NIOFileSystem.temporaryDirectory: Consider falling back to TMPDIR

[weissi]

swift-nio/Sources/NIOFileSystem/FileSystem.swift

Line 638 in 30df855

return "/tmp"

Currently, NIOFS's temporaryDirectory uses _CS_DARWIN_USER_TEMP_DIR on Darwin and /tmp//data/local/tmp anywhere else. I think we should consider the env var TMPDIR if set.

So maybe:

• Darwin: _CS_DARWIN_USER_TEMP_DIR -> TMPDIR -> /tmp
• Linux: TMPDIR -> /tmp
• Android: TMPDIR -> /data/local/tmp
  ?

[glbrntt]

That seems pretty reasonable to me. I wonder if TMPDIR should be checked first on Darwin as it's a user-expressed preference?

[weissi]

That seems pretty reasonable to me. I wonder if TMPDIR should be checked first on Darwin as it's a user-expressed preference?

For reference this is what swift-foundation does: https://github.com/apple/swift-foundation/blob/9d57f36de757b3d5e3a2f7ffcf27aaec3033509f/Sources/FoundationEssentials/String/String%2BPath.swift#L484-L533

[vlm]

I would think ${TMPDIR} should be consulted first. The other way around makes limited sense.

Besides the "expressed preference" comment from @glbrntt, there are other considerations:

• Since _CS_DARWIN_USER_TEMP_DIR might only be unavailable in some extreme circumstances, its reliance on ${TMPDIR} as a fallback is always going to come as a surprise. It can't be relied upon, and if it comes to that that'd be very surprising.
• In addition to that, consulting ${TMPDIR} first aligns with cross-platform developer's expectations. Swift-on-server is perhaps the swift-nio's most important focus, and this consideration may have correspondingly different weight compared to swift-foundation's.

For completeness, I can also see some arguments for aligning with swift-foundation.

[weissi]

CC @parkera also

[parkera]

swift-foundation should be able to accommodate both use cases, and it would be nice to have a single implementation of this kind of logic. As you can see from the one we have there already, it is unfortunately not trivial. It's also something which varies dramatically depending on platform, so abstracting it once also makes sense.