deb: cross-compilation, ephemeral contexts, local builds

Multiple changes:
- New contexts (schroot, unshare)
- Cross-building quirks, with ephemeral contexts and repositories management
- Contexts with parents, global context manager, better lifetime handling
- Local building of binary packages
- Pull: pulling dsc files by default
- Many small bugfixes and changes

Co-authored-by: Valentin Haudiquet <valentin.haudiquet@canonical.com>
Co-committed-by: Valentin Haudiquet <valentin.haudiquet@canonical.com>

src/context/schroot.rs

@@ -0,0 +1,265 @@
+/// Schroot context: execute commands in a schroot session
+/// Not tested, will need more work!
+use super::api::ContextDriver;
+use std::io;
+use std::path::{Path, PathBuf};
+use std::sync::Arc;
+
+pub struct SchrootDriver {
+    pub name: String,
+    pub session: std::sync::Mutex<Option<String>>,
+    pub parent: Option<Arc<super::api::Context>>,
+}
+
+use super::api::{Context, ContextConfig};
+
+impl SchrootDriver {
+    fn parent(&self) -> Arc<Context> {
+        self.parent
+            .clone()
+            .unwrap_or_else(|| Arc::new(Context::new(ContextConfig::Local)))
+    }
+
+    fn ensure_session(&self) -> io::Result<String> {
+        let mut session_lock = self.session.lock().unwrap();
+        if let Some(id) = session_lock.as_ref() {
+            return Ok(id.clone());
+        }
+
+        // Create new session
+        let output = self
+            .parent()
+            .command("schroot")
+            .arg("-b")
+            .arg("-c")
+            .arg(&self.name)
+            .output()?;
+
+        if !output.status.success() {
+            return Err(io::Error::other(format!(
+                "Failed to create schroot session: {}",
+                String::from_utf8_lossy(&output.stderr)
+            )));
+        }
+
+        let session_id = String::from_utf8(output.stdout)
+            .map_err(|e| io::Error::new(io::ErrorKind::InvalidData, e))?
+            .trim()
+            .to_string();
+
+        *session_lock = Some(session_id.clone());
+        Ok(session_id)
+    }
+
+    fn get_session_location(&self, session_id: &str) -> io::Result<String> {
+        let output = self
+            .parent()
+            .command("schroot")
+            .arg("--location")
+            .arg("-c")
+            .arg(session_id)
+            .output()?;
+
+        if !output.status.success() {
+            return Err(io::Error::other(format!(
+                "Failed to get schroot location: {}",
+                String::from_utf8_lossy(&output.stderr)
+            )));
+        }
+
+        Ok(String::from_utf8(output.stdout)
+            .map_err(|e| io::Error::new(io::ErrorKind::InvalidData, e))?
+            .trim()
+            .to_string())
+    }
+}
+
+impl ContextDriver for SchrootDriver {
+    fn ensure_available(&self, src: &Path, _dest_root: &str) -> io::Result<PathBuf> {
+        src.canonicalize()
+    }
+
+    fn retrieve_path(&self, src: &Path, dest: &Path) -> io::Result<()> {
+        let session_id = self.ensure_session()?;
+        let location = self.get_session_location(&session_id)?;
+
+        let path_in_chroot = src.strip_prefix("/").unwrap_or(src);
+        let host_src = Path::new(&location).join(path_in_chroot);
+
+        self.parent().retrieve_path(&host_src, dest)
+    }
+
+    fn list_files(&self, path: &Path) -> io::Result<Vec<PathBuf>> {
+        let session_id = self.ensure_session()?;
+        let location = self.get_session_location(&session_id)?;
+
+        let path_in_chroot = path.strip_prefix("/").unwrap_or(path);
+        let host_path = Path::new(&location).join(path_in_chroot);
+
+        let files = self.parent().list_files(&host_path)?;
+        let mut chroot_files = Vec::new();
+
+        // TODO: Check if we *need* to strip the prefix.
+        // If we don't, we can just return `files`.
+        for file in files {
+            if let Ok(rel) = file.strip_prefix(&location) {
+                chroot_files.push(Path::new("/").join(rel));
+            } else {
+                chroot_files.push(file);
+            }
+        }
+        Ok(chroot_files)
+    }
+
+    fn run(
+        &self,
+        program: &str,
+        args: &[String],
+        env: &[(String, String)],
+        cwd: Option<&str>,
+    ) -> io::Result<std::process::ExitStatus> {
+        let session_id = self.ensure_session()?;
+
+        // Construct the schroot command
+        // schroot -p -r -c session_id -- program args...
