Configurable target URI rewrites

[tgeoghegan]

Add a TARGET_REWRITES environment variable that allows rewriting the URI in an encapsulated request. See changes to README.md for discussion of motivation and utilization.

Closes #56

[tgeoghegan]

If the maintainers agree with this approach, then I'd be happy to add some tests to exercise it.

[bwesterb]

I don't see this happening in the code change.

[tgeoghegan]

Yeah, I will add a test that exercises the target rewrite feature before merging this.

[cjpatton]

The documentation should clarify whether the set up described is suitable for production OHTTP deployment.

If the maintainers agree with this approach, then I'd be happy to add some tests to exercise it.

The approach seems reasonable, go ahead and work on tests. Are unit tests feasible?

[tgeoghegan]

The documentation should clarify whether the set up described is suitable for production OHTTP deployment.

As I explained in #56, I do want this for production setups, assuming the maintainers agree this isn't dangerous in some way I haven't seen.

If the maintainers agree with this approach, then I'd be happy to add some tests to exercise it.

The approach seems reasonable, go ahead and work on tests. Are unit tests feasible?

Yeah, I can copy some setup from the existing tests to exercise this.

[tgeoghegan]

I had to refactor these tests a little because the mock gateway created in createMockEchoGatewayServer never actually used FilteredHttpRequestHandler, which is where both forbidden/allowed origins and target rewrites are implemented. Now, instead of using ForbiddenCheckHttpRequestHandler which would just fire metrics and send a canned response, we wire MockHttpRequestHandler into ProtoHTTPAppHandler or BinaryHTTPAppHandler. FilteredHttpRequestHandler takes an implementation of interface HttpRequestHandler so that we can swap out MockHttpRequestHandler instead of a real http.Client.

@bwesterb, @cjpatton: PTAL

[bwesterb]

Looks good to me. Just need approval from a second owner.

[cjpatton]

Looks good to me. Just need approval from a second owner.

in my queue.

[cjpatton]

Change looks pretty good, just one question.

Plus: unfortunately we have a mix of "Http" and "HTTP" in this codebase. For new variables I'd like to lean towards "HTTP" as it matches Go convention.

[cjpatton]

LGTM, @tgeoghegan. Please squash and I'll merge.