fix: handle signed URL download failures (#66)

* fix: improve download failure handling

* test: cover download failure handling

Author: amanharshx

src-tauri/src/downloader.rs

@@ -118,22 +118,7 @@ enum UrlExpiry {
     Expired(DateTime<Utc>),
 }
 
-fn parse_url_expiry(url: &str, now: DateTime<Utc>) -> UrlExpiry {
-    let Ok(parsed) = Url::parse(url) else {
-        return UrlExpiry::Missing;
-    };
-    let Some(value) = parsed
-        .query_pairs()
-        .find_map(|(key, value)| (key == "Expires").then_some(value))
-    else {
-        return UrlExpiry::Missing;
-    };
-    let Ok(timestamp) = value.parse::<i64>() else {
-        return UrlExpiry::Malformed;
-    };
-    let Some(expires_at) = DateTime::from_timestamp(timestamp, 0) else {
-        return UrlExpiry::Malformed;
-    };
+fn classify_url_expiry(expires_at: DateTime<Utc>, now: DateTime<Utc>) -> UrlExpiry {
     let confidently_expired = expires_at
         .checked_add_signed(chrono::Duration::seconds(CLOCK_SKEW_TOLERANCE_SECS))
         .is_some_and(|deadline| deadline < now);
@@ -145,6 +130,72 @@ fn parse_url_expiry(url: &str, now: DateTime<Utc>) -> UrlExpiry {
     }
 }
 
+fn parse_relative_url_expiry(
+    parsed: &Url,
+    date_key: &str,
+    lifetime_key: &str,
+    now: DateTime<Utc>,
+) -> UrlExpiry {
+    let signed_at = parsed
+        .query_pairs()
+        .find_map(|(key, value)| (key == date_key).then_some(value));
+    let lifetime = parsed
+        .query_pairs()
+        .find_map(|(key, value)| (key == lifetime_key).then_some(value));
+    match (signed_at, lifetime) {
+        (None, None) => UrlExpiry::Missing,
+        (Some(signed_at), Some(lifetime)) => {
+            let Ok(signed_at) = chrono::NaiveDateTime::parse_from_str(&signed_at, "%Y%m%dT%H%M%SZ")
+            else {
+                return UrlExpiry::Malformed;
+            };
+            let Ok(lifetime_seconds) = lifetime.parse::<i64>() else {
+                return UrlExpiry::Malformed;
+            };
+            if lifetime_seconds < 0 {
+                return UrlExpiry::Malformed;
+            }
+            let Some(lifetime) = chrono::Duration::try_seconds(lifetime_seconds) else {
+                return UrlExpiry::Malformed;
+            };
+            let Some(expires_at) = signed_at.and_utc().checked_add_signed(lifetime) else {
+                return UrlExpiry::Malformed;
+            };
+            classify_url_expiry(expires_at, now)
+        }
+        _ => UrlExpiry::Malformed,
+    }
+}
+
+fn parse_url_expiry(url: &str, now: DateTime<Utc>) -> UrlExpiry {
+    let Ok(parsed) = Url::parse(url) else {
+        return UrlExpiry::Missing;
+    };
+    if let Some(value) = parsed
+        .query_pairs()
+        .find_map(|(key, value)| (key == "Expires").then_some(value))
+    {
+        let Ok(timestamp) = value.parse::<i64>() else {
+            return UrlExpiry::Malformed;
+        };
+        let Some(expires_at) = DateTime::from_timestamp(timestamp, 0) else {
+            return UrlExpiry::Malformed;
+        };
+        return classify_url_expiry(expires_at, now);
+    }
+
+    for (date_key, lifetime_key) in [
+        ("X-Goog-Date", "X-Goog-Expires"),
+        ("X-Amz-Date", "X-Amz-Expires"),
+    ] {
+        let expiry = parse_relative_url_expiry(&parsed, date_key, lifetime_key, now);
+        if expiry != UrlExpiry::Missing {
+            return expiry;
+        }
+    }
+    UrlExpiry::Missing
+}
+
 #[derive(Debug, Error, Clone, Copy, PartialEq, Eq)]
 enum UrlRejection {
     #[error("download URL is malformed")]
@@ -1059,6 +1110,99 @@ mod tests {
         );
     }
 
