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Android batch upload example?

I'm looking for a full example of batch upload (using simple uploads, not chunked) using Android. I have found bits and pieces of info scattered around:

SDK docs for uploadSeesionStartBatch, but these seem to refer to the HTTP docs and don't provide and Android example: https://dropbox.github.io/dropbox-sdk-java/api-docs/v7.0.0/com/dropbox/core/v2/files/DbxUserFilesRequests.html#uploadSessionStartBatch(long,com.dropbox.core.v2.files.UploadSessionType)
This random guide https://developers.dropbox.com/dbx-performance-guide#file-uploads but also doesn't provide an example
This post https://www.dropboxforum.com/t5/Dropbox-API-Support-Feedback/Java-SDK-V2-How-to-do-batch-upload/m-p/195942 which links to an example which doesn't seem to exist anymore: https://github.com/dropbox/dropbox-sdk-java/blob/master/examples/upload-file/src/main/java/com/dropbox/core/examples/upload_file/Main.java#L68
This example https://github.com/dropbox/dropbox-sdk-java/blob/main/examples/android/src/main/java/com/dropbox/core/examples/android/FilesActivity.kt but it seems to only show single uploads, not batch

I'm just looking for an example which shows how all the pieces fit together (sessions, cursors, starting, appending, finishing etc) because I'm really struggling to figure it all out. Does one exist?

Thanks

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Comments

Здравко

Hi @jimbobbles,

Batch upload is very similar to upload a big file using session upload, so you can start with some example showing single big file (more than 150MB) upload - there are such examples; select most familiar one to you. You should use such upload style for both big and small files!

There are 2 main specifics/differences you should keep in mind:

In single file upload you may select whether to finish/close session during last append (or even on start for small files) or on finishing. Most examples upload last piece of data on finishing. In batch upload you DON'T have such a choice; all upload sessions MUST BE FINISHED/CLOSED during last append (or during start for small files)! During batch finishing every passed session has to be finished/closed already.
Instead of finish, finish batch has to be used of course.

Everything else may stay the same. It's up to you whether to start with batch start or not - it's not something mandatory; all upload sessions are the same type.

Hope this gives direction.

Здравко

@henrylopez, Did you check your proposals? 🤔 Is it working in such a way?

Where do you close the sessions?! 😯 Write something check it and when everything works, push here. 😉

Greg-DB

@jimbobbles Here's the current link to the example of using upload sessions in the Java SDK, to replace the broken link you found: https://github.com/dropbox/dropbox-sdk-java/blob/main/examples/examples/src/main/java/com/dropbox/core/examples/upload_file/UploadFileExample.java#L57 This example shows how to use an upload session to upload one large file (and it also earlier in the code shows how to use non-upload session functionality to upload one small file). It doesn't show any of the batch functionality, but it can be useful as an introduction to the concepts of upload sessions, cursors, etc. If you want to add the batch functionality, you could use that as a starting point. Note though that there is no "uploadBatch" method; the batch functionality only exists for upload sessions. You can use upload sessions to upload small files too though; that will still require multiple calls (to start, append, and finish). It's not possible to upload multiple different files in just one call though.

There's also this example, which shows a sample of using some of the upload session batch functionality: https://github.com/dropbox/Developer-Samples/tree/master/Blog/performant_upload That happens to be written in Python, but the logic is the same, since the different SDKs use the same HTTPS API endpoints.

jimbobbles

Thank you very much for the pointers. I think I've nearly pieced everything together, just not sure how to finish the batch:

After calling uploadSessionFinishBatchV2 I get an instance of UploadSessionFinishBatchResult https://dropbox.github.io/dropbox-sdk-java/api-docs/v7.0.0/com/dropbox/core/v2/files/DbxUserFilesRequests.html#uploadSessionFinishBatchV2(java.util.List)

I'm not sure what Im supposed to do with this. Do I somehow need to use this result in combination with uploadSessionFinishBatchCheck to check whether the result is complete, or do I need to keep polling the result entries until they complete, or do I just check the result entries immediately (i.e. is uploadSessionFinishBatchV2 a sync method which only returns once the batch finishing is complete ?) It's a little unclear.

Once I get this working I will post my code for others to use as an example for android.

Здравко

@jimbobbles wrote:
... (i.e. is uploadSessionFinishBatchV2 a sync method which only returns once the batch finishing is complete ?) ...

@jimbobbles, You're correct - version 2 of that method (and API call accordingly) is sync method. The deprecated version 1 can be sync or async - somethin that need to be checked and traced using the check accordingly (something you don't need to consider).

