| | | 1 | | // Copyright (c) Microsoft Corporation. All rights reserved. |
| | | 2 | | // Licensed under the MIT License. |
| | | 3 | | |
| | | 4 | | using System; |
| | | 5 | | using System.Collections.Generic; |
| | | 6 | | using System.Collections.ObjectModel; |
| | | 7 | | using System.IO; |
| | | 8 | | using System.Linq; |
| | | 9 | | using System.Runtime.ExceptionServices; |
| | | 10 | | using System.Threading; |
| | | 11 | | using System.Threading.Tasks; |
| | | 12 | | using System.Xml; |
| | | 13 | | using System.Xml.Linq; |
| | | 14 | | using Azure; |
| | | 15 | | using Azure.Storage.Blobs; |
| | | 16 | | using Azure.Storage.Blobs.Models; |
| | | 17 | | using Microsoft.AspNetCore.DataProtection.Repositories; |
| | | 18 | | |
| | | 19 | | #pragma warning disable AZC0001 // |
| | | 20 | | namespace Azure.Extensions.AspNetCore.DataProtection.Blobs |
| | | 21 | | #pragma warning restore |
| | | 22 | | { |
| | | 23 | | /// <summary> |
| | | 24 | | /// An <see cref="IXmlRepository"/> which is backed by Azure Blob Storage. |
| | | 25 | | /// </summary> |
| | | 26 | | /// <remarks> |
| | | 27 | | /// Instances of this type are thread-safe. |
| | | 28 | | /// </remarks> |
| | | 29 | | internal sealed class AzureBlobXmlRepository : IXmlRepository |
| | | 30 | | { |
| | | 31 | | private const int ConflictMaxRetries = 5; |
| | 1 | 32 | | private static readonly TimeSpan ConflictBackoffPeriod = TimeSpan.FromMilliseconds(200); |
| | 1 | 33 | | private static readonly XName RepositoryElementName = "repository"; |
| | 1 | 34 | | private static BlobHttpHeaders _blobHttpHeaders = new BlobHttpHeaders() { ContentType = "application/xml; charse |
| | | 35 | | |
| | | 36 | | private readonly Random _random; |
| | | 37 | | private BlobData _cachedBlobData; |
| | | 38 | | private readonly BlobClient _blobClient; |
| | | 39 | | |
| | | 40 | | /// <summary> |
| | | 41 | | /// Creates a new instance of the <see cref="AzureBlobXmlRepository"/>. |
| | | 42 | | /// </summary> |
| | | 43 | | /// <param name="blobClient">A <see cref="BlobClient"/> that is connected to the blob we are reading from and wr |
| | 3 | 44 | | public AzureBlobXmlRepository(BlobClient blobClient) |
| | | 45 | | { |
| | 3 | 46 | | _random = new Random(); |
| | 3 | 47 | | _blobClient = blobClient; |
| | 3 | 48 | | } |
| | | 49 | | |
| | | 50 | | /// <inheritdoc /> |
| | | 51 | | public IReadOnlyCollection<XElement> GetAllElements() |
| | | 52 | | { |
| | | 53 | | // Shunt the work onto a ThreadPool thread so that it's independent of any |
| | | 54 | | // existing sync context or other potentially deadlock-causing items. |
| | | 55 | | |
| | 0 | 56 | | var elements = Task.Run(() => GetAllElementsAsync()).GetAwaiter().GetResult(); |
| | 0 | 57 | | return new ReadOnlyCollection<XElement>(elements); |
| | | 58 | | } |
| | | 59 | | |
| | | 60 | | /// <inheritdoc /> |
| | | 61 | | public void StoreElement(XElement element, string friendlyName) |
| | | 62 | | { |
| | 2 | 63 | | if (element == null) |
| | | 64 | | { |
| | 0 | 65 | | throw new ArgumentNullException(nameof(element)); |
| | | 66 | | } |
| | | 67 | | |
| | | 68 | | // Shunt the work onto a ThreadPool thread so that it's independent of any |
| | | 69 | | // existing sync context or other potentially deadlock-causing items. |
| | | 70 | | |
| | 4 | 71 | | Task.Run(() => StoreElementAsync(element)).GetAwaiter().GetResult(); |
| | 2 | 72 | | } |
| | | 73 | | |
| | | 74 | | private XDocument CreateDocumentFromBlob(byte[] blob) |
| | | 75 | | { |
| | 1 | 76 | | using (var memoryStream = new MemoryStream(blob)) |
| | | 77 | | { |
| | 1 | 78 | | var xmlReaderSettings = new XmlReaderSettings() |
| | 1 | 79 | | { |
| | 1 | 80 | | DtdProcessing = DtdProcessing.Prohibit, IgnoreProcessingInstructions = true |
| | 1 | 81 | | }; |
| | | 82 | | |
| | 1 | 83 | | using (var xmlReader = XmlReader.Create(memoryStream, xmlReaderSettings)) |
| | | 84 | | { |
