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/ssh.rs

@@ -2,7 +2,9 @@
 /// Context driver: Copies over SFTP with ssh2, executes commands over ssh2 channels
 use super::api::ContextDriver;
 use log::debug;
+use ssh2;
 use std::fs;
+use std::io::Write;
 use std::io::{self, Read};
 use std::net::TcpStream;
 #[cfg(unix)]
@@ -90,12 +92,30 @@ impl ContextDriver for SshDriver {
         Ok(files)
     }
 
-    fn run(&self, program: &str, args: &[String]) -> io::Result<std::process::ExitStatus> {
+    fn run(
+        &self,
+        program: &str,
+        args: &[String],
+        env: &[(String, String)],
+        cwd: Option<&str>,
+    ) -> io::Result<std::process::ExitStatus> {
         let sess = connect_ssh(&self.host, self.user.as_deref(), self.port)?;
         let mut channel = sess.channel_session().map_err(io::Error::other)?;
 
-        // Construct command line
-        let mut cmd_line = program.to_string();
+        // Construct command line with env vars
+        // TODO: No, use ssh2 channel.set_env
+        let mut cmd_line = String::new();
+        for (key, value) in env {
+            cmd_line.push_str(&format!(
+                "export {}='{}'; ",
+                key,
+                value.replace("'", "'\\''")
+            ));
+        }
+        if let Some(dir) = cwd {
+            cmd_line.push_str(&format!("cd {} && ", dir));
+        }
+        cmd_line.push_str(program);
         for arg in args {
             cmd_line.push(' ');
             cmd_line.push_str(arg); // TODO: escape
@@ -119,12 +139,29 @@ impl ContextDriver for SshDriver {
         Ok(ExitStatus::from_raw(code))
     }
 
-    fn run_output(&self, program: &str, args: &[String]) -> io::Result<std::process::Output> {
+    fn run_output(
+        &self,
+        program: &str,
+        args: &[String],
+        env: &[(String, String)],
+        cwd: Option<&str>,
+    ) -> io::Result<std::process::Output> {
         let sess = connect_ssh(&self.host, self.user.as_deref(), self.port)?;
         let mut channel = sess.channel_session().map_err(io::Error::other)?;
 
-        // Construct command line
-        let mut cmd_line = program.to_string();
+        // Construct command line with env vars
+        let mut cmd_line = String::new();
+        for (key, value) in env {
+            cmd_line.push_str(&format!(
+                "export {}='{}'; ",
+                key,
+                value.replace("'", "'\\''")
+            ));
+        }
+        if let Some(dir) = cwd {
+            cmd_line.push_str(&format!("cd {} && ", dir));
+        }
+        cmd_line.push_str(program);
         for arg in args {
             cmd_line.push(' ');
             cmd_line.push_str(arg); // TODO: escape
@@ -155,7 +192,7 @@ impl ContextDriver for SshDriver {
         })
     }
 
-    fn prepare_work_dir(&self) -> io::Result<String> {
+    fn create_temp_dir(&self) -> io::Result<String> {
         let sess = connect_ssh(&self.host, self.user.as_deref(), self.port)?;
         let mut channel = sess.channel_session().map_err(io::Error::other)?;
 
@@ -173,6 +210,40 @@ impl ContextDriver for SshDriver {
 
         Ok(stdout.trim().to_string())
     }
+
+    fn copy_path(&self, src: &Path, dest: &Path) -> io::Result<()> {
+        let sess = connect_ssh(&self.host, self.user.as_deref(), self.port)?;
+        let mut channel = sess.channel_session().map_err(io::Error::other)?;
+        // TODO: use sftp
+        let cmd = format!("cp -a {:?} {:?}", src, dest);
+        debug!("Executing remote copy: {}", cmd);
+        channel.exec(&cmd).map_err(io::Error::other)?;
+        channel.wait_close().map_err(io::Error::other)?;
+        if channel.exit_status().unwrap_or(-1) != 0 {
+            return Err(io::Error::other(format!("Remote copy failed: {}", cmd)));
+        }
+        Ok(())
+    }
+
+    fn read_file(&self, path: &Path) -> io::Result<String> {
+        let sess = connect_ssh(&self.host, self.user.as_deref(), self.port)?;
+        let sftp = sess.sftp().map_err(io::Error::other)?;
+        let mut remote_file = sftp.open(path).map_err(io::Error::other)?;
+        let mut content = String::new();
+        remote_file.read_to_string(&mut content)?;
+        Ok(content)
+    }
+
+    fn write_file(&self, path: &Path, content: &str) -> io::Result<()> {
+        let sess = connect_ssh(&self.host, self.user.as_deref(), self.port)?;
+        let sftp = sess.sftp().map_err(io::Error::other)?;
+        if let Some(parent) = path.parent() {
+            let _ = sftp.mkdir(parent, 0o755);
+        }
+        let mut remote_file = sftp.create(path).map_err(io::Error::other)?;
+        remote_file.write_all(content.as_bytes())?;
+        Ok(())
+    }
 }
 
 impl SshDriver {