You need to check the success of all returned entries though. You can take a look here or here.

Hope this helps.

jimbobbles

Thank you@"Здравко" and @Greg-DB I think I have this working now, thanks for the pointers. Here's my code, in case this is useful for anyone else attempting to do this. I'm using Flutter so the code is littered with my own error handling classes which I can serialize and pass back to dart, but it should be a decent starting template for others. It's not fully tested, and also I'm new to Kotlin coroutines so I'm not sure I'm using coroutines / async etc. correctly!

import com.dropbox.core.InvalidAccessTokenException
import com.dropbox.core.NetworkIOException
import com.dropbox.core.RetryException
import com.dropbox.core.v2.DbxClientV2
import com.dropbox.core.v2.files.CommitInfo
import com.dropbox.core.v2.files.UploadSessionCursor
import com.dropbox.core.v2.files.UploadSessionFinishArg
import com.dropbox.core.v2.files.UploadSessionFinishErrorException
import com.dropbox.core.v2.files.UploadSessionType
import com.dropbox.core.v2.files.WriteError
import com.dropbox.core.v2.files.WriteMode
import kotlinx.coroutines.Deferred
import timber.log.Timber
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.async
import kotlinx.coroutines.awaitAll
import kotlinx.coroutines.delay
import kotlinx.coroutines.withContext
import java.io.File
import java.io.InputStream


class DropboxWriter {

    companion object {
        private const val BYTES_IN_MEGABYTE = 1048576
        // Must be multiple of 4MB
        // Larger chunk sizes will upload large files faster and usually with fewer network requests
        // but if a chunk upload fails the whole chunk must be re-uploaded
        private const val CHUNKED_UPLOAD_CHUNK_SIZE: Long = 4L * BYTES_IN_MEGABYTE
        // How many times to retry upload (with exponential time backoff) before returning with failure
        private const val MAX_RETRY_ATTEMPTS: Int = 5
    }

    suspend fun writeFilesToDropbox(
        credentialJsonString: String,
        filePaths: List<String>,
        remoteFolderPath: String
     MethodChannelResult<Unit?> = withContext(Dispatchers.IO) {
        assert(filePaths.size <= 1000) { "Max batch size is 1000" }
        Timber.i("Starting batch of ${filePaths.size} upload sessions")

        try {
            val client = DropboxClientFactory.getAuthenticatedClient(credentialJsonString)

            // Tell Dropbox a batch will be uploaded with the given number of files
            val uploadSessionStartBatchResult = client.files().uploadSessionStartBatch(
                filePaths.size.toLong(), UploadSessionType.CONCURRENT)

            // Upload each file in the batch
            val uploadResults: List<MethodChannelResult<UploadSessionFinishArg>> = filePaths.mapIndexed { index, filePath ->
                async {
                    uploadSessionAppend(client, uploadSessionStartBatchResult.sessionIds[index], filePath, remoteFolderPath)
                }
            }.map {it.await()}

            // If there were any failures in uploading
            val failureOrNull = uploadResults.firstOrNull { result -> result is MethodChannelResult.Failure }

            if(failureOrNull != null) {
                // Return the first failure
                return@withContext MethodChannelResult.Failure<Unit?>((failureOrNull as MethodChannelResult.Failure).error)
            }
            else {
                // Else we can now commit the batch using the UploadSessionFinishArgs
                val finishBatchResult = client.files().uploadSessionFinishBatchV2(
                    uploadResults.map{ result -> (result as MethodChannelResult.Success).value }
                )

                // If there were any failures in committing the batch
                val firstCommitFailureOrNull = finishBatchResult.entries.firstOrNull { entry -> entry.isFailure }

                if(firstCommitFailureOrNull != null) {
                    if(firstCommitFailureOrNull.failureValue.isPath
                        && firstCommitFailureOrNull.failureValue.pathValue is WriteError) {

