bunpen: support --bunpen-env KEY=VALUE flag

this performs some variable expansion, and will be useful for e.g. `--bunpen-env 'MESA_SHADER_CACHE_DIR=$HOME/.cache/my-app/mesa_shader_cache_db'`

pkgs/by-name/bunpen/config/cli.ha

@@ -13,6 +13,8 @@ export type cli_opts = struct {
   debug: uint,
   disable: str,
   drop_shell: bool,
+  // [ "KEY=VALUE" ]
+  env: []str,
   // `--bunpen-help`
   help: bool,
   home_paths: []str,
@@ -44,6 +46,12 @@ export fn usage() void = {
   fmt::println("      omit `n` for light debugging, or specify n=0/1/2/3/4 where higher = more verbose")!;
   fmt::println("  --bunpen-drop-shell")!;
   fmt::println("      instead of running the program, drop into an interactive shell")!;
+  fmt::println("  --bunpen-env FOO=VALUE")!;
+  fmt::println("      set the environment variable FOO to VALUE within the launched program")!;
+  fmt::println("      certain shell-style substitutions are performed on the raw string ('FOO=VALUE'), including:")!;
+  fmt::println("        $HOME")!;
+  fmt::println("        $XDG_RUNTIME_DIR")!;
+  fmt::println("        $$ to escape a literal $")!;
   fmt::println("  --bunpen-autodetect <existing|existingFile|existingFileOrParent|existingDirOrParent|existingOrParent|parent>")!;
   fmt::println("      add files which appear later as CLI arguments into the sandbox")!;
   fmt::println("  --bunpen-cap <all|sys_admin|net_raw|net_admin|...>")!;
@@ -155,6 +163,7 @@ fn parse_args_into(parsed: *cli_opts, args: []str) (void | errors::invalid) = {
       case "--bunpen-debug=4"         =>  parsed.debug = 4;
       case "--bunpen-dns"             =>  idx += 1; parsed.dns = expect_arg("--bunpen-dns", next)?;
       case "--bunpen-drop-shell"      =>  parsed.drop_shell = true;
+      case "--bunpen-env"             =>  idx += 1; append(parsed.env, expect_arg("--bunpen-env", next)?);
       case "--bunpen-help"            =>  parsed.help = true;
       case "--bunpen-home-path"       =>  idx += 1; append(parsed.home_paths, expect_arg("--bunpen-home-path", next)?);
       case "--bunpen-keep-ipc"        =>  parsed.keep_ipc = true;

pkgs/by-name/bunpen/config/translate_opts.ha

@@ -27,6 +27,8 @@ export type exec_params = struct {
   // `args[0]` is, by convention, the name of the executable,
   // relevant for multi-call binaries like `busybox`.
   args: []str,
+  // *complete* environment with which to execute the binary
+  env: []str,
   // path to the binary to be exec'd inside the sandbox.
   // if the user requested `--bunpen-drop-shell`, this will be their shell (e.g. /bin/sh), assuming `BUNPEN_DISABLE=1` wasn't specified.
   bin: str,
@@ -57,6 +59,30 @@ fn cli_opts_get_exec_params(opts: cli_opts) exec_params = {
     };
   };
 
+  //---- ingest `env` ----//
+
+  let home = getenv_default("HOME");
+  let xdg_runtime_dir = getenv_default("XDG_RUNTIME_DIR");
+
+  for (let old .. os::getenvs()) {
+    let (old_key, _old_value) = strings::cut(old, "=");
+    let keep_old = true;
+    for (let new .. opts.env) {
+      let (new_key, _new_value) = strings::cut(new, "=");
+      if (old_key == new_key) {
+        keep_old = false;
+      };
+    };
+    if (keep_old) {
+      append(params.env, old);
+    };
+  };
+  for (let new .. opts.env) {
+    let substituted = strings::multireplace(new, ("$$", "$"), ("$HOME", home), ("$XDG_RUNTIME_DIR", xdg_runtime_dir));
+    append(params.env, substituted);
+  };
+
+
   return params;
 };
 
