Just leaving it out here that the iOS/macOS app experience with paths is likely to be
very different from the server (or system program) experience. Most of your paths are
relative to a container because the effective root of your data is the container. I would
tend to believe that a lot of your paths, not while fully static, could be expressed with
something like "${DOCUMENTS}/static/part", where ${DOCUMENTS} is the only thing
that effectively changes. A system-level program just happens to use / as its prefix.
Most platforms already have some notion of file domains, which are really just
path prefixes (the user's home folder, the file system root, the network root,
etc). I think that some level of support for these would be desirable (would it
be only a set of functions that return different path prefixes). It's also my
humble opinion that tilde expansion should be part of a larger shell expansion
feature to avoid surprises.
I think that I support the conclusion.
Félix
Le 22 août 2017 à 12:02, Dave DeLong <[email protected]> a écrit :
I suppose, if you squint at it weirdly.
My current Path API is a “Path” protocol, with “AbsolutePath” and
“RelativePath” struct versions. The protocol defines a path to be an array of
path components. The only real difference between an AbsolutePath and a
RelativePath is that all file system operations would only take an
AbsolutePath. A URL would also only provide an AbsolutePath as its “path” bit.
public enum PathComponent {
case this // “."
case up // “..”
case item(name: String, extension: String?)
}
public protocol Path {
var components: Array<PathComponent> { get }
init(_ components: Array<PathComponent>) // used on protocol extensions
that mutate paths, such as appending components
}
public struct AbsolutePath: Path { }
public struct RelativePath: Path { }
By separating out the concept of an Absolute and a Relative path, I can put
additional functionality on each one to make semantic sense (you cannot
concatenate two absolute paths, but you can concat any path with a relative
path, for example). Or all file system operations must take an AbsolutePath.
One of the key things I realized is that a “Path” type should not be
ExpressibleByStringLiteral, because you cannot statically determine if a Path
should be absolute or relative. However, one of the initializers for an
AbsolutePath would handle things like expanding a tilde, and both types try to
reduce a set of components as much as possible (by filtering out “.this”
components, and handling “.up” components where possible, etc). Also in my
experience, it’s fairly rare to want to deal with a known-at-compile-time,
hard-coded path. Usually you’re dealing with paths relative to known
“containers” that are determined at runtime (current user’s home folder, app’s
sandboxed documents directory, etc).
Another thing I’ve done is that no direct file system operations exist on
AbsolutePath (like “.exists” or “.createDirectory(…)” or whatever); those are
still on FileManager/FileHandle/etc in the form of extensions to handle the new
types. In my app, a path is just a path, and it only has meaning based on the
thing that is using it. An AbsolutePath for a URL is used differently than an
AbsolutePath on a file system, although they are represented with the same
“AbsolutePath” type.
I’m not saying this is a perfect API of course, or even that a hypothetical
stdlib-provided Path should mimic this. I’m just saying that for my use-case,
this has vastly simplified how I deal with paths, because both URL and String
smell really bad for what I’m doing.
Dave
On Aug 22, 2017, at 12:37 PM, Taylor Swift <[email protected]> wrote:
So are you saying we need three distinct “URI” types for local-absolute,
local-relative, and remote? That’s a lot of API surface to support.
On Tue, Aug 22, 2017 at 12:24 PM, Dave DeLong <[email protected]> wrote:
I completely agree. URL packs a lot of punch, but IMO it’s the wrong
abstraction for file system paths.
I maintain an app that deals a lot with file system paths, and using URL has
always felt cumbersome, but String is the absolute wrong type to use. Lately as
I’ve been working on it, I’ve been experimenting with a concrete “Path” type,
similar to PathKit (https://github.com/kylef/PathKit/). Working in terms of
AbsolutePath and RelativePath (what I’ve been calling things) has been
extremely refreshing, because it allows me to better articulate the kind of
data I’m dealing with. URL doesn’t handle pure-relative paths very well, and
it’s always a bit of a mystery how resilient I need to be about checking
.isFileURL or whatever. All the extra properties (port, user, password, host)
feel hugely unnecessary as well.
Dave
On Aug 20, 2017, at 11:23 PM, Félix Cloutier via swift-evolution
<[email protected]> wrote:
I'm not convinced that URLs are the appropriate abstraction for a file system
path. For the record, I'm not a fan of existing Foundation methods that create
objects from an URL. There is a useful and fundamental difference between a
local path and a remote path, and conflating the two has been a security pain
point in many languages and frameworks that allow it. Examples include remote
file inclusion in PHP and malicious doctypes in XML. Windows also had its share
of issues with UNC paths.
Even when loading an arbitrary URL looks innocuous, many de-anonymizing hacks
work by causing a program to access an URL controlled by an attacker to make it
disclose the user's IP address or some other identifier.
IMO, this justifies that there should be separate types to handle local and
remote resources, so that at least developers have to be explicit about
allowing remote resources. This makes a new URL type less necessary towards
supporting file I/O.
Félix
Le 20 août 2017 à 21:37, Taylor Swift via swift-evolution
<[email protected]> a écrit :
Okay so a few days ago there was a discussion about getting pure swift file system
support into Foundation or another core library, and in my opinion, doing this
requires a total overhaul of the `URL` type (which is currently little more than a
wrapper for NSURL), so I’ve just started a pure Swift URL library project at
<https://github.com/kelvin13/url>.
The library’s parsing and validation core (~1K loc pure swift) is already in
place and functional; the goal is to eventually support all of the Foundation
URL functionality.
The new `URL` type is implemented as a value type with utf8 storage backed by
an array buffer. The URLs are just 56 bytes long each, so they should be able
to fit into cache lines. (NSURL by comparison is over 128 bytes in size; it’s
only saved by the fact that the thing is passed as a reference type.)
As I said, this is still really early on and not a mature library at all but
everyone is invited to observe, provide feedback, or contribute!
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