                        // Catch some common errors and return handled error codes
                        if((firstCommitFailureOrNull.failureValue.pathValue as WriteError) == WriteError.INSUFFICIENT_SPACE) {
                            return@withContext MethodChannelResult.Failure(
                                MethodChannelError(BackupErrorCode.INSUFFICIENT_SPACE,"Insufficient space")
                            )
                        }
                        else if((firstCommitFailureOrNull.failureValue.pathValue as WriteError) == WriteError.NO_WRITE_PERMISSION) {
                            return@withContext MethodChannelResult.Failure(
                                MethodChannelError(BackupErrorCode.PERMISSIONS,"No write permission")
                            )
                        }
                    }
                    // Else return the first failure
                    return@withContext MethodChannelResult.Failure<Unit?>(
                        MethodChannelError(
                            BackupErrorCode.UNKNOWN,
                            firstCommitFailureOrNull.failureValue.toString())
                    )
                }
                else {
                    // Upload has succeeded
                    return@withContext MethodChannelResult.Success(null)
                }
            }
        }
        catch (e: Throwable) {
            return@withContext when (e) {
                is NetworkIOException -> {
                    MethodChannelResult.Failure(
                        MethodChannelError(BackupErrorCode.OFFLINE,"Can't reach Dropbox")
                    )
                }
                is InvalidAccessTokenException -> {
                    // Gets thrown when the access token you're using to make API calls is invalid.
                    // A more typical situation is that your access token was valid, but the user has since
                    // "unlinked" your application via the Dropbox website (http://www.dropbox.com/account#applications ).
                    // When a user unlinks your application, your access tokens for that user become invalid.
                    // You can re-run the authorization process to obtain a new access token.
                    MethodChannelResult.Failure(
                        MethodChannelError(
                            BackupErrorCode.AUTHENTICATION_FAILED,
                            e.message ?: "Access token was invalid",
                            e.stackTraceToString())
                    )
                }
                else -> {
                    MethodChannelResult.Failure(
                        MethodChannelError(
                            BackupErrorCode.UNKNOWN,
                            e.message ?: "Unknown error writing to dropbox",
                            e.stackTraceToString())
                    )
                }
            }
        }
    }

    private suspend fun uploadSessionAppend(client: DbxClientV2, sessionId: String,
                                            filePath: String, remoteFolderPath: String): MethodChannelResult<UploadSessionFinishArg> = withContext(Dispatchers.IO) {

        Timber.i("Using upload session with ID '${sessionId}' for file '${filePath}'")
        val file = File(filePath)
        if(file.exists()) {

            val remotePath = "/$remoteFolderPath/${file.name}"

            file.inputStream().buffered().use { bufferedInputStream ->

                val appendTasks: ArrayList<Deferred<Unit>> = arrayListOf()
                val sizeOfFileInBytes = file.length()
                var cursor: UploadSessionCursor? = null

                if(sizeOfFileInBytes > 0L) {
                    var totalNumberOfBytesRead = 0L

                    while(totalNumberOfBytesRead < sizeOfFileInBytes) {
                        cursor = UploadSessionCursor(sessionId, totalNumberOfBytesRead)
                        totalNumberOfBytesRead += CHUNKED_UPLOAD_CHUNK_SIZE
                        val close = totalNumberOfBytesRead >= sizeOfFileInBytes

                        appendTasks.add(
                            async {createAppendChunkTask(
                                client, bufferedInputStream, cursor!!, CHUNKED_UPLOAD_CHUNK_SIZE, sizeOfFileInBytes, close)
                            }
                        )
                    }

                }
                else {
                    // For empty files, just call append once to close the upload session.
                    cursor = UploadSessionCursor(sessionId, 0L)
                    appendTasks.add(
                        async {
                            createAppendChunkTask(
                                client,
                                bufferedInputStream,
                                cursor,
                                chunkSize = 0,
                                sizeOfFileInBytes,
                                close = true
                            )
                        })
                }

                try {
                    awaitAll(*appendTasks.toTypedArray())

                    return@withContext MethodChannelResult.Success(
                        UploadSessionFinishArg(cursor!!, CommitInfo(
                            remotePath,
                            WriteMode.OVERWRITE,
                            false, // autorename
                            null, // clientModified date
                            // Normally, users are made aware of any file modifications in their
                            // Dropbox account via notifications in the client software. If true,
                            // this tells the clients that this modification shouldn't result in a user notification.
                            false,  // mute
                            // List of custom properties to add to file
                            null, // propertyGroups
                            // Be more strict about how each WriteMode detects conflict. For example, always return a conflict error when getMode() = WriteMode.getUpdateValue() and the given "rev" doesn't match the existing file's "rev", even if the existing file has been deleted. This also forces a conflict even when the target path refers to a file with identical contents
                            false // strictConflict
                        ))
                    )
                }
                catch (e: FailedAfterMaxRetryAttemptsException) {
                    return@withContext MethodChannelResult.Failure(
                        MethodChannelError(
                            BackupErrorCode.OFFLINE,
                            e.message!!
                        )
                    )
                }
                catch (e: NetworkIOException) {
                    return@withContext MethodChannelResult.Failure(
                        MethodChannelError(BackupErrorCode.OFFLINE,"Can't reach Dropbox")
                    )
                }
                catch (e: Exception) {
                    return@withContext MethodChannelResult.Failure(
                        MethodChannelError(
                            BackupErrorCode.UNKNOWN,
                            e.message ?: "Unknown error writing to dropbox",
                            e.stackTraceToString())
                    )
                }
            }
        }
        else {
            return@withContext MethodChannelResult.Failure(
                MethodChannelError(
                    BackupErrorCode.UNKNOWN,
                    "Error writing to dropbox: file $filePath does not exist"))
        }
    }


