middleware.RouteHeaders: new middleware to allow header based routing…

… flows (#503)

middleware/middleware.go

@@ -1,5 +1,16 @@
 package middleware
 
+import "net/http"
+
+// New will create a new middleware handler from a http.Handler.
+func New(h http.Handler) func(next http.Handler) http.Handler {
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			h.ServeHTTP(w, r)
+		})
+	}
+}
+
 // contextKey is a value for use with context.WithValue. It's used as
 // a pointer so it fits in an interface{} without allocation. This technique
 // for defining context keys was copied from Go 1.7's new use of context in net/http.

middleware/route_headers.go

@@ -0,0 +1,160 @@
+package middleware
+
+import (
+	"net/http"
+	"strings"
+)
+
+// RouteHeaders is a neat little header-based router that allows you to direct
+// the flow of a request through a middleware stack based on a request header.
+//
+// For example, lets say you'd like to setup multiple routers depending on the
+// request Host header, you could then do something as so:
+//
+// r := chi.NewRouter()
+// rSubdomain := chi.NewRouter()
+//
+// r.Use(middleware.RouteHeaders().
+//   Route("Host", "example.com", middleware.New(r)).
+//   Route("Host", "*.example.com", middleware.New(rSubdomain)).
+//   Handler)
+//
+// r.Get("/", h)
+// rSubdomain.Get("/", h2)
+//
+//
+// Another example, imagine you want to setup multiple CORS handlers, where for
+// your origin servers you allow authorized requests, but for third-party public
+// requests, authorization is disabled.
+//
+// r := chi.NewRouter()
+//
+// r.Use(middleware.RouteHeaders().
+//   Route("Origin", "https://app.skyweaver.net", cors.Handler(cors.Options{
+// 	   AllowedOrigins:   []string{"https://api.skyweaver.net"},
+// 	   AllowedMethods:   []string{"GET", "POST", "PUT", "DELETE", "OPTIONS"},
+// 	   AllowedHeaders:   []string{"Accept", "Authorization", "Content-Type"},
+// 	   AllowCredentials: true, // <----------<<< allow credentials
+//   })).
+//   Route("Origin", "*", cors.Handler(cors.Options{
+// 	   AllowedOrigins:   []string{"*"},
+// 	   AllowedMethods:   []string{"GET", "POST", "PUT", "DELETE", "OPTIONS"},
+// 	   AllowedHeaders:   []string{"Accept", "Content-Type"},
+// 	   AllowCredentials: false, // <----------<<< do not allow credentials
+//   })).
+//   Handler)
+//
+func RouteHeaders() HeaderRouter {
+	return HeaderRouter{}
+}
+
+type HeaderRouter map[string][]HeaderRoute
+
+func (hr HeaderRouter) Route(header string, match string, middlewareHandler func(next http.Handler) http.Handler) HeaderRouter {
+	header = strings.ToLower(header)
+	k := hr[header]
+	if k == nil {
+		hr[header] = []HeaderRoute{}
+	}
+	hr[header] = append(hr[header], HeaderRoute{MatchOne: NewPattern(match), Middleware: middlewareHandler})
+	return hr
+}
+
+func (hr HeaderRouter) RouteAny(header string, match []string, middlewareHandler func(next http.Handler) http.Handler) HeaderRouter {
+	header = strings.ToLower(header)
+	k := hr[header]
+	if k == nil {
+		hr[header] = []HeaderRoute{}
+	}
+	patterns := []Pattern{}
+	for _, m := range match {
+		patterns = append(patterns, NewPattern(m))
+	}
+	hr[header] = append(hr[header], HeaderRoute{MatchAny: patterns, Middleware: middlewareHandler})
+	return hr
+}
+
+func (hr HeaderRouter) RouteDefault(handler func(next http.Handler) http.Handler) HeaderRouter {
+	hr["*"] = []HeaderRoute{{Middleware: handler}}
+	return hr
+}
+
+func (hr HeaderRouter) Handler(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if len(hr) == 0 {
+			// skip if no routes set
+			next.ServeHTTP(w, r)
+		}
+
+		// find first matching header route, and continue
+		for header, matchers := range hr {
+			headerValue := r.Header.Get(header)
+			if headerValue == "" {
+				continue
+			}
+			headerValue = strings.ToLower(headerValue)
+			for _, matcher := range matchers {
+				if matcher.IsMatch(headerValue) {
+					matcher.Middleware(next).ServeHTTP(w, r)
+					return
+				}
+			}
+		}
+
+		// if no match, check for "*" default route
+		matcher, ok := hr["*"]
+		if !ok || matcher[0].Middleware == nil {
+			next.ServeHTTP(w, r)
+			return
+		}
+		matcher[0].Middleware(next).ServeHTTP(w, r)
+	})
+}
+
+type HeaderRoute struct {
+	MatchAny   []Pattern
+	MatchOne   Pattern
+	Middleware func(next http.Handler) http.Handler
+}
+
+func (r HeaderRoute) IsMatch(value string) bool {
+	if len(r.MatchAny) > 0 {
+		for _, m := range r.MatchAny {
+			if m.Match(value) {
+				return true
+			}
+		}
+	} else if r.MatchOne.Match(value) {
+		return true
+	}
+	return false
+}
+
+type Pattern struct {
+	prefix   string
+	suffix   string
+	wildcard bool
+}
+
+func NewPattern(value string) Pattern {
+	p := Pattern{}
+	if i := strings.IndexByte(value, '*'); i >= 0 {
+		p.wildcard = true
+		p.prefix = value[0:i]
+		p.suffix = value[i+1:]
+	} else {
+		p.prefix = value
+	}
+	return p
+}
+
+func (p Pattern) Match(v string) bool {
+	if !p.wildcard {
+		if p.prefix == v {
+			return true
+		} else {
+			return false
+		}
+	}
+	return len(v) >= len(p.prefix+p.suffix) && strings.HasPrefix(v, p.prefix) && strings.HasSuffix(v, p.suffix)
+}