Prevent zero length pipeline (#813)

fixes: https://github.com/azure/azure-sdk-for-cpp/issues/726

sdk/core/azure-core/CHANGELOG.md

@@ -14,6 +14,10 @@
 
 - Add high-level and simplified core.hpp file for simpler include experience for customers.
 
+### Bug Fixes
+
+- Prevent pipeline of length zero to be created.
+
 ## 1.0.0-beta.2 (2020-10-09)
 
 ### Breaking Changes

sdk/core/azure-core/inc/azure/core/http/pipeline.hpp

@@ -37,9 +37,16 @@ namespace Azure { namespace Core { namespace Http {
      *
      * @param policies A sequence of #HttpPolicy representing a stack, first element corresponding
      * to the top of the stack.
+     *
+     * @throw `std::invalid_argument` when policies is empty.
      */
     explicit HttpPipeline(const std::vector<std::unique_ptr<HttpPolicy>>& policies)
     {
+      if (policies.size() == 0)
+      {
+        throw std::invalid_argument("policies cannot be empty");
+      }
+
       m_policies.reserve(policies.size());
       for (auto&& policy : policies)
       {
@@ -52,13 +59,25 @@ namespace Azure { namespace Core { namespace Http {
      *
      * @param policies A sequence of #HttpPolicy representing a stack, first element corresponding
      * to the top of the stack.
+     *
+     * @throw `std::invalid_argument` when policies is empty.
      */
     explicit HttpPipeline(std::vector<std::unique_ptr<HttpPolicy>>&& policies)
         : m_policies(std::move(policies))
     {
+      if (m_policies.size() == 0)
+      {
+        throw std::invalid_argument("policies cannot be empty");
+      }
     }
 
-    /// Copy constructor.
+    /**
+     * @brief Copy constructor.
+     *
+     * @remark \p other is expected to have at least one policy.
+     *
+     * @param other
+     */
     HttpPipeline(const HttpPipeline& other)
     {
       m_policies.reserve(other.m_policies.size());
@@ -78,6 +97,8 @@ namespace Azure { namespace Core { namespace Http {
      */
     std::unique_ptr<RawResponse> Send(Context const& ctx, Request& request) const
     {
+      // Accessing position zero is fine because pipeline must be constructed with at least one
+      // policy.
       return m_policies[0]->Send(ctx, request, NextHttpPolicy(0, &m_policies));
     }
   };

sdk/core/azure-core/test/ut/CMakeLists.txt

@@ -28,6 +28,7 @@ add_executable (
      logging.cpp
      main.cpp
      nullable.cpp
+     pipeline.cpp
      string.cpp
      telemetry_policy.cpp
      transport_adapter.cpp

sdk/core/azure-core/test/ut/pipeline.cpp

@@ -0,0 +1,50 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+#include "gtest/gtest.h"
+#include <azure/core/http/pipeline.hpp>
+#include <azure/core/http/policy.hpp>
+
+#include <vector>
+
+TEST(Logging, createPipeline)
+{
+  // Construct pipeline without exception
+  std::vector<std::unique_ptr<Azure::Core::Http::HttpPolicy>> policies;
+  policies.push_back(std::make_unique<Azure::Core::Http::TelemetryPolicy>("test", "test"));
+
+  EXPECT_NO_THROW(Azure::Core::Http::HttpPipeline pipeline(policies));
+}
+
+TEST(Logging, createEmptyPipeline)
+{
+  // throw invalid arg for empty policies
+  std::vector<std::unique_ptr<Azure::Core::Http::HttpPolicy>> policies;
+  EXPECT_THROW(Azure::Core::Http::HttpPipeline pipeline(policies), std::invalid_argument);
+}
+
+TEST(Logging, clonePipeline)
+{
+  // Construct pipeline without exception and clone
+  std::vector<std::unique_ptr<Azure::Core::Http::HttpPolicy>> policies;
+  policies.push_back(std::make_unique<Azure::Core::Http::TelemetryPolicy>("test", "test"));
+
+  Azure::Core::Http::HttpPipeline pipeline(policies);
+  EXPECT_NO_THROW(Azure::Core::Http::HttpPipeline pipeline2(pipeline));
+}
+
+TEST(Logging, refrefPipeline)
+{
+  // Construct pipeline without exception
+  EXPECT_NO_THROW(Azure::Core::Http::HttpPipeline pipeline(
+      std::vector<std::unique_ptr<Azure::Core::Http::HttpPolicy>>(1)));
+}
+
+TEST(Logging, refrefEmptyPipeline)
+{
+  // Construct pipeline with invalid exception with move constructor
+  EXPECT_THROW(
+      Azure::Core::Http::HttpPipeline pipeline(
+          std::vector<std::unique_ptr<Azure::Core::Http::HttpPolicy>>(0)),
+      std::invalid_argument);
+}