commit 0165343c362277e7c5c898329e9032791dddedd4
Author: Aiden McClelland <me@drbonez.dev>
Date:   Wed Jan 6 02:05:28 2021 -0700

    mvp

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..1096b27
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,3 @@
+/target
+Cargo.lock
+test.db
\ No newline at end of file
diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..a116870
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,21 @@
+[package]
+name = "patch-db"
+version = "0.1.0"
+authors = ["Aiden McClelland <me@drbonez.dev>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+async-trait = "0.1.42"
+fd-lock-rs = "0.1.3"
+futures = "0.3.8"
+json-patch = { path = "../json-patch" }
+json-ptr = { path = "../json-ptr" }
+nix = "0.19.1"
+qutex-2 = { path = "../qutex" }
+serde = { version = "1.0.118", features = ["rc"] }
+serde_json = "1.0.61"
+serde_cbor = { git = "https://github.com/dr-bonez/cbor.git" }
+thiserror = "1.0.23"
+tokio = { version = "1.0.1", features = ["sync", "fs", "rt", "io-util", "macros"] }
diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..45bdf91
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,516 @@
+use std::collections::HashMap;
+use std::fs::OpenOptions;
+use std::io::Error as IOError;
+use std::path::Path;
+use std::sync::Arc;
+
+use fd_lock_rs::FdLock;
+use futures::future::{BoxFuture, FutureExt};
+use json_patch::{Patch, PatchOperation};
+use json_ptr::{JsonPointer, SegList};
+use qutex_2::{QrwLock, ReadGuard, WriteGuard};
+use serde::{Deserialize, Serialize};
+use serde_json::Value;
+use thiserror::Error;
+use tokio::{
+    fs::File,
+    sync::{
+        broadcast::{Receiver, Sender},
+        RwLock,
+    },
+};
+
+#[cfg(test)]
+mod test;
+
+#[derive(Error, Debug)]
+pub enum Error {
+    #[error("IO Error: {0}")]
+    IO(#[from] IOError),
+    #[error("JSON (De)Serialization Error: {0}")]
+    JSON(#[from] serde_json::Error),
+    #[error("CBOR (De)Serialization Error: {0}")]
+    CBOR(#[from] serde_cbor::Error),
+    #[error("Index Error: {0:?}")]
+    Pointer(#[from] json_ptr::IndexError),
+    #[error("Patch Error: {0}")]
+    Patch(#[from] json_patch::PatchError),
+    #[error("Join Error: {0}")]
+    Join(#[from] tokio::task::JoinError),
+    #[error("FD Lock Error: {0}")]
+    FDLock(#[from] fd_lock_rs::Error),
+}
+
+#[derive(Debug, Clone, Deserialize, Serialize)]
+pub struct Revision {
+    pub id: u64,
+    pub patch: Patch,
+}
+
+#[derive(Debug, Clone)]
+pub struct DiffPatch(Patch);
+
+pub struct Store {
+    file: FdLock<File>,
+    data: Value,
+    revision: u64,
+}
+impl Store {
+    pub async fn open<P: AsRef<Path> + Send + 'static>(path: P) -> Result<Self, Error> {
+        Ok(tokio::task::spawn_blocking(move || {
+            use std::io::Write;
+
+            let p = path.as_ref();
+            let bak = p.with_extension("bak");
+            if bak.exists() {
+                std::fs::rename(&bak, p)?;
+            }
+            let mut f = FdLock::lock(
+                OpenOptions::new()
+                    .create(true)
+                    .read(true)
+                    .append(true)
+                    .open(p)?,
+                fd_lock_rs::LockType::Exclusive,
+                true,
+            )?;
+            let mut stream =
+                serde_cbor::StreamDeserializer::new(serde_cbor::de::IoRead::new(&mut *f));
+            let mut revision: u64 = stream.next().transpose()?.unwrap_or(0);
+            let mut stream = stream.change_output_type();
+            let mut data = stream.next().transpose()?.unwrap_or_else(|| Value::Null);
+            let mut stream = stream.change_output_type();
+            while let Some(Ok(patch)) = stream.next() {
+                json_patch::patch(&mut data, &patch)?;
+                revision += 1;
+            }
+            serde_cbor::to_writer(std::fs::File::create(&bak)?, &data)?;
+            nix::unistd::ftruncate(std::os::unix::io::AsRawFd::as_raw_fd(&*f), 0)
+                .map_err(|e| std::io::Error::new(std::io::ErrorKind::Other, e))?;
+            serde_cbor::to_writer(&mut *f, &revision)?;
+            serde_cbor::to_writer(&mut *f, &data)?;
+            f.flush()?;
+            f.sync_all()?;
+            std::fs::remove_file(&bak)?;
+
+            Ok::<_, Error>(Store {
+                file: f.map(File::from_std),
+                data,
+                revision,
+            })
+        })
+        .await??)