+    #[test]
+    fn parses_gcs_v4_expiry() {
+        let now = DateTime::parse_from_rfc3339("2026-02-01T19:45:00Z")
+            .unwrap()
+            .with_timezone(&Utc);
+        let expired_at = DateTime::parse_from_rfc3339("2026-02-01T19:40:47Z")
+            .unwrap()
+            .with_timezone(&Utc);
+
+        assert_eq!(
+            parse_url_expiry(
+                "https://storage.googleapis.com/bucket/image.jpg?X-Goog-Date=20260125T194047Z&X-Goog-Expires=604800&X-Goog-Signature=secret",
+                now,
+            ),
+            UrlExpiry::Expired(expired_at)
+        );
+        assert_eq!(
+            parse_url_expiry(
+                "https://storage.googleapis.com/bucket/image.jpg?X-Goog-Expires=604800&X-Goog-Date=20260125T195000Z",
+                now,
+            ),
+            UrlExpiry::Active(
+                DateTime::parse_from_rfc3339("2026-02-01T19:50:00Z")
+                    .unwrap()
+                    .with_timezone(&Utc)
+            )
+        );
+        assert_eq!(
+            parse_url_expiry(
+                "https://storage.googleapis.com/bucket/image.jpg?X-Goog-Date=invalid&X-Goog-Expires=604800",
+                now,
+            ),
+            UrlExpiry::Malformed
+        );
+        assert_eq!(
+            parse_url_expiry(
+                "https://storage.googleapis.com/bucket/image.jpg?X-Goog-Date=20260125T194047Z",
+                now,
+            ),
+            UrlExpiry::Malformed
+        );
+        assert_eq!(
+            parse_url_expiry(
+                "https://storage.googleapis.com/bucket/image.jpg?X-Goog-Date=20260125T194047Z&X-Goog-Expires=-1",
+                now,
+            ),
+            UrlExpiry::Malformed
+        );
+    }
+
+    #[test]
+    fn parses_aws_v4_expiry() {
+        let now = DateTime::parse_from_rfc3339("2013-05-25T00:03:00Z")
+            .unwrap()
+            .with_timezone(&Utc);
+        let expired_at = DateTime::parse_from_rfc3339("2013-05-25T00:00:00Z")
+            .unwrap()
+            .with_timezone(&Utc);
+
+        assert_eq!(
+            parse_url_expiry(
+                "https://examplebucket.s3.amazonaws.com/test.txt?X-Amz-Date=20130524T000000Z&X-Amz-Expires=86400&X-Amz-Signature=secret",
+                now,
+            ),
+            UrlExpiry::Expired(expired_at)
+        );
+        assert_eq!(
+            parse_url_expiry(
+                "https://examplebucket.s3.amazonaws.com/test.txt?X-Amz-Expires=86400&X-Amz-Date=20130524T120000Z",
+                now,
+            ),
+            UrlExpiry::Active(
+                DateTime::parse_from_rfc3339("2013-05-25T12:00:00Z")
+                    .unwrap()
+                    .with_timezone(&Utc)
+            )
+        );
+        assert_eq!(
+            parse_url_expiry(
+                "https://examplebucket.s3.amazonaws.com/test.txt?X-Amz-Date=invalid&X-Amz-Expires=86400",
+                now,
+            ),
+            UrlExpiry::Malformed
+        );
+        assert_eq!(
+            parse_url_expiry(
+                "https://examplebucket.s3.amazonaws.com/test.txt?X-Amz-Date=20130524T000000Z",
+                now,
+            ),
+            UrlExpiry::Malformed
+        );
+    }
+
     #[test]
     fn aggregates_failures_with_safe_bounded_examples() {
         let mut summary = FailureSummary::default();

src/components/__tests__/converter-screen.test.tsx

@@ -40,6 +40,9 @@ describe("DownloadFailureDetails", () => {
       />,
     );
 
+    const copyStatus = screen.getByRole("status");
+    expect(copyStatus).toBeEmptyDOMElement();
+    expect(copyStatus).toHaveClass("sr-only");
     expect(screen.getByText("Download details")).toBeInTheDocument();
     expect(screen.getByText("1 download link expired — one.jpg")).toBeInTheDocument();
     await act(async () => {
@@ -49,13 +52,17 @@ describe("DownloadFailureDetails", () => {
     expect(writeText).toHaveBeenCalledWith(
       "expired_url: 1; one.jpg\nnot_found: 1; HTTP 404; two.jpg",
     );
-    expect(screen.getByRole("status")).toHaveTextContent("Copied");
+    expect(screen.getByRole("button", { name: "Copied" })).toBeInTheDocument();
+    expect(copyStatus).toHaveTextContent("Copied");
 
     act(() => {
       vi.advanceTimersByTime(2_000);
     });
 
-    expect(screen.queryByText("Copied")).not.toBeInTheDocument();
+    expect(copyStatus).toBeEmptyDOMElement();
+    expect(
+      screen.getByRole("button", { name: "Copy details" }),
+    ).toBeInTheDocument();
   });
 
   it("clears copied reset timer on unmount", async () => {
@@ -110,6 +117,9 @@ describe("DownloadFailureDetails", () => {
     expect(
       await screen.findByText("Couldn't copy details"),
     ).toBeInTheDocument();
+    expect(
+      screen.getByRole("button", { name: "Copy failed" }),
+    ).toBeInTheDocument();
   });
 
   it("renders structured hard failures through the error card", () => {
@@ -155,6 +165,7 @@ describe("DownloadFailureDetails", () => {
     expect(screen.getByTestId("error-message")).toHaveTextContent(
       "Your download links expired on 19 Jul 2026.",
     );
+    expect(screen.getByTestId("error-card")).toHaveClass("overflow-hidden");
     expect(screen.getByText("Download details")).toBeInTheDocument();
   });
 });