| | 1 | 85 | | return XDocument.Load(xmlReader); |
| | | 86 | | } |
| | | 87 | | } |
| | 1 | 88 | | } |
| | | 89 | | |
| | | 90 | | private async Task<IList<XElement>> GetAllElementsAsync() |
| | | 91 | | { |
| | 0 | 92 | | var data = await GetLatestDataAsync().ConfigureAwait(false); |
| | | 93 | | |
| | 0 | 94 | | if (data == null || data.BlobContents.Length == 0) |
| | | 95 | | { |
| | | 96 | | // no data in blob storage |
| | 0 | 97 | | return Array.Empty<XElement>(); |
| | | 98 | | } |
| | | 99 | | |
| | | 100 | | // The document will look like this: |
| | | 101 | | // |
| | | 102 | | // <root> |
| | | 103 | | // <child /> |
| | | 104 | | // <child /> |
| | | 105 | | // ... |
| | | 106 | | // </root> |
| | | 107 | | // |
| | | 108 | | // We want to return the first-level child elements to our caller. |
| | | 109 | | |
| | 0 | 110 | | var doc = CreateDocumentFromBlob(data.BlobContents); |
| | 0 | 111 | | return doc.Root.Elements().ToList(); |
| | 0 | 112 | | } |
| | | 113 | | |
| | | 114 | | private async Task<BlobData> GetLatestDataAsync() |
| | | 115 | | { |
| | | 116 | | // Set the appropriate AccessCondition based on what we believe the latest |
| | | 117 | | // file contents to be, then make the request. |
| | | 118 | | |
| | 1 | 119 | | var latestCachedData = Volatile.Read(ref _cachedBlobData); // local ref so field isn't mutated under our fee |
| | 1 | 120 | | var requestCondition = (latestCachedData != null) |
| | 1 | 121 | | ? new BlobRequestConditions() { IfNoneMatch = latestCachedData.ETag } |
| | 1 | 122 | | : null; |
| | | 123 | | |
| | | 124 | | try |
| | | 125 | | { |
| | 1 | 126 | | using (var memoryStream = new MemoryStream()) |
| | | 127 | | { |
| | 1 | 128 | | var response = await _blobClient.DownloadToAsync( |
| | 1 | 129 | | destination: memoryStream, |
| | 1 | 130 | | conditions: requestCondition).ConfigureAwait(false); |
| | | 131 | | |
| | 1 | 132 | | if (response.Status == 304) |
| | | 133 | | { |
| | | 134 | | // 304 Not Modified |
| | | 135 | | // Thrown when we already have the latest cached data. |
| | | 136 | | // This isn't an error; we'll return our cached copy of the data. |
| | 0 | 137 | | return latestCachedData; |
| | | 138 | | } |
| | | 139 | | |
| | | 140 | | // At this point, our original cache either didn't exist or was outdated. |
| | | 141 | | // We'll update it now and return the updated value |
| | 1 | 142 | | latestCachedData = new BlobData() |
| | 1 | 143 | | { |
| | 1 | 144 | | BlobContents = memoryStream.ToArray(), |
| | 1 | 145 | | ETag = response.Headers.ETag |
| | 1 | 146 | | }; |
| | | 147 | | |
| | 1 | 148 | | } |
| | 1 | 149 | | Volatile.Write(ref _cachedBlobData, latestCachedData); |
| | 1 | 150 | | } |
| | 0 | 151 | | catch (RequestFailedException ex) when (ex.Status == 404) |
| | | 152 | | { |
| | | 153 | | // 404 Not Found |
| | | 154 | | // Thrown when no file exists in storage. |
| | | 155 | | // This isn't an error; we'll delete our cached copy of data. |
| | | 156 | | |
| | 0 | 157 | | latestCachedData = null; |
| | 0 | 158 | | Volatile.Write(ref _cachedBlobData, latestCachedData); |
| | 0 | 159 | | } |
| | | 160 | | |
| | 1 | 161 | | return latestCachedData; |
| | 1 | 162 | | } |
| | | 163 | | |
| | | 164 | | private int GetRandomizedBackoffPeriod() |
| | | 165 | | { |
| | | 166 | | // returns a TimeSpan in the range [0.8, 1.0) * ConflictBackoffPeriod |
| | | 167 | | // not used for crypto purposes |
| | 0 | 168 | | var multiplier = 0.8 + (_random.NextDouble() * 0.2); |
| | 0 | 169 | | return (int) (multiplier * ConflictBackoffPeriod.Ticks); |
| | | 170 | | } |
| | | 171 | | |
| | | 172 | | private async Task StoreElementAsync(XElement element) |
| | | 173 | | { |
| | | 174 | | // holds the last error in case we need to rethrow it |
| | 2 | 175 | | ExceptionDispatchInfo lastError = null; |
| | | 176 | | |
| | 6 | 177 | | for (var i = 0; i < ConflictMaxRetries; i++) |
| | | 178 | | { |
| | 3 | 179 | | if (i > 1) |