+        // If cwd is specified, we wrap in sh -c "cd cwd && ..."
+
+        let mut command_args = vec![
+            "-p".to_string(),
+            "-r".to_string(),
+            "-c".to_string(),
+            session_id,
+            "--".to_string(),
+        ];
+
+        let mut actual_program = program.to_string();
+        let mut actual_args = args.to_vec();
+
+        // Simplest: Wrap everything in `sh -c` if CWD or ENV is needed.
+        if cwd.is_some() || !env.is_empty() {
+            let mut shell_cmd = String::new();
+
+            if let Some(dir) = cwd {
+                shell_cmd.push_str(&format!("cd {} && ", dir));
+            }
+
+            if !env.is_empty() {
+                shell_cmd.push_str("env ");
+                for (k, v) in env {
+                    shell_cmd.push_str(&format!("{}={} ", k, v));
+                }
+            }
+
+            shell_cmd.push_str(&format!("{} {}", program, args.join(" ")));
+
+            actual_program = "sh".to_string();
+            actual_args = vec!["-c".to_string(), shell_cmd];
+        }
+
+        command_args.push(actual_program);
+        command_args.extend(actual_args);
+
+        self.parent().command("schroot").args(command_args).status()
+    }
+
+    fn run_output(
+        &self,
+        program: &str,
+        args: &[String],
+        env: &[(String, String)],
+        cwd: Option<&str>,
+    ) -> io::Result<std::process::Output> {
+        let session_id = self.ensure_session()?;
+
+        let mut command_args = vec![
+            "-r".to_string(),
+            "-c".to_string(),
+            session_id,
+            "--".to_string(),
+        ];
+
+        let mut actual_program = program.to_string();
+        let mut actual_args = args.to_vec();
+
+        if cwd.is_some() || !env.is_empty() {
+            let mut shell_cmd = String::new();
+
+            if let Some(dir) = cwd {
+                shell_cmd.push_str(&format!("cd {} && ", dir));
+            }
+
+            if !env.is_empty() {
+                shell_cmd.push_str("env ");
+                for (k, v) in env {
+                    shell_cmd.push_str(&format!("{}={} ", k, v));
+                }
+            }
+
+            shell_cmd.push_str(&format!("{} {}", program, args.join(" ")));
+
+            actual_program = "sh".to_string();
+            actual_args = vec!["-c".to_string(), shell_cmd];
+        }
+
+        command_args.push(actual_program);
+        command_args.extend(actual_args);
+
+        self.parent().command("schroot").args(command_args).output()
+    }
+
+    fn create_temp_dir(&self) -> io::Result<String> {
+        let output = self.run_output("mktemp", &["-d".to_string()], &[], None)?;
+        if !output.status.success() {
+            return Err(io::Error::other("schroot mktemp failed"));
+        }
+        Ok(String::from_utf8_lossy(&output.stdout).trim().to_string())
+    }
+
+    fn copy_path(&self, src: &Path, dest: &Path) -> io::Result<()> {
+        let status = self.run(
+            "cp",
+            &[
+                "-a".to_string(),
+                src.to_string_lossy().to_string(),
+                dest.to_string_lossy().to_string(),
+            ],
+            &[],
+            None,
+        )?;
+        if !status.success() {
+            return Err(io::Error::other("schroot copy failed"));
+        }
+        Ok(())
+    }
+
+    fn read_file(&self, path: &Path) -> io::Result<String> {
+        let output = self.run_output("cat", &[path.to_string_lossy().to_string()], &[], None)?;
+        if !output.status.success() {
+            return Err(io::Error::other(format!(
+                "schroot read failed: {}",
+                String::from_utf8_lossy(&output.stderr)
+            )));
+        }
+        String::from_utf8(output.stdout).map_err(|e| io::Error::new(io::ErrorKind::InvalidData, e))
+    }
+
+    fn write_file(&self, path: &Path, content: &str) -> io::Result<()> {
+        let status = self.run(
+            "sh",
+            &[
+                "-c".to_string(),
+                format!(
+                    "echo -ne '{}' > '{}'",
+                    content.replace("'", "'\\''"),
+                    path.to_string_lossy()
+                ),
+            ],
+            &[],
+            None,
+        )?;
+        if !status.success() {
+            return Err(io::Error::other("schroot write failed"));
+        }
+        Ok(())
+    }
+}