http.sys (7.0 backport): new option for response buffering

[mgravell]

HttpSys: new option for response buffering

8.0 feature: #47776

(same functionally as #48072)

Description

As per old PR 418 (direct copy), enables kernel mode response-buffering in http.sys - with modification to use app-context switch rather than public API change

Customer Impact

Without this buffer, writes are sent as-written direct thru http.sys; this has two problems:

• fragmentation if writes are small
• issues with latency

Regression?

• Yes
• No

[If yes, specify the version the behavior has regressed from]

Risk

• High
• Medium
• Low - opt in, no impact to consumers not using this flag

[Justify the selection above]

Verification

• Manual (required) - will try to verify with internal MSFT consumer (targeting net6.0)
• Automated

Packaging changes reviewed?

• Yes
• No
• N/A

---

When servicing release/2.1

• Make necessary changes in eng/PatchConfig.props

[ghost]

Hi @mgravell. If this is not a tell-mode PR, please make sure to follow the instructions laid out in the servicing process document.
Otherwise, please add tell-mode label.

[adityamandaleeka]

LGTM other than the minor comment.

[mgravell]

@wtgodbe for servicing when possible

[adityamandaleeka]

Tactics mail sent, awaiting approval.

[adityamandaleeka]

Approved.

[ghost]

Hi @mgravell. This PR was just approved to be included in the upcoming servicing release. Somebody from the @dotnet/aspnet-build team will get it merged when the branches are open. Until then, please make sure all the CI checks pass and the PR is reviewed.