Implement S3 Style ErrorCodes and Response

This patchset also brings in lot of cleanup in terms of minioapi codebase

pkg/api/minioapi/handler.go

@@ -0,0 +1,90 @@
+package minioapi
+
+import (
+	"net/http"
+	"strings"
+
+	"github.com/minio-io/minio/pkg/utils/config"
+	"github.com/minio-io/minio/pkg/utils/crypto/signers"
+)
+
+type vHandler struct {
+	conf    config.Config
+	handler http.Handler
+}
+
+// grab AccessKey from authorization header
+func stripAccessKey(r *http.Request) string {
+	fields := strings.Fields(r.Header.Get("Authorization"))
+	if len(fields) < 2 {
+		return ""
+	}
+	splits := strings.Split(fields[1], ":")
+	if len(splits) < 2 {
+		return ""
+	}
+	return splits[0]
+}
+
+func validateHandler(conf config.Config, h http.Handler) http.Handler {
+	return vHandler{conf, h}
+}
+
+func (h vHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	accessKey := stripAccessKey(r)
+	if accessKey != "" {
+		if err := h.conf.ReadConfig(); err != nil {
+			w.WriteHeader(http.StatusInternalServerError)
+		} else {
+			user := h.conf.GetKey(accessKey)
+			ok, err := signers.ValidateRequest(user, r)
+			if ok {
+				h.handler.ServeHTTP(w, r)
+			} else {
+				w.WriteHeader(http.StatusUnauthorized)
+				w.Write([]byte(err.Error()))
+			}
+		}
+	} else {
+		//No access key found, handle this more appropriately
+		//TODO: Remove this after adding tests to support signature
+		//request
+		h.handler.ServeHTTP(w, r)
+		//Add this line, to reply back for invalid requests
+		//w.WriteHeader(http.StatusUnauthorized)
+		//w.Write([]byte("Authorization header malformed")
+	}
+}
+
+func ignoreUnimplementedResources(h http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if ignoreUnImplementedObjectResources(r) || ignoreUnImplementedBucketResources(r) {
+			w.WriteHeader(http.StatusNotImplemented)
+		} else {
+			h.ServeHTTP(w, r)
+		}
+	})
+}
+
+//// helpers
+
+// Checks requests for unimplemented resources
+func ignoreUnImplementedBucketResources(req *http.Request) bool {
+	q := req.URL.Query()
+	for name := range q {
+		if unimplementedBucketResourceNames[name] {
+			return true
+		}
+	}
+	return false
+}
+
+func ignoreUnImplementedObjectResources(req *http.Request) bool {
+	q := req.URL.Query()
+	for name := range q {
+		if unimplementedObjectResourceNames[name] {
+			return true
+		}
+	}
+	return false
+}