feat(nix/nint): accept attribute set with stdout, stderr and exit

This extends the calling convention for nint in a non-breaking way: If
the called script returns an attribute set instead of a string the
following is done:

* If the attributes `stdout` and/or `stderr` exist, their content (which
  must be a string currently) is written to the respective output.

* If the attribute `exit` exists, nint will exit with the given exit
  code. Must be a number that can be converted to an `i32`. If it's
  missing, nint will exit without indicating an error.

Change-Id: I209cf178fee3d970fdea3b26e4049e944af47457
Reviewed-on: https://cl.tvl.fyi/c/depot/+/3547
Tested-by: BuildkiteCI
Reviewed-by: tazjin <mail@tazj.in>
This commit is contained in:
sterni 2021-09-14 23:50:01 +02:00
parent 5dec982334
commit 852d059e2f
2 changed files with 57 additions and 3 deletions

View file

@ -15,8 +15,16 @@ to the following calling convention:
program name at `builtins.head argv`.
* Extra arguments can be manually passed as described below.
* The return value should always be a string (throwing is also okay)
which is printed to stdout by `nint`.
* The return value must either be
* A string which is rendered to `stdout`.
* An attribute set with the following optional attributes:
* `stdout`: A string that's rendered to `stdout`
* `stderr`: A string that's rendered to `stderr`
* `exit`: A number which is used as an exit code.
If missing, nint always exits with 0 (or equivalent).
## Usage

View file

@ -5,6 +5,7 @@ use std::ffi::OsString;
use std::os::unix::ffi::{OsStringExt, OsStrExt};
use std::io::{Error, ErrorKind, Write, stdout, stderr};
use std::process::Command;
use std::convert::{TryFrom};
fn render_nix_string(s: &OsString) -> OsString {
let mut rendered = Vec::new();
@ -40,6 +41,26 @@ fn render_nix_list(arr: &[OsString]) -> OsString {
OsString::from_vec(rendered)
}
/// Slightly overkill helper macro which takes a `Map<String, Value>` obtained
/// from `Value::Object` and an output name (`stderr` or `stdout`) as an
/// identifier. If a value exists for the given output in the object it gets
/// written to the appropriate output.
macro_rules! handle_set_output {
($map_name:ident, $output_name:ident) => {
match $map_name.get(stringify!($output_name)) {
Some(Value::String(s)) =>
$output_name().write_all(s.as_bytes()),
Some(_) => Err(
Error::new(
ErrorKind::Other,
format!("Attribute {} must be a string!", stringify!($output_name)),
)
),
None => Ok(()),
}
}
}
fn main() -> std::io::Result<()> {
let mut nix_args = Vec::new();
@ -90,6 +111,7 @@ fn main() -> std::io::Result<()> {
nix_args.push(render_nix_list(&argv[..]));
nix_args.push(OsString::from("--eval"));
nix_args.push(OsString::from("--strict"));
nix_args.push(OsString::from("--json"));
nix_args.push(argv[0].clone());
@ -100,7 +122,31 @@ fn main() -> std::io::Result<()> {
match serde_json::from_slice(&run.stdout[..]) {
Ok(Value::String(s)) => stdout().write_all(s.as_bytes()),
Ok(_) => Err(Error::new(ErrorKind::Other, "output must be a string")),
Ok(Value::Object(m)) => {
handle_set_output!(m, stdout)?;
handle_set_output!(m, stderr)?;
match m.get("exit") {
Some(Value::Number(n)) => {
let code = n.as_i64().and_then(|v| i32::try_from(v).ok());
match code {
Some(i) => std::process::exit(i),
None => Err(
Error::new(
ErrorKind::Other,
"Attribute exit is not an i32"
)
),
}
},
Some(_) => Err(
Error::new(ErrorKind::Other, "exit must be a number")
),
None => Ok(()),
}
},
Ok(_) => Err(Error::new(ErrorKind::Other, "output must be a string or an object")),
_ => {
stderr().write_all(&run.stderr[..]);
Err(Error::new(ErrorKind::Other, "internal nix error"))