Implement RawValue type

fixes #355

Author: srijs

src/de.rs

@@ -8,6 +8,7 @@
 
 //! Deserialize JSON data to a Rust data structure.
 
+use std::borrow::Cow;
 use std::io;
 use std::marker::PhantomData;
 use std::result;
@@ -946,6 +947,22 @@ impl<'de, R: Read<'de>> Deserializer<R> {
             }
         }
     }
+
+    fn deserialize_raw_value<V>(&mut self, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        if let None = try!(self.parse_whitespace()) {
+            return Err(self.peek_error(ErrorCode::EofWhileParsingValue));
+        }
+
+        self.read.toggle_raw_buffering();
+        de::Deserializer::deserialize_any(&mut *self, de::IgnoredAny)?;
+        match self.read.toggle_raw_buffering().unwrap() {
+            Cow::Owned(byte_buf) => visitor.visit_byte_buf(byte_buf),
+            Cow::Borrowed(bytes) => visitor.visit_borrowed_bytes(bytes),
+        }
+    }
 }
 
 impl FromStr for Number {
@@ -1412,10 +1429,14 @@ impl<'de, 'a, R: Read<'de>> de::Deserializer<'de> for &'a mut Deserializer<R> {
 
     /// Parses a newtype struct as the underlying value.
     #[inline]
-    fn deserialize_newtype_struct<V>(self, _name: &str, visitor: V) -> Result<V::Value>
+    fn deserialize_newtype_struct<V>(self, name: &str, visitor: V) -> Result<V::Value>
     where
         V: de::Visitor<'de>,
     {
+        if name == ::raw::SERDE_STRUCT_NAME {
+            return self.deserialize_raw_value(visitor);
+        }
+
         visitor.visit_newtype_struct(self)
     }
 

src/lib.rs

@@ -364,7 +364,7 @@ pub use self::ser::{
     to_string, to_string_pretty, to_vec, to_vec_pretty, to_writer, to_writer_pretty, Serializer,
 };
 #[doc(inline)]
-pub use self::value::{from_value, to_value, Map, Number, Value};
+pub use self::value::{from_value, to_value, Map, Number, RawValue, Value};
 
 // We only use our own error type; no need for From conversions provided by the
 // standard library's try! macro. This reduces lines of LLVM IR by 4%.
@@ -388,4 +388,5 @@ pub mod value;
 
 mod iter;
 mod number;
+mod raw;
 mod read;

src/raw.rs

@@ -0,0 +1,93 @@
+use std::borrow::Cow;
+use std::fmt;
+
+use serde::de::Visitor;
+use serde::{Deserialize, Deserializer, Serialize, Serializer};
+
+/// Represents any valid JSON value as a series of raw bytes.
+///
+/// This type can be used to defer parsing parts of a payload until later,
+/// or to embed it verbatim into another JSON payload.
+///
+/// When serializing, a value of this type will retain its original formatting
+/// and will not be minified or pretty-printed.
+///
+/// When deserializing, this type can not be used with the `#[serde(flatten)]` attribute,
+/// as it relies on the original input buffer.
+
+#[derive(Debug, Clone, PartialEq)]
+pub struct RawValue<'a>(Cow<'a, str>);
+
+impl<'a> AsRef<str> for RawValue<'a> {
+    fn as_ref(&self) -> &str {
+        &self.0
+    }
+}
+
+impl<'a> fmt::Display for RawValue<'a> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.write_str(&self.0)
+    }
+}
+
+/// Not public API. Should be pub(crate).
+#[doc(hidden)]
+pub const SERDE_STRUCT_NAME: &'static str = "$__serde_private_RawValue";
+
+impl<'a> Serialize for RawValue<'a> {
+    #[inline]
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        serializer.serialize_newtype_struct(SERDE_STRUCT_NAME, &self.0)
+    }
+}
+
+impl<'a, 'de> Deserialize<'de> for RawValue<'a>
+where
+    'de: 'a,
+{
+    #[inline]
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        struct RawValueVisitor;
+
+        impl<'de> Visitor<'de> for RawValueVisitor {
+            type Value = RawValue<'de>;
+
+            fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                write!(formatter, "a deserializable RawValue")
+            }
+
+            fn visit_string<E>(self, s: String) -> Result<Self::Value, E>
+            where
+                E: ::serde::de::Error,
+            {
+                Ok(RawValue(Cow::Owned(s)))
+            }
+
+            fn visit_byte_buf<E>(self, b: Vec<u8>) -> Result<Self::Value, E>
+            where
+                E: ::serde::de::Error,
+            {
+                String::from_utf8(b)
+                    .map(|s| RawValue(Cow::Owned(s)))
+                    .map_err(|err| ::serde::de::Error::custom(err))
+            }
+
+            fn visit_borrowed_bytes<E>(self, b: &'de [u8]) -> Result<Self::Value, E>
+            where
+                E: ::serde::de::Error,
+            {
+                ::std::str::from_utf8(b)
+                    .map(|s| RawValue(Cow::Borrowed(s)))
+                    .map_err(|err| ::serde::de::Error::custom(err))
+            }
+        }
+
+        deserializer.deserialize_newtype_struct(SERDE_STRUCT_NAME, RawValueVisitor)
+    }
+}

src/read.rs

@@ -6,6 +6,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+use std::borrow::Cow;
 use std::ops::Deref;
 use std::{char, cmp, io, str};
 
