Clean up smelly code in inject.rs

src/build.rs

@@ -76,9 +76,8 @@ fn build_inner(
 ) -> Result<()> {
     let config = inject::inspect_config(image)?;
     let command = cmd.unwrap_or_else(|| inject::infer_command(&config));
-    let env = inject::env(&config);
-    let working_dir = inject::working_dir(&config);
-    let exec_script = inject::build_exec_script(&command, &env, working_dir);
+    let exec_script =
+        inject::build_exec_script(&command, &config.env, config.working_dir.as_deref());
     inject::inject(mount_path, &exec_script)?;
     println!("Injected /slim/ (init + exec)");
 

src/inject.rs

@@ -3,6 +3,7 @@
 
 use anyhow::{Context, Result, anyhow};
 use serde::Deserialize;
+use std::fmt::Write as _;
 use std::fs;
 use std::path::Path;
 
@@ -14,13 +15,13 @@ const SLIM_INIT: &str = include_str!("scripts/slim-init.sh");
 #[serde(rename_all = "PascalCase")]
 pub struct Config {
     #[serde(default)]
-    cmd: Option<Vec<String>>,
+    pub cmd: Vec<String>,
     #[serde(default)]
-    entrypoint: Option<Vec<String>>,
+    pub entrypoint: Vec<String>,
     #[serde(default)]
-    env: Option<Vec<String>>,
+    pub env: Vec<String>,
     #[serde(default)]
-    working_dir: Option<String>,
+    pub working_dir: Option<String>,
 }
 
 pub fn inspect_config(image: &str) -> Result<Config> {
@@ -42,40 +43,21 @@ pub fn inspect_config(image: &str) -> Result<Config> {
 /// Concatenates ENTRYPOINT + CMD (Docker semantics). If neither is present,
 /// falls back to `/bin/sh`.
 pub fn infer_command(config: &Config) -> String {
-    let entrypoint = config.entrypoint.as_deref().filter(|e| !e.is_empty());
-    let cmd = config.cmd.as_deref().filter(|c| !c.is_empty());
+    let parts = config.entrypoint.iter().chain(config.cmd.iter());
+    let parts: Vec<_> = parts.map(|s| s.as_str()).collect();
 
-    let parts: Vec<String> = match (entrypoint, cmd) {
-        (Some(ep), Some(c)) => {
-            let mut parts = ep.to_vec();
-            parts.extend(c.iter().cloned());
-            parts
+    match &parts[..] {
+        [] => "/bin/sh".into(),
+        ["/bin/sh" | "sh", "-c", cmd] => cmd.to_string(),
+        _ => shell_join(&parts),
     }
-        (Some(ep), None) => ep.to_vec(),
-        (None, Some(c)) => c.to_vec(),
-        (None, None) => vec!["/bin/sh".to_string()],
-    };
-
-    if parts.len() == 3 && (parts[0] == "/bin/sh" || parts[0] == "sh") && parts[1] == "-c" {
-        parts[2].clone()
-    } else {
-        shell_join(&parts)
-    }
-}
-
-pub fn env(config: &Config) -> Vec<String> {
-    config.env.clone().unwrap_or_default()
-}
-
-pub fn working_dir(config: &Config) -> Option<&str> {
-    config.working_dir.as_deref()
 }
 
 fn shell_escape(s: &str) -> String {
     format!("'{}'", s.replace('\'', "'\\''"))
 }
 
-fn shell_join(parts: &[String]) -> String {
+fn shell_join(parts: &[&str]) -> String {
     parts
         .iter()
         .map(|p| shell_escape(p))
@@ -87,18 +69,19 @@ fn shell_join(parts: &[String]) -> String {
 pub fn build_exec_script(command: &str, env: &[String], working_dir: Option<&str>) -> String {
     let mut lines = String::from("#!/bin/sh\n");
     if let Some(dir) = working_dir.filter(|d| !d.is_empty()) {
-        lines.push_str(&format!("cd {} 2>/dev/null\n", shell_escape(dir)));
+        _ = writeln!(&mut lines, "cd {} 2>/dev/null", shell_escape(dir));
     }
     for var in env {
         if let Some((key, val)) = var.split_once('=') {
-            lines.push_str(&format!(
-                "export {}={}\n",
+            _ = writeln!(
+                &mut lines,
+                "export {}={}",
                 shell_escape(key),
                 shell_escape(val)
-            ));
+            );
         }
     }
-    lines.push_str(&format!("exec /bin/sh -c {}\n", shell_escape(command)));
+    _ = writeln!(&mut lines, "exec /bin/sh -c {}", shell_escape(command));
     lines
 }