/// <summary>Constructs a BlobLogBase object.</summary>
/// <param name="container">Indicates the container where log blobs should be placed.</param>
/// <param name="extension">Indicates the extension (initial period is optional) of the log blob.</param>
/// <param name="mimeType">Indicates the mime type of the log blob.</param>
/// <param name="header">Indicates the header (first block) of the log blob. Pass 'null' if you do not want a header.</param>
/// <param name="maxEntries">Indicates the maximum number of blocks the blob should have. Old blocks are deleted when going over this limit.</param>
protected internal BlobLogBase(CloudBlobContainer container, String extension, String mimeType, Byte[] header = null, Int32 maxEntries = 49000)
{
m_container = container;
m_extension = extension.StartsWith(".") ? extension : "." + extension;
m_info = new AppendBlobBlockInfo {
MimeType = mimeType, Header = header, MaxEntries = maxEntries
};
}
/// <summary>Appends a block to the end of a block blob.</summary>
/// <param name="blob">The blob to append a block to.</param>
/// <param name="info">Additional info used when the blob is first being created.</param>
/// <param name="dataToAppend">The data to append as a block to the end of the blob.</param>
/// <param name="options">The blob request options.</param>
/// <param name="operationContext">The operation context.</param>
/// <param name="cancellationToken">The cancellation token.</param>
/// <returns>A Task indicating when the operation has completed.</returns>
public static async Task AppendBlockAsync(this CloudBlockBlob blob, AppendBlobBlockInfo info,
Byte[] dataToAppend, BlobRequestOptions options = null, OperationContext operationContext = null,
CancellationToken cancellationToken = default(CancellationToken))
{
blob.Properties.ContentType = info.MimeType;
//blob.Properties.ContentDisposition = "attachment; filename=\"fname.ext\"";
// NOTE: Put Block ignores access condition and so it always succeeds
List <String> blockList = new List <String>();
while (true)
{
blockList.Clear();
AccessCondition accessCondition;
try {
blockList.AddRange((await blob.DownloadBlockListAsync(BlockListingFilter.Committed,
null, options, operationContext, cancellationToken).ConfigureAwait(false)).Select(lbi => lbi.Name)); // 404 if blob not found
accessCondition = AccessCondition.GenerateIfMatchCondition(blob.Properties.ETag); // Write if blob matches what we read
}
catch (StorageException se) {
if (!se.Matches(HttpStatusCode.NotFound, BlobErrorCodeStrings.BlobNotFound))
{
throw;
}
accessCondition = AccessCondition.GenerateIfNoneMatchCondition("*"); // Write if blob doesn't exist
}
try {
if (blockList.Count == 0) // Blob doesn't exist yet, add header (if specified)
// Notify client code that new blob is about to be created
{
info.OnCreatingBlob(blob);
if (info.Header != null) // Write header to new blob
{
String headerBlockId = Guid.NewGuid().ToString().Encode().ToBase64String();
await blob.PutBlockAsync(headerBlockId, new MemoryStream(info.Header), null).ConfigureAwait(false);
blockList.Add(headerBlockId);
}
}
// Upload new block & add it's Id to the block list
String blockId = Guid.NewGuid().ToString().Encode().ToBase64String();
await blob.PutBlockAsync(blockId, new MemoryStream(dataToAppend), null).ConfigureAwait(false);
blockList.Add(blockId);
// If too many blocks, remove old block (but not the header if it exists)
var maxEntries = info.MaxEntries + ((info.Header == null) ? 0 : 1);
if (blockList.Count > maxEntries)
{
blockList.RemoveAt((info.Header == null) ? 0 : 1);
}
// Upload the new block list
await blob.PutBlockListAsync(blockList, AccessCondition.GenerateIfMatchCondition(blob.Properties.ETag),
options, operationContext, cancellationToken).ConfigureAwait(false); // 409 if blob created behind our back; 400 if block Id doesn't exist (happens in another PC calls PutBlockList after our PutBlock)
break; // If successful, we're done; don't retry
}
catch (StorageException se) {
// Blob got created behind our back, retry
if (se.Matches(HttpStatusCode.Conflict, BlobErrorCodeStrings.BlobAlreadyExists))
{
continue;
}
// Blob got created or modified behind our back, retry
if (se.Matches(HttpStatusCode.PreconditionFailed))
{
continue;
}
// Another PC called PutBlockList between our PutBlock & PutBlockList,
// our block(s) got destroyed, retry
if (se.Matches(HttpStatusCode.BadRequest, BlobErrorCodeStrings.InvalidBlockList))
{
continue;
}
throw;
}
}
}
