fix: Refactor string truncation logic into reusable utility function to avoid panic (#2818) (#2819)

Signed-off-by: toyamagu2021 <tomoki-yamaguchi@c-fo.com>

crates/goose-cli/src/commands/project.rs

@@ -4,6 +4,7 @@ use cliclack::{self, intro, outro};
 use std::path::Path;
 
 use crate::project_tracker::ProjectTracker;
+use crate::utils::safe_truncate;
 
 /// Format a DateTime for display
 fn format_date(date: DateTime<chrono::Utc>) -> String {
@@ -199,11 +200,7 @@ pub fn handle_projects_interactive() -> Result<()> {
                     .last_instruction
                     .as_ref()
                     .map_or(String::new(), |instr| {
-                        let truncated = if instr.len() > 40 {
-                            format!("{}...", &instr[0..37])
-                        } else {
-                            instr.clone()
-                        };
+                        let truncated = safe_truncate(instr, 40);
                         format!(" [{}]", truncated)
                     });
 

crates/goose-cli/src/commands/session.rs

@@ -1,4 +1,5 @@
 use crate::session::message_to_markdown;
+use crate::utils::safe_truncate;
 use anyhow::{Context, Result};
 use cliclack::{confirm, multiselect, select};
 use goose::session::info::{get_valid_sorted_sessions, SessionInfo, SortOrder};
@@ -50,11 +51,7 @@ fn prompt_interactive_session_removal(sessions: &[SessionInfo]) -> Result<Vec<Se
             } else {
                 &s.metadata.description
             };
-            let truncated_desc = if desc.len() > TRUNCATED_DESC_LENGTH {
-                format!("{}...", &desc[..TRUNCATED_DESC_LENGTH - 3])
-            } else {
-                desc.to_string()
-            };
+            let truncated_desc = safe_truncate(desc, TRUNCATED_DESC_LENGTH);
             let display_text = format!("{} - {} ({})", s.modified, truncated_desc, s.id);
             (display_text, s.clone())
         })
@@ -320,11 +317,7 @@ pub fn prompt_interactive_session_selection() -> Result<session::Identifier> {
             };
 
             // Truncate description if too long
-            let truncated_desc = if desc.len() > 40 {
-                format!("{}...", &desc[..37])
-            } else {
-                desc.to_string()
-            };
+            let truncated_desc = safe_truncate(desc, 40);
 
             let display_text = format!("{} - {} ({})", s.modified, truncated_desc, s.id);
             (display_text, s.clone())

crates/goose-cli/src/lib.rs

@@ -7,6 +7,7 @@ pub mod project_tracker;
 pub mod recipes;
 pub mod session;
 pub mod signal;
+pub mod utils;
 // Re-export commonly used types
 pub use session::Session;
 

crates/goose-cli/src/utils.rs

@@ -0,0 +1,50 @@
+/// Utility functions for safe string handling and other common operations
+/// Safely truncate a string at character boundaries, not byte boundaries
+///
+/// This function ensures that multi-byte UTF-8 characters (like Japanese, emoji, etc.)
+/// are not split in the middle, which would cause a panic.
+///
+/// # Arguments
+/// * `s` - The string to truncate
+/// * `max_chars` - Maximum number of characters to keep
+///
+/// # Returns
+/// A truncated string with "..." appended if truncation occurred
+pub fn safe_truncate(s: &str, max_chars: usize) -> String {
+    if s.chars().count() <= max_chars {
+        s.to_string()
+    } else {
+        let truncated: String = s.chars().take(max_chars.saturating_sub(3)).collect();
+        format!("{}...", truncated)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_safe_truncate_ascii() {
+        assert_eq!(safe_truncate("hello world", 20), "hello world");
+        assert_eq!(safe_truncate("hello world", 8), "hello...");
+        assert_eq!(safe_truncate("hello", 5), "hello");
+        assert_eq!(safe_truncate("hello", 3), "...");
+    }
+
+    #[test]
+    fn test_safe_truncate_japanese() {
+        // Japanese characters: "こんにちは世界" (Hello World)
+        let japanese = "こんにちは世界";
+        assert_eq!(safe_truncate(japanese, 10), japanese);
+        assert_eq!(safe_truncate(japanese, 5), "こん...");
+        assert_eq!(safe_truncate(japanese, 7), japanese);
+    }
+
+    #[test]
+    fn test_safe_truncate_mixed() {
+        // Mixed ASCII and Japanese
+        let mixed = "Hello こんにちは";
+        assert_eq!(safe_truncate(mixed, 20), mixed);
+        assert_eq!(safe_truncate(mixed, 8), "Hello...");
+    }
+}