Running a script with large input on Heroku (part 2)

2022-06-21

Note: If you need heroku run:detached <command> or want to run interactively using heroku run bash take a look at the previous blog post Running a script with large input on Heroku. For all other cases this method is easier.

If you’re anything like me, you occassionaly want to run a one-off job on Heroku with a bunch of code in a script that you’ve made locally on your machine.

But you don’t want to commit it to the repo and then to wait for CI (e.g. integration tests can take a long time). Especially if it’s a single-use data analysis script that you don’t want to clutter up the repository. Good news! You don’t have to – Heroku allows piping into the heroku run-command:

> echo 'abcdef' | heroku run -a test-app 'wc -c'
Running wc -c on ⬢ test-app... up, run.1543 (Standard-1X)
abcdef
7

You can use this to upload new code to the temporary dyno (the code will only be available in that particular dyno)

> cat my_script.py | heroku run -a test-app 'cat > my_script.py; python my_script.py'
Running cat > test.py; python test.py on ⬢ test-app... up, run.6181 (Standard-1X)
print('Hello from my_script.py')
Hello from my_script.py

That’s it! – just pipe the file into the heroku run-command, use cat to write it to a file on the dyno, and then run the file.

Sending multiple files

If your Heroku image has the tar-utility you can do:

# on macOS (gbase64 is in the `coreutils` Homebrew package)
tar -c input.txt sum.py | gbase64 | heroku run -a test-app -- 'base64 -d | tar -x; python sum.py'
# on Linux
tar -c input.txt sum.py | base64 | heroku run -a test-app -- 'base64 -d | tar -x; python sum.py'
# on FreeBSD the command is the same as macOS and gbase64 is in the `coreutils` port

The long story about sending multiple files

To get to the above, I initially did tar -c input.txt sum.py | heroku run -a test-app 'tar -x; python sum.py'. However, the first issue that I had was the error tar: Refusing to read archive contents from terminal (missing -f option?).

So I expanded a bit and created an intermediate file: tar -c input.txt sum.py | heroku run -a test-app 'cat bundle.tar; tar -xf bundle.tar; python sum.py'

However, that command never finishes. Also, all of the three commands show the actual content of the tar-file in your terminal:

 > cat bundle.tar | heroku run -a test-app 'tar -x; python sum.py'
 Running tar -x; python sum.py on ⬢ test-app... starting, run.4590 (Standard-1X)
 Running tar -x; python sum.py on ⬢ test-app... connecting, run.4590 (Standard-1X)
 Running tar -x; python sum.py on ⬢ test-app... up, run.4590 (Standard-1X)
 input.txt^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@000644 ^@000765 ^@000024 ^@00000000006 14254272731 013376^@ 0^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@ustar^@00malthe^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@staff^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@000000 ^@000000 ^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@1 2 3
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 tar: Error is not recoverable: exiting now
 python: can't open file '/app/sum.py': [Errno 2] No such file or directory

It seems that cat hangs in Heroku once “control-characters” like ^@ are sent through the pipe. But we can use base64 to encode and hide those forbidden characters from cat.

> tar -cf bundle.tar input.txt sum.py
> base64 bundle.tar | heroku run -a uvicorn-issue-344 'base64 -d > bundle.tar; tar -xf bundle.tar; python sum.py'
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA[ ... and lots more of these ... ]AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAHN1bS5weQAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAwMDA2NDQgADAwMDc2NSAAMDAwMDI0IAAwMDAwMDAwMDEwMiAxNDI1NTE1MTU3NiAwMTI2NTUAIDAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAdXN0YXIAMDBtYWx0aGUAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAHN0YWZmAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAMDAwMDAwIAAwMDAwMDAgAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAcHJpbnQoc3VtKFtpbnQocykgZm9yIHMgaW4gb3BlbignaW5wdXQudHh0JykucmVhZCgpLnNwbGl0KCcgJyldKSkKAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
base64: invalid input
tar: A lone zero block at 5
6

It worked!

Even though we got some error messages, it worked. For larger input data or scripts you may want to checksum (e.g. md5/shasum/sum) the files on both ends to ensure that everything was transferred and untarred correctly.

Or the oneliner (I’m still sad that Linux tar doesn’t allow input from a pipe):

> tar -c input.txt sum.py | base64 | heroku run -a uvicorn-issue-344 'base64 -d > bundle.tar; tar -xf bundle.tar; python sum.py'

Why do we get `base64: invalid input`? (BSD vs GNU `base64`)

Your Heroku image is almost certainly runnign Linux, meaning that it’ll be using the GNU-version of base64. That is also why we’re getting base64: invalid input. I’m on macOS and therefore using the BSD-version of base64, so we’re piping the output of BSD base64 into GNU base64.

If you install coreutils via Homebrew brew install coreutils, you’ll get the gbase64-command (GNU base64) and using that on your side you’ll have no errors:

> tar -cf bundle.tar input.txt sum.py
> base64 bundle.tar | heroku run -a uvicorn-issue-344 'base64 -d > bundle.tar; tar -xf bundle.tar; python sum.py'
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
                  [ ... and lots more of these lines ... ]
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
6

The difference between base64 and gbase64 is that base64 puts a newline at the end of the output, whereas gbase64 does not. However, gbase64 put newlines everywhere else – specifically after every 76th character – wrapping the output at 76 terminal columns.

And you can’t just remove the newline – this hangs:

base64 bundle.tar | tr -d '\n' | heroku run -a uvicorn-issue-344 'base64 -d > bundle.tar; tar -xf bundle.tar; python sum.py'

Probably due to some buffering based on newlines inside the Heroku CLI or further down the Heroku stack.

Caveats

In order to pipe you need a tty, so --no-tty and similarly run:detached can’t be used (e.g. for long-running scripts)
You can’t regain control of stdin once you pipe into a process, so you can’t do cat file.txt | heroku run 'cat > file.text; bash'

Notes

Usually tar-flags are passed without the - in front, e.g. tar xzvf archive.tar.gz however I felt it was more clear to add the dashes in this case.