Fix crash on small image preview (#198)

src/message/mod.rs

@@ -841,10 +841,10 @@ impl Message {
             if let Some(placeholder) = match &self.image_preview {
                 ImageStatus::None => None,
                 ImageStatus::Downloading(image_preview_size) => {
-                    Some(Message::placeholder_frame(Some("Downloading..."), image_preview_size))
+                    Message::placeholder_frame(Some("Downloading..."), width, image_preview_size)
                 },
                 ImageStatus::Loaded(backend) => {
-                    Some(Message::placeholder_frame(None, &backend.rect().into()))
+                    Message::placeholder_frame(None, width, &backend.rect().into())
                 },
                 ImageStatus::Error(err) => Some(format!("[Image error: {err}]\n")),
             } {
@@ -864,21 +864,32 @@ impl Message {
     }
 
     /// Before the image is loaded, already display a placeholder frame of the image size.
-    fn placeholder_frame(text: Option<&str>, image_preview_size: &ImagePreviewSize) -> String {
+    fn placeholder_frame(
+        text: Option<&str>,
+        outer_width: usize,
+        image_preview_size: &ImagePreviewSize,
+    ) -> Option<String> {
         let ImagePreviewSize { width, height } = image_preview_size;
+        if outer_width < *width || (*width < 2 || *height < 2) {
+            return None;
+        }
         let mut placeholder = "\u{230c}".to_string();
         placeholder.push_str(&" ".repeat(width - 2));
         placeholder.push_str("\u{230d}\n");
-        placeholder.push(' ');
+        if *height > 2 {
             if let Some(text) = text {
+                if text.width() <= width - 2 {
+                    placeholder.push(' ');
                     placeholder.push_str(text);
                 }
+            }
+        }
 
         placeholder.push_str(&"\n".repeat(height - 2));
         placeholder.push('\u{230e}');
         placeholder.push_str(&" ".repeat(width - 2));
         placeholder.push_str("\u{230f}\n");
-        placeholder
+        Some(placeholder)
     }
 
     fn show_sender<'a>(
@@ -1122,4 +1133,82 @@ pub mod tests {
             "<h1>Heading</h1>\n<h2>Subheading</h2>\n<p>text</p>\n"
         );
     }
+
+    #[test]
+    fn test_placeholder_frame() {
+        fn pretty_frame_test(str: &str) -> Option<String> {
+            Some(str[1..].to_string())
+        }
+
+        assert_eq!(
+            Message::placeholder_frame(None, 4, &ImagePreviewSize { width: 4, height: 4 }),
+            pretty_frame_test(
+                r#"
+⌌  ⌍
+
+
+⌎  ⌏
+"#
+            )
+        );
+
+        assert_eq!(
+            Message::placeholder_frame(None, 2, &ImagePreviewSize { width: 4, height: 4 }),
+            None
+        );
+        assert_eq!(
+            Message::placeholder_frame(None, 4, &ImagePreviewSize { width: 1, height: 4 }),
+            None
+        );
+
+        assert_eq!(
+            Message::placeholder_frame(None, 4, &ImagePreviewSize { width: 4, height: 1 }),
+            None
+        );
+
+        assert_eq!(
+            Message::placeholder_frame(Some("OK"), 4, &ImagePreviewSize { width: 4, height: 4 }),
+            pretty_frame_test(
+                r#"
+⌌  ⌍
+ OK
+
+⌎  ⌏
+"#
+            )
+        );
+        assert_eq!(
+            Message::placeholder_frame(Some("idontfit"), 4, &ImagePreviewSize {
+                width: 4,
+                height: 4,
+            }),
+            pretty_frame_test(
+                r#"
+⌌  ⌍
+
+
+⌎  ⌏
+"#
+            )
+        );
+        assert_eq!(
+            Message::placeholder_frame(Some("OK"), 4, &ImagePreviewSize { width: 4, height: 2 }),
+            pretty_frame_test(
+                r#"
+⌌  ⌍
+⌎  ⌏
+"#
+            )
+        );
+        assert_eq!(
+            Message::placeholder_frame(Some("OK"), 4, &ImagePreviewSize { width: 2, height: 3 }),
+            pretty_frame_test(
+                r#"
+⌌⌍
+
+⌎⌏
+"#
+            )
+        );
+    }
 }