implement server timing entry parsing

Author: yoshuawuyts

src/trace/server_timing/entry.rs

@@ -1,6 +1,9 @@
+use std::str::FromStr;
 use std::time::Duration;
 
 use crate::headers::HeaderValue;
+use crate::Status;
+use crate::{ensure, format_err};
 
 /// An individual `ServerTiming` entry.
 //
@@ -47,8 +50,8 @@ impl Entry {
     }
 
     /// The timing description.
-    pub fn description(&self) -> Option<&String> {
-        self.desc.as_ref()
+    pub fn description(&self) -> Option<&str> {
+        self.desc.as_ref().map(|s| s.as_str())
     }
 }
 
@@ -73,12 +76,93 @@ impl From<Entry> for HeaderValue {
     }
 }
 
+impl FromStr for Entry {
+    type Err = crate::Error;
+    // Create an entry from a string. Parsing rules in ABNF are:
+    //
+    // ```
+    // Server-Timing             = #server-timing-metric
+    // server-timing-metric      = metric-name *( OWS ";" OWS server-timing-param )
+    // metric-name               = token
+    // server-timing-param       = server-timing-param-name OWS "=" OWS server-timing-param-value
+    // server-timing-param-name  = token
+    // server-timing-param-value = token / quoted-string
+    // ```
+    //
+    // Source: https://w3c.github.io/server-timing/#the-server-timing-header-field
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        let mut parts = s.trim().split(';');
+
+        // Get the name. This is non-optional.
+        let name = parts
+            .next()
+            .ok_or_else(|| format_err!("Server timing headers must include a name"))?
+            .trim_end();
+
+        // We must extract these values from the k-v pairs that follow.
+        let mut dur = None;
+        let mut desc = None;
+
+        for mut part in parts {
+            ensure!(
+                !part.is_empty(),
+                "Server timing params cannot end with a trailing `;`"
+            );
+
+            part = part.trim_start();
+
+            let mut params = part.split('=');
+            let name = params
+                .next()
+                .ok_or_else(|| format_err!("Server timing params must have a name"))?
+                .trim_end();
+            let mut value = params
+                .next()
+                .ok_or_else(|| format_err!("Server timing params must have a value"))?
+                .trim_start();
+
+            match name {
+                "dur" => {
+                    let millis: f64 = value.parse().status(400).map_err(|_| {
+                        format_err!("Server timing duration params must be a valid double-precision floating-point number.")
+                    })?;
+                    dur = Some(Duration::from_secs_f64(millis / 1000.0));
+                }
+                "desc" => {
+                    // Ensure quotes line up, and strip them from the resulting output
+                    if value.starts_with('"') {
+                        value = &value[1..value.len()];
+                        ensure!(
+                            value.ends_with('"'),
+                            "Server timing description params must use matching quotes"
+                        );
+                        value = &value[0..value.len() - 1];
+                    } else {
+                        ensure!(
+                            !value.ends_with('"'),
+                            "Server timing description params must use matching quotes"
+                        );
+                    }
+                    desc = Some(value.to_string());
+                }
+                _ => continue,
+            }
+        }
+
+        Ok(Entry {
+            name: name.to_string(),
+            dur,
+            desc,
+        })
+    }
+}
+
 #[cfg(test)]
 mod test {
     use super::*;
 
     #[test]
-    fn create_header_value() -> crate::Result<()> {
+    fn encode() -> crate::Result<()> {
         let name = String::from("Server");
         let dur = Duration::from_secs(1);
         let desc = String::from("A server timing");
@@ -89,8 +173,78 @@ mod test {
         let val: HeaderValue = Entry::new(name.clone(), Some(dur), None)?.into();
         assert_eq!(val, "Server; dur=1000");
 
+        let val: HeaderValue = Entry::new(name.clone(), None, Some(desc.clone()))?.into();
+        assert_eq!(val, r#"Server; desc="A server timing""#);
+
         let val: HeaderValue = Entry::new(name.clone(), Some(dur), Some(desc.clone()))?.into();
         assert_eq!(val, r#"Server; dur=1000; desc="A server timing""#);
         Ok(())
     }
+
+    #[test]
+    fn decode() -> crate::Result<()> {
+        // Metric name only.
+        assert_entry("Server", "Server", None, None)?;
+        assert_entry("Server ", "Server", None, None)?;
+        assert_entry_err(
+            "Server ;",
+            "Server timing params cannot end with a trailing `;`",
+        );
+        assert_entry_err(
+            "Server; ",
+            "Server timing params cannot end with a trailing `;`",
+        );
+
+        // Metric name + param
+        assert_entry("Server; dur=1000", "Server", Some(1000), None)?;
+        assert_entry("Server; dur =1000", "Server", Some(1000), None)?;
+        assert_entry("Server; dur= 1000", "Server", Some(1000), None)?;
+        assert_entry("Server; dur = 1000", "Server", Some(1000), None)?;
+        assert_entry_err(
+            "Server; dur=1000;",
+            "Server timing params cannot end with a trailing `;`",
+        );
+
+        // Metric name + desc
+        assert_entry(r#"DB; desc="a db""#, "DB", None, Some("a db"))?;
+        assert_entry(r#"DB; desc ="a db""#, "DB", None, Some("a db"))?;
+        assert_entry(r#"DB; desc= "a db""#, "DB", None, Some("a db"))?;
+        assert_entry(r#"DB; desc = "a db""#, "DB", None, Some("a db"))?;
+        assert_entry(r#"DB; desc=a_db"#, "DB", None, Some("a_db"))?;
+        assert_entry_err(
+            r#"DB; desc="db"#,
+            "Server timing description params must use matching quotes",
+        );
+        assert_entry_err(
+            "Server; desc=a_db;",
+            "Server timing params cannot end with a trailing `;`",
+        );
+
+        // Metric name + dur + desc
+        assert_entry(
+            r#"Server; dur=1000; desc="a server""#,
+            "Server",
+            Some(1000),
+            Some("a server"),
+        )?;
+        assert_entry_err(
+            r#"Server; dur=1000; desc="a server";"#,
+            "Server timing params cannot end with a trailing `;`",
+        );
+        Ok(())
+    }
+
+    fn assert_entry_err(s: &str, msg: &str) {
+        let err = Entry::from_str(s).unwrap_err();
+        assert_eq!(format!("{}", err), msg);
+    }
+
+    /// Assert an entry and all of its fields.
+    fn assert_entry(s: &str, n: &str, du: Option<u64>, de: Option<&str>) -> crate::Result<()> {
+        let e = Entry::from_str(s)?;
+        assert_eq!(e.name(), n);
+        assert_eq!(e.duration(), du.map(|du| Duration::from_millis(du)));
+        assert_eq!(e.description(), de);
+        Ok(())
+    }
 }