Fix performance issue in Reader reamaining method.

packages/hurl_core/src/parser/json.rs

@@ -58,7 +58,7 @@ fn string_template(reader: &mut Reader) -> ParseResult<'static, Template> {
     let mut chars = vec![];
     let start = reader.state.pos.clone();
     loop {
-        if reader.remaining().starts_with('"') || reader.is_eof() {
+        if reader.peek() == Some('"') || reader.is_eof() {
             break;
         }
         let char = any_char(reader)?;
@@ -209,7 +209,7 @@ pub fn number_value(reader: &mut Reader) -> ParseResult<'static, JsonValue> {
         Err(_) => "".to_string(),
     };
 
-    let exponent = if reader.remaining().starts_with('e') || reader.remaining().starts_with('E') {
+    let exponent = if reader.peek() == Some('e') || reader.peek() == Some('E') {
         reader.read();
         let exponent_sign = match try_literal("-", reader) {
             Ok(_) => "-".to_string(),
@@ -240,15 +240,15 @@ fn list_value(reader: &mut Reader) -> ParseResult<'static, JsonValue> {
     let mut elements = vec![];
 
     // at least one element
-    if !reader.remaining().starts_with(']') {
+    if reader.peek() != Some(']') {
         let first_element = list_element(reader)?;
         elements.push(first_element);
 
         loop {
-            if reader.remaining().starts_with(']') {
+            if reader.peek() == Some(']') {
                 break;
             }
-            if !reader.remaining().starts_with(',') {
+            if reader.peek() != Some(',') {
                 break;
             }
             literal(",", reader)?;
@@ -286,15 +286,15 @@ pub fn object_value(reader: &mut Reader) -> ParseResult<'static, JsonValue> {
     try_literal("{", reader)?;
     let space0 = whitespace(reader);
     let mut elements = vec![];
-    if !reader.remaining().starts_with('}') {
+    if reader.peek() != Some('}') {
         let first_element = object_element(reader)?;
         elements.push(first_element);
 
         loop {
-            if reader.remaining().starts_with('}') {
+            if reader.peek() == Some('}') {
                 break;
             }
-            if !reader.remaining().starts_with(',') {
+            if reader.peek() != Some(',') {
                 break;
             }
             literal(",", reader)?;

packages/hurl_core/src/parser/multiline.rs

@@ -83,7 +83,7 @@ fn graphql(reader: &mut Reader) -> ParseResult<'static, MultilineString> {
     let mut chars = vec![];
 
     let start = reader.state.pos.clone();
-    while !reader.remaining().starts_with("```") && !reader.is_eof() {
+    while reader.peek_n(3) != "```" && !reader.is_eof() {
         let pos = reader.state.pos.clone();
         let c = reader.read().unwrap();
         chars.push((c, c.to_string(), pos));
@@ -233,7 +233,7 @@ fn multiline_string_value(reader: &mut Reader) -> ParseResult<'static, Template>
     let mut chars = vec![];
 
     let start = reader.state.pos.clone();
-    while !reader.remaining().starts_with("```") && !reader.is_eof() {
+    while reader.peek_n(3) != "```" && !reader.is_eof() {
         let pos = reader.state.pos.clone();
         let c = reader.read().unwrap();
         chars.push((c, c.to_string(), pos));
@@ -262,7 +262,7 @@ fn oneline_string_value(reader: &mut Reader) -> ParseResult<'static, Template> {
     let mut chars = vec![];
 
     let start = reader.state.pos.clone();
-    while !reader.remaining().starts_with("```") && !reader.is_eof() {
+    while reader.peek_n(3) != "```" && !reader.is_eof() {
         let pos = reader.state.pos.clone();
         let c = reader.read().unwrap();
         if c == '\n' {

packages/hurl_core/src/parser/reader.rs

@@ -15,6 +15,8 @@
  * limitations under the License.
  *
  */
+use std::cmp::min;
+
 use crate::ast::Pos;
 
 #[derive(Clone, Debug, PartialEq, Eq)]
@@ -30,6 +32,7 @@ pub struct ReaderState {
 }
 
 impl Reader {
+    // FIXME: change name to the more idiomatic new
     pub fn init(s: &str) -> Reader {
         Reader {
             buffer: s.chars().collect(),
@@ -65,6 +68,12 @@ impl Reader {
         self.buffer.get(self.state.cursor).copied()
     }
 
+    pub fn peek_n(&self, n: usize) -> String {
+        let start = self.state.cursor;
+        let end = min(start + n, self.buffer.len());
+        self.buffer[start..end].iter().collect()
+    }
+
     pub fn read_while(&mut self, predicate: fn(&char) -> bool) -> String {
         let mut s = String::from("");
         loop {
@@ -118,7 +127,7 @@ impl Reader {
     }
 
     pub fn try_literal(&mut self, value: &str) -> bool {
-        if self.remaining().starts_with(value.to_string().as_str()) {
+        if self.peek_n(value.len()) == value {
             self.read_n(value.len());
             true
         } else {
@@ -126,16 +135,7 @@ impl Reader {
         }
     }
 
-    pub fn remaining(&self) -> String {
-        self.buffer.as_slice()[self.state.cursor..self.buffer.len()]
-            .iter()
-            .collect()
-    }
-
-    pub fn slice(&self, start: usize, end: usize) -> String {
-        self.buffer.as_slice()[start..end].iter().collect()
-    }
-
+    // FIXME: explain this method, find a better name mayebe?
     pub fn from(&self, start: usize) -> String {
         let end = self.state.cursor;
         self.buffer.as_slice()[start..end].iter().collect()
@@ -155,7 +155,7 @@ mod tests {
         let mut reader = Reader::init("hi");
         assert_eq!(reader.state.cursor, 0);
         assert!(!reader.is_eof());
-        assert_eq!(reader.remaining(), "hi".to_string());
+        assert_eq!(reader.peek_n(2), "hi".to_string());
 
         assert_eq!(reader.read().unwrap(), 'h');
         assert_eq!(reader.state.cursor, 1);

packages/hurl_core/src/parser/xml.rs

@@ -110,7 +110,7 @@ mod tests {
             String::from("<users><user /></users>")
         );
         assert_eq!(reader.state.cursor, 23);
-        assert_eq!(reader.remaining(), String::from("xx"));
+        assert_eq!(reader.peek_n(2), String::from("xx"));
 
         let mut reader = Reader::init("<?xml version=\"1.0\"?><users/>xxx");
         assert_eq!(