| | | 180 | | { |
| | | 181 | | // If multiple conflicts occurred, wait a small period of time before retrying |
| | | 182 | | // the operation so that other writers can make forward progress. |
| | 0 | 183 | | await Task.Delay(GetRandomizedBackoffPeriod()).ConfigureAwait(false); |
| | | 184 | | } |
| | | 185 | | |
| | 3 | 186 | | if (i > 0) |
| | | 187 | | { |
| | | 188 | | // If at least one conflict occurred, make sure we have an up-to-date |
| | | 189 | | // view of the blob contents. |
| | 1 | 190 | | await GetLatestDataAsync().ConfigureAwait(false); |
| | | 191 | | } |
| | | 192 | | |
| | | 193 | | // Merge the new element into the document. If no document exists, |
| | | 194 | | // create a new default document and inject this element into it. |
| | | 195 | | |
| | 3 | 196 | | var latestData = Volatile.Read(ref _cachedBlobData); |
| | 3 | 197 | | var doc = (latestData != null) |
| | 3 | 198 | | ? CreateDocumentFromBlob(latestData.BlobContents) |
| | 3 | 199 | | : new XDocument(new XElement(RepositoryElementName)); |
| | 3 | 200 | | doc.Root.Add(element); |
| | | 201 | | |
| | | 202 | | // Turn this document back into a byte[]. |
| | | 203 | | |
| | 3 | 204 | | var serializedDoc = new MemoryStream(); |
| | 3 | 205 | | doc.Save(serializedDoc, SaveOptions.DisableFormatting); |
| | 3 | 206 | | serializedDoc.Position = 0; |
| | | 207 | | |
| | | 208 | | // Generate the appropriate precondition header based on whether or not |
| | | 209 | | // we believe data already exists in storage. |
| | | 210 | | |
| | | 211 | | BlobRequestConditions requestConditions; |
| | 3 | 212 | | if (latestData != null) |
| | | 213 | | { |
| | 1 | 214 | | requestConditions = new BlobRequestConditions() { IfMatch = latestData.ETag }; |
| | | 215 | | } |
| | | 216 | | else |
| | | 217 | | { |
| | 2 | 218 | | requestConditions = new BlobRequestConditions() { IfNoneMatch = ETag.All }; |
| | | 219 | | } |
| | | 220 | | |
| | | 221 | | try |
| | | 222 | | { |
| | | 223 | | // Send the request up to the server. |
| | 3 | 224 | | var response = await _blobClient.UploadAsync( |
| | 3 | 225 | | serializedDoc, |
| | 3 | 226 | | httpHeaders: _blobHttpHeaders, |
| | 3 | 227 | | conditions: requestConditions).ConfigureAwait(false); |
| | | 228 | | |
| | | 229 | | // If we got this far, success! |
| | | 230 | | // We can update the cached view of the remote contents. |
| | | 231 | | |
| | 2 | 232 | | Volatile.Write(ref _cachedBlobData, new BlobData() |
| | 2 | 233 | | { |
| | 2 | 234 | | BlobContents = serializedDoc.ToArray(), |
| | 2 | 235 | | ETag = response.Value.ETag // was updated by Upload routine |
| | 2 | 236 | | }); |
| | | 237 | | |
| | 2 | 238 | | return; |
| | | 239 | | } |
| | | 240 | | catch (RequestFailedException ex) |
| | 1 | 241 | | when (ex.Status == 409 || ex.Status == 412) |
| | | 242 | | { |
| | | 243 | | // 409 Conflict |
| | | 244 | | // This error is rare but can be thrown in very special circumstances, |
| | | 245 | | // such as if the blob in the process of being created. We treat it |
| | | 246 | | // as equivalent to 412 for the purposes of retry logic. |
| | | 247 | | |
| | | 248 | | // 412 Precondition Failed |
| | | 249 | | // We'll get this error if another writer updated the repository and we |
| | | 250 | | // have an outdated view of its contents. If this occurs, we'll just |
| | | 251 | | // refresh our view of the remote contents and try again up to the max |
| | | 252 | | // retry limit. |
| | | 253 | | |
| | 1 | 254 | | lastError = ExceptionDispatchInfo.Capture(ex); |
| | 1 | 255 | | } |
| | 1 | 256 | | } |
| | | 257 | | |
| | | 258 | | // if we got this far, something went awry |
| | 0 | 259 | | lastError.Throw(); |
| | 2 | 260 | | } |
| | | 261 | | |
| | | 262 | | private sealed class BlobData |
| | | 263 | | { |
| | | 264 | | internal byte[] BlobContents; |
| | | 265 | | internal ETag? ETag; |
| | | 266 | | } |
| | | 267 | | } |
| | | 268 | | } |