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[SR-12843] NSString.expandingTildeInPath not working correctly if HOME variable is set #3255

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fabianfett opened this issue May 20, 2020 · 1 comment
Open

[SR-12843] NSString.expandingTildeInPath not working correctly if HOME variable is set #3255

fabianfett opened this issue May 20, 2020 · 1 comment
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bug Foundation

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@fabianfett
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Previous ID SR-12843
Radar None
Original Reporter @fabianfett
Type Bug
Additional Detail from JIRA
Votes 0
Component/s Foundation
Labels Bug
Assignee None
Priority Medium

md5: d00baaf0707960035a9b504222e29460

Issue Description:

If the default `$HOME` path is changed by an environment variable, `NSString.expandingTildeInPath` does not reflect this change.

As a user I would expect that `NSString.expandingTildeInPath` returns the same as `echo $HOME` or `echo ~` on the command line or a direct call against libc.

This problem surfaces when using GitHub actions where the default HOME path is changed to: `/github/home`

See: https://help.github.com/en/actions/reference/virtual-environments-for-github-hosted-runners

Code to reproduce:

#if os(Linux)
import Glibc
#else
import Darwin
#endif
import Foundation
 
func expandTildeInFilePath(_ filePath: String) -> String {
    filePath.withCString { (ptr) -> String in
        var wexp = wordexp_t()
        guard 0 == wordexp(ptr, &wexp, 0), let we_wordv = wexp.we_wordv else {
            return filePath
        }
        defer {
            wordfree(&wexp)
        }
        
        guard let resolved = we_wordv[0], let pth = String(cString: resolved, encoding: .utf8) else {
             return filePath
        }
        
        return pth
    }
}
 
let expandableFilePath = "~/test"
 
let expandedNewPath = expandTildeInFilePath(expandableFilePath)
let expandedNSString = NSString(string: expandableFilePath).expandingTildeInPath
 
print("results")
print("  Glibc/Darwin: \(expandedNewPath)")
print("  Foundation  : \(expandedNSString)")

Logs:

[ fat@fatBook-WLAN ] ~/Developer/nio/test
$> docker run -it --rm -v $(pwd):/src --workdir /src swift:5.2 /bin/bash                                  
root@4d76cca8d7e0:/src# swift build
root@4d76cca8d7e0:/src# .build/debug/test
results
  Glibc/Darwin: /root/test
  Foundation  : /root/test

[ fat@fatBook-WLAN ] ~/Developer/nio/test
$> docker run -it --rm -e HOME="/github/home" -v $(pwd):/src --workdir /src swift:5.2 /bin/bash
root@4d9507e716e5:/src# echo ~
/github/home
root@4d9507e716e5:/src# echo $HOME
/github/home
root@4d9507e716e5:/src# .build/debug/test
results
  Glibc/Darwin: /github/home/test
  Foundation  : /root/test

Verified with:

  • swift:5.2

  • swiftlang/swift:nightly-master-xenial
@spevans
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spevans commented Jun 3, 2020

Although NSString.expandingTildeInPath does make use of $HOME it checks the user's home directory using getpwnam(3) first so the $HOME is not considered

(see _CFCopyHomeDirURLForUser in

swift-corelibs-foundation/CoreFoundation/Base.subproj/CFPlatform.c

Line 228 in 092c58a

static CFURLRef _CFCopyHomeDirURLForUser(const char *username, bool fallBackToHome) {
)

However a re-reading of https://developer.apple.com/documentation/foundation/1413045-nshomedirectory, the documentation for NSHomeDirectory, says that it returns "In macOS, it is the application’s sandbox directory or the current user’s home directory (if the application is not in a sandbox)"

The sandboxing sets the CFFIXED_USER_HOME environment variable which overrides the use of getpwnam so it can be used as follows:

$ docker run -it --rm -e HOME="/github/home" -v $(pwd):/src --workdir /src swift:5.2 /bin/bash
root@65419c9f1a73:/src# cat home.swift
import Foundation

print("NSHomeDirectory()", NSHomeDirectory())
let homedir = ("~/somedir" as NSString).expandingTildeInPath
print(homedir)

print("NSHomeDirectoryForUser(\"unknown\")", NSHomeDirectoryForUser("unknown") as Any)
let homedir2 = ("~unknown/somedir" as NSString).expandingTildeInPath
print(homedir2)
root@65419c9f1a73:/src# swiftc -o home home.swift
root@65419c9f1a73:/src# ./home
NSHomeDirectory() /root
/root/somedir
NSHomeDirectoryForUser("unknown") nil
~unknown/somedir
root@65419c9f1a73:/src# CFFIXED_USER_HOME=${HOME} ./home 
NSHomeDirectory() /github/home
/github/home/somedir
NSHomeDirectoryForUser("unknown") Optional("/github/home")
/github/home/somedir
root@65419c9f1a73:/src#

So the best workaround to use $HOME would be to use

export CFFIXED_USER_HOME=${HOME}

The code that uses $HOME cant really be changed in CoreFoundation as it would probably break other programs depending on the behaviour.

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
@shahmishal shahmishal transferred this issue from apple/swift May 5, 2022
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@spevans @fabianfett