy adds a custom policy to the proxy.
-func RegisterPolicy(name string, policy func() Policy) {
+func RegisterPolicy(name string, policy func(string) Policy) {
 	supportedPolicies[name] = policy
 }
 

caddyhttp/proxy/upstream_test.go

@@ -106,7 +106,7 @@ func TestSelect(t *testing.T) {
 func TestRegisterPolicy(t *testing.T) {
 	name := "custom"
 	customPolicy := &customPolicy{}
-	RegisterPolicy(name, func() Policy { return customPolicy })
+	RegisterPolicy(name, func(string) Policy { return customPolicy })
 	if _, ok := supportedPolicies[name]; !ok {
 		t.Error("Expected supportedPolicies to have a custom policy.")
 	}