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/*! A small, no-std, object-safe, serialization-only framework. The `sval` API is built around two key traits: - [`Value`] is a trait for data with a streamable structure. It's like `serde::Serialize`. - [`Stream`] is a trait for receiving the structure of a value. It's like `serde::Serializer`. # Getting started Add `sval` to your `Cargo.toml`: ```toml,ignore [dependencies.sval] version = "0.4.3" ``` # Supported formats - [JSON](https://crates.io/crates/sval_json), the ubiquitous JavaScript Object Notation used by many HTTP APIs. # Streaming values The structure of a [`Value`] can be streamed to a [`Stream`]. ## in a single call For simple use-cases, use the [`stream`](function.stream.html) function to stream the structure of a value: ```no_run # #[cfg(not(feature = "std"))] # fn main() {} # #[cfg(feature = "std")] # fn main() -> Result<(), Box<dyn std::error::Error>> { sval::stream(MyStream, 42)?; # Ok(()) # } # use sval::stream::{self, Stream}; # struct MyStream; # impl Stream for MyStream { # fn fmt(&mut self, _: stream::Arguments) -> stream::Result { unimplemented!() } # } ``` where `42` is a [`Value`] and `MyStream` is a [`Stream`]. ## over multiple calls More involved use-cases may want to build up structure over time. Use a [`stream::OwnedStream`](stream/struct.OwnedStream.html) to hang on to a stream and pass it values over time: ```no_run # #[cfg(not(feature = "std"))] # fn main() {} # #[cfg(feature = "std")] # fn main() -> Result<(), Box<dyn std::error::Error>> { use sval::{ Value, stream::{self, OwnedStream}, }; // We begin the wrapper over `MyStream` let mut stream = StreamPairs::new()?; // Pairs can be streamed independently stream.pair("a", 42)?; stream.pair("b", 17)?; // Eventually we end the wrapper and return the underlying `MyStream` let my_stream = stream.end()?; struct StreamPairs { // Using `OwnedStream<MyStream>` instead of just `MyStream` // gives us better ergonomics and validation stream: OwnedStream<MyStream>, } impl StreamPairs { fn new() -> Result<Self, stream::Error> { let mut stream = OwnedStream::new(MyStream); stream.map_begin(None)?; Ok(StreamPairs { stream, }) } fn pair(&mut self, k: impl Value, v: impl Value) -> Result<(), stream::Error> { self.stream.map_key(k)?; self.stream.map_value(v)?; Ok(()) } fn end(mut self) -> Result<MyStream, stream::Error> { self.stream.map_end()?; Ok(self.stream.into_inner()) } } # Ok(()) # } # use sval::stream::{self, Stream}; # struct MyStream; # impl Stream for MyStream { # fn fmt(&mut self, _: stream::Arguments) -> stream::Result { unimplemented!() } # } ``` The above example captures an `OwnedStream<MyStream>` and then allows multiple key-value pairs to be streamed through it before finishing. # Implementing the `Value` trait Use the `derive` Cargo feature to allow `Value` to be derived: ```toml,ignore [dependencies.sval] features = ["derive"] ``` Then derive the [`Value`] trait for simple datastructures: ``` # fn main() {} # #[cfg(feature = "derive")] # mod test { use sval::Value; #[derive(Value)] pub struct Data { id: u32, title: String, } # } ``` The trait can also be implemented manually: ``` use sval::value::{self, Value}; pub struct Id(u64); impl Value for Id { fn stream(&self, stream: &mut value::Stream) -> value::Result { stream.u64(self.0) } } ``` ## for a sequence A sequence can be visited by iterating over its elements: ``` use sval::value::{self, Value}; pub struct Seq(Vec<u64>); impl Value for Seq { fn stream(&self, stream: &mut value::Stream) -> value::Result { stream.seq_begin(Some(self.0.len()))?; for v in &self.0 { stream.seq_elem(v)?; } stream.seq_end() } } ``` ## for a map A map can be visited by iterating over its key-value pairs: ``` # fn main() {} # #[cfg(feature = "std")] # mod test { use std::collections::BTreeMap; use sval::value::{self, Value}; pub struct Map(BTreeMap<String, u64>); impl Value for Map { fn stream(&self, stream: &mut value::Stream) -> value::Result { stream.map_begin(Some(self.0.len()))?; for (k, v) in &self.0 { stream.map_key(k)?; stream.map_value(v)?; } stream.map_end() } } # } ``` ## for values that aren't known upfront Types can stream a structure that's different than what they use internally. In the following example, the `Map` type doesn't have any keys or values, but serializes a nested map like `{"nested": {"key": 42}}`: ``` use sval::value::{self, Value}; pub struct Map; impl Value for Map { fn stream(&self, stream: &mut value::Stream) -> value::Result { stream.map_begin(Some(1))?; stream.map_key_begin()?.str("nested")?; stream.map_value_begin()?.map_begin(Some(1))?; stream.map_key_begin()?.str("key")?; stream.map_value_begin()?.u64(42)?; stream.map_end()?; stream.map_end() } } ``` # Implementing the `Stream` trait ## without state Implement the [`Stream`] trait to visit the structure of a [`Value`]: ``` use sval::stream::{self, Stream}; struct Fmt; impl Stream for Fmt { fn fmt(&mut self, v: stream::Arguments) -> stream::Result { println!