From f45bf3aa07a7e4850d3827ebb2fe60699c17b6b9 Mon Sep 17 00:00:00 2001
From: Jake Willey <jawilley@microsoft.com>
Date: Thu, 3 Sep 2020 13:46:39 -0700
Subject: [PATCH 1/2] HttpClient: Adds optimization to avoid buffering response
 twice

---
 .../src/HttpClient/CosmosHttpClientCore.cs    | 22 +++++--------------
 1 file changed, 5 insertions(+), 17 deletions(-)

diff --git a/Microsoft.Azure.Cosmos/src/HttpClient/CosmosHttpClientCore.cs b/Microsoft.Azure.Cosmos/src/HttpClient/CosmosHttpClientCore.cs
index 25878406c3..7dbd17711a 100644
--- a/Microsoft.Azure.Cosmos/src/HttpClient/CosmosHttpClientCore.cs
+++ b/Microsoft.Azure.Cosmos/src/HttpClient/CosmosHttpClientCore.cs
@@ -86,6 +86,7 @@ public static CosmosHttpClient CreateWithConnectionPolicy(
             }
 
             HttpClient httpClient = new HttpClient(httpMessageHandler);
+            httpClient.MaxResponseContentBufferSize = 1;
 
             return CosmosHttpClientCore.CreateHelper(
                 httpClient: httpClient,
@@ -184,7 +185,6 @@ ValueTask<HttpRequestMessage> CreateRequestMessage()
 
             return this.SendHttpAsync(
                 CreateRequestMessage,
-                HttpCompletionOption.ResponseHeadersRead,
                 resourceType,
                 diagnosticsContext,
                 cancellationToken);
@@ -195,21 +195,6 @@ public override Task<HttpResponseMessage> SendHttpAsync(
             ResourceType resourceType,
             CosmosDiagnosticsContext diagnosticsContext,
             CancellationToken cancellationToken)
-        {
-            return this.SendHttpAsync(
-                createRequestMessageAsync,
-                HttpCompletionOption.ResponseContentRead,
-                resourceType,
-                diagnosticsContext,
-                cancellationToken);
-        }
-
-        private Task<HttpResponseMessage> SendHttpAsync(
-            Func<ValueTask<HttpRequestMessage>> createRequestMessageAsync,
-            HttpCompletionOption httpCompletionOption,
-            ResourceType resourceType,
-            CosmosDiagnosticsContext diagnosticsContext,
-            CancellationToken cancellationToken)
         {
             diagnosticsContext ??= new CosmosDiagnosticsContextCore();
             HttpRequestMessage requestMessage = null;
@@ -230,9 +215,12 @@ private Task<HttpResponseMessage> SendHttpAsync(
                             resourceType.ToResourceTypeString(),
                             requestMessage.Headers);
 
+                        // Only read the header initially. The content gets copied into a memory stream later
+                        // if we read the content http client will buffer the message and then it will get buffered
+                        // again when it is copied to the memory stream.
                         HttpResponseMessage responseMessage = await this.httpClient.SendAsync(
                                 requestMessage,
-                                httpCompletionOption,
+                                HttpCompletionOption.ResponseHeadersRead,
                                 cancellationToken);
 
                         DateTime receivedTimeUtc = DateTime.UtcNow;

From b3c2b0faeaae4381f221e692a1845c6cbc438fac Mon Sep 17 00:00:00 2001
From: Jake Willey <jawilley@microsoft.com>
Date: Thu, 3 Sep 2020 16:14:11 -0700
Subject: [PATCH 2/2] Removed httpclient buffer setting.

---
 Microsoft.Azure.Cosmos/src/HttpClient/CosmosHttpClientCore.cs | 1 -
 1 file changed, 1 deletion(-)

diff --git a/Microsoft.Azure.Cosmos/src/HttpClient/CosmosHttpClientCore.cs b/Microsoft.Azure.Cosmos/src/HttpClient/CosmosHttpClientCore.cs
index 7dbd17711a..e834f94756 100644
--- a/Microsoft.Azure.Cosmos/src/HttpClient/CosmosHttpClientCore.cs
+++ b/Microsoft.Azure.Cosmos/src/HttpClient/CosmosHttpClientCore.cs
@@ -86,7 +86,6 @@ public static CosmosHttpClient CreateWithConnectionPolicy(
             }
 
             HttpClient httpClient = new HttpClient(httpMessageHandler);
-            httpClient.MaxResponseContentBufferSize = 1;
 
             return CosmosHttpClientCore.CreateHelper(
                 httpClient: httpClient,