+    }
+    pub async fn close(mut self) -> Result<(), Error> {
+        use tokio::io::AsyncWriteExt;
+
+        self.file.flush().await?;
+        self.file.shutdown().await?;
+        self.file.unlock(true).map_err(|e| e.1)?;
+        Ok(())
+    }
+    pub fn get<T: for<'de> Deserialize<'de>, S: AsRef<str>, V: SegList>(
+        &self,
+        ptr: &JsonPointer<S, V>,
+    ) -> Result<T, Error> {
+        Ok(serde_json::from_value(
+            ptr.get(&self.data).unwrap_or(&Value::Null).clone(),
+        )?)
+    }
+    pub fn dump(&self) -> Value {
+        self.data.clone()
+    }
+    pub async fn put<T: Serialize, S: AsRef<str>, V: SegList>(
+        &mut self,
+        ptr: &JsonPointer<S, V>,
+        value: &T,
+    ) -> Result<Arc<Revision>, Error> {
+        let mut patch = DiffPatch(json_patch::diff(
+            ptr.get(&self.data).unwrap_or(&Value::Null),
+            &serde_json::to_value(value)?,
+        ));
+        patch.0.prepend(ptr);
+        self.apply(patch).await
+    }
+    pub async fn apply(&mut self, patch: DiffPatch) -> Result<Arc<Revision>, Error> {
+        use tokio::io::AsyncWriteExt;
+
+        let patch_bin = serde_cbor::to_vec(&patch.0)?;
+        json_patch::patch(&mut self.data, &patch.0)?;
+
+        async fn sync_to_disk(file: &mut File, patch_bin: &[u8]) -> Result<(), IOError> {
+            file.write_all(patch_bin).await?;
+            file.flush().await?;
+            file.sync_data().await?;
+            Ok(())
+        }
+        if let Err(e) = sync_to_disk(&mut *self.file, &patch_bin).await {
+            eprintln!("I/O Error: {}", e);
+            eprintln!("Failed to sync data to disk after successfully applying changes in memory. Aborting...");
+            std::process::abort();
+            // TODO: try to recover.
+        }
+
+        let id = self.revision;
+        self.revision += 1;
+        let res = Arc::new(Revision { id, patch: patch.0 });
+
+        Ok(res)
+    }
+}
+
+#[derive(Clone)]
+pub struct PatchDb {
+    store: Arc<RwLock<Store>>,
+    subscriber: Arc<Sender<Arc<Revision>>>,
+    locker: Locker,
+}
+impl PatchDb {
+    pub async fn open<P: AsRef<Path> + Send + 'static>(path: P) -> Result<Self, Error> {
+        let (subscriber, _) = tokio::sync::broadcast::channel(16);
+
+        Ok(PatchDb {
+            store: Arc::new(RwLock::new(Store::open(path).await?)),
+            locker: Locker::new(),
+            subscriber: Arc::new(subscriber),
+        })
+    }
+    pub async fn get<T: for<'de> Deserialize<'de>, S: AsRef<str>, V: SegList>(
+        &self,
+        ptr: &JsonPointer<S, V>,
+    ) -> Result<T, Error> {
+        self.store.read().await.get(ptr)
+    }
+    pub async fn put<T: Serialize, S: AsRef<str>, V: SegList>(
+        &self,
+        ptr: &JsonPointer<S, V>,
+        value: &T,
+    ) -> Result<Arc<Revision>, Error> {
+        self.store.write().await.put(ptr, value).await
