Allow configuration of chunksize parameter

The code using values from the yaml package wasn't careful enought with the
possible incoming types. Turns out, it is just an int but we've made this
section somewhat bulletproof in case that package changes the behavior.

This code likely never worked. The configuration system should be decoupled
from the object instantiation.

Signed-off-by: Stephen J Day <stephen.day@docker.com>

docs/storage/driver/s3/s3.go

@@ -20,6 +20,7 @@ import (
 	"io"
 	"io/ioutil"
 	"net/http"
+	"reflect"
 	"strconv"
 	"strings"
 	"time"
@@ -148,9 +149,23 @@ func FromParameters(parameters map[string]interface{}) (*Driver, error) {
 	chunkSize := int64(defaultChunkSize)
 	chunkSizeParam, ok := parameters["chunksize"]
 	if ok {
-		chunkSize, ok = chunkSizeParam.(int64)
-		if !ok || chunkSize < minChunkSize {
-			return nil, fmt.Errorf("The chunksize parameter should be a number that is larger than 5*1024*1024")
+		switch v := chunkSizeParam.(type) {
+		case string:
+			vv, err := strconv.ParseInt(v, 0, 64)
+			if err != nil {
+				return nil, fmt.Errorf("chunksize parameter must be an integer, %v invalid", chunkSizeParam)
+			}
+			chunkSize = vv
+		case int64:
+			chunkSize = v
+		case int, uint, int32, uint32, uint64:
+			chunkSize = reflect.ValueOf(v).Convert(reflect.TypeOf(chunkSize)).Int()
+		default:
+			return nil, fmt.Errorf("invalid valud for chunksize: %#v", chunkSizeParam)
+		}
+
+		if chunkSize <= minChunkSize {
+			return nil, fmt.Errorf("The chunksize %#v parameter should be a number that is larger than or equal to %d", chunkSize, minChunkSize)
 		}
 	}