From 8d2728a7677218901795518613497d5bbb3fb5e5 Mon Sep 17 00:00:00 2001
From: Tom Alexander <tom@fizz.buzz>
Date: Sat, 23 May 2020 18:40:09 -0400
Subject: [PATCH] Implement javascript string escaping.

---
 js/test_cases/filters/input1.json |  2 +-
 js/test_cases/filters/main.dust   |  6 ++++++
 src/bin.rs                        | 25 ++++++++++++++++++++++++-
 3 files changed, 31 insertions(+), 2 deletions(-)

diff --git a/js/test_cases/filters/input1.json b/js/test_cases/filters/input1.json
index c0bb598..0dfba3a 100644
--- a/js/test_cases/filters/input1.json
+++ b/js/test_cases/filters/input1.json
@@ -11,5 +11,5 @@
   "object": {
     "foo": "bar"
   },
-  "special_characters": "<>&\"'"
+  "special_characters": "<>xx\b&\"'\t\f\n\r\\"
 }
diff --git a/js/test_cases/filters/main.dust b/js/test_cases/filters/main.dust
index df5b2d4..f18a342 100644
--- a/js/test_cases/filters/main.dust
+++ b/js/test_cases/filters/main.dust
@@ -20,3 +20,9 @@ Object html escaping disabled: {object|s}{~n}
 Object stringified: {object|js}{~n}
 Object stringified and parsed: {object|js|jp}{~n}
 Object stringified, html escaping disabled, parsed, stringified, and html escaped: {object|js|s|jp|js|h}{~n}
+
+Special characters: {special_characters}{~n}
+Special characters html escaping disabled and javascript escaped: {special_characters|s|j}{~n}
+Special characters javascript escaped and html escaping disabled: {special_characters|j|s}{~n}
+Special characters javascript escaped once: {special_characters|j}{~n}
+Special characters javascript escaped twice: {special_characters|j|j}{~n}
diff --git a/src/bin.rs b/src/bin.rs
index 102d53d..668d527 100644
--- a/src/bin.rs
+++ b/src/bin.rs
@@ -88,6 +88,23 @@ fn html_escape(inp: &str) -> String {
     output
 }
 
+fn javascript_escape(inp: &str) -> String {
+    // Adding 10% space from the original to avoid re-allocations by
+    // leaving room for escaped sequences.
+    let mut output = String::with_capacity(((inp.len() as f64) * 1.1) as usize);
+    inp.chars().for_each(|c| match c {
+        '"' => output.push_str(r#"\""#),
+        '\'' => output.push_str(r#"\'"#),
+        '\t' => output.push_str(r#"\t"#),
+        '\x0C' => output.push_str(r#"\f"#),
+        '\n' => output.push_str(r#"\n"#),
+        '\r' => output.push_str(r#"\r"#),
+        '\\' => output.push_str(r#"\\"#),
+        _ => output.push(c),
+    });
+    output
+}
+
 fn apply_filter(
     json_value: &serde_json::Value,
     filter: &Filter,
@@ -114,7 +131,13 @@ fn apply_filter(
         (_, Filter::JsonStringify) => {
             Ok(serde_json::Value::String(json_value.to_string()))
         }
-        // TODO: javascript string escape
+        // Javascript escape filter
+        (serde_json::Value::String(string), Filter::JavascriptStringEncode) => {
+            Ok(serde_json::Value::String(javascript_escape(string)))
+        }
+        (_, Filter::JavascriptStringEncode) => Ok(serde_json::Value::String(javascript_escape(
+            &json_value.render(&Vec::new())?,
+        ))),
         // TODO: EncodeUri
         // TODO: EncodeUriComponent
         _ => panic!("Unimplemented"),