+    }
+    pub async fn apply(&self, patch: DiffPatch) -> Result<Arc<Revision>, Error> {
+        self.store.write().await.apply(patch).await
+    }
+    pub fn subscribe(&self) -> Receiver<Arc<Revision>> {
+        self.subscriber.subscribe()
+    }
+    pub fn begin(&self) -> Transaction {
+        Transaction {
+            db: self.clone(),
+            locks: Vec::new(),
+            updates: DiffPatch(Patch(Vec::new())),
+        }
+    }
+}
+pub trait Checkpoint {
+    type SubTx: Checkpoint;
+    fn get_value<'a, S: AsRef<str> + Send + Sync + 'a, V: SegList + Send + Sync + 'a>(
+        &'a self,
+        ptr: &'a JsonPointer<S, V>,
+    ) -> BoxFuture<Result<Value, Error>>;
+    fn locks(&self) -> &[(JsonPointer, LockerGuard)];
+    fn locker(&self) -> &Locker;
+    fn apply(&mut self, patch: DiffPatch);
+}
+
+pub struct Transaction {
+    db: PatchDb,
+    locks: Vec<(JsonPointer, LockerGuard)>,
+    updates: DiffPatch,
+}
+impl Transaction {
+    async fn get_value<S: AsRef<str>, V: SegList>(
+        &self,
+        ptr: &JsonPointer<S, V>,
+    ) -> Result<Value, Error> {
+        let mut data: Value = ptr
+            .get(&self.db.store.read().await.data)
+            .unwrap_or(&Value::Null)
+            .clone();
+        for op in (self.updates.0).0.iter() {
+            match op {
+                PatchOperation::Add(ref op) => {
+                    if let Some(path) = op.path.strip_prefix(ptr) {
+                        path.insert(&mut data, op.value.clone(), false)?;
+                    }
+                }
+                PatchOperation::Remove(ref op) => {
+                    if let Some(path) = op.path.strip_prefix(ptr) {
+                        path.remove(&mut data, false);
+                    }
+                }
+                PatchOperation::Replace(ref op) => {
+                    if let Some(path) = op.path.strip_prefix(ptr) {
+                        path.set(&mut data, op.value.clone(), false)?;
+                    }
+                }
+                _ => unreachable!("Diff patches cannot contain other operations."),
+            }
+        }
+        Ok(data)
+    }
+    pub async fn lock<S: AsRef<str> + Clone, V: SegList + Clone>(
+        &mut self,
+        ptr: &JsonPointer<S, V>,
+        lock: LockType,
+    ) {
+        match lock {
+            LockType::None => (),
+            LockType::Read => self.db.locker.add_read_lock(ptr, &mut self.locks).await,
+            LockType::Write => self.db.locker.add_write_lock(ptr, &mut self.locks).await,
+        }
+    }
+    pub async fn get<T: for<'de> Deserialize<'de>, S: AsRef<str> + Clone, V: SegList + Clone>(
+        &mut self,
+        ptr: &JsonPointer<S, V>,
+        lock: LockType,
+    ) -> Result<T, Error> {
+        self.lock(ptr, lock).await;
+        Ok(serde_json::from_value(
+            Transaction::get_value(self, ptr).await?,
+        )?)
