Refactor command construction out of herder

src/run_mode.rs

@@ -1,3 +1,13 @@
+use std::{borrow::Cow, fmt::Debug};
+
+use process_path::get_executable_path;
+use serde::{de::DeserializeOwned, Serialize};
+use valuable::Valuable;
+
+use crate::{
+    escalation::Command, logging::get_log_paths, writer_process::ipc::WriterProcessConfig,
+};
+
 pub const RUN_MODE_ENV_NAME: &str = "__CALIGULA_RUN_MODE";
 
 /// [RunMode] is a flag set in the environment variable `__CALIGULA_RUN_MODE`
@@ -46,11 +56,40 @@ impl RunMode {
         }
     }
 
-    pub fn as_str(&self) -> &str {
+    pub fn as_str(&self) -> &'static str {
         match self {
             RunMode::Main => "main",
             RunMode::Writer => "writer",
             RunMode::EscalatedDaemon => "escalated_daemon",
         }
     }
 }
+
+/// Build a [Command] that, when run, spawns a process with a specific configuration.
+pub fn make_spawn_command<'a, C: Serialize + Debug + Valuable>(
+    socket: Cow<'a, str>,
+    log_path: Cow<'a, str>,
+    run_mode: RunMode,
+    init_config: C,
+) -> Command<'a> {
+    let proc = get_executable_path().unwrap();
+
+    Command {
+        proc: proc.to_str().unwrap().to_owned().into(),
+        envs: vec![(RUN_MODE_ENV_NAME.into(), run_mode.as_str().into())],
+        // Arg order is documented in childproc_common.
+        args: vec![
+            log_path.into(),
+            socket.into(),
+            serde_json::to_string(&init_config).unwrap().into(),
+        ],
+    }
+}
+
+pub fn make_writer_spawn_command<'a>(
+    socket: Cow<'a, str>,
+    log_path: Cow<'a, str>,
+    init_config: &WriterProcessConfig,
+) -> Command<'a> {
+    make_spawn_command(socket, log_path, RunMode::Writer, init_config)
+}

src/ui/herder/herder.rs

@@ -1,6 +1,7 @@
 use crate::{
     ipc_common::read_msg_async,
     logging::get_log_paths,
+    run_mode::make_writer_spawn_command,
     ui::herder::{
         socket::HerderSocket,
         writer::handle::{StartProcessError, WriterHandle},
@@ -45,19 +46,11 @@ impl Herder {
             "Read absolute path to this program"
         );
 
-        let args = serde_json::to_string(args)?;
-        debug!(?args, "Converted WriterProcessConfig to JSON");
-
-        let cmd = Command {
-            proc: proc.to_string_lossy(),
-            envs: vec![(RUN_MODE_ENV_NAME.into(), RunMode::Writer.as_str().into())],
-            // Arg order is documented in childproc_common.
-            args: vec![
-                get_log_paths().child.to_string_lossy().into(),
-                self.socket.socket_name().to_string_lossy().into(),
-                args.into(),
-            ],
-        };
+        let cmd = make_writer_spawn_command(
+            self.socket.socket_name().to_string_lossy(),
+            get_log_paths().child.to_string_lossy(),
+            args,
+        );
 
         debug!("Starting child process with command: {:?}", cmd);
         fn modify_cmd(cmd: &mut tokio::process::Command) {

src/writer_process/mod.rs

@@ -1,6 +1,7 @@
 //! This module has logic for the child process that writes to the disk.
 //!
 //! IT IS NOT TO BE USED DIRECTLY BY THE USER! ITS API HAS NO STABILITY GUARANTEES!
+
 pub mod child;
 pub mod ipc;
 mod xplat;