src/components/converter-screen.tsx

@@ -35,6 +35,18 @@ export function DownloadFailureDetails({
   const [copyStatus, setCopyStatus] = useState<
     "idle" | "copied" | "failed"
   >("idle");
+  const copyButtonLabel =
+    copyStatus === "copied"
+      ? "Copied"
+      : copyStatus === "failed"
+        ? "Copy failed"
+        : "Copy details";
+  const copyAnnouncement =
+    copyStatus === "copied"
+      ? "Copied"
+      : copyStatus === "failed"
+        ? "Couldn't copy details"
+        : "";
 
   useEffect(() => {
     if (copyStatus !== "copied") {
@@ -85,18 +97,16 @@ export function DownloadFailureDetails({
           </ul>
           <button
             type="button"
-            className="mt-2 underline underline-offset-2"
+            className="mt-2 font-medium underline underline-offset-2"
             onClick={() => {
               void copyDetails();
             }}
           >
-            Copy details
+            {copyButtonLabel}
           </button>
-          {copyStatus !== "idle" && (
-            <span className="ml-2" role="status">
-              {copyStatus === "copied" ? "Copied" : "Couldn't copy details"}
-            </span>
-          )}
+          <span className="sr-only" role="status">
+            {copyAnnouncement}
+          </span>
         </details>
       )}
     </div>
@@ -316,7 +326,7 @@ export function ConverterScreen({ onBack }: { onBack: () => void }) {
                 </>
               ) : (
                 <div className="space-y-4">
-                  <Card data-testid="success-card" className="bg-primary/5 p-6">
+                  <Card data-testid="success-card" className="overflow-hidden bg-primary/5 p-6">
                     <div className="flex items-center gap-3 mb-4">
                       <div className="flex h-10 w-10 items-center justify-center rounded-full bg-primary/20">
                         <Check className="h-5 w-5 text-primary" />
@@ -358,7 +368,7 @@ export function ConverterScreen({ onBack }: { onBack: () => void }) {
 
           {/* Error Display */}
           {error && (
-            <Card data-testid="error-card" className="bg-destructive/10 p-4 text-center">
+            <Card data-testid="error-card" className="overflow-hidden bg-destructive/10 p-4 text-center">
               {errorDownloadMessage ? (
                 <DownloadFailureDetails
                   message={errorDownloadMessage}

src/lib/__tests__/download-failures.test.ts

@@ -172,6 +172,33 @@ describe("buildDownloadFailureMessage", () => {
     ).toBe(expected);
   });
 
+  it("keeps rejected-download remedies consistent", () => {
+    const message = buildDownloadFailureMessage(
+      summary(["http_error", 4, ["one.jpg", "two.jpg", "three.jpg"]]),
+      4,
+      true,
+    );
+
+    expect(message?.primary).toBe(
+      "The image server rejected 4 downloads. Export the dataset again or try later.",
+    );
+    expect(message?.breakdown).toEqual([
+      "4 downloads were rejected by the image server, including one.jpg, two.jpg, three.jpg. Export the dataset again or try later.",
+    ]);
+  });
+
+  it("marks truncated examples as non-exhaustive", () => {
+    expect(
+      buildDownloadFailureMessage(
+        summary(["expired_url", 8, ["one.jpg", "two.jpg", "three.jpg"]]),
+        8,
+        true,
+      )?.breakdown,
+    ).toEqual([
+      "8 download links expired, including one.jpg, two.jpg, three.jpg. Export the dataset again.",
+    ]);
+  });
+
   it("uses generic mixed copy and only references existing details", () => {
     const message = buildDownloadFailureMessage(
       summary(

src/lib/download-failures.ts

@@ -110,8 +110,9 @@ function breakdownLabel(group: FailureGroup): string {
     case "unsupported_scheme":
       return `${count} download ${plural(count, "link")} used an unsupported format`;
     case "server_error":
-    case "http_error":
       return `${count} image server ${plural(count, "error")}`;
+    case "http_error":
+      return `${count} ${plural(count, "download")} ${count === 1 ? "was" : "were"} rejected by the image server`;
     case "response_error":
       return `${count} incomplete ${plural(count, "download")}`;
     case "too_large":
@@ -139,8 +140,9 @@ function breakdownRemedy(kind: FailureKind): string {
     case "blocked_address":
       return "Try a different network or ask your network administrator.";
     case "server_error":
-    case "http_error":
       return "Wait a moment and try again.";
+    case "http_error":
+      return "Export the dataset again or try later.";
     case "too_large":
       return "Use smaller images and try again.";
   }
@@ -149,8 +151,11 @@ function breakdownRemedy(kind: FailureKind): string {
 function formatBreakdown(group: FailureGroup): string {
   const examples = group.examples.slice(0, 3).map(safeExample);
   const label = breakdownLabel(group);
-  const cause =
-    examples.length > 0 ? `${label} — ${examples.join(", ")}` : label;
+  const examplesPrefix =
+    group.count > examples.length ? ", including " : " — ";
+  const cause = examples.length > 0
+    ? `${label}${examplesPrefix}${examples.join(", ")}`
+    : label;
   return `${cause}. ${breakdownRemedy(group.kind)}`;
 }