    private suspend fun createAppendChunkTask(
        client: DbxClientV2,
        inputStream: InputStream,
        cursor: UploadSessionCursor,
        chunkSize: Long,
        sizeOfFileInBytes: Long,
        close: Boolean
    ) {
        var mutableCursor = cursor
        var mutableClose = close

        for(i in 0..MAX_RETRY_ATTEMPTS) {
            // Try to upload the chunk
            val result = appendChunkTask(client, inputStream, mutableCursor, chunkSize, mutableClose)
            when(result.type) {
                AppendResult.ResultType.Success -> {
                    return
                }

                // If it fails with a result type of Retry, retry after waiting
                AppendResult.ResultType.Retry -> {
                    // Wait for the specified amount of time
                    delay(result.backoffMillis!!)
                    // and try again next time around the loop
                }

                // If it fails with a result type of RetryWithCorrectedOffset
                AppendResult.ResultType.RetryWithCorrectedOffset -> {
                    // Correct the cursor position
                    mutableCursor = UploadSessionCursor(cursor.sessionId, result.correctedOffset!!)
                    mutableClose = result.correctedOffset + CHUNKED_UPLOAD_CHUNK_SIZE >= sizeOfFileInBytes
                    Timber.w("Append failed because the provided offset ${cursor.offset} " +
                            "should have been ${mutableCursor.offset}, retrying with corrected offset")
                    // and try again next time around the loop
                }
            }
        }
        // If we reach here, uploading the chunk failed after reaching the max
        // number of upload attempts
        throw FailedAfterMaxRetryAttemptsException()
    }

    private fun appendChunkTask(
        client: DbxClientV2,
        inputStream: InputStream,
        cursor: UploadSessionCursor,
        chunkSize: Long,
        close: Boolean
     AppendResult {
        try {
            Timber.d("Appending to upload session with ID '${cursor.sessionId}' " +
                    "at offset: ${cursor.offset}")
            client.files()
                .uploadSessionAppendV2Builder(cursor)
                .withClose(close)
                .uploadAndFinish(inputStream, chunkSize)
            return AppendResult(AppendResult.ResultType.Success)
        }
        catch(e: RetryException) {
            return AppendResult(AppendResult.ResultType.Retry, backoffMillis = e.backoffMillis)
        }
        catch(e: NetworkIOException) {
            return AppendResult(AppendResult.ResultType.Retry)
        }
        catch (e: UploadSessionFinishErrorException) {
            if (e.errorValue.isLookupFailed && e.errorValue.lookupFailedValue.isIncorrectOffset) {
                // server offset into the stream doesn't match our offset (uploaded). Seek to
                // the expected offset according to the server and try again.
                return AppendResult(
                    AppendResult.ResultType.RetryWithCorrectedOffset,
                    correctedOffset = e.errorValue
                        .lookupFailedValue
                        .incorrectOffsetValue
                        .correctOffset)
            } else {
                // some other error occurred
                throw e
            }
        }
    }
}

class FailedAfterMaxRetryAttemptsException() : Exception("Upload failed after reaching maximum number of retries")

class AppendResult(val type: ResultType, val correctedOffset: Long? = null, val backoffMillis: Long? = null) {
    enum class ResultType {
        Success,
        Retry,
        RetryWithCorrectedOffset;
    }
}

enum class BackupErrorCode(val code: Int) {
    UNKNOWN(0),
    OFFLINE(1),
    INSUFFICIENT_SPACE(2),
    PERMISSIONS(3),
    AUTHENTICATION_FAILED(4),
}

sealed class MethodChannelResult<out S> {
    data class Success<out S>(val value: S) : MethodChannelResult<S>()
    data class Failure<out S>(val error: MethodChannelError) : MethodChannelResult<S>()
}

data class MethodChannelError(val code: BackupErrorCode, val message: String, val stackTraceAsString: String? = null)