1613564 - Rust nsACString should be able to produce a String without copying

Status: RESOLVED INCOMPLETE

(Core :: XPCOM, task)

Description

[Zibi Braniecki [:zbraniecki][:gandalf]]

Came up while working on bug 1560038.

From :emilio on #rust on Matrix:

zbraniecki: but then you want a no-copy way to turn that nsACString into a String
zbraniecki: and I'm not sure we have that... But it seems conceptually possible
zbraniecki: I think we should be able to add an nsCString::into_string(self) or such

Comment 1

[Nathan Froyd [:froydnj]]

There are ~4 things that an nsACString can represent:

1. A fully owned char* buffer.
2. A char* that points into data that somebody else owns.
3. A char* that points at a static char[] (which is really a special case of number 2).
4. An nsStringBuffer object (potentially) shared by other nsACString objects.

So you can really only do this in a zero-copy way for the first representation. If you're OK with that limitation (and realizing that--at least in the C++ code--most strings are probably using the last representation), I guess the API makes sense?

Comment 2

[Emilio Cobos Álvarez (:emilio)]

Yes, this would need to return an Option or a Cow or something... For Zibi's purposes I think (1) is the case he'll hit.

Comment 3

[Emilio Cobos Álvarez (:emilio)]

Attachment: Bug 1613564 - Minor nsstring cleanup / tweaks. r=froydnj

Comment 4

[Emilio Cobos Álvarez (:emilio)]

Attachment: Bug 1613564 - Add some APIs to try to steal the buffer of an ns(A)CString. r=froydnj

Depends on D63968

Comment 5

[Emilio Cobos Álvarez (:emilio)]

Will land the first bit for now.

Comment 6

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/c123ce0ac63c
Minor nsstring cleanup / tweaks. r=froydnj

Comment 7

[Arthur Iakab [arthur_iakab]]

https://hg.mozilla.org/mozilla-central/rev/c123ce0ac63c

Comment 8

[Zibi Braniecki [:zbraniecki][:gandalf]]

should we close this now?

Comment 9

[Emilio Cobos Álvarez (:emilio)]

Probably.