Implement a builder-style provisioning API

As discussed in PR #86, this is a builder-style interface to allow
library users to select the backend for tools when provisioning.

Library users must specify one or more provisioners for each setting.
This allows users to decide which tool or tools to use when
provisioning. Some feature flags have been added to `azure-init` which
enable provisioning with a tool, letting you build binaries for a
particular platform relatively easily.

Cargo.toml

@@ -32,3 +32,12 @@ path = "tests/functional_tests.rs"
 members = [
     "libazureinit",
 ]
+
+[features]
+passwd = []
+hostnamectl = []
+useradd = []
+
+systemd_linux = ["passwd", "hostnamectl", "useradd"]
+
+default = ["systemd_linux"]

libazureinit/src/error.rs

@@ -31,4 +31,15 @@ pub enum Error {
     NonEmptyPassword,
     #[error("Unable to get list of block devices")]
     BlockUtils(#[from] block_utils::BlockUtilsError),
+
+    // TODO: Better to include all the Errs from the backends in the error so we can explain to
+    // users what we tried.
+    #[error(
+        "Failed to set the hostname; none of the available backends succeeded"
+    )]
+    NoHostnameProvisioner,
+    #[error(
+        "Failed to create a user; none of the available backends succeeded"
+    )]
+    NoUserProvisioner,
 }

libazureinit/src/lib.rs

@@ -1,12 +1,11 @@
 // Copyright (c) Microsoft Corporation.
 // Licensed under the MIT License.
 
-pub mod distro;
 pub mod error;
 pub mod goalstate;
 pub mod imds;
 pub mod media;
-pub mod user;
+pub mod provision;
 
 // Re-export as the Client is used in our API.
 pub use reqwest;

libazureinit/src/provision/hostname.rs

@@ -0,0 +1,42 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+use std::process::Command;
+
+use tracing::instrument;
+
+use crate::error::Error;
+
+pub enum Provisioner {
+    Hostnamectl,
+    #[cfg(test)]
+    FakeHostnamectl,
+}
+
+impl Provisioner {
+    pub(crate) fn set(self, hostname: impl AsRef<str>) -> Result<(), Error> {
+        match self {
+            Self::Hostnamectl => hostnamectl(hostname.as_ref()),
+            #[cfg(test)]
+            Self::FakeHostnamectl => Ok(()),
+        }
+    }
+}
+
+#[instrument(skip_all)]
+fn hostnamectl(hostname: &str) -> Result<(), Error> {
+    let path_hostnamectl = env!("PATH_HOSTNAMECTL");
+
+    let status = Command::new(path_hostnamectl)
+        .arg("set-hostname")
+        .arg(hostname)
+        .status()?;
+    if status.success() {
+        Ok(())
+    } else {
+        Err(Error::SubprocessFailed {
+            command: path_hostnamectl.to_string(),
+            status,
+        })
+    }
+}

