Simplify data verification with HashReader. (#5071)

Verify() was being called by caller after the data
has been successfully read after io.EOF. This disconnection
opens a race under concurrent access to such an object.
Verification is not necessary outside of Read() call,
we can simply just do checksum verification right inside
Read() call at io.EOF.

This approach simplifies the usage.

cmd/api-errors.go

@@ -19,6 +19,8 @@ package cmd
 import (
 	"encoding/xml"
 	"net/http"
+
+	"github.com/minio/minio/pkg/hash"
 )
 
 // APIError structure
@@ -681,8 +683,6 @@ func toAPIErrorCode(err error) (apiErr APIErrorCode) {
 	switch err {
 	case errSignatureMismatch:
 		apiErr = ErrSignatureDoesNotMatch
-	case errContentSHA256Mismatch:
-		apiErr = ErrContentSHA256Mismatch
 	case errDataTooLarge:
 		apiErr = ErrEntityTooLarge
 	case errDataTooSmall:
@@ -701,7 +701,7 @@ func toAPIErrorCode(err error) (apiErr APIErrorCode) {
 	switch err.(type) {
 	case StorageFull:
 		apiErr = ErrStorageFull
-	case BadDigest:
+	case hash.BadDigest:
 		apiErr = ErrBadDigest
 	case AllAccessDisabled:
 		apiErr = ErrAllAccessDisabled
@@ -747,7 +747,7 @@ func toAPIErrorCode(err error) (apiErr APIErrorCode) {
 		apiErr = ErrEntityTooSmall
 	case SignatureDoesNotMatch:
 		apiErr = ErrSignatureDoesNotMatch
-	case SHA256Mismatch:
+	case hash.SHA256Mismatch:
 		apiErr = ErrContentSHA256Mismatch
 	case ObjectTooLarge:
 		apiErr = ErrEntityTooLarge