1 files changed, 79 insertions, 0 deletions

diff --git a/httputil/negotiate.go b/httputil/negotiate.go
new file mode 100644
index 0000000..6af3e4c
--- /dev/null
+++ b/httputil/negotiate.go
@@ -0,0 +1,79 @@
+// Copyright 2013 The Go Authors. All rights reserved.
+//
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file or at
+// https://developers.google.com/open-source/licenses/bsd.
+
+package httputil
+
+import (
+        "github.com/golang/gddo/httputil/header"
+        "net/http"
+        "strings"
+)
+
+// NegotiateContentEncoding returns the best offered content encoding for the
+// request's Accept-Encoding header. If two offers match with equal weight and
+// then the offer earlier in the list is preferred. If no offers are
+// acceptable, then "" is returned.
+func NegotiateContentEncoding(r *http.Request, offers []string) string {
+        bestOffer := "identity"
+        bestQ := -1.0
+        specs := header.ParseAccept(r.Header, "Accept-Encoding")
+        for _, offer := range offers {
+                for _, spec := range specs {
+                        if spec.Q > bestQ &&
+                                (spec.Value == "*" || spec.Value == offer) {
+                                bestQ = spec.Q
+                                bestOffer = offer
+                        }
+                }
+        }
+        if bestQ == 0 {
+                bestOffer = ""
+        }
+        return bestOffer
+}
+
+// NegotiateContentType returns the best offered content type for the request's
+// Accept header. If two offers match with equal weight, then the more specific
+// offer is preferred.  For example, text/* trumps */*. If two offers match
+// with equal weight and specificity, then the offer earlier in the list is
+// preferred. If no offers match, then defaultOffer is returned.
+func NegotiateContentType(r *http.Request, offers []string, defaultOffer string) string {
+        bestOffer := defaultOffer
+        bestQ := -1.0
+        bestWild := 3
+        specs := header.ParseAccept(r.Header, "Accept")
+        for _, offer := range offers {
+                for _, spec := range specs {
+                        switch {
+                        case spec.Q == 0.0:
+                                // ignore
+                        case spec.Q < bestQ:
+                                // better match found
+                        case spec.Value == "*/*":
+                                if spec.Q > bestQ || bestWild > 2 {
+                                        bestQ = spec.Q
+                                        bestWild = 2
+                                        bestOffer = offer
+                                }
+                        case strings.HasSuffix(spec.Value, "/*"):
+                                if strings.HasPrefix(offer, spec.Value[:len(spec.Value)-1]) &&
+                                        (spec.Q > bestQ || bestWild > 1) {
+                                        bestQ = spec.Q
+                                        bestWild = 1
+                                        bestOffer = offer
+                                }
+                        default:
+                                if spec.Value == offer &&
+                                        (spec.Q > bestQ || bestWild > 0) {
+                                        bestQ = spec.Q
+                                        bestWild = 0
+                                        bestOffer = offer
+                                }
+                        }
+                }
+        }
+        return bestOffer
+}