Implement basic deaserializer

boa_cli/src/debug/snapshot.rs

@@ -1,29 +1,59 @@
-use std::{fs::OpenOptions, io::Write};
+use std::{
+    fs::{File, OpenOptions},
+    io::{Read, Write},
+};
 
 use boa_engine::{
-    object::ObjectInitializer, snapshot::SnapshotSerializer, Context, JsNativeError, JsObject,
-    JsResult, JsValue, NativeFunction,
+    object::ObjectInitializer,
+    snapshot::{Snapshot, SnapshotSerializer},
+    Context, JsNativeError, JsObject, JsResult, JsValue, NativeFunction,
 };
 
 const SNAPSHOT_PATH: &str = "./snapshot.bin";
 
+fn get_file_as_byte_vec(filename: &str) -> Vec<u8> {
+    let mut f = File::open(&filename).expect("no file found");
+    let metadata = std::fs::metadata(&filename).expect("unable to read metadata");
+    let mut buffer = vec![0; metadata.len() as usize];
+    f.read(&mut buffer).expect("buffer overflow");
+
+    buffer
+}
+
 fn create(_: &JsValue, _: &[JsValue], context: &mut Context<'_>) -> JsResult<JsValue> {
     let Ok(mut file) = OpenOptions::new().write(true).create(true).open(SNAPSHOT_PATH) else {
         return Err(JsNativeError::error().with_message("could not create snapshot.bin file").into());
     };
 
-    let mut serializer = SnapshotSerializer::new();
+    let serializer = SnapshotSerializer::new();
 
-    serializer.serialize(context).unwrap();
+    let snapshot = serializer.serialize(context).unwrap();
 
-    file.write_all(serializer.bytes()).unwrap();
+    file.write_all(snapshot.bytes()).unwrap();
     file.flush().unwrap();
 
     Ok(JsValue::undefined())
 }
 
+fn load(_: &JsValue, _: &[JsValue], context: &mut Context<'_>) -> JsResult<JsValue> {
+    // let Ok(mut file) = OpenOptions::new().read(true).open(SNAPSHOT_PATH) else {
+    //     return Err(JsNativeError::error().with_message("could not open snapshot.bin file").into());
+    // };
+
+    let bytes = get_file_as_byte_vec(SNAPSHOT_PATH);
+
+    let snapshot = Snapshot::new(bytes);
+
+    let deser_context = snapshot.deserialize().unwrap();
+
+    *context = deser_context;
+
+    Ok(JsValue::undefined())
+}
+
 pub(super) fn create_object(context: &mut Context<'_>) -> JsObject {
     ObjectInitializer::new(context)
         .function(NativeFunction::from_fn_ptr(create), "create", 0)
+        .function(NativeFunction::from_fn_ptr(load), "load", 1)
         .build()
 }

boa_cli/src/main.rs

@@ -72,6 +72,7 @@ use boa_engine::{
     optimizer::OptimizerOptions,
     property::Attribute,
     script::Script,
+    snapshot::Snapshot,
     vm::flowgraph::{Direction, Graph},
     Context, JsError, JsNativeError, JsResult, Source,
 };
@@ -81,7 +82,13 @@ use colored::Colorize;
 use debug::init_boa_debug_object;
 use rustyline::{config::Config, error::ReadlineError, EditMode, Editor};
 use std::{
-    cell::RefCell, collections::VecDeque, eprintln, fs::read, fs::OpenOptions, io, path::PathBuf,
+    cell::RefCell,
+    collections::VecDeque,
+    eprintln,
+    fs::OpenOptions,
+    fs::{read, File},
+    io::{self, Read},
+    path::{Path, PathBuf},
     println,
 };
 
@@ -168,6 +175,9 @@ struct Opt {
     /// Root path from where the module resolver will try to load the modules.
     #[arg(long, short = 'r', default_value_os_t = PathBuf::from("."), requires = "mod")]
     root: PathBuf,
+
+    #[arg(long)]
+    snapshot: Option<PathBuf>,
 }
 
 impl Opt {
@@ -363,37 +373,60 @@ fn evaluate_files(
     Ok(())
 }
 
+fn get_file_as_byte_vec(filename: &Path) -> Vec<u8> {
+    let mut f = File::open(&filename).expect("no file found");
+    let metadata = std::fs::metadata(&filename).expect("unable to read metadata");
+    let mut buffer = vec![0; metadata.len() as usize];
+    f.read(&mut buffer).expect("buffer overflow");
+
+    buffer
+}
+
 fn main() -> Result<(), io::Error> {
     let args = Opt::parse();
 
