Add persistent storage to exporter - Public API (#1359)

* Storage Public API

* PR feedback

* Renamed from IOffline to IPersistent

* Update copyright

* PutBlob with IPersistentBlob

* Reword GetBlobs

* Change PutBlob signature

* Update Lease summary

* Update src/OpenTelemetry.Shared/IPersistentBlob.cs

Co-authored-by: Reiley Yang <reyang@microsoft.com>

* PR feedback

Co-authored-by: Cijo Thomas <cithomas@microsoft.com>
Co-authored-by: Reiley Yang <reyang@microsoft.com>

OpenTelemetry.sln

@@ -202,6 +202,8 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "OpenTelemetry.Exporter.InMe
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "extending-the-sdk", "docs\logs\extending-the-sdk\extending-the-sdk.csproj", "{13C10C9A-07E8-43EB-91F5-C2B116FBE0FC}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "OpenTelemetry.Shared", "src\OpenTelemetry.Shared\OpenTelemetry.Shared.csproj", "{1E504265-1E32-4C61-8CC5-8FA373E16699}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -396,6 +398,10 @@ Global
 		{13C10C9A-07E8-43EB-91F5-C2B116FBE0FC}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{13C10C9A-07E8-43EB-91F5-C2B116FBE0FC}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{13C10C9A-07E8-43EB-91F5-C2B116FBE0FC}.Release|Any CPU.Build.0 = Release|Any CPU
+		{1E504265-1E32-4C61-8CC5-8FA373E16699}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{1E504265-1E32-4C61-8CC5-8FA373E16699}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{1E504265-1E32-4C61-8CC5-8FA373E16699}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{1E504265-1E32-4C61-8CC5-8FA373E16699}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE

src/OpenTelemetry.Shared/IPersistentBlob.cs

@@ -0,0 +1,62 @@
+// <copyright file="IPersistentBlob.cs" company="OpenTelemetry Authors">
+// Copyright The OpenTelemetry Authors
+//
+// 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.
+// </copyright>
+
+namespace OpenTelemetry.Shared
+{
+    /// <summary>
+    /// API to Read, Write and Delete a blob.
+    /// </summary>
+    public interface IPersistentBlob
+    {
+        /// <summary>
+        /// Read content of a blob from storage.
+        /// </summary>
+        /// <returns>
+        /// Blob content.
+        /// </returns>
+        public byte[] Read();
+
+        /// <summary>
+        /// Write a blob content to storage.
+        /// </summary>
+        /// <param name="buffer">
+        /// Buffer to write to storage.
+        /// </param>
+        /// <param name="leasePeriodMilliseconds">
+        /// Lease period in milliseconds.
+        /// </param>
+        /// <returns>
+        /// A blob if there is an available one, or null if there is no blob available.
+        /// </returns>
+        public IPersistentBlob Write(byte[] buffer, int leasePeriodMilliseconds = 0);
+
+        /// <summary>
+        /// Create and manage a lease on the blob.
+        /// </summary>
+        /// <param name="leasePeriodMilliseconds">
+        /// Lease period in milliseconds.
+        /// </param>
+        /// <returns>
+        /// A blob if there is an available one, or null if there is no blob available.
+        /// </returns>
+        public IPersistentBlob Lease(int leasePeriodMilliseconds);
+
+        /// <summary>
+        /// Attempt to delete the blob.
+        /// </summary>
+        public void Delete();
+    }
+}

src/OpenTelemetry.Shared/IPersistentStorage.cs

@@ -0,0 +1,57 @@
+// <copyright file="IPersistentStorage.cs" company="OpenTelemetry Authors">
+// Copyright The OpenTelemetry Authors
+//
+// 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.
+// </copyright>
+
+using System.Collections.Generic;
+
+namespace OpenTelemetry.Shared
+{
+    /// <summary>
+    /// Persistent storage API.
+    /// </summary>
+    public interface IPersistentStorage
+    {
+        /// <summary>
+        /// Read a sequence of blobs from storage.
+        /// </summary>
+        /// <returns>
+        /// Sequence of blobs from storage.
+        /// </returns>
+        public IEnumerable<IPersistentBlob> GetBlobs();
+
+        /// <summary>
+        /// Attempt to get a blob from storage.
+        /// This function never throws.
+        /// </summary>
+        /// <returns>
+        /// A blob if there is an available one, or null if there is no blob available.
+        /// </returns>
+        IPersistentBlob GetBlob();
+
+        /// <summary>
+        /// Create a new blob with the provided data.
+        /// </summary>
+        /// <param name="buffer">
+        /// Blob content.
+        /// </param>
+        /// <param name="leasePeriodMilliseconds">
+        /// Lease period in milliseconds.
+        /// </param>
+        /// <returns>
+        /// A blob if there is an available one, or null if there is no blob available.
+        /// </returns>
+        public IPersistentBlob CreateBlob(byte[] buffer, int leasePeriodMilliseconds = 0);
+    }
+}

src/OpenTelemetry.Shared/OpenTelemetry.Shared.csproj

@@ -0,0 +1,13 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFrameworks>net452;net46;net461;netstandard2.0</TargetFrameworks>
+    <Description>Shared project for OpenTelemetry .NET</Description>
+    <PackageTags>$(PackageTags);Shared</PackageTags>
+  </PropertyGroup>
+
+  <PropertyGroup>
+    <NoWarn>$(NoWarn),1591</NoWarn>
+  </PropertyGroup>
+
+</Project>