@@ -76,6 +77,13 @@ pub trait Read<'de>: private::Sealed {
     /// string until the next quotation mark but discards the data.
     #[doc(hidden)]
     fn ignore_str(&mut self) -> Result<()>;
+
+    /// Switch raw buffering mode on/off. When switching off, returns a copy-on-write
+    /// buffer with the captured data.
+    ///
+    /// This is used to deserialize `RawValue`.
+    #[doc(hidden)]
+    fn toggle_raw_buffering(&mut self) -> Option<Cow<'de, [u8]>>;
 }
 
 pub struct Position {
@@ -107,6 +115,7 @@ where
     iter: LineColIterator<io::Bytes<R>>,
     /// Temporary storage of peeked byte.
     ch: Option<u8>,
+    raw_buffer: Option<Vec<u8>>,
 }
 
 /// JSON input source that reads from a slice of bytes.
@@ -117,6 +126,7 @@ pub struct SliceRead<'a> {
     slice: &'a [u8],
     /// Index of the *next* byte that will be returned by next() or peek().
     index: usize,
+    raw_buffering_start_index: Option<usize>,
 }
 
 /// JSON input source that reads from a UTF-8 string.
@@ -142,6 +152,7 @@ where
         IoRead {
             iter: LineColIterator::new(reader.bytes()),
             ch: None,
+            raw_buffer: None,
         }
     }
 }
@@ -193,10 +204,20 @@ where
     #[inline]
     fn next(&mut self) -> io::Result<Option<u8>> {
         match self.ch.take() {
-            Some(ch) => Ok(Some(ch)),
+            Some(ch) => {
+                if let Some(ref mut buf) = self.raw_buffer {
+                    buf.push(ch);
+                }
+                Ok(Some(ch))
+            }
             None => match self.iter.next() {
                 Some(Err(err)) => Err(err),
-                Some(Ok(ch)) => Ok(Some(ch)),
+                Some(Ok(ch)) => {
+                    if let Some(ref mut buf) = self.raw_buffer {
+                        buf.push(ch);
+                    }
+                    Ok(Some(ch))
+                }
                 None => Ok(None),
             },
         }
@@ -219,7 +240,11 @@ where
 
     #[inline]
     fn discard(&mut self) {
-        self.ch = None;
+        if let Some(ch) = self.ch.take() {
+            if let Some(ref mut buf) = self.raw_buffer {
+                buf.push(ch);
+            }
+        }
     }
 
     fn position(&self) -> Position {
@@ -274,6 +299,15 @@ where
             }
         }
     }
+
+    fn toggle_raw_buffering(&mut self) -> Option<Cow<'de, [u8]>> {
+        if let Some(buffer) = self.raw_buffer.take() {
+            Some(Cow::Owned(buffer))
+        } else {
+            self.raw_buffer = Some(Vec::new());
+            None
+        }
+    }
 }
 
 //////////////////////////////////////////////////////////////////////////////
@@ -284,6 +318,7 @@ impl<'a> SliceRead<'a> {
         SliceRead {
             slice: slice,
             index: 0,
+            raw_buffering_start_index: None,
         }
     }
 
@@ -437,6 +472,15 @@ impl<'a> Read<'a> for SliceRead<'a> {
             }
         }
     }
+
+    fn toggle_raw_buffering(&mut self) -> Option<Cow<'a, [u8]>> {
+        if let Some(start_index) = self.raw_buffering_start_index.take() {
+            Some(Cow::Borrowed(&self.slice[start_index..self.index]))
+        } else {
+            self.raw_buffering_start_index = Some(self.index);
+            None
+        }
+    }
 }
 
 //////////////////////////////////////////////////////////////////////////////
@@ -498,6 +542,10 @@ impl<'a> Read<'a> for StrRead<'a> {
     fn ignore_str(&mut self) -> Result<()> {
         self.delegate.ignore_str()
     }
+
+    fn toggle_raw_buffering(&mut self) -> Option<Cow<'a, [u8]>> {
+        self.delegate.toggle_raw_buffering()
+    }
 }
 
 //////////////////////////////////////////////////////////////////////////////