Fix HTTP/1.1 concurrent request content read race condition

[MihaZupan]

Fixes the HTTP/1.1 part of #53914 (comment)

From reading the code, it looks like it is possible that the request content will be read multiple times concurrently on HTTP 1:

• Thread A creates an expect100Timer
• Thread A reads an EOF from the server, sees _startedSendingRequestBody == false, sets _canRetry = true and throws an IO exception
• Timer wakes up thread B, signals allowExpect100ToContinue with true and starts reading the request content
• Thread A enters catch, sees sendRequestContentTask hasn't completed, but doesn't await it
• Thread A throws a retryable exception and retries the request on a new connection, reading the request content again
• Both A and B are reading the content, the CT may not be signaled for either

This change fixes that by checking whether allowExpect100ToContinue was already signaled when we encounter an exception and disables retries if so.

[ghost]

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Issue Details

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Fixes the HTTP/1.1 part of #53914 (comment)

From reading the code, it looks like it is possible that the request content will be read multiple times concurrently on HTTP 1:

• Thread A creates an expect100Timer
• Thread A reads an EOF from the server, sees _startedSendingRequestBody == false, sets _canRetry = true and throws an IO exception
• Timer wakes up thread B, signals allowExpect100ToContinue with true and starts reading the request content
• Thread A enters catch, sees sendRequestContentTask hasn't completed, but doesn't await it
• Thread A throws a retryable exception and retries the request on a new connection, reading the request content again
• Both A and B are reading the content, the CT may not be signaled for either

This change fixes that by checking whether allowExpect100ToContinue was already signaled when we encounter an exception and disables retries if so.

Author:	MihaZupan
Assignees:	MihaZupan
Labels:	area-System.Net.Http
Milestone:	8.0.0

[karelz]

Moving to Draft for now as we won't have time to work on it for some time.

[ghost]

Draft Pull Request was automatically closed for 30 days of inactivity. Please let us know if you'd like to reopen it.

[MihaZupan]

@dotnet/ncl if someone gets a chance, this one should be pretty easy to review

[MihaZupan]

Thanks