Get username either by IMDS or from a local OVF file

Username can be obtained either via fetching instance metadata from IMDS
or mounting a local device for OVF environment file. It should not fail
immediately in a single failure, instead it should fall back to the other
mechanism. So it is not a good idea to use `?` for query() or
get_environment().

libazureinit/src/error.rs

@@ -27,6 +27,8 @@ pub enum Error {
     Nix(#[from] nix::Error),
     #[error("The user {user} does not exist")]
     UserMissing { user: String },
+    #[error("failed to get username from IMDS or local OVF files")]
+    UsernameFailure,
     #[error("Provisioning a user with a non-empty password is not supported")]
     NonEmptyPassword,
     #[error("Unable to get list of block devices")]

src/main.rs

@@ -34,25 +34,35 @@ fn get_environment() -> Result<Environment, anyhow::Error> {
 }
 
 fn get_username(
-    instance_metadata: &InstanceMetadata,
-    environment: &Environment,
+    instance_metadata: Option<&InstanceMetadata>,
+    environment: Option<&Environment>,
 ) -> Result<String, anyhow::Error> {
-    if instance_metadata
-        .compute
-        .os_profile
-        .disable_password_authentication
-    {
-        // password authentication is disabled
-        Ok(instance_metadata.compute.os_profile.admin_username.clone())
-    } else {
-        // password authentication is enabled
-
-        Ok(environment
+    if let Some(metadata) = instance_metadata {
+        if metadata.compute.os_profile.disable_password_authentication {
+            // password authentication is disabled
+            return Ok(metadata.compute.os_profile.admin_username.clone());
+        } else {
+            // password authentication is enabled
+
+            if let Some(env) = environment {
+                return Ok(env
+                    .clone()
+                    .provisioning_section
+                    .linux_prov_conf_set
+                    .username);
+            }
+        }
+    }
+
+    if let Some(env) = environment {
+        return Ok(env
             .clone()
             .provisioning_section
             .linux_prov_conf_set
-            .username)
+            .username);
     }
+
+    Err(libazureinit::error::Error::UsernameFailure.into())
 }
 
 #[tokio::main]
@@ -86,8 +96,23 @@ async fn provision() -> Result<(), anyhow::Error> {
         .default_headers(default_headers)
         .build()?;
 
-    let instance_metadata = imds::query(&client).await?;
-    let username = get_username(&instance_metadata, &get_environment()?)?;
+    // Username can be obtained either via fetching instance metadata from IMDS
+    // or mounting a local device for OVF environment file. It should not fail
+    // immediately in a single failure, instead it should fall back to the other
+    // mechanism. So it is not a good idea to use `?` for query() or
+    // get_environment().
+    let instance_metadata = match imds::query(&client).await {
+        Ok(m) => Some(m),
+        Err(_) => None,
+    };
+
+    let environment = match get_environment() {
+        Ok(env) => Some(env),
+        Err(_) => None,
+    };
+
+    let username =
+        get_username(instance_metadata.as_ref(), environment.as_ref())?;
 
     let mut file_path = "/home/".to_string();
     file_path.push_str(username.as_str());
@@ -99,11 +124,19 @@ async fn provision() -> Result<(), anyhow::Error> {
         || format!("Unabled to set an empty password for user '{username}'"),
     )?;
 
-    user::set_ssh_keys(instance_metadata.compute.public_keys, &username)
-        .with_context(|| "Failed to write ssh public keys.")?;
+    user::set_ssh_keys(
+        instance_metadata.clone().unwrap().compute.public_keys,
+        &username,
+    )
+    .with_context(|| "Failed to write ssh public keys.")?;
 
     distro::set_hostname_with_hostnamectl(
-        instance_metadata.compute.os_profile.computer_name.as_str(),
+        instance_metadata
+            .unwrap()
+            .compute
+            .os_profile
+            .computer_name
+            .as_str(),
     )
     .with_context(|| "Failed to set hostname.")?;