proposal: net/http: thoughts for Go 2.0

[bradfitz]

Wishlist bug for what net/http would look like if we could make backwards-incompatible
changes.

Anything goes.

I'll start:

* Handler (http://golang.org/pkg/net/http/#Handler) currently takes a pointer to a 208
byte Request struct.  

* The Request struct (http://golang.org/pkg/net/http/#Request) has all its fields
publicly exposed, most of which require memory allocation:

  -- Method
  -- URL (itself 104 bytes, with a bunch of strings requiring allocation)
  -- Header map + slices + strings (even if never accessed)
  -- TransferEncoding slice (even if not accessed)
  -- Host string (even if not accessed)
  -- RemoteAddr string (even if not accessed)
  -- RequestURI (even if not accessed)
  -- TLS state struct (even if not accessed)

For a lightweight handler that doesn't touch anything (say, serves some static content
from memory), this means we can't do any better than generating ~1KB of garbage per
request.

I'd prefer to make a ServerRequest interface with accessor methods which can generate
needed data on demand.

This would also simplify our docs on our doubly-abused-in-different-ways *Request, which
contains documentation gems like:

    // PostForm contains the parsed form data from POST or PUT
    // body parameters.
    // This field is only available after ParseForm is called.
    // The HTTP client ignores PostForm and uses Body instead.
    PostForm url.Values

If we had byte views (issue #5376), I would also say that most fields in the
ServerRequest, URL, Header, and FormValues are all byte views with validity scoped to
the duration of the http.Handler call, instead of strings.

[nigeltao]

Comment 1:

A CookieJar's methods should return error, and maybe be renamed from http.CookieJar to
cookiejar.Interface.

[gopherbot]

Comment 2 by robryk:

In http.Client, there should be a uniform way of specifying request headers on the
initial request and subsequent requests when following a redirect. Current the
Request.Header field is useless if the request might get redirected. See issue #5782.
Maybe something like a func(*Request) field in the request, that gets called on this
request and each redirected one before it gets sent?

[gopherbot]

Comment 3 by jeff.allen:

The fact that headers are parsed into a map is a mega bummer for garbage reduction. If
the main way headers were exposed was more opaque, the headers map could be made up of
offsets into the buffer that came straight from Read.

[rsc]

Comment 4:

Labels changed: added repo-main.

[nigeltao]

Comment 5:

Related to comment #1, net/http/cookiejar.PublicSuffixList's PublicSuffix method should
perhaps return (string, error) instead of (string), in case the PSL implementation is
passed non-canonicalized input such as upper-cased "EXAMPLE.COM.AU". Returning an
explicit error is probably safer than silently returning a "" that would mean a liberal
cookie policy.

[alberts]

Comment 6:

It would be nice to have a handle on when all the goroutines that handle requests have
terminated after closing the listener (thereby breaking out of the accept loop) for
cases where they are using a shared resource that needs to be cleaned up (e.g. an
in-process database that needs to be closed). And maybe a way to force-close all their
connections. Especially useful for tests and SIGTERM situations.

[gopherbot]

Comment 7 by robryk:

You can do that by counting open connections returned by Listener's
Accept: http://play.golang.org/p/sPmvXaR-2M
(Disclaimer: I didn't test that code.)
Robert

[alberts]

Comment 8:

@Robert thanks, I did something similar in the end.

[alberts]

Comment 9:

@Robert For what it's worth, I think your listener breaks in the more general case where
you hand off the socket to both a reader and a writer goroutine. There a "done" channel
might be better.

[gopherbot]

Comment 10 by robryk:

Summarizing a discussion with fullung@: That version didn't handle multiple calls to
Close and had a (likely irrelevant) ReadWrite/Close race condition. The corrected
version is here: http://play.golang.org/p/WTKa021ipJ

[gopherbot]

Comment 11 by robryk:

Summarizing a discussion with fullung@: That version didn't handle multiple calls to
Close and had a (likely irrelevant) ReadWrite/Close race condition. The corrected
version is here: http://play.golang.org/p/WTKa021ipJ

[rsc]

Comment 12:

Labels changed: added release-none.

[gopherbot]

Comment 13 by robryk:

We have http.StripPrefix which modifies Request.URL.Path and passes the modified request
to a handler. We also have http.Redirect, which assumes that Request.URL.Path is
absolute.
Thus, if one tries to use http.Redirect within a handler that is wrapped in
http.StripPrefix the redirect will point to a wrong URL. In fact, we don't use
http.Redirect in http.FileServer for this very reason:
https://code.google.com/p/go/source/browse/src/pkg/net/http/fs.go#339
We could abandon StripPrefix and have another way of passing the prefix to handlers. We
could also keep the original path and the possibly-shortened path in request, so that
redirect could use the original path.