-    let queue: &dyn JobQueue = &Jobs::default();
     let loader = &SimpleModuleLoader::new(&args.root)
         .map_err(|e| io::Error::new(io::ErrorKind::Other, e.to_string()))?;
+
+    let queue: &dyn JobQueue = &Jobs::default();
     let dyn_loader: &dyn ModuleLoader = loader;
-    let mut context = ContextBuilder::new()
-        .job_queue(queue)
-        .module_loader(dyn_loader)
-        .build()
-        .expect("cannot fail with default global object");
 
-    // Strict mode
-    context.strict(args.strict);
+    let mut context = if let Some(path) = &args.snapshot {
+        let bytes = get_file_as_byte_vec(&path);
 
-    // Add `console`.
-    add_runtime(&mut context);
+        let snapshot = Snapshot::new(bytes);
 
-    // Trace Output
-    context.set_trace(args.trace);
+        let deser_context = snapshot.deserialize().unwrap();
 
-    if args.debug_object {
-        init_boa_debug_object(&mut context);
-    }
+        deser_context
+    } else {
+        let mut context = ContextBuilder::new()
+            .job_queue(queue)
+            .module_loader(dyn_loader)
+            .build()
+            .expect("cannot fail with default global object");
+
+        // Strict mode
+        context.strict(args.strict);
+
+        // Add `console`.
+        add_runtime(&mut context);
+
+        // Trace Output
+        context.set_trace(args.trace);
 
-    // Configure optimizer options
-    let mut optimizer_options = OptimizerOptions::empty();
-    optimizer_options.set(OptimizerOptions::STATISTICS, args.optimizer_statistics);
-    optimizer_options.set(OptimizerOptions::OPTIMIZE_ALL, args.optimize);
-    context.set_optimizer_options(optimizer_options);
+        if args.debug_object {
+            init_boa_debug_object(&mut context);
+        }
+
+        // Configure optimizer options
+        let mut optimizer_options = OptimizerOptions::empty();
+        optimizer_options.set(OptimizerOptions::STATISTICS, args.optimizer_statistics);
+        optimizer_options.set(OptimizerOptions::OPTIMIZE_ALL, args.optimize);
+        context.set_optimizer_options(optimizer_options);
+
+        context
+    };
 
     if args.files.is_empty() {
         let config = Config::builder()

boa_engine/src/context/mod.rs

@@ -996,3 +996,16 @@ impl crate::snapshot::Serialize for Context<'_> {
         Ok(())
     }
 }
+
+impl crate::snapshot::Deserialize for Context<'_> {
+    fn deserialize(
+        d: &mut crate::snapshot::SnapshotDeserializer<'_>,
+    ) -> Result<Self, crate::snapshot::SnapshotError> {
+        let strict = d.read_bool()?;
+        let mut context = Context::default();
+
+        context.strict(strict);
+
+        Ok(context)
+    }
+}

boa_engine/src/snapshot/mod.rs

@@ -7,6 +7,18 @@ use crate::{Context, JsBigInt, JsObject, JsString, JsSymbol};
 use indexmap::{IndexMap, IndexSet};
 use std::fmt::{Debug, Display};
 
+/// TODO: doc
+pub trait Serialize {
+    /// Serialize type
+    fn serialize(&self, s: &mut SnapshotSerializer) -> Result<(), SnapshotError>;
+}
+
+/// TODO: doc
+pub trait Deserialize: Sized {
+    /// TODO: doc
+    fn deserialize(d: &mut SnapshotDeserializer<'_>) -> Result<Self, SnapshotError>;
+}
+
 /// TODO: doc
 #[derive(Debug, Clone, Copy)]
 pub struct Header {
@@ -15,12 +27,6 @@ pub struct Header {
     // checksum: u64,
 }
 
-/// TODO: doc
-pub trait Serialize {
-    /// Serialize type
-    fn serialize(&self, s: &mut SnapshotSerializer) -> Result<(), SnapshotError>;
-}
-
 impl Serialize for Header {
     fn serialize(&self, s: &mut SnapshotSerializer) -> Result<(), SnapshotError> {
         s.write_bytes(&self.signature)?;
@@ -29,6 +35,17 @@ impl Serialize for Header {
     }
 }
 
