support specifying the part of the path

pkg/filter/headerlookup/headerlookup.go

@@ -21,6 +21,7 @@ import (
 	"context"
 	"fmt"
 	"net/http"
+	"regexp"
 	"strings"
 	"time"
 
@@ -55,6 +56,7 @@ type (
 		spec       *Spec
 		etcdPrefix string
 		headerKey  string
+		pathRegExp *regexp.Regexp
 
 		cache   *lru.Cache
 		cluster cluster.Cluster
@@ -71,13 +73,15 @@ type (
 	// Spec defines header key and etcd prefix that form etcd key like /custom-data/{etcdPrefix}/{headerKey's value}.
 	// This /custom-data/{etcdPrefix}/{headerKey's value} is retrieved from etcd and HeaderSetters extract keys from the
 	// from the retrieved etcd item.
-	// When AppendPath is true, the path (without leading slash) is appended to the etcd key in following format:
-	// /custom-data/{etcdPrefix}/{headerKey's value}-{path} . For example, for path "/bananas", the etcd key is
+	// When PathRegExp is defined, PathRegExp is used with `regexp.FindStringSubmatch` to identify a group from path.
+	// The first captured group is appended to the etcd key in following format:
+	// /custom-data/{etcdPrefix}/{headerKey's value}-{regex group} . For example, for path
+	// "/api/bananas/33" and pathRegExp: "^/api/([a-z]+)/[0-9]*", the group "bananas" is extracted and etcd key is
 	// /custom-data/{etcdPrefix}/{headerKey's value}-bananas.
 	Spec struct {
 		HeaderKey     string              `yaml:"headerKey" jsonschema:"required"`
 		EtcdPrefix    string              `yaml:"etcdPrefix" jsonschema:"required"`
-		AppendPath    bool                `yaml:"appendPath" jsonschema:"omitempty"`
+		PathRegExp    string              `yaml:"pathRegExp" jsonschema:"omitempty"`
 		HeaderSetters []*HeaderSetterSpec `yaml:"headerSetters" jsonschema:"required"`
 	}
 )
@@ -101,6 +105,10 @@ func (spec Spec) Validate() error {
 			return fmt.Errorf("headerSetters[i].headerKey is required")
 		}
 	}
+
+	if _, err := regexp.Compile(spec.PathRegExp); err != nil {
+		return err
+	}
 	return nil
 }
 
@@ -134,6 +142,7 @@ func (hl *HeaderLookup) Init(filterSpec *httppipeline.FilterSpec) {
 	hl.headerKey = http.CanonicalHeaderKey(hl.spec.HeaderKey)
 	hl.cache, _ = lru.New(cacheSize)
 	hl.stopCtx, hl.cancel = context.WithCancel(context.Background())
+	hl.pathRegExp = regexp.MustCompile(hl.spec.PathRegExp)
 	hl.watchChanges()
 }
 
@@ -253,8 +262,11 @@ func (hl *HeaderLookup) handle(ctx httpcontext.HTTPContext) string {
 		logger.Warnf("request does not have header '%s'", hl.spec.HeaderKey)
 		return ""
 	}
-	if hl.spec.AppendPath {
-		headerVal = headerVal + "-" + strings.TrimPrefix(ctx.Request().Path(), "/")
+	if hl.spec.PathRegExp != "" {
+		path := ctx.Request().Path()
+		if match := hl.pathRegExp.FindStringSubmatch(path); match != nil && len(match) > 1 {
+			headerVal = headerVal + "-" + match[1]
+		}
 	}
 	headersToAdd, err := hl.lookup(headerVal)
 	if err != nil {

pkg/filter/headerlookup/headerlookup_test.go

@@ -114,6 +114,16 @@ headerKey: "X-AUTH-USER"
 etcdPrefix: "/credentials/"
 headerSetters:
   - headerKey: "X-ext-id"
+`,
+		`
+name: headerLookup
+kind: HeaderLookup
+headerKey: "X-AUTH-USER"
+pathRegExp: "**"
+etcdPrefix: "/credentials/"
+headerSetters:
+  - headerKey: "X-ext-id"
+    etcdKey: "ext-id"
 `,
 	}
 
@@ -266,7 +276,7 @@ name: headerLookup
 kind: HeaderLookup
 headerKey: "X-AUTH-USER"
 etcdPrefix: "credentials/"
-appendPath: true
+pathRegExp: "^/api/([a-z]+)/[0-9]*"
 headerSetters:
   - etcdKey: "ext-id"
     headerKey: "user-ext-id"
@@ -291,17 +301,20 @@ extra-entry: "extra"
 	check(err)
 
 	ctx, header := prepareCtxAndHeader()
-
 	header.Set("X-AUTH-USER", "bob")
+	hl.Handle(ctx) // path does not match
+	if header.Get("user-ext-id") != "" {
+		t.Errorf("failed")
+	}
 	ctx.MockedRequest.MockedPath = func() string {
-		return "/bananas"
+		return "/api/bananas/9281"
 	}
 	hl.Handle(ctx)
 	if header.Get("user-ext-id") != "333" {
 		t.Errorf("failed")
 	}
 	ctx.MockedRequest.MockedPath = func() string {
-		return "/pearls"
+		return "/api/pearls/"
 	}
 	hl.Handle(ctx)
 	if header.Get("user-ext-id") != "4444" {