http2: add configuration options when constructing http2 transport

[caesarxuchao]

This allows the caller to change some configurations of the http2 transport when constructing it from an http1 transport.

Fixes golang/go#40201.

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Message from Chao Xu:

Patch Set 1:

This directly solves https://go-review.googlesource.com/c/net/+/198040/18#message-d1a7ce662534f798bb6b6702d6af575bebf41e45.

I'm happy to open an issue in golang/go if that's preferred.

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Message from Russ Cox:

Patch Set 1:

We're closing in on the Go 1.15 beta.
It's probably too late to be adding new API.
Why would you need to change these parameters?

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Message from Chao Xu:

Patch Set 1:

Patch Set 1:

We're closing in on the Go 1.15 beta.
It's probably too late to be adding new API.
Why would you need to change these parameters?

In order to put the health check I added in https://go-review.googlesource.com/c/net/+/198040 in use. The feature by default is off.

Without this change, it's very difficult to change the ReadIdleTimeout and PingTimeout. One would need to use the unsafe package like what I did in the test.

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Message from Chao Xu:

Patch Set 3:

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Message from Michael Fraenkel:

Patch Set 3:

(1 comment)

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Message from Chao Xu:

Patch Set 3:

(1 comment)

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Message from Chao Xu:

Patch Set 3:

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Message from Michael Fraenkel:

Patch Set 3:

(1 comment)

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Message from Chao Xu:

Patch Set 4:

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Message from Bryan C. Mills:

Patch Set 6: Commit message was updated.

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Message from Bryan C. Mills:

Patch Set 6:

(2 comments)

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Message from Brad Fitzpatrick:

Patch Set 6: Code-Review-2

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Message from Chao Xu:

Patch Set 6:

(3 comments)

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Message from Bryan C. Mills:

Patch Set 6:

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Message from Chao Xu:

Patch Set 6:

(1 comment)

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Message from Chao Xu:

Patch Set 6:

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[caesarxuchao]

Superseded by https://go-review.googlesource.com/c/net/+/264017/.