+impl Deserialize for Header {
+    fn deserialize(d: &mut SnapshotDeserializer<'_>) -> Result<Self, SnapshotError> {
+        let signature = d.read_bytes(4)?;
+        let signature = [signature[0], signature[1], signature[2], signature[3]];
+
+        let version = d.read_u32()?;
+
+        Ok(Self { signature, version })
+    }
+}
+
 impl Serialize for JsObject {
     fn serialize(&self, s: &mut SnapshotSerializer) -> Result<(), SnapshotError> {
         let value = s.objects.insert_full(self.clone()).0;
@@ -40,8 +57,149 @@ impl Serialize for JsObject {
 
 /// TODO: doc
 pub struct Snapshot {
-    header: Header,
     bytes: Vec<u8>,
+    external_references: IndexSet<usize>,
+}
+
+impl Snapshot {
+    /// TODO: doc
+    pub fn new(bytes: Vec<u8>) -> Self {
+        Self {
+            bytes,
+            external_references: IndexSet::default(),
+        }
+    }
+
+    /// TODO: doc
+    pub fn bytes(&self) -> &[u8] {
+        &self.bytes
+    }
+
+    /// TODO: doc
+    pub fn deserialize<'a>(&self) -> Result<Context<'a>, SnapshotError> {
+        let mut deserializer = SnapshotDeserializer {
+            index: 0,
+            bytes: &self.bytes,
+            external_references: &self.external_references,
+        };
+
+        let header = Header::deserialize(&mut deserializer)?;
+
+        // TODO: Do error handling and snapshot integrity checks.
+        assert_eq!(&header.signature, b".boa");
+        assert_eq!(header.version, 42);
+
+        let context = Context::deserialize(&mut deserializer)?;
+
+        // Assert that all bytes are consumed.
+        // assert_eq!(deserializer.index, deserializer.bytes.len());
+
+        Ok(context)
+    }
+}
+
+/// TODO: doc
+pub struct SnapshotDeserializer<'snapshot> {
+    bytes: &'snapshot [u8],
+    index: usize,
+    external_references: &'snapshot IndexSet<usize>,
+}
+
+impl SnapshotDeserializer<'_> {
+    /// TODO: doc
+    pub fn read_bool(&mut self) -> Result<bool, SnapshotError> {
+        let byte = self.read_u8()?;
+        assert!(byte == 0 || byte == 1);
+        Ok(byte == 1)
+    }
+    /// TODO: doc
+    pub fn read_u8(&mut self) -> Result<u8, SnapshotError> {
+        let byte = self.bytes[self.index];
+        self.index += 1;
+        Ok(byte)
+    }
+    /// TODO: doc
+    pub fn read_i8(&mut self) -> Result<i8, SnapshotError> {
+        let byte = self.bytes[self.index];
+        self.index += 1;
+        Ok(byte as i8)
+    }
+
+    /// TODO: doc
+    pub fn read_u16(&mut self) -> Result<u16, SnapshotError> {
+        let bytes = self.read_bytes(std::mem::size_of::<u16>())?;
+        let value = u16::from_le_bytes([bytes[0], bytes[1]]);
+        Ok(value)
+    }
+    /// TODO: doc
+    pub fn read_i16(&mut self) -> Result<i16, SnapshotError> {
+        let value = self.read_u16()?;
+        Ok(value as i16)
+    }
+
+    /// TODO: doc
+    pub fn read_u32(&mut self) -> Result<u32, SnapshotError> {
+        let bytes = self.read_bytes(4)?;
+        let value = u32::from_le_bytes([bytes[0], bytes[1], bytes[2], bytes[3]]);
+        Ok(value)
+    }
+    /// TODO: doc
+    pub fn read_i32(&mut self) -> Result<i32, SnapshotError> {
+        let value = self.read_u32()?;
+        Ok(value as i32)
+    }
+
+    /// TODO: doc
+    pub fn read_f32(&mut self) -> Result<f32, SnapshotError> {
+        let value = self.read_u32()?;
+        Ok(f32::from_bits(value))
+    }
+    /// TODO: doc
+    pub fn read_f64(&mut self) -> Result<f64, SnapshotError> {
+        let value = self.read_u64()?;
+        Ok(f64::from_bits(value))
+    }
+
+    /// TODO: doc
+    pub fn read_u64(&mut self) -> Result<u64, SnapshotError> {
+        let bytes = self.read_bytes(std::mem::size_of::<u64>())?;
+        let value = u64::from_le_bytes([
+            bytes[0], bytes[1], bytes[2], bytes[3], bytes[4], bytes[5], bytes[6], bytes[7],
+        ]);
+        Ok(value)
+    }
+    /// TODO: doc
+    pub fn read_i64(&mut self) -> Result<i64, SnapshotError> {
+        let value = self.read_u64()?;
+        Ok(value as i64)
+    }
+
+    /// TODO: doc
+    pub fn read_usize(&mut self) -> Result<usize, SnapshotError> {
+        let value = self.read_u64()?;
+        // TODO: handle error.
+        Ok(usize::try_from(value).unwrap())
+    }
+    /// TODO: doc
+    pub fn read_isize(&mut self) -> Result<isize, SnapshotError> {
+        let value = self.read_usize()?;
+        Ok(value as isize)
+    }
+    /// TODO: doc
+    pub fn read_string(&mut self) -> Result<&str, SnapshotError> {
+        let len = self.read_usize()?;
+        let bytes = self.read_bytes(len)?;
+        // TODO: handle error
+        Ok(std::str::from_utf8(bytes).unwrap())
+    }
+    /// TODO: doc
+    pub fn read_bytes(&mut self, count: usize) -> Result<&[u8], SnapshotError> {
+        let index = self.index;
+        self.index += count;
+        // TODO: use .get() so we can handle the error.
+        let bytes = &self.bytes[index..(index + count)];
+        Ok(bytes)
+    }
 }
 
