| 1 | package lease |
| 2 | |
| 3 | import ( |
| 4 | "bytes" |
| 5 | "context" |
| 6 | "encoding/json" |
| 7 | "errors" |
| 8 | "fmt" |
| 9 | "time" |
| 10 | |
| 11 | "github.com/aws/aws-sdk-go-v2/aws" |
| 12 | awss3 "github.com/aws/aws-sdk-go-v2/service/s3" |
| 13 | "github.com/aws/smithy-go" |
| 14 | "github.com/benbjohnson/litestream" |
| 15 | lss3 "github.com/benbjohnson/litestream/s3" |
| 16 | ) |
| 17 | |
| 18 | // errLockPresent is createLease's answer when a lock object exists, live or |
| 19 | // expired: litestream's AcquireLease decides it, as it always has. |
| 20 | var errLockPresent = errors.New("lease: a lock is present") |
| 21 | |
| 22 | // createLease is litestream's AcquireLease for the common case, the lock |
| 23 | // absent (a release deletes it), in one round trip instead of two. It |
| 24 | // writes what AcquireLease writes for an absent lock: generation 1, the |
| 25 | // leaser's owner, now plus its TTL, the same JSON and content type, and the |
| 26 | // same create-only condition (If-None-Match: *). So the lock it leaves, and |
| 27 | // what a reader of it decides, are AcquireLease's. A 412 means a lock is |
| 28 | // there, and errLockPresent hands the decision back to AcquireLease (the |
| 29 | // takeover of an expired lock, the refusal of a live one). Any other error |
| 30 | // is the acquire's, as AcquireLease's own write failing would be. |
| 31 | func createLease(ctx context.Context, client *awss3.Client, l *lss3.Leaser) (*litestream.Lease, error) { |
| 32 | lease := &litestream.Lease{Generation: 1, ExpiresAt: time.Now().Add(l.TTL), Owner: l.Owner} |
| 33 | data, err := json.Marshal(lease) |
| 34 | if err != nil { |
| 35 | return nil, fmt.Errorf("marshal lock file: %w", err) |
| 36 | } |
| 37 | key := lss3.DefaultLeasePath |
| 38 | if l.Path != "" { |
| 39 | key = l.Path + "/" + lss3.DefaultLeasePath |
| 40 | } |
| 41 | out, err := client.PutObject(ctx, &awss3.PutObjectInput{ |
| 42 | Bucket: aws.String(l.Bucket), |
| 43 | Key: aws.String(key), |
| 44 | Body: bytes.NewReader(data), |
| 45 | ContentType: aws.String("application/json"), |
| 46 | IfNoneMatch: aws.String("*"), |
| 47 | }) |
| 48 | if err != nil { |
| 49 | if preconditionFailed(err) { |
| 50 | return nil, errLockPresent |
| 51 | } |
| 52 | return nil, fmt.Errorf("put lock file: %w", err) |
| 53 | } |
| 54 | if out.ETag != nil { |
| 55 | lease.ETag = *out.ETag |
| 56 | } |
| 57 | return lease, nil |
| 58 | } |
| 59 | |
| 60 | // preconditionFailed is litestream's isPreconditionFailed (unexported |
| 61 | // there), plus the 409 S3 answers when two conditional writes of one key |
| 62 | // race: either way a lock is, or is about to be, present. |
| 63 | func preconditionFailed(err error) bool { |
| 64 | var apiErr smithy.APIError |
| 65 | if errors.As(err, &apiErr) { |
| 66 | switch apiErr.ErrorCode() { |
| 67 | case "PreconditionFailed", "412", "ConditionalRequestConflict": |
| 68 | return true |
| 69 | } |
| 70 | } |
| 71 | var opErr *smithy.OperationError |
| 72 | if errors.As(err, &opErr) { |
| 73 | if h, ok := opErr.Err.(interface{ HTTPStatusCode() int }); ok { |
| 74 | return h.HTTPStatusCode() == 412 || h.HTTPStatusCode() == 409 |
| 75 | } |
| 76 | } |
| 77 | return false |
| 78 | } |
| 79 | |
amadan