Beginning of applying filters for json types. Currently only supports html escaping.

src/bin.rs

@@ -73,11 +73,60 @@ fn read_context_from_stdin() -> serde_json::Value {
     serde_json::from_str(&buffer).expect("Failed to parse json")
 }
 
+fn html_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("&lt;"),
+        '>' => output.push_str("&gt;"),
+        '"' => output.push_str("&quot;"),
+        '\'' => output.push_str("&#39;"),
+        '&' => output.push_str("&amp;"),
+        _ => output.push(c),
+    });
+    output
+}
+
+fn apply_filter(
+    json_value: &serde_json::Value,
+    filter: &Filter,
+) -> Result<serde_json::Value, RenderError> {
+    match (json_value, filter) {
+        (serde_json::Value::String(string), Filter::HtmlEncode) => {
+            Ok(serde_json::Value::String(html_escape(string)))
+        }
+        (_, Filter::HtmlEncode) => Ok(serde_json::Value::String(html_escape(
+            &json_value.render(&Vec::new())?,
+        ))),
+        _ => panic!("Unimplemented"),
+    }
+}
+
+fn apply_filters(
+    json_value: &serde_json::Value,
+    filters: &[Filter],
+) -> Result<serde_json::Value, RenderError> {
+    let mut final_value: serde_json::Value = apply_filter(json_value, &filters[0])?;
+
+    for filter in &filters[1..] {
+        final_value = apply_filter(&final_value, filter)?;
+    }
+
+    Ok(final_value)
+}
+
 impl ContextElement for serde_json::Value {}
 
 impl Renderable for serde_json::Value {
     fn render(&self, _filters: &Vec<Filter>) -> Result<String, RenderError> {
-        match self {
+        let after_apply = if _filters.is_empty() {
+            Some(apply_filters(self, _filters)?)
+        } else {
+            None
+        };
+
+        match after_apply.as_ref().unwrap_or(self) {
             serde_json::Value::Null => Ok("".to_owned()),
             serde_json::Value::Bool(boolean) => Ok(boolean.to_string()),
             serde_json::Value::Number(num) => Ok(num.to_string()),
@@ -395,4 +444,9 @@ mod tests {
             Ok::<_, RenderError>("3,5,7,9".to_owned())
         );
     }
+
+    #[test]
+    fn test_html_escape() {
+        assert_eq!(html_escape("<>&\"'"), "&lt;&gt;&amp;&quot;&#39;".to_owned())
+    }
 }