+    }
+    pub async fn put<T: Serialize, S: AsRef<str>, V: SegList>(
+        &mut self,
+        ptr: &JsonPointer<S>,
+        value: &T,
+    ) -> Result<(), Error> {
+        let old = Transaction::get_value(self, ptr).await?;
+        let new = serde_json::to_value(value)?;
+        let mut patch = json_patch::diff(&old, &new);
+        patch.prepend(ptr);
+        (self.updates.0).0.extend(patch.0);
+        Ok(())
+    }
+    pub async fn commit(self) -> Result<Arc<Revision>, Error> {
+        self.db.apply(self.updates).await
+    }
+}
+impl<'a> Checkpoint for &'a mut Transaction {
+    type SubTx = &'a mut SubTransaction<Self>;
+    fn get_value<'b, S: AsRef<str> + Send + Sync + 'b, V: SegList + Send + Sync + 'b>(
+        &'b self,
+        ptr: &'b JsonPointer<S, V>,
+    ) -> BoxFuture<'b, Result<Value, Error>> {
+        Transaction::get_value(self, ptr).boxed()
+    }
+    fn locks(&self) -> &[(JsonPointer, LockerGuard)] {
+        &self.locks
+    }
+    fn locker(&self) -> &Locker {
+        &self.db.locker
+    }
+    fn apply(&mut self, patch: DiffPatch) {
+        (self.updates.0).0.extend((patch.0).0)
+    }
+}
+
+pub struct SubTransaction<Tx: Checkpoint> {
+    parent: Tx,
+    locks: Vec<(JsonPointer, LockerGuard)>,
+    updates: DiffPatch,
+}
+impl<Tx: Checkpoint> SubTransaction<Tx> {
+    async fn get_value<S: AsRef<str> + Send + Sync, V: SegList + Send + Sync>(
+        &self,
+        ptr: &JsonPointer<S, V>,
+    ) -> Result<Value, Error> {
+        let mut data: Value = self.parent.get_value(ptr).await?;
+        for op in (self.updates.0).0.iter() {
+            match op {
+                PatchOperation::Add(ref op) => {
+                    if let Some(path) = op.path.strip_prefix(ptr) {
+                        path.insert(&mut data, op.value.clone(), false)?;
+                    }
+                }
+                PatchOperation::Remove(ref op) => {
+                    if let Some(path) = op.path.strip_prefix(ptr) {
+                        path.remove(&mut data, false);
+                    }
+                }
+                PatchOperation::Replace(ref op) => {
+                    if let Some(path) = op.path.strip_prefix(ptr) {
+                        path.set(&mut data, op.value.clone(), false)?;
+                    }
+                }
+                _ => unreachable!("Diff patches cannot contain other operations."),
+            }
+        }
+        Ok(data)
+    }
+    pub async fn lock<S: AsRef<str> + Clone, V: SegList + Clone>(
+        &mut self,
+        ptr: &JsonPointer<S, V>,
+        lock: LockType,
+    ) {
+        for lock in self.locks.iter() {
+            if ptr.starts_with(&lock.0) {
+                return;
+            }
+        }
+        match lock {
+            LockType::None => (),
+            LockType::Read => {
+                self.parent
+                    .locker()
+                    .add_read_lock(ptr, &mut self.locks)
+                    .await
+            }
+            LockType::Write => {
+                self.parent
+                    .locker()
+                    .add_write_lock(ptr, &mut self.locks)
+                    .await
+            }
+        }
+    }
+    pub async fn get<
+        T: for<'de> Deserialize<'de>,
+        S: AsRef<str> + Clone + Send + Sync,
+        V: SegList + Clone + Send + Sync,
+    >(
+        &mut self,
+        ptr: &JsonPointer<S, V>,
+        lock: LockType,
+    ) -> Result<T, Error> {
+        self.lock(ptr, lock).await;
+        Ok(serde_json::from_value(
+            SubTransaction::get_value(self, ptr).await?,
+        )?)
+    }
+    pub async fn put<T: Serialize, S: AsRef<str> + Send + Sync, V: SegList + Send + Sync>(
+        &mut self,
+        ptr: &JsonPointer<S>,
+        value: &T,
+    ) -> Result<(), Error> {
+        let old = SubTransaction::get_value(self, ptr).await?;
+        let new = serde_json::to_value(value)?;
+        let mut patch = json_patch::diff(&old, &new);
+        patch.prepend(ptr);
+        (self.updates.0).0.extend(patch.0);
+        Ok(())
+    }
+    pub fn commit(mut self) {
+        self.parent.apply(self.updates)
+    }
+}
