begin Format impl wrapper for FORMATS array

src/formats.rs

@@ -1,17 +1,31 @@
 //! The available formats to convert
 use super::*;
 use std::io;
+use std::{
+    error, fmt,
+};
+
 use object::Object;
 
+/// `Format` impl for JSON.
+mod json;
+
 /// Config for the encode/decode
-pub struct Config;
+pub struct Config; //TODO: What goes here?
 
 /// A directive for a format on how to encode and decode objects.
 #[derive(Clone, Copy)]
 pub struct FormatDirective
 {
-    encode: fn (&Config, &mut dyn io::Write, &Object) -> io::Result<usize>,
+    encode: fn (&Config, &mut dyn io::Write, &Object) -> Result<usize, Error>,
-    decode: fn (&Config, &mut dyn io::Read) -> io::Result<(Object, usize)>,
+    decode: fn (&Config, &mut dyn io::Read) -> Result<(Object, usize), Error>,
+}
+
+/// Trait for statically implementing formatters to/from `Object`. 
+pub trait Format
+{
+    fn encode<W: io::Write>(cfg: &Config, to: W, obj: &Object) -> Result<usize, Error>;
+    fn decode<R: io::Read>(cfg: &Config, from: R) -> Result<Object, Error>; //TODO: An `io::Read` wrapper that counter num of bytes read internally. That way we can extract `(Object, usize)` from just `Object` here.
 }
 
 macro_rules! directive {
@@ -21,11 +35,117 @@ macro_rules! directive {
 	    decode: $decode,
 	})
     };
+    (for $fmt:path => $($name:literal),+) => {
+	//TODO: $fmt will be a struct implementing `Format`.
+	// Will perform input conversions to trait methods.
+	// Will perform input/output conversions for `Format::decode` to extract `(Object, usize)` from `Object` function output and a `io::Read` input wrapper that counts bytes read from the stream.
+	directive!($($name),+ => |c, w, o| {
+	    <$fmt as Format>::encode(c, w, o)
+	}, |c, r| {
+	    todo!("We need a io::Read stream wrapper that counts the bytes read `r` to satisfy the return value requirements of this function pointer")
+	})
+    }
 }
 
 /// All format directives and their name(s)
 pub static FORMATS: &[(&'static [&'static str], FormatDirective)] = &[
-    directive!("json", "js", "javascript" => |_, _, _| todo!(), |_, _| todo!()),
+    directive!(for json::JsonFormatter => "json", "js", "javascript"),
     directive!("s-expression", "sexpr", "lisp", "lexpr" => |_, _, _| todo!(), |_, _| todo!()),
     directive!("cbor" => |_, _, _| todo!(), |_, _| todo!()),
 ];
+
+/// A formatting error kind. See `Error`.
+#[derive(Debug)]
+pub enum ErrorKind
+{
+    IO(io::Error),
+    Unknown,
+}
+
+impl From<io::Error> for ErrorKind
+{
+    fn from(from: io::Error) -> Self
+    {
+	Self::IO(from)
+    }
+}
+
+/// A formatting error.
+#[derive(Debug)]
+pub struct Error(ErrorKind, bool);
+
+impl Error
+{
+    /// An encode error
+    #[inline] pub fn encode(kind: impl Into<ErrorKind>) -> Self
+    {
+	Self(kind.into(), true)
+    }
+    /// A decode error
+    #[inline] pub fn decode(kind: impl Into<ErrorKind>) -> Self
+    {
+	Self(kind.into(), false)
+    }
+
+    /// What kind of error was it?
+    #[inline] pub fn kind(&self) -> &ErrorKind
+    {
+	&self.0
+    }
+
+    /// Is an encode error? 
+    #[inline] pub fn is_encode(&self) -> bool
+    {
+	self.1
+    }
+    
+    /// Is a decode error? 
+    #[inline] pub fn is_decode(&self) -> bool
+    {
+	!self.1
+    }
+}
+
+impl error::Error for Error
+{
+    fn source(&self) -> Option<&(dyn error::Error + 'static)> {
+	Some(match &self.0 {
+	    ErrorKind::IO(i) => i,
+	    _ => return None,
+	})
+    }
+}
+
+impl fmt::Display for Error
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result
+    {
+	write!(f, "formatting error: ")?;
+	if self.1 {
+	    write!(f, "encode")
+	} else {
+	    write!(f, "decode")
+	}
+    }
+}
+
+impl From<(io::Error, bool)> for Error
+{
+    #[inline] fn from(from: (io::Error, bool)) -> Self
+    {
+	Self(ErrorKind::IO(from.0), from.1)
+    }
+}
+
+
+impl From<Error> for io::Error
+{
+    fn from(from: Error) -> Self
+    {
+	match from.0
+	{
+	    ErrorKind::IO(io) => io,
+	    _ => io::Error::new(io::ErrorKind::Other, from),
+	}
+    }
+}

src/formats/json.rs

@@ -0,0 +1,14 @@
+use super::*;
+
+#[derive(Debug)]
+pub struct JsonFormatter;
+
+impl Format for JsonFormatter
+{
+    fn encode<W: io::Write>(cfg: &Config, to: W, obj: &Object) -> Result<usize, Error> {
+	todo!()
+    }
+    fn decode<R: io::Read>(cfg: &Config, from: R) -> Result<Object, Error> {
+	todo!()
+    }
+}