blob/s3blob: url encode CopySource

[srerickson]

Describe the bug

For s3 buckets, Copy() returns NoSuchKey: The specified key does not exist if the object source key includes the url path escape sequence %2f. See the example below, which uses the source key test/example%2fkey.

I think the problem is that CopyObjectInput.CopySource is supposed to be URL encoded.

To Reproduce

package main

import (
	"context"
	"log"
	"net/url"

	"gocloud.dev/blob"
	_ "gocloud.dev/blob/s3blob"
)

func main() {
	var (
		ctx  = context.Background()
		key  = "test/example%2fkey"
		dst  = "test/copy"
		byts = []byte("testing")
	)
	bucket, err := blob.OpenBucket(ctx, "s3://yourtestbucket?region=us-west-2&awssdk=v2")
	if err != nil {
		log.Fatal(err)
	}
	defer bucket.Close()
	if err := bucket.WriteAll(ctx, key, byts, nil); err != nil {
		log.Fatal(err)
	}

	// works if source key is url-encoded
	if err := bucket.Copy(ctx, dst, url.PathEscape(key), nil); err != nil {
		log.Fatalf("with url encoded source: %v\n", err)
	}

	// but this fails with error: `NoSuchKey: The specified key does not exist`
	if err := bucket.Copy(ctx, dst, key, nil); err != nil {
		log.Fatalf("without url encoded source: %v\n", err)
	}
}

Expected behavior

If an object key works with WriteAll(), I expect it to work withCopy()

Version

go.mod:

go 1.22.1

require gocloud.dev v0.37.0