1 files changed, 52 insertions, 4 deletions
diff --git a/askama_escape/src/lib.rs b/askama_escape/src/lib.rs
index ad08e55..1788843 100644
--- a/askama_escape/src/lib.rs
+++ b/askama_escape/src/lib.rs
@@ -1,10 +1,7 @@
-#![no_std]
+#![cfg_attr(not(any(feature = "json", test)), no_std)]
 #![deny(elided_lifetimes_in_paths)]
 #![deny(unreachable_pub)]
 
-#[cfg(test)]
-extern crate std;
-
 use core::fmt::{self, Display, Formatter, Write};
 use core::str;
 
@@ -175,6 +172,57 @@ pub trait Escaper {
 
 const FLAG: u8 = b'>' - b'"';
 
+/// Escape chevrons, ampersand and apostrophes for use in JSON
+#[cfg(feature = "json")]
+#[derive(Debug, Clone, Default)]
+pub struct JsonEscapeBuffer(Vec<u8>);
+
+#[cfg(feature = "json")]
+impl JsonEscapeBuffer {
+    pub fn new() -> Self {
+        Self(Vec::new())
+    }
+
+    pub fn finish(self) -> String {
+        unsafe { String::from_utf8_unchecked(self.0) }
+    }
+}
+
+#[cfg(feature = "json")]
+impl std::io::Write for JsonEscapeBuffer {
+    fn write(&mut self, bytes: &[u8]) -> std::io::Result<usize> {
+        macro_rules! push_esc_sequence {
+            ($start:ident, $i:ident, $self:ident, $bytes:ident, $quote:expr) => {{
+                if $start < $i {
+                    $self.0.extend_from_slice(&$bytes[$start..$i]);
+                }
+                $self.0.extend_from_slice($quote);
+                $start = $i + 1;
+            }};
+        }
+
+        self.0.reserve(bytes.len());
+        let mut start = 0;
+        for (i, b) in bytes.iter().enumerate() {
+            match *b {
+                b'&' => push_esc_sequence!(start, i, self, bytes, br#"\u0026"#),
+                b'\'' => push_esc_sequence!(start, i, self, bytes, br#"\u0027"#),
+                b'<' => push_esc_sequence!(start, i, self, bytes, br#"\u003c"#),
+                b'>' => push_esc_sequence!(start, i, self, bytes, br#"\u003e"#),
+                _ => (),
+            }
+        }
+        if start < bytes.len() {
+            self.0.extend_from_slice(&bytes[start..]);
+        }
+        Ok(bytes.len())
+    }
+
+    fn flush(&mut self) -> std::io::Result<()> {
+        Ok(())
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;