tools/aconfig/src/cache.rs

/*
 * Copyright (C) 2023 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

use anyhow::{bail, ensure, Result};
use serde::{Deserialize, Serialize};
use std::io::{Read, Write};

use crate::aconfig::{FlagDeclaration, FlagState, FlagValue, Permission};
use crate::commands::Source;

const DEFAULT_FLAG_STATE: FlagState = FlagState::Disabled;
const DEFAULT_FLAG_PERMISSION: Permission = Permission::ReadWrite;

#[derive(Serialize, Deserialize, Debug)]
pub struct Tracepoint {
    pub source: Source,
    pub state: FlagState,
    pub permission: Permission,
}

#[derive(Serialize, Deserialize, Debug)]
pub struct Item {
    // TODO: duplicating the Cache.namespace as Item.namespace makes the internal representation
    // closer to the proto message `parsed_flag`; hopefully this will enable us to replace the Item
    // struct and use a newtype instead once aconfig has matured. Until then, namespace should
    // really be a Cow<String>.
    pub namespace: String,
    pub name: String,
    pub description: String,
    pub state: FlagState,
    pub permission: Permission,
    pub trace: Vec<Tracepoint>,
}

#[derive(Serialize, Deserialize, Debug)]
pub struct Cache {
    namespace: String,
    items: Vec<Item>,
}

impl Cache {
    pub fn new(namespace: String) -> Cache {
        Cache { namespace, items: vec![] }
    }

    pub fn read_from_reader(reader: impl Read) -> Result<Cache> {
        serde_json::from_reader(reader).map_err(|e| e.into())
    }

    pub fn write_to_writer(&self, writer: impl Write) -> Result<()> {
        serde_json::to_writer(writer, self).map_err(|e| e.into())
    }

    pub fn add_flag_declaration(
        &mut self,
        source: Source,
        declaration: FlagDeclaration,
    ) -> Result<()> {
        ensure!(
            self.items.iter().all(|item| item.name != declaration.name),
            "failed to declare flag {} from {}: flag already declared",
            declaration.name,
            source
        );
        self.items.push(Item {
            namespace: self.namespace.clone(),
            name: declaration.name.clone(),
            description: declaration.description,
            state: DEFAULT_FLAG_STATE,
            permission: DEFAULT_FLAG_PERMISSION,
            trace: vec![Tracepoint {
                source,
                state: DEFAULT_FLAG_STATE,
                permission: DEFAULT_FLAG_PERMISSION,
            }],
        });
        Ok(())
    }

    pub fn add_flag_value(&mut self, source: Source, value: FlagValue) -> Result<()> {
        ensure!(
            value.namespace == self.namespace,
            "failed to set values for flag {}/{} from {}: expected namespace {}",
            value.namespace,
            value.name,
            source,
            self.namespace
        );
        let Some(existing_item) = self.items.iter_mut().find(|item| item.name == value.name) else {
            bail!("failed to set values for flag {}/{} from {}: flag not declared", value.namespace, value.name, source);
        };
        existing_item.state = value.state;
        existing_item.permission = value.permission;
        existing_item.trace.push(Tracepoint {
            source,
            state: value.state,
            permission: value.permission,
        });
        Ok(())
    }

    pub fn iter(&self) -> impl Iterator<Item = &Item> {
        self.items.iter()
    }

    pub fn into_iter(self) -> impl Iterator<Item = Item> {
        self.items.into_iter()
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::aconfig::{FlagState, Permission};

    #[test]
    fn test_add_flag_declaration() {
        let mut cache = Cache::new("ns".to_string());
        cache
            .add_flag_declaration(
                Source::File("first.txt".to_string()),
                FlagDeclaration { name: "foo".to_string(), description: "desc".to_string() },
            )
            .unwrap();
        let error = cache
            .add_flag_declaration(
                Source::File("second.txt".to_string()),
                FlagDeclaration { name: "foo".to_string(), description: "desc".to_string() },
            )
            .unwrap_err();
        assert_eq!(
            &format!("{:?}", error),
            "failed to declare flag foo from second.txt: flag already declared"
        );
    }

    #[test]
    fn test_add_flag_value() {
        fn check(cache: &Cache, name: &str, expected: (FlagState, Permission)) -> bool {
            let item = cache.iter().find(|&item| item.name == name).unwrap();
            item.state == expected.0 && item.permission == expected.1
        }

        let mut cache = Cache::new("ns".to_string());
        let error = cache
            .add_flag_value(
                Source::Memory,
                FlagValue {
                    namespace: "ns".to_string(),
                    name: "foo".to_string(),
                    state: FlagState::Enabled,
                    permission: Permission::ReadOnly,
                },
            )
            .unwrap_err();
        assert_eq!(
            &format!("{:?}", error),
            "failed to set values for flag ns/foo from <memory>: flag not declared"
        );

        cache
            .add_flag_declaration(
                Source::File("first.txt".to_string()),
                FlagDeclaration { name: "foo".to_string(), description: "desc".to_string() },
            )
            .unwrap();
        assert!(check(&cache, "foo", (DEFAULT_FLAG_STATE, DEFAULT_FLAG_PERMISSION)));

        cache
            .add_flag_value(
                Source::Memory,
                FlagValue {
                    namespace: "ns".to_string(),
                    name: "foo".to_string(),
                    state: FlagState::Disabled,
                    permission: Permission::ReadOnly,
                },
            )
            .unwrap();
        assert!(check(&cache, "foo", (FlagState::Disabled, Permission::ReadOnly)));

        cache
            .add_flag_value(
                Source::Memory,
                FlagValue {
                    namespace: "ns".to_string(),
                    name: "foo".to_string(),
                    state: FlagState::Enabled,
                    permission: Permission::ReadWrite,
                },
            )
            .unwrap();
        assert!(check(&cache, "foo", (FlagState::Enabled, Permission::ReadWrite)));

        // different namespace -> no-op
        let error = cache
            .add_flag_value(
                Source::Memory,
                FlagValue {
                    namespace: "some-other-namespace".to_string(),
                    name: "foo".to_string(),
                    state: FlagState::Enabled,
                    permission: Permission::ReadOnly,
                },
            )
            .unwrap_err();
        assert_eq!(&format!("{:?}", error), "failed to set values for flag some-other-namespace/foo from <memory>: expected namespace ns");
        assert!(check(&cache, "foo", (FlagState::Enabled, Permission::ReadWrite)));
    }
}