("{}", v); Ok(()) } } ``` A `Stream` might only care about a single kind of value. The following example overrides the provided `u64` method to see whether a given value is a `u64`: ``` use sval::{ Value, stream::{self, Stream, OwnedStream}, }; assert!(is_u64(42u64)); pub fn is_u64(v: impl Value) -> bool { OwnedStream::stream(IsU64(None), v) .map(|is_u64| is_u64.0.is_some()) .unwrap_or(false) } struct IsU64(Option<u64>); impl Stream for IsU64 { fn u64(&mut self, v: u64) -> stream::Result { self.0 = Some(v); Ok(()) } } ``` ## with state There are more methods on `Stream` that can be overriden for more complex datastructures like sequences and maps. The following example uses a [`stream::Stack`] to track the state of any sequences and maps and ensure they're valid: ``` use std::{fmt, mem}; use sval::stream::{self, stack, Stream, Stack}; struct Fmt { stack: stream::Stack, delim: &'static str, } impl Fmt { fn next_delim(pos: stack::Pos) -> &'static str { if pos.is_key() { return ": "; } if pos.is_value() || pos.is_elem() { return ", "; } return ""; } } impl Stream for Fmt { fn fmt(&mut self, v: stream::Arguments) -> stream::Result { let pos = self.stack.primitive()?; let delim = mem::replace(&mut self.delim, Self::next_delim(pos)); print!("{}{:?}", delim, v); Ok(()) } fn i128(&mut self, v: i128) -> stream::Result { self.fmt(format_args!("{:?}", v)) } fn u128(&mut self, v: u128) -> stream::Result { self.fmt(format_args!("{:?}", v)) } fn f64(&mut self, v: f64) -> stream::Result { self.fmt(format_args!("{:?}", v)) } fn bool(&mut self, v: bool) -> stream::Result { self.fmt(format_args!("{:?}", v)) } fn str(&mut self, v: &str) -> stream::Result { self.fmt(format_args!("{:?}", v)) } fn none(&mut self) -> stream::Result { self.fmt(format_args!("{:?}", ())) } fn seq_begin(&mut self, _: Option<usize>) -> stream::Result { self.stack.seq_begin()?; let delim = mem::replace(&mut self.delim, ""); print!("{}[", delim); Ok(()) } fn seq_elem(&mut self) -> stream::Result { self.stack.seq_elem()?; Ok(()) } fn seq_end(&mut self) -> stream::Result { let pos = self.stack.seq_end()?; self.delim = Self::next_delim(pos); print!("]"); Ok(()) } fn map_begin(&mut self, _: Option<usize>) -> stream::Result { self.stack.map_begin()?; let delim = mem::replace(&mut self.delim, ""); print!("{}{{", delim); Ok(()) } fn map_key(&mut self) -> stream::Result { self.stack.map_key()?; Ok(()) } fn map_value(&mut self) -> stream::Result { self.stack.map_value()?; Ok(()) } fn map_end(&mut self) -> stream::Result { let pos = self.stack.map_end()?; self.delim = Self::next_delim(pos); print!("}}"); Ok(()) } } ``` By default, the `Stack` type has a fixed depth. That means deeply nested structures aren't supported. See the [`Stack` type for more details](stream/stack/struct.Stack.html#depth). # `serde` integration Use the `serde` Cargo feature to enable integration with `serde`: ```toml,ignore [dependencies.sval] features = ["serde"] ``` When `serde` is available, the `Value` trait can also be derived based on an existing `Serialize` implementation: ```ignore use sval::Value; #[derive(Serialize, Value)] #[sval(derive_from = "serde")] pub enum Data { Variant(i32, String), } # } ``` In no-std environments, `serde` support can be enabled using the `serde_no_std` feature instead: ```toml,ignore [dependencies.sval] features = ["serde_no_std"] ``` # `std::fmt` integration Use the `fmt` Cargo feature to enable extended integration with `std::fmt`: ```toml,ignore [dependencies.sval] features = ["fmt"] ``` When `fmt` is available, arbitrary `Value`s can be treated like `std::fmt::Debug`: ``` # fn main() {} # #[cfg(feature = "fmt")] # mod test { fn with_value(value: impl sval::Value) { dbg!(sval::fmt::to_debug(&value)); // Do something with the value } # } ``` */ #![doc(html_root_url = "https://docs.rs/sval/0.4.3")] #![no_std] #[doc(hidden)] #[cfg(feature = "derive")] pub mod derive; #[doc(inline)] #[cfg(feature = "derive")] pub use sval_derive::*; #[cfg(feature = "std")] #[macro_use] #[allow(unused_imports)] extern crate std; #[cfg(not(feature = "std"))] #[macro_use] #[allow(unused_imports)] extern crate core as std; #[macro_use] mod error; mod collect; #[cfg(any(test, feature = "test"))] pub mod test; #[cfg(feature = "fmt")] pub mod fmt; #[cfg(feature = "serde_lib")] pub mod serde; pub mod stream; pub mod value; pub use self::{ error::Error, stream::Stream, value::Value, }; /** Stream the structure of a [`Value`] using the given [`Stream`]. This method is a convenient way of calling [`OwnedStream::stream`](stream/struct.OwnedStream.html#method.stream). */ pub fn stream(stream: impl Stream, value: impl Value) -> Result<(), Error> { crate::stream::OwnedStream::stream(stream, value)?; Ok(()) }