[gopherbot]

Comment 14 by nigel.tao.gnome:

Make http.Server recovering from panics opt-in instead of opt-out.
https://groups.google.com/forum/#!msg/golang-dev/rXs4TG1gdXw/7BQ29S4NPrgJ

[tv42]

I wish there was a way to delegate URL path subtrees to another handler in a way where recipient doesn't have to specifically understand the whole path, but can still easily do redirects and such. A convention for "this is the unprocessed part of the path".

For example, try using the same handler for /foo/ and /bar/quux/, having the handler extract the immediate child segment as a numeric ID, doing a database lookup, and creating a redirect to a canonical non-numerically named child (e.g. http://macworld.com/article/2367748 )

Right now, mutating Request.URL.Path (like StripPrefix) destroys knowledge of the requested URL (and re-parsing Request.RequestURI seems wrong).

[CAFxX]

Only partially related (it belongs more in the scheduler/netpoller) but since net/http has ListenAndServe* I'll add it here: integrate support for REUSEPORT in the netpoller (i.e. open multiple listening sockets on the same port -one for proc?- and accept() on multiple procs)

[bradfitz]

@nhooyr, it would break code like this: https://play.golang.org/p/Z3HSnulUDJR

(not uncommon in tests)

[docmerlin]

The compiler auto converting/wrapping return types to the proper accepted interface would fix this problem, and make code a lot cleaner.

…

On Mon, May 7, 2018 at 12:24 PM Brad Fitzpatrick ***@***.***> wrote: @nhooyr <https://github.com/nhooyr>, it would break code like this: https://play.golang.org/p/Z3HSnulUDJR (not uncommon in tests) — You are receiving this because you commented. Reply to this email directly, view it on GitHub <#5465 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ABLfW9ZIUSf6ahvGNY85d4EVlj5PEq9Kks5twIM6gaJpZM4F0slU> .

[bradfitz]

@docmerlin, the compiler implements the language spec, so you're proposing a language change, which is way out of scope for this particular bug.

[docmerlin]

Right, but if we are talking about 2.0, I thought language changes would be in scope?

…

On Mon, May 7, 2018 at 12:30 PM Brad Fitzpatrick ***@***.***> wrote: @docmerlin <https://github.com/docmerlin>, the compiler implements the language spec, so you're proposing a language change, which is way out of scope for this particular bug. — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#5465 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ABLfW8hPopQlDMgUp3Vk_RxuyIemeG8Pks5twISngaJpZM4F0slU> .

[bradfitz]

@docmerlin, perhaps, but language changes have a high bar. They need their own bug and a large write-up and discussion, not just a casual aside on some library issue. Any language changes that do happen in Go 2 will of course affect the standard library.

[docmerlin]

@bradfitz Alright, thats fair. I'll make an issue for it (the language change). I think that this sort of change to the language would allow these sorts of fixes to be compatible with existing code and make code that relies a lot on closures a lot cleaner.

[nhooyr]

It'd be neat if we could just use *httputil.ReverseProxy and support WebSocket connection upgrades transparently.

[bradfitz]

@nhooyr, there's no reason that needs to wait for Go 2. I'll do it for Go 1.12. I filed #26937.

[nhooyr]

Awesome! I figured we'd need an API change to do this correctly as we have to hijack the client connection. Curious to see how you managed to do it.

[nhooyr]

Nvm, I see now. We just don't use the transport.

[jasonmf]

The http/Server.ErrorLog is *log.Logger.

If you want to log server errors in a custom way you have to create a custom io.Writer that assumes each call to Write() is a single, complete log message or you have to buffer, parse, and restructure a stream of calls to Write().

It would be much more flexible to have ErrorLog be an interface such as:

type ErrorLog interface {
    Printf(string, ...interface{})
}

[bradfitz]

@AgentZombie, there's another bug open about rethinking log/log interfaces. Whatever we did across std would also be done in net/http.

[mklencke]

How about explicit context support?

ServeHTTP(context.Context, ResponseWriter, *Request)

and then get rid of (*Request).Context(). That way, middleware can also more easily augment the context without suffering #28737.

[nhooyr]

Would be nice to rename http.Header to http.Headers as it is a map of headers and not a single header.

[RalphCorderoy]

Hi @nhooyr, but Header["foo"] gives the single Foo header so it reads okay. I agree another style is to use a plural for an array or map so it really depends on the normal style within http and stdlib as a whole.

[nhooyr]

It’s not the worst thing but most usages of maps and array are plural in the stdlib.

[shinny-chengzhi]

The auto recovering of http.Server didn't generate core dump even if GOTRACEBACK=crash, which make it hard to debug. All the information I get is the call stack which is not enough as I need to examine the value of various variable.