scripts/build/.variables: Support SOURCE_DATE_EPOCH

[Foxboron]

Repeated builds of docker is currently unreproducible as the embedded
time does not support SOURCE_DATE_EPOCH. This patch ensures we check for
the defined variable before utilizing current date.

This has been fixed previously with manpages as well

2d7091a

Signed-off-by: Morten Linderud morten@linderud.pw

- How to verify it

λ cli morten/reprobuilds» export SOURCE_DATE_EPOCH=1606660000
λ cli morten/reprobuilds» export DISABLE_WARN_OUTSIDE_CONTAINER=1
λ cli morten/reprobuilds» make
WARNING: binary creates a Linux executable. Use cross for macOS or Windows.
./scripts/build/binary
Building statically linked build/docker-linux-amd64
+ go build -o build/docker-linux-amd64 --ldflags '    -w 
  -X "github.com/docker/cli/cli/version.GitCommit=9d40c7464e" 
  -X "github.com/docker/cli/cli/version.BuildTime=2020-11-29T14:26:40Z" 
  -X "github.com/docker/cli/cli/version.Version=unknown-version"      ' github.com/docker/cli/cmd/docker
++ basename build/docker-linux-amd64
+ ln -sf docker-linux-amd64 build/docker

- Description for the changelog
Support reproducible builds by checking SOURCE_DATE_EPOCH before build.

- A picture of a cute animal (not mandatory but encouraged)

[elboulangero]

Regarding the format of the date, the docker engine does that:

hack/make.sh
43:! BUILDTIME=$(date -u -d "@${SOURCE_DATE_EPOCH:-$(date +%s)}" --rfc-3339 ns 2> /dev/null | sed -e 's/ /T/')

While docker-ce-packaging does that:

common.mk
2:BUILDTIME=$(shell date -u -d "@$${SOURCE_DATE_EPOCH:-$$(date +%s)}" --rfc-3339 ns 2> /dev/null | sed -e 's/ /T/')

So I'd suggest going for --rfc-3339 ns 2> /dev/null | sed -e 's/ /T/' here as well, just for consistency.

[elboulangero]

So I'd suggest going for --rfc-3339 ns 2> /dev/null | sed -e 's/ /T/' here as well, just for consistency

Unless you have backward compatibility concerns regarding the format of this date?

[cpuguy83]

LGTM

[Foxboron]

Whats the holdup on this change?

[Foxboron]

@cpuguy83 ping :)? It's a long wait for a fairly simple change in my eyes.

[cpuguy83]

Maybe @tianon can give it a 2nd review.

[tianon]

👍

[thaJeztah]

Looks like this broke make binary when running on macOS, which uses a different flavour of date 😓

./scripts/build/binary
date: illegal option -- -
usage: date [-jnRu] [-d dst] [-r seconds] [-t west] [-v[+|-]val[ymwdHMS]] ...
            [-f fmt date | [[[mm]dd]HH]MM[[cc]yy][.ss]] [+format]
make: *** [binary] Error 1

[elboulangero]

Interesting. Looking at the man page, they have a COMPLETELY different date command in macOS. Seems like macOS needs to use date -r to display Epoch time

-r seconds Print the date and time represented by seconds, where seconds is the number of seconds since the Epoch (00:00:00 UTC, January 1, 1970; see time(3)), and can be specified in decimal, octal, or hex.

Ref: https://www.unix.com/man-page/osx/1/date/

[thaJeztah]

Yes, I recall some hacks in other repositories to try to get it to work both on Linux and Mac. I need to dig up how it was handled there