cli: Add an edit verb

This interactively replaces the specified state, in a similar way
as `kubectl edit`.

As of right now, the only supported state to change is the desired
image.

But this will help unblock [configmap support].

[configmap support]: containers#22

lib/src/cli.rs

@@ -16,9 +16,12 @@ use ostree_ext::keyfileext::KeyFileExt;
 use ostree_ext::ostree;
 use ostree_ext::sysroot::SysrootLock;
 use std::ffi::OsString;
+use std::io::Seek;
+use std::os::unix::prelude::OsStringExt;
 use std::os::unix::process::CommandExt;
 use std::process::Command;
 
+use crate::spec::Host;
 use crate::spec::HostSpec;
 use crate::spec::ImageReference;
 
@@ -64,7 +67,18 @@ pub(crate) struct SwitchOpts {
     pub(crate) target: String,
 }
 
-/// Perform a status operation
+/// Perform an edit operation
+#[derive(Debug, Parser)]
+pub(crate) struct EditOpts {
+    /// Path to new system specification; use `-` for stdin
+    pub(crate) filename: String,
+
+    /// Don't display progress
+    #[clap(long)]
+    pub(crate) quiet: bool,
+}
+
+/// Perform an status operation
 #[derive(Debug, Parser)]
 pub(crate) struct StatusOpts {
     /// Output in JSON format.
@@ -111,6 +125,8 @@ pub(crate) enum Opt {
     Upgrade(UpgradeOpts),
     /// Target a new container image reference to boot.
     Switch(SwitchOpts),
+    /// Change host specification
+    Edit(EditOpts),
     /// Display status
     Status(StatusOpts),
     /// Add a transient writable overlayfs on `/usr` that will be discarded on reboot.
@@ -405,6 +421,59 @@ async fn switch(opts: SwitchOpts) -> Result<()> {
     Ok(())
 }
 
+/// Implementation of the `bootc edit` CLI command.
+#[context("Editing spec")]
+async fn edit(opts: EditOpts) -> Result<()> {
+    prepare_for_write().await?;
+    let sysroot = &get_locked_sysroot().await?;
+    let repo = &sysroot.repo();
+    let booted_deployment = &sysroot.require_booted_deployment()?;
+    let (_deployments, host) = crate::status::get_status(sysroot, Some(booted_deployment))?;
+
+    let new_host: Host = if opts.filename == "-" {
+        let v = "EDITOR";
+        let editor = std::env::var_os(v)
+            .ok_or_else(|| anyhow::anyhow!("{v} is unset"))?
+            .into_vec();
+        let editor = String::from_utf8(editor).with_context(|| format!("{v} is invalid UTF-8"))?;
+        let mut editor_args = editor.split_ascii_whitespace();
+        let argv0 = editor_args
+            .next()
+            .ok_or_else(|| anyhow::anyhow!("Invalid {v}: {editor}"))?;
+        let tmpf = tempfile::NamedTempFile::new()?;
+        serde_yaml::to_writer(std::io::BufWriter::new(tmpf.as_file()), &host)?;
+        let status = Command::new(argv0)
+            .args(editor_args)
+            .arg(tmpf.path())
+            .status()?;
+        if !status.success() {
+            anyhow::bail!("Invoking {v}: {editor} failed: {status:?}");
+        }
+        tmpf.as_file().seek(std::io::SeekFrom::Start(0))?;
+        serde_yaml::from_reader(&mut tmpf.as_file())?
+    } else {
+        let mut r = std::io::BufReader::new(std::fs::File::open(opts.filename)?);
+        serde_yaml::from_reader(&mut r)?
+    };
+
+    if new_host.spec == host.spec {
+        anyhow::bail!("No changes in current host spec");
+    }
+    let new_image = new_host
+        .spec
+        .image
+        .as_ref()
+        .ok_or_else(|| anyhow::anyhow!("Unable to transition to unset image"))?;
+    let fetched = pull(repo, new_image, opts.quiet).await?;
+
+    // TODO gc old layers here
+
+    let stateroot = booted_deployment.osname();
+    stage(sysroot, &stateroot, fetched, &new_host.spec).await?;
+
+    Ok(())
+}
+
 /// Implementation of `bootc usroverlay`
 async fn usroverlay() -> Result<()> {
     // This is just a pass-through today.  At some point we may make this a libostree API
@@ -426,6 +495,7 @@ where
     match opt {
         Opt::Upgrade(opts) => upgrade(opts).await,
         Opt::Switch(opts) => switch(opts).await,
+        Opt::Edit(opts) => edit(opts).await,
         Opt::UsrOverlay => usroverlay().await,
         #[cfg(feature = "install")]
         Opt::Install(opts) => crate::install::install(opts).await,