feat(storage/transfermanager): prototype #10045
finish tests, some cleanup
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| // Copyright 2024 Google LLC | ||
| // | ||
| // Licensed under the Apache License, Version 2.0 (the "License"); | ||
| // you may not use this file except in compliance with the License. | ||
| // You may obtain a copy of the License at | ||
| // | ||
| // http://www.apache.org/licenses/LICENSE-2.0 | ||
| // | ||
| // Unless required by applicable law or agreed to in writing, software | ||
| // distributed under the License is distributed on an "AS IS" BASIS, | ||
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
| // See the License for the specific language governing permissions and | ||
| // limitations under the License. | ||
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| /* | ||
| Package transfermanager provides an easy way to parallelize downloads in Google | ||
| Cloud Storage. | ||
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| More information about Google Cloud Storage is available at | ||
| https://cloud.google.com/storage/docs. | ||
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| See https://pkg.go.dev/cloud.google.com/go for authentication, timeouts, | ||
| connection pooling and similar aspects of this package. | ||
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| NOTE: This package is in alpha. It is not stable, and is likely to change. | ||
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| # Example usage | ||
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| // Pass in any client opts or set retry policy here | ||
| client, err := storage.NewClient(ctx) // can also use NewGRPCClient | ||
| if err != nil { | ||
| // handle error | ||
| } | ||
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| // Create Downloader with desired options, including number of workers, | ||
| // part size, per operation timeout, etc. | ||
| d, err := transfermanager.NewDownloader(client, transfermanager.WithWorkers(16)) | ||
| if err != nil { | ||
| // handle error | ||
| } | ||
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| // Create local file writer for output | ||
| f, err := os.Create("/path/to/localfile") | ||
| if err != nil { | ||
| // handle error | ||
| } | ||
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| // Create download input | ||
| in := &transfermanager.DownloadObjectInput{ | ||
| Bucket: "mybucket", | ||
| Object: "myblob", | ||
| Destination: f, | ||
| // Optionally specify params to apply to download. | ||
| EncryptionKey: []byte("mykey"), | ||
| } | ||
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| // Can set timeout on this download using context. Note that this download | ||
| // may not start immediately if all workers are busy, so this may time out | ||
| // before the download even starts. To set a timeout that starts with the | ||
| // download, use transfermanager.WithPerOpTimeout(time.Duration). | ||
| ctx, cancel = context.WithTimeout(ctx, 1*time.Minute) | ||
| defer cancel() | ||
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| // Add to Downloader | ||
| d.DownloadObject(ctx, in) | ||
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| // Repeat if desired | ||
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| // Wait for all downloads to complete. | ||
| d.WaitAndClose() | ||
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| // Iterate through completed downloads and process results. This can | ||
| // also happen async in a go routine as the downloads run. | ||
| results := d.Results() | ||
| for _, out := range results { | ||
| if out.Err != nil { | ||
| log.Printf("download of %v failed with error %v", out.Name, out.Err) | ||
| } else { | ||
| log.Printf("download of %v succeeded", out.Object) | ||
| } | ||
| } | ||
| */ | ||
| package transfermanager // import "cloud.google.com/go/storage/transfermanager" |
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What is the expected behavior here if someone calls this without using the Callback option when creating a downloader? Or vice versa with DownloadObject? There are some corner cases to think through here.
I'm leaning towards just having one entry point function for DownloadObject and moving the callback to a field on the DownloadObjectInput -- what do you think?
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I forgot to remove the callback Option - right now it's completely unused. We could enforce it's usage (erroring in the output or here if the option does not match the call); as of now callbacks and no callbacks could be used in the same downloader (and it should work - though it's untested).
I lean towards the two separate entry points. I think the distinction in behaviour is big enough that we should make a similar distinction in our surface - I feel like having it just as a field isn't as nice an experience for people using it and encourages more mixing of using both callback and no callbacks. If we do add it as a field, I'd suggest then also adding the output to the results returned by Results(), in addition to calling the callback if available. That way the callback is more of an optional field that would get called and less of something that will cause different behaviour.
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As discussed offline, we'll enforce usage of the option and set callback as a field.