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net/url: add URL.ForceFragment like ForceQuery for empty fragments to stringify with '#' #29603

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Gregable opened this issue Jan 8, 2019 · 6 comments
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@Gregable
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Gregable commented Jan 8, 2019

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

go version go1.11.2 linux/amd64

What did you do?

import (
  "fmt"
  "log"
  "net/url"
)

func main() {
    u, err := url.Parse("http://example.com/#")
	if err != nil {
		log.Fatal(err)
	}
	fmt.Println(u.String())
    fmt.Println(u.Fragment)
}

What did you expect to see?

http://example.com/#
#

What did you see instead?

http://example.com/

What's the issue?

At first glance, http://example.com/# and http://example.com/ are logically the same URL. This is largely true in the context of a browser navigating to that URL as typed into the URL bar, but they are subtly different in a link. If a user clicks the following link:

<a href="http://example.com/#">foo</a>

If the document URL (or <base href>) is http://example.com/ then this click does not cause a navigation - it is a within document link. However, if the link was instead to:

<a href="http://example.com/">foo</a>

Then clicking it causes a navigation. A reload really, but still a navigation.

This becomes more of an issue when net/url is used to resolve a relative URL:

<html>
<head>
  <base href="http://example.com/">
</head>
<body>
  <a href="/">reload</a>
  <a href="#">inert</a>
</body>
</html>
base, _ = url.Parse("http://example.com/")
nav, _ = base.Parse("/")
local, _ = base.Parse("#")

nav and local are now equal, which means it's not possible to distinguish a document local link and a navigation link.

@agnivade agnivade changed the title net/url empty fragment indistinguishable from no fragment net/url: empty fragment indistinguishable from no fragment Jan 8, 2019
@agnivade
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agnivade commented Jan 8, 2019

/cc @bradfitz

@agnivade agnivade added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Jan 8, 2019
@agnivade agnivade added this to the Unplanned milestone Jan 8, 2019
@bradfitz
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bradfitz commented Jan 8, 2019

In your "What did you expect to see?" section, you expected the value of u.Fragment to be # but it's documented as:

https://golang.org/pkg/net/url/#URL.Fragment

        Fragment   string    // fragment for references, without '#'

So clearly that can't work as you expect.

What we could do perhaps is add URL.ForceFragment like we did for https://golang.org/pkg/net/url/#URL.ForceQuery

@bradfitz bradfitz changed the title net/url: empty fragment indistinguishable from no fragment net/url: add URL.ForceFragment like ForceQuery for empty fragments to stringify with '#' Jan 8, 2019
@bradfitz bradfitz added the NeedsDecision Feedback is required from experts, contributors, and/or the community before a change can be made. label Jan 8, 2019
@bradfitz bradfitz modified the milestones: Unplanned, Go1.13 Jan 8, 2019
@gopherbot gopherbot removed the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Jan 8, 2019
@Gregable
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Gregable commented Jan 9, 2019

Right. "What did you expect to see?" is perhaps the wrong phrasing of the question. I'm only arguing that the API has no way to distinguish these two cases.

It does look like ForceFragment would be the best API for fixing this.

@Gregable
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@bradfitz so he sees my reply.

@Gregable Gregable reopened this Jan 17, 2019
@bradfitz
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I see all replies and saw yours last week. I just had nothing further to add.

We're in the Go 1.12 release freeze right now (https://github.com/golang/go/wiki/Go-Release-Cycle) so this isn't a priority.

@Gregable
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No worries, just wanted to check. Cheers.

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