+impl<'a, Tx: Checkpoint + Send + Sync> Checkpoint for &'a mut SubTransaction<Tx> {
+    type SubTx = &'a mut SubTransaction<Self>;
+    fn get_value<'b, S: AsRef<str> + Send + Sync + 'b, V: SegList + Send + Sync + 'b>(
+        &'b self,
+        ptr: &'b JsonPointer<S, V>,
+    ) -> BoxFuture<'b, Result<Value, Error>> {
+        SubTransaction::get_value(self, ptr).boxed()
+    }
+    fn locks(&self) -> &[(JsonPointer, LockerGuard)] {
+        &self.locks
+    }
+    fn locker(&self) -> &Locker {
+        &self.parent.locker()
+    }
+    fn apply(&mut self, patch: DiffPatch) {
+        (self.updates.0).0.extend((patch.0).0)
+    }
+}
+
+#[derive(Debug)]
+pub enum LockType {
+    None,
+    Read,
+    Write,
+}
+
+pub enum LockerGuard {
+    Empty,
+    Read(ReadGuard<HashMap<String, Locker>>),
+    Write(WriteGuard<HashMap<String, Locker>>),
+}
+impl LockerGuard {
+    pub fn take(&mut self) -> Self {
+        std::mem::replace(self, LockerGuard::Empty)
+    }
+}
+
+#[derive(Clone, Debug)]
+pub struct Locker(QrwLock<HashMap<String, Locker>>);
+impl Locker {
+    pub fn new() -> Self {
+        Locker(QrwLock::new(HashMap::new()))
+    }
+    pub async fn lock_read<S: AsRef<str>, V: SegList>(
+        &self,
+        ptr: &JsonPointer<S, V>,
+    ) -> ReadGuard<HashMap<String, Locker>> {
+        let mut lock = Some(self.0.clone().read().await.unwrap());
+        for seg in ptr.iter() {
+            let new_lock = if let Some(locker) = lock.as_ref().unwrap().get(seg) {
+                locker.0.clone().read().await.unwrap()
+            } else {
+                let mut writer = ReadGuard::upgrade(lock.take().unwrap()).await.unwrap();
+                writer.insert(seg.to_owned(), Locker::new());
+                let reader = WriteGuard::downgrade(writer);
+                reader.get(seg).unwrap().0.clone().read().await.unwrap()
+            };
+            lock = Some(new_lock);
+        }
+        lock.unwrap()
+    }
+    pub async fn add_read_lock<S: AsRef<str> + Clone, V: SegList + Clone>(
+        &self,
+        ptr: &JsonPointer<S, V>,
+        locks: &mut Vec<(JsonPointer, LockerGuard)>,
+    ) {
+        for lock in locks.iter() {
+            if ptr.starts_with(&lock.0) {
+                return;
+            }
+        }
+        locks.push((
+            JsonPointer::to_owned(ptr.clone()),
+            LockerGuard::Read(self.lock_read(ptr).await),
+        ));
+    }
+    pub async fn lock_write<S: AsRef<str>, V: SegList>(
+        &self,
+        ptr: &JsonPointer<S>,
+    ) -> WriteGuard<HashMap<String, Locker>> {
+        let mut lock = self.0.clone().write().await.unwrap();
+        for seg in ptr.iter() {
+            let new_lock = if let Some(locker) = lock.get(seg) {
+                locker.0.clone().write().await.unwrap()
+            } else {
+                lock.insert(seg.to_owned(), Locker::new());
+                lock.get(seg).unwrap().0.clone().write().await.unwrap()
+            };
+            lock = new_lock;
+        }
+        lock
+    }
+    pub async fn add_write_lock<S: AsRef<str> + Clone, V: SegList + Clone>(
+        &self,
+        ptr: &JsonPointer<S, V>,
+        locks: &mut Vec<(JsonPointer, LockerGuard)>,
+    ) {
+        for lock in locks.iter_mut() {
+            if ptr.starts_with(&lock.0) {
+                let guard = lock.1.take();
+                lock.1 = match guard {
+                    LockerGuard::Read(l) => {
+                        LockerGuard::Write(ReadGuard::upgrade(l).await.unwrap())
+                    }
+                    a => a,
+                };
+                return;
+            }
+        }
+        locks.push((
+            JsonPointer::to_owned(ptr.clone()),
+            LockerGuard::Read(self.lock_read(ptr).await),
+        ));
+    }
+}
+impl Default for Locker {
+    fn default() -> Self {
+        Locker::new()
+    }
+}
diff --git a/src/test.rs b/src/test.rs
new file mode 100644
index 0000000..a3c9d80
--- /dev/null
+++ b/src/test.rs
@@ -0,0 +1,10 @@
+use super::*;
+
+#[tokio::test]
+async fn basic() {
+    let db = PatchDb::open("test.db").await.unwrap();
+    let _rev = db
+        .put(&JsonPointer::<&'static str>::default(), &"test")
+        .await
+        .unwrap();
+}