@@ -211,7 +237,7 @@ fn try_as_path(
 
 // ensure that the specified path exists.
 // if it exists but not as a directory, succeed only if `dir_ok = true`.
-fn check_exists(pathbuf: *path::buffer, noexist_ok: bool, file_ok: bool, dir_ok: bool) (void | fs::error | path::error)  = {
+fn check_exists(pathbuf: *path::buffer, noexist_ok: bool, file_ok: bool, dir_ok: bool) (void | fs::error | path::error) = {
   if (noexist_ok)
     return void;
   if (!file_ok && !dir_ok)
@@ -228,3 +254,12 @@ fn check_exists(pathbuf: *path::buffer, noexist_ok: bool, file_ok: bool, dir_ok:
   log::printfln("[config/path/try] not adding path (exists, but as wrong type): {}", path::string(pathbuf));
   return fs::wrongtype;
 };
+
+// return the value of the environment variable keyed by `key`, or "" if it
+// doesn't exist
+fn getenv_default(key: str) str = {
+  return match (os::getenv(key)) {
+    case void => yield "";
+    case let value: str => yield value;
+  };
+};

pkgs/by-name/bunpen/integration_test

@@ -114,6 +114,33 @@ test_15_reap_children() {
   ps x | grep -E 'Zs +[0-9]+:[0-9]+ \[true\] <defunct>' && return 1 || return 0
 }
 
+test_16_keep_env() {
+  ORIG_ENV=orig bunpen --bunpen-path / bash -c '[[ "$ORIG_ENV" = orig && -z "$NOT_ENV" ]]'
+}
+
+test_17_new_env() {
+  bunpen --bunpen-path / --bunpen-env NEW_ENV=new bash -c '[[ "$NEW_ENV" = new && -z "$NOT_ENV" ]]'
+}
+
+test_18_updated_env() {
+  UPD_ENV=orig bunpen --bunpen-path / --bunpen-env UPD_ENV=new bash -c '[[ "$UPD_ENV" = new && -z "$NOT_ENV" ]]'
+}
+
+test_19_substitute_env_home() {
+  # HOME defaults to /homeless-shelter
+  # XDG_RUNTIME_DIR defaults to (unset)
+  bunpen --bunpen-path / --bunpen-env 'H_ENV=/head$HOME/tail' --bunpen-env 'R_ENV=$XDG_RUNTIME_DIR/tail' bash -c \
+    '[[ "$H_ENV" = /head/homeless-shelter/tail && "$R_ENV" = /tail ]]'
+}
+test_20_substitute_env_all() {
+  XDG_RUNTIME_DIR=/r/t bunpen --bunpen-path / --bunpen-env 'H_ENV=/head$HOME/tail' --bunpen-env 'R_ENV=$XDG_RUNTIME_DIR/tail' bash -c \
+    '[[ "$H_ENV" = /head/homeless-shelter/tail && "$R_ENV" = /r/t/tail ]]'
+}
+test_21_substitute_env_escapes() {
+  bunpen --bunpen-path / --bunpen-env 'H_ENV=/head$$HOME/tail' --bunpen-env 'H_ENV2=$$$HOME/tail' bash -c \
+    'echo "$H_ENV2" && [[ "$H_ENV" = '"'"'/head$HOME/tail'"'"' && "$H_ENV2" = '"'"'$/homeless-shelter/tail'"'"' ]]'
+}
+
 
 tested=
 rc=0

pkgs/by-name/bunpen/main.ha

@@ -13,14 +13,14 @@ use os;
 use os::exec;
 use types::c;
 
-fn do_exec(path: str, args: []str) (os::exec::error | void) = {
+fn do_exec(path: str, args: []str, env: []str) (os::exec::error | void) = {
   {
     let joined = strings::join(" ", args...);
     defer free(joined);
     log::printfln("exec {} with argv: {}", path, joined);
   };
 
-  errors::ext::check("exec", rt::ext::execvpe(path, args, os::getenvs()));
+  errors::ext::check("exec", rt::ext::execvpe(path, args, env));
 
   // XXX: os::exec::exec offers no way to preserve argv0, but it does
   // work if you don't care about that:
@@ -71,5 +71,5 @@ export fn main() void = {
       yield prepare_env(req);
   };
 
-  errors::ext::check("exec <user command>", do_exec(exec_params.bin, exec_params.args));
+  errors::ext::check("exec <user command>", do_exec(exec_params.bin, exec_params.args, exec_params.env));
 };