session token article

Author: vinhms

articles/cosmos-db/how-to-convert-session-token.md

@@ -0,0 +1,110 @@
+---
+title: How to convert session token formats in .NET SDK - Azure Cosmos DB
+description: Learn how to convert session token formats to ensure compatibilities between different .NET SDK versions
+author: vinhms
+ms.service: cosmos-db
+ms.topic: conceptual
+ms.date: 04/30/2020
+ms.author: vitrinh
+---
+
+# Convert session token formats in .NET SDK
+
+This article explains how to convert between different session token formats to ensure compatibility between SDK versions.
+
+> [!NOTE]
+> By default, the SDK keeps track of the session token automatically and it will use the most recent session token.  For more information, please visit [Utilize session tokens](how-to-manage-consistency.md#utilize-session-tokens). This article only applies to the following conditions:
+> * The Azure Cosmos DB account has Session consistency
+> * The session tokens are managed manually
+> * Multiple versions of the SDK are used at the same time
+
+## Session token formats
+
+There are two session token formats: **simple** and **vector**.  These two formats are not interchangeable and will need to be converted when passing to the client with different versions.
+- The **simple** session token format is used by the .NET SDK V1 
+- The **vector** session token format is used by the .NET SDK V2.  
+
+### Simple session token
+
+A simple session token has this format: `{pkrangeid}:{globalLSN}`
+
+### Vector session token
+
+A vector session token has the following format: 
+`{pkrangeid}:{Version}#{GlobalLSN}#{RegionId1}={LocalLsn1}#{RegionId2}={LocalLsn2}....#{RegionIdN}={LocalLsnN}`
+
+## Convert to Simple session token
+
+To pass a session token to client using .NET SDK V1, use a **simple** session token format.  For example, use the following sample code to convert it.
+
+```csharp
+private static readonly char[] SegmentSeparator = (new[] { '#' });
+private static readonly char[] PkRangeSeparator = (new[] { ':' });
+
+string[] items = sessionTokenToConvert.Split(PkRangeSeparator, StringSplitOptions.RemoveEmptyEntries);
+string[] sessionTokenSegments = items[1].Split(SessionTokenHelpers.SegmentSeparator, StringSplitOptions.RemoveEmptyEntries);
+
+string sessionTokenInSimpleFormat;
+
+if (sessionTokenSegments.Length == 1)
+{
+    // returning the same token since it already has the correct format
+    sessionTokenInSimpleFormat = sessionTokenToConvert;
+}
+else
+{
+    long version = 0;
+    long globalLSN = 0;
+
+    if (!long.TryParse(sessionTokenSegments[0], out version)
+        || !long.TryParse(sessionTokenSegments[1], out globalLSN))
+    {
+        throw new ArgumentException("Invalid session token format", sessionTokenToConvert);
+    }
+
+    sessionTokenInSimpleFormat = string.Format("{0}:{1}", items[0], globalLSN);
+}
+```
+
+## Convert to Vector session token
+
+To pass a session token to client using .NET SDK V2, use the **vector** session token format.  For example, use the following sample code to convert it.
+
+```csharp
+
+private static readonly char[] SegmentSeparator = (new[] { '#' });
+private static readonly char[] PkRangeSeparator = (new[] { ':' });
+
+// sessionTokenToConvert = session token from previous response
+string[] items = sessionTokenToConvert.Split(PkRangeSeparator, StringSplitOptions.RemoveEmptyEntries);
+string[] sessionTokenSegments = items[1].Split(SegmentSeparator, StringSplitOptions.RemoveEmptyEntries);
+
+string sessionTokenInVectorFormat;
+
+if (sessionTokenSegments.Length == 1)
+{
+    long globalLSN = 0;
+    if (long.TryParse(sessionTokenSegments[0], out globalLSN))
+    {
+        sessionTokenInVectorFormat = string.Format("{0}:-2#{1}", items[0], globalLSN);
+    }
+    else
+    {
+        throw new ArgumentException("Invalid session token format", sessionTokenToConvert);
+    }
+}
+else
+{
+    // returning the same token since it already has the correct format
+    sessionTokenInVectorFormat = sessionTokenToConvert;
+}
+```
+
+## Next steps
+
+Read the following articles:
+
+* [Use session tokens to manage consistency in Azure Cosmos DB](how-to-manage-consistency.md#utilize-session-tokens)
+* [Choose the right consistency level in Azure Cosmos DB](consistency-levels-choosing.md)
+* [Consistency, availability, and performance tradeoffs in Azure Cosmos DB](consistency-levels-tradeoffs.md)
+* [Availability and performance tradeoffs for various consistency levels](consistency-levels-tradeoffs.md)