An upload that did not arrive says why

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GT37Z1Xtfd9pUuQtMTg6Yt

src/app.rs

@@ -1310,6 +1310,12 @@ fn AlternativeCard(
                 };
                 let Some(files) = input.files() else { continue };
                 let Some(file) = files.get(0) else { continue };
+                // Too big is known before a byte is sent.
+                if file.size() > MAX_UPLOAD_BYTES as f64 {
+                    send_error.set(Some(t(&lang().get_untracked(), "upload_too_large").to_string()));
+                    sending.set(false);
+                    return;
+                }
                 match upload_file(&file, &question_id_for_submit, &alt_name_for_submit).await {
                     Ok(key) => {
                         map.insert(name.clone(), serde_json::Value::String(key));
@@ -1319,7 +1325,8 @@ fn AlternativeCard(
                     // say so.
                     Err(e) => {
                         leptos::logging::error!("upload of {name} failed: {e:?}");
-                        send_error.set(Some(t(&lang().get_untracked(), "upload_failed").to_string()));
+                        let status = e.as_string().and_then(|m| m.rsplit(' ').next().and_then(|n| n.parse().ok()));
+                        send_error.set(Some(t(&lang().get_untracked(), upload_refusal(status)).to_string()));
                         sending.set(false);
                         return;
                     }
@@ -2283,6 +2290,24 @@ pub fn uploaded_filename(value: &str) -> Option<&str> {
     rest.strip_prefix('-').filter(|name| shaped && !name.is_empty())
 }
 
+/// The largest file one upload may carry. Here, not in `upload.rs`,
+/// so the browser checks the same number before it sends anything.
+pub const MAX_UPLOAD_BYTES: usize = 20 * 1024 * 1024;
+
+/// Why an upload did not arrive, in words a person can act on, from
+/// the status `POST /upload` answered with (see `upload.rs`): too big,
+/// a site that takes no files, a page they may not send from, or
+/// anything else.
+#[cfg_attr(not(feature = "hydrate"), allow(dead_code))]
+fn upload_refusal(status: Option<u16>) -> &'static str {
+    match status {
+        Some(413) => "upload_too_large",
+        Some(503) => "upload_unavailable",
+        Some(403) => "upload_forbidden",
+        _ => "upload_failed",
+    }
+}
+
 /// What a refused server call says, without the wrapping a person
 /// has no use for.
 fn server_message(e: &ServerFnError) -> String {
@@ -3241,6 +3266,21 @@ mod responsible_tests {
 mod picture_tests {
     use super::*;
 
+    #[test]
+    fn an_upload_refusal_says_which_it_was() {
+        assert_eq!(upload_refusal(Some(413)), "upload_too_large");
+        assert_eq!(upload_refusal(Some(503)), "upload_unavailable");
+        assert_eq!(upload_refusal(Some(403)), "upload_forbidden");
+        assert_eq!(upload_refusal(Some(502)), "upload_failed");
+        assert_eq!(upload_refusal(None), "upload_failed");
+        for lang in ["en", "no"] {
+            for status in [Some(413), Some(503), Some(403), None] {
+                let key = upload_refusal(status);
+                assert_ne!(crate::i18n::t(lang, key), key, "{lang} has words for {key}");
+            }
+        }
+    }
+
     #[test]
     fn a_record_with_a_picture_is_shown_by_it() {
         assert!(is_picture("Portrett.JPG") && is_picture("a.webp") && !is_picture("rapport.pdf"));