libazureinit/src/provision/mod.rs

@@ -0,0 +1,202 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+pub mod hostname;
+pub mod password;
+pub mod user;
+
+use std::{
+    fs::Permissions,
+    io::Write,
+    marker::PhantomData,
+    os::unix::fs::{DirBuilderExt, PermissionsExt},
+    path::PathBuf,
+};
+
+use private::*;
+use tracing::instrument;
+
+use crate::{error::Error, imds::PublicKeys};
+
+// State transitions for the Provision structure which are used to force
+// the user to provide backends for things they wish to provision.
+mod private {
+    #[derive(Default)]
+    pub struct NoBackends;
+    #[derive(Default)]
+    pub struct HostnameBackend;
+    #[derive(Default)]
+    pub struct PasswordBackend;
+    #[derive(Default)]
+    pub struct AllBackends;
+}
+
+#[derive(Default)]
+pub struct Provision<State = NoBackends> {
+    hostname: String,
+    username: String,
+    keys: Vec<PublicKeys>,
+    password: Option<String>,
+    hostname_backends: Vec<hostname::Provisioner>,
+    user_backends: Vec<user::Provisioner>,
+    password_backends: Vec<password::Provisioner>,
+    state: PhantomData<State>,
+}
+
+impl Provision<NoBackends> {
+    pub fn new(hostname: String, username: String) -> Self {
+        Self {
+            hostname,
+            username,
+            ..Default::default()
+        }
+    }
+
+    pub fn hostname_provisioners(
+        mut self,
+        backends: impl Into<Vec<hostname::Provisioner>>,
+    ) -> Provision<HostnameBackend> {
+        self.hostname_backends = backends.into();
+        Provision {
+            hostname: self.hostname,
+            username: self.username,
+            keys: self.keys,
+            password: self.password,
+            hostname_backends: self.hostname_backends,
+            user_backends: self.user_backends,
+            password_backends: self.password_backends,
+            state: PhantomData,
+        }
+    }
+}
+
+impl Provision<HostnameBackend> {
+    pub fn user_provisioners(
+        mut self,
+        backends: impl Into<Vec<user::Provisioner>>,
+    ) -> Provision<AllBackends> {
+        self.user_backends = backends.into();
+        Provision {
+            hostname: self.hostname,
+            username: self.username,
+            keys: self.keys,
+            password: self.password,
+            hostname_backends: self.hostname_backends,
+            user_backends: self.user_backends,
+            password_backends: self.password_backends,
+            state: PhantomData,
+        }
+    }
+}
+
+impl Provision<PasswordBackend> {
+    pub fn password_provisioners(
+        mut self,
+        backend: impl Into<Vec<password::Provisioner>>,
+    ) -> Provision<AllBackends> {
+        self.password_backends = backend.into();
+        Provision {
+            hostname: self.hostname,
+            username: self.username,
+            keys: self.keys,
+            password: self.password,
+            hostname_backends: self.hostname_backends,
+            user_backends: self.user_backends,
+            password_backends: self.password_backends,
+            state: PhantomData,
+        }
+    }
+}
+
+impl Provision<AllBackends> {
+    /// Set a password for the user being created.
+    ///
+    /// If a password is set, the caller must also set at least one provisioner with
+    /// [`Provision<PasswordBackend>::password_provisioners`].
+    pub fn password(mut self, password: String) -> Provision<PasswordBackend> {
+        self.password = Some(password);
+        Provision {
+            hostname: self.hostname,
+            username: self.username,
+            keys: self.keys,
+            password: self.password,
+            hostname_backends: self.hostname_backends,
+            user_backends: self.user_backends,
+            password_backends: self.password_backends,
+            state: PhantomData,
+        }
+    }
+
+    /// Add the provided SSH keys to the authorized key file of the user being provisioned.
+    pub fn ssh_keys(mut self, keys: impl Into<Vec<PublicKeys>>) -> Self {
+        self.keys = keys.into();
+        self
+    }
+
+    /// Provision the host.
+    #[instrument(skip_all)]
+    pub fn provision(self) -> Result<(), Error> {
+        self.user_backends
+            .into_iter()
+            .find_map(|backend| backend.create(&self.username).ok())
+            .ok_or(Error::NoUserProvisioner)?;
+
+        self.password_backends
+            .into_iter()
+            .find_map(|backend| {
+                backend
+                    .set(&self.username, self.password.as_deref().unwrap_or(""))
+                    .ok()
+            })
+            .ok_or(Error::NoUserProvisioner)?;
+
+        if !self.keys.is_empty() {
+            provision_ssh(&self.username, &self.keys)?;
+        }
+
+        self.hostname_backends
+            .into_iter()
+            .find_map(|backend| backend.set(&self.hostname).ok())
+            .ok_or(Error::NoHostnameProvisioner)?;
+
+        Ok(())
+    }
+}
+
+#[instrument(skip_all, name = "ssh")]
+fn provision_ssh(username: &str, keys: &[PublicKeys]) -> Result<(), Error> {
+    let ssh_dir = PathBuf::from(format!("/home/{}/.ssh", username));
+    let user = nix::unistd::User::from_name(username)?.ok_or_else(|| {
+        Error::UserMissing {
+            user: username.to_string(),
+        }
+    })?;
+    std::fs::DirBuilder::new().mode(0o700).create(&ssh_dir)?;
+    nix::unistd::chown(&ssh_dir, Some(user.uid), Some(user.gid))?;
+
+    let authorized_keys_path = ssh_dir.join("authorized_keys");
+    let mut authorized_keys = std::fs::File::create(&authorized_keys_path)?;
+    authorized_keys.set_permissions(Permissions::from_mode(0o600))?;
+    keys.iter()
+        .try_for_each(|key| writeln!(authorized_keys, "{}", key.key_data))?;
+    nix::unistd::chown(&authorized_keys_path, Some(user.uid), Some(user.gid))?;
+
+    Ok(())
+}
+
+#[cfg(test)]
+mod tests {
+
+    use super::{hostname, password, user, Provision};
+
+    #[test]
+    fn test_successful_provision() {
+        let _p =
+            Provision::new("my-hostname".to_string(), "my-user".to_string())
+                .hostname_provisioners([hostname::Provisioner::FakeHostnamectl])
+                .user_provisioners([user::Provisioner::FakeUseradd])
+                .password("password".to_string())
+                .password_provisioners([password::Provisioner::FakePasswd])
+                .provision()
+                .unwrap();
+    }
+}