feat(hono-base): add replaceRequest option for app.mount

[yusukebe]

Resolves #2781

This PR introduces the rewritePath option to app.mount(). With the current spec, if you use app.mount(), the path to pass to your mounted application will be changed. The base path will be removed.

app.mount('/sub-app', subApp.handle)

If you access /sub-app/hello/foo, the subApp receives /hello/foo. This is good behavior for some apps, but it's bad for some apps like #2781.

With the rewritePath option, you can specify the path to pass to the sub-application. If you don't want to remove the base path, you can write the following:

app.mount('/sub-app', subApp.handle, {
  rewritePath: (path) => path,
})

The pain point

The logic will be a little bit complex. As for this, the application size will be slightly increased. Eitherway, I think we can reduce the size in other places.

The author should do the following, if applicable

• Add tests
• Run tests
• bun run format:fix && bun run lint:fix to format the code
• Add TSDoc/JSDoc to document the code

[yusukebe]

Hey @usualoma ! What do you think about this feature?

[yusukebe]

Or, I've created the Mounting Helper:

const app = new Hono()

app.all(
  '/sub-app/*',
  toHandler(subApp.handle, {
    basePath: '/sub-app',
  })
)

This is interesting since the sub-app will act as a handler. It can be separated from hono-base.ts, and we can obsolete app.mount.

But I've noticed this is redundant.

[yusukebe]

Or simply, it is okay to be boolean since I can't imagine the use case of the function if rewritePath is a function.

app.mount('/sub-app', subApp.handle, {
  rewritePath: false,
})

[yusukebe]

@usualoma Sorry for pinging again!

In summary, there are three ways to resolve #2781.

1. rewritePath option - (path: string) => string
2. rewritePath option - boolean
3. Mounting Helper

What do you think about it?

[usualoma]

@yusukebe Sorry, I missed it. I will check now.

[usualoma]

@yusukebe
This PR approach is good! I think the following option is better.

rewritePath option - (path: string) => string

Here, when (path) => path, the Request replacement is unnecessary, and the original c.req.raw can be passed directly to the sub-application. Given that, it seems that we should be providing not a handler for path replacement, but a handler for request replacement. That way, you could do things like (I wonder how much demand there would be) 'add headers in requests to sub-application'.

The following.
#2873

[mvares]

hey @usualoma, I sent an email for you, so could you see? it's about hono

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.91%. Comparing base (8cc8a05) to head (998b01a).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2852      +/-   ##
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+ Coverage   87.88%   87.91%   +0.03%     
==========================================
  Files         139      139              
  Lines       14208    14244      +36     
  Branches     2228     2258      +30     
==========================================
+ Hits        12486    12522      +36     
  Misses       1722     1722              

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[yusukebe]

@usualoma

Thank you for the suggestion and the PR! replaceRequest is good! I've merged the PR to this branch. It's ready to integrate into the main. Maybe I'll release it as a patch release since it's only an update of the options.

[usualoma]

@yusukebe
Thank you!
I think it's good.

Maybe I'll release it as a patch release since it's only an update of the options.