section config: parse additional properties when schema allows it

Additional properties will be parsed according to the default string
schema.

This is relevant for use cases when the full schema is not known for
some reason or another. In particular this allows support for parsing
older/newer versions of configuration files. One example of this is
the proposed proxmox-mail-forward helper binary, which currently
doesn't have access to the PBS API types for dependency reasons and
is only interested in the email field for the root user. If it can
only use a minimal schema with additional_properties set to true, it
will be robust against changes.

Writing already works, because the ObjectSchema's verify_json()
already handles additional_properties correctly and
format_section_content() handles them like all other properties
(method doesn't depend on the schema).

Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>

proxmox-section-config/src/lib.rs

@@ -31,6 +31,9 @@ use proxmox_lang::try_block;
 use proxmox_schema::format::{dump_properties, wrap_text, ParameterDisplayStyle};
 use proxmox_schema::*;
 
+/// Used for additional properties when the schema allows them.
+const ADDITIONAL_PROPERTY_SCHEMA: Schema = StringSchema::new("Additional property").schema();
+
 /// Associates a section type name with a `Schema`.
 pub struct SectionConfigPlugin {
     type_name: String,
@@ -446,7 +449,10 @@ impl SectionConfig {
                                         (true, items)
                                     }
                                     Some((_optional, ref prop_schema)) => (false, prop_schema),
-                                    None => bail!("unknown property '{}'", key),
+                                    None => match plugin.properties.additional_properties() {
+                                        true => (false, &&ADDITIONAL_PROPERTY_SCHEMA),
+                                        false => bail!("unknown property '{}'", key),
+                                    },
                                 };
 
                                 let value = match prop_schema.parse_simple_value(&value) {
@@ -884,6 +890,77 @@ lvmthin: local-lvm2
     assert_eq!(raw, created);
 }
 
+#[test]
+fn test_section_config_with_additional_properties() {
+    let filename = "user.cfg";
+
+    const ID_SCHEMA: Schema = StringSchema::new("default id schema.")
+        .min_length(3)
+        .schema();
+    let mut config = SectionConfig::new(&ID_SCHEMA);
+    let mut config_with_additional = SectionConfig::new(&ID_SCHEMA);
+
+    const PROPERTIES: [(&str, bool, &proxmox_schema::Schema); 2] = [
+        (
+            "email",
+            false,
+            &StringSchema::new("The e-mail of the user").schema(),
+        ),
+        (
+            "userid",
+            true,
+            &StringSchema::new("The id of the user (name@realm).")
+                .min_length(3)
+                .schema(),
+        ),
+    ];
+
+    const USER_PROPERTIES: ObjectSchema = ObjectSchema {
+        description: "user properties",
+        properties: &PROPERTIES,
+        additional_properties: false,
+        default_key: None,
+    };
+
+    const USER_PROPERTIES_WITH_ADDTIONAL: ObjectSchema = ObjectSchema {
+        description: "user properties with additional",
+        properties: &PROPERTIES,
+        additional_properties: true,
+        default_key: None,
+    };
+
+    let plugin = SectionConfigPlugin::new(
+        "user".to_string(),
+        Some("userid".to_string()),
+        &USER_PROPERTIES,
+    );
+    config.register_plugin(plugin);
+
+    let plugin = SectionConfigPlugin::new(
+        "user".to_string(),
+        Some("userid".to_string()),
+        &USER_PROPERTIES_WITH_ADDTIONAL,
+    );
+    config_with_additional.register_plugin(plugin);
+
+    let raw = r"
+
+user: root@pam
+        email root@example.com
+        shinynewoption somevalue
+";
+
+    let res = config_with_additional.parse(filename, raw);
+    println!("RES: {:?}", res);
+    let written = config_with_additional.write(filename, &res.unwrap());
+    println!("CONFIG:\n{}", written.unwrap());
+
+    assert!(config.parse(filename, raw).is_err());
+    // SectionConfigData doesn't have Clone and it would only be needed here currently.
+    let res = config_with_additional.parse(filename, raw);
+    assert!(config.write(filename, &res.unwrap()).is_err());
+}
+
 /// Generate ReST Documentaion for ``SectionConfig``
 pub fn dump_section_config(config: &SectionConfig) -> String {
     let mut res = String::new();