error: Signature errors should be returned with APIErrorCode.

The reasoning is that we can reply back with wide range of
S3 error responses, which would provide more richer context
to S3 client.

Fixes #1267

generic-handlers.go

@@ -17,7 +17,6 @@
 package main
 
 import (
-	"errors"
 	"net/http"
 	"path"
 	"regexp"
@@ -120,51 +119,43 @@ func (h minioPrivateBucketHandler) ServeHTTP(w http.ResponseWriter, r *http.Requ
 	h.handler.ServeHTTP(w, r)
 }
 
-// Supported incoming date formats.
-var timeFormats = []string{
+// Supported Amz date formats.
+var amzDateFormats = []string{
 	time.RFC1123,
 	time.RFC1123Z,
 	iso8601Format,
+	// Add new AMZ date formats here.
 }
 
-// Attempts to parse date string into known date layouts. Date layouts
-// currently supported are
-//  - ``time.RFC1123``
-//  - ``time.RFC1123Z``
-//  - ``iso8601Format``
-func parseDate(date string) (parsedTime time.Time, e error) {
-	for _, layout := range timeFormats {
-		parsedTime, e = time.Parse(layout, date)
+// parseAmzDate - parses date string into supported amz date formats.
+func parseAmzDate(amzDateStr string) (amzDate time.Time, apiErr APIErrorCode) {
+	for _, dateFormat := range amzDateFormats {
+		amzDate, e := time.Parse(dateFormat, amzDateStr)
 		if e == nil {
-			return parsedTime, nil
+			return amzDate, ErrNone
 		}
 	}
-	return time.Time{}, e
+	return time.Time{}, ErrMalformedDate
 }
 
-// Parse date string from incoming header, current supports and verifies
-// follow HTTP headers.
-//
-//  - X-Amz-Date
-//  - X-Minio-Date
-//  - Date
-//
-// In following time layouts ``time.RFC1123``, ``time.RFC1123Z`` and
-// ``iso8601Format``.
-var dateHeaders = []string{
+// Supported Amz date headers.
+var amzDateHeaders = []string{
 	"x-amz-date",
 	"x-minio-date",
 	"date",
 }
 
-func parseDateHeader(req *http.Request) (time.Time, error) {
-	for _, dateHeader := range dateHeaders {
-		date := req.Header.Get(http.CanonicalHeaderKey(dateHeader))
-		if date != "" {
-			return parseDate(date)
+// parseAmzDateHeader - parses supported amz date headers, in
+// supported amz date formats.
+func parseAmzDateHeader(req *http.Request) (time.Time, APIErrorCode) {
+	for _, amzDateHeader := range amzDateHeaders {
+		amzDateStr := req.Header.Get(http.CanonicalHeaderKey(amzDateHeader))
+		if amzDateStr != "" {
+			return parseAmzDate(amzDateStr)
 		}
 	}
-	return time.Time{}, errors.New("Date header missing, invalid request.")
+	// Date header missing.
+	return time.Time{}, ErrMissingDateHeader
 }
 
 type timeHandler struct {
@@ -179,17 +170,17 @@ func setTimeValidityHandler(h http.Handler) http.Handler {
 func (h timeHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	// Verify if date headers are set, if not reject the request
 	if _, ok := r.Header["Authorization"]; ok {
-		date, e := parseDateHeader(r)
-		if e != nil {
+		amzDate, apiErr := parseAmzDateHeader(r)
+		if apiErr != ErrNone {
 			// All our internal APIs are sensitive towards Date
 			// header, for all requests where Date header is not
 			// present we will reject such clients.
-			writeErrorResponse(w, r, ErrRequestTimeTooSkewed, r.URL.Path)
+			writeErrorResponse(w, r, apiErr, r.URL.Path)
 			return
 		}
 		// Verify if the request date header is more than 5minutes
 		// late, reject such clients.
-		if time.Now().UTC().Sub(date)/time.Minute > time.Duration(5)*time.Minute {
+		if time.Now().UTC().Sub(amzDate)/time.Minute > time.Duration(5)*time.Minute {
 			writeErrorResponse(w, r, ErrRequestTimeTooSkewed, r.URL.Path)
 			return
 		}