fix(runner): check whether artifact contains any elements

The zstd compressed file will never be empty on disk, so we need to check the contents.

Author: not-matthias

crates/runner-shared/src/artifacts/memtrack.rs

@@ -1,6 +1,6 @@
 use libc::pid_t;
 use serde::{Deserialize, Serialize};
-use std::io::{BufWriter, Read, Write};
+use std::io::{BufReader, BufWriter, Read, Write};
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct MemtrackArtifact {
@@ -26,6 +26,13 @@ impl MemtrackArtifact {
             deserializer: rmp_serde::Deserializer::new(decoder),
         })
     }
+
+    pub fn is_empty<R: std::io::Read>(reader: R) -> bool {
+        let Ok(mut stream) = MemtrackArtifact::decode_streamed(BufReader::new(reader)) else {
+            return true;
+        };
+        stream.next().is_none()
+    }
 }
 
 #[derive(Debug, Clone, Copy, Serialize, Deserialize, PartialEq, Eq)]
@@ -138,4 +145,17 @@ mod tests {
 
         Ok(())
     }
+
+    #[test]
+    fn test_artifact_is_empty() -> anyhow::Result<()> {
+        let artifact = MemtrackArtifact { events: vec![] };
+
+        let mut buf = Vec::new();
+        artifact.encode_to_writer(&mut buf)?;
+
+        let reader = Cursor::new(buf);
+        assert!(MemtrackArtifact::is_empty(reader));
+
+        Ok(())
+    }
 }

src/executor/memory/executor.rs

@@ -128,8 +128,8 @@ impl Executor for MemoryExecutor {
                     .to_string_lossy()
                     .contains(MemtrackArtifact::name())
             })
-            // Filter empty files:
-            .filter(|entry| entry.metadata().map(|m| m.len() == 0).unwrap_or_default())
+            .flat_map(|f| std::fs::File::open(f.path()))
+            .filter(|file| !MemtrackArtifact::is_empty(file))
             .collect();
         if files.is_empty() {
             bail!(