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net/http: Expose the normal transport RoundTripper for WASM/js #27495

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antong opened this issue Sep 4, 2018 · 9 comments

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@antong
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@antong antong commented Sep 4, 2018

On WASM, the standard http.Transfer RoundTripper is not exposed for external use. Buildflags for wasm replace the standard implementation of RoundTripper with a special version that uses the browser Fetch API. The special JS RoundTripper does not seem to use or honor any of the documented settings provided by http.Transport, such as Dial or DialContext. But the way the special JS RoundTripper is implemented as methods on http.Transport, it prevents using the standard RoundTripper.

There are use cases for using the normal RoundTripper, for instance for testing and simulation in the browser. The normal RoundTripper is compiled and included in the binary anyway, and works perfectly well, but is masked by the browser version.

What version of Go are you using (go version)?

go1.11

What operating system and processor architecture are you using (go env)?

GOOS=js
GOARCH=wasm

What did you do?

I tried to configure a http.Client to use a transport with a custom dial function:
https://play.golang.org/p/dnyTivQ643J

This works on all other platforms including the playground, but on WASM, the same, special Roundtripper is always used and there is no way to use the standard Roundtripper.

What did you expect to see?

Get https://api.ipify.org/: expected error, all ok

What did you see instead?

On WASM:

192.0.2.77
Done.

On other platforms, I get the expected result

@andybons

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@andybons andybons commented Sep 4, 2018

@antong

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@antong antong commented Sep 4, 2018

I quickly tested two hacks to do this, and both seemed to work. Both pass the tests on normal platforms, but I don't know how to run the unit tests on WASM.

Hack 1: Don't implement the special RoundTripper on http.Transport, but make an own jsTransport. Set an instance of this as http.DefaultTransport for GOARCH=wasm. Example: e8050da

Hack 2: Mod the special RoundTripper to instead use the normal RoundTripper if the caller has set options on the Transport. Example: 8137bf5

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@agnivade agnivade commented Sep 4, 2018

@dmitshur

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@dmitshur dmitshur commented Sep 4, 2018

This is also related to #25695.

@rubensayshi

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@rubensayshi rubensayshi commented Mar 7, 2019

running into this problem when trying to do HTTPS requests in wasm/js (using self signed certs over a websocket connection).

e8050da seems like an easy and clean solution to enable a lot more flexibility when desired.

as far as I can tell the only place where http.Client and http.Transport are coupled to something that does not work in wasm/js is the DefaultTransport using net.Dialer{}).DialContext.
Given a working net.Dialer the code in roundTrip actually works just fine.

I understand #25695 discusses a more major problem, but specially considering the impact of fixing that as a whole, maybe a simple fix like this would be a good start?

@johanbrandhorst

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@johanbrandhorst johanbrandhorst commented Mar 7, 2019

I agree Hack 1 as proposed by @antong is a reasonable short term approach. Are you interested in contributing this?

@antong

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@antong antong commented Mar 7, 2019

Sure! Do you mean that I should make a CL based on Hack 1 (e8050da)?

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@johanbrandhorst johanbrandhorst commented Mar 7, 2019

Yes, that sounds good.

antong added a commit to antong/go that referenced this issue Mar 11, 2019
Implement a separate type jsTransport that implements RoundTripper using
the WHATWG Fetch API, and make it the DefaultTransport on js/wasm. This
allows using the standard Transport implementation on js/wasm by
specifying a DialContext for the Transport. Note that the default would
use net.Dial, that can not be used in the browser.

Before this change the same Transport type was used also on js, but with
a different implementation. This implementation disregarded any of the
documented Transport settings and just used the browser Fetch API. This
made it impossible to use the Transport implementation, e.g., by
supplying a DialContext that works in the browser.

Fixes golang#27495
antong added a commit to antong/go that referenced this issue Mar 11, 2019
Implement a separate type jsTransport that implements RoundTripper using
the WHATWG Fetch API, and make it the DefaultTransport on js/wasm. This
allows using the standard Transport implementation on js/wasm by
specifying a DialContext for the Transport. Note that the default would
use net.Dial, that can not be used in the browser.

Before this change the same Transport type was used also on js, but with
a different implementation. This implementation disregarded any of the
documented Transport settings and just used the browser Fetch API. This
made it impossible to use the Transport implementation, e.g., by
supplying a DialContext that works in the browser.

Fixes golang#27495
@gopherbot

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@gopherbot gopherbot commented Mar 11, 2019

Change https://golang.org/cl/166617 mentions this issue: net/http: expose standard transport for js

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