 /// TODO: doc
@@ -91,18 +249,12 @@ impl SnapshotSerializer {
         }
     }
 
-    /// TODO: doc
-    pub fn bytes(&self) -> &[u8] {
-        &self.bytes
-    }
-
     /// Serialize the given [`Context`].
-    pub fn serialize(&mut self, context: &mut Context<'_>) -> Result<(), SnapshotError> {
+    pub fn serialize(mut self, context: &mut Context<'_>) -> Result<Snapshot, SnapshotError> {
         // Remove any garbage objects before serialization.
         boa_gc::force_collect();
 
         // boa_gc::walk_gc_alloc_pointers(|address| {
-
         // });
 
         let header = Header {
@@ -110,8 +262,8 @@ impl SnapshotSerializer {
             version: 42,
         };
 
-        header.serialize(self)?;
-        context.serialize(self)?;
+        header.serialize(&mut self)?;
+        context.serialize(&mut self)?;
 
         for i in 0..self.objects.len() {
             let object = self
@@ -119,7 +271,7 @@ impl SnapshotSerializer {
                 .get_index(i)
                 .expect("There should be an object")
                 .clone();
-            object.inner().serialize(self)?;
+            object.inner().serialize(&mut self)?;
         }
 
         for i in 0..self.symbols.len() {
@@ -132,7 +284,7 @@ impl SnapshotSerializer {
             self.write_u64(hash)?;
             if let Some(desc) = symbol.description() {
                 self.write_bool(true)?;
-                desc.serialize(self)?;
+                desc.serialize(&mut self)?;
             } else {
                 self.write_bool(false)?;
             }
@@ -146,7 +298,7 @@ impl SnapshotSerializer {
                 .1
                 .clone();
             // string.
-            string.serialize(self)?;
+            string.serialize(&mut self)?;
 
             self.write_bool(string.is_static())?;
             self.write_usize(string.len())?;
@@ -155,7 +307,10 @@ impl SnapshotSerializer {
             }
         }
 
-        Ok(())
+        Ok(Snapshot {
+            bytes: self.bytes,
+            external_references: self.external_references,
+        })
     }
 
     /// TODO: doc

docs/snapshot.md

@@ -61,6 +61,6 @@ If it's a static string then it's elements comprise the index into the `STATIC_S
 
 ## JsValue Encoding
 
-type `: u8` (JsValue discriminant, Boolean, Null, etc) followed by the value if it exits.
+type `: u8` (JsValue discriminant, Boolean, Null, etc) followed by the value if it applied for the type (`Null` and `Undefined` does not have a value part).
 If following the `JsValue` is an `JsString`, `JsSymbol`, `JsBigInt`, `JsObject` then the
 following value will be an index into the appropriate tables.