refactor: isolate OPDS download setup

src-tauri/src/commands/opds/download.rs

@@ -1,15 +1,14 @@
+use super::download_service::prepare_download_setup;
 use super::transport::sanitize_error_message;
 use crate::error::AppError;
 use crate::opds::{
-    download_file, plan_download_destination, CatalogConfig, DownloadContext, DownloadError,
-    ProgressCallback, Publication,
+    download_file, plan_download_destination, DownloadError, ProgressCallback, Publication,
 };
 use serde::Serialize;
 use std::collections::HashMap;
 use std::sync::{LazyLock, Mutex};
 use tauri::{command, AppHandle, Emitter};
 use tokio_util::sync::CancellationToken;
-use url::Url;
 
 #[derive(Debug, Clone, Serialize)]
 pub struct OpdsDownloadProgress {
@@ -97,31 +96,10 @@ pub async fn download_opds_publication(
     content_root: String,
     app: AppHandle,
 ) -> Result<DownloadResult, AppError> {
-    let parsed_url = Url::parse(&catalog_url)
-        .map_err(|_| AppError::OpdsTransport("Invalid URL: unable to parse".to_string()))?;
-
-    if parsed_url.scheme() != "http" && parsed_url.scheme() != "https" {
-        return Err(AppError::OpdsTransport(
-            "Invalid URL: only HTTP and HTTPS schemes are allowed".to_string(),
-        ));
-    }
-
-    if !parsed_url.username().is_empty() {
-        return Err(AppError::OpdsTransport(
-            "Invalid URL: credentials must not be embedded in URL".to_string(),
-        ));
-    }
-
-    let config = CatalogConfig::new("download", parsed_url.clone(), username, password)?;
-
-    let client = reqwest::Client::builder()
-        .timeout(std::time::Duration::from_secs(30))
-        .redirect(reqwest::redirect::Policy::none())
-        .use_rustls_tls()
-        .build()
-        .map_err(|e| AppError::OpdsTransport(format!("Failed to build HTTP client: {}", e)))?;
-
-    let context = DownloadContext::new(client, config.clone());
+    let setup = prepare_download_setup(&catalog_url, &username, &password)?;
+    let parsed_url = setup.url;
+    let config = setup.config;
+    let context = setup.context;
 
     let content_root_path = std::path::Path::new(&content_root);
     let plan = plan_download_destination(
@@ -201,8 +179,10 @@ pub async fn download_opds_publication(
 #[cfg(test)]
 mod tests {
     use super::*;
+    use crate::opds::{CatalogConfig, DownloadContext};
     use axum::{routing::get, Router};
     use axum_test::TestServer;
+    use url::Url;
 
     #[tokio::test]
     async fn cancellable_download_stops_when_token_fires() {

src-tauri/src/commands/opds/download_service.rs

@@ -0,0 +1,138 @@
+//! Application-layer service for the OPDS download command.
+//!
+//! Owns download input validation and HTTP client/context construction so the
+//! Tauri command stays a thin adapter over the download pipeline. The error
+//! messages produced here are intentionally stable: the frontend IPC contract
+//! matches on the serialized `AppError::OpdsTransport` strings, and the
+//! command-derived messages must not change.
+
+use crate::error::AppError;
+use crate::opds::{CatalogConfig, DownloadContext};
+use url::Url;
+
+/// A validated, ready-to-use setup for a single publication download.
+pub struct DownloadSetup {
+    pub url: Url,
+    pub config: CatalogConfig,
+    pub context: DownloadContext,
+}
+
+/// Prepares a download setup from raw command inputs.
+///
+/// Validates the catalog URL, derives a `CatalogConfig`, and constructs the
+/// HTTP client + `DownloadContext`. Failure produces the exact
+/// `AppError::OpdsTransport` messages the previous inline command produced.
+pub fn prepare_download_setup(
+    catalog_url: &str,
+    username: &str,
+    password: &str,
+) -> Result<DownloadSetup, AppError> {
+    let parsed_url = Url::parse(catalog_url)
+        .map_err(|_| AppError::OpdsTransport("Invalid URL: unable to parse".to_string()))?;
+
+    if parsed_url.scheme() != "http" && parsed_url.scheme() != "https" {
+        return Err(AppError::OpdsTransport(
+            "Invalid URL: only HTTP and HTTPS schemes are allowed".to_string(),
+        ));
+    }
+
+    if !parsed_url.username().is_empty() {
+        return Err(AppError::OpdsTransport(
+            "Invalid URL: credentials must not be embedded in URL".to_string(),
+        ));
+    }
+
+    let config = CatalogConfig::new(
+        "download",
+        parsed_url.clone(),
+        username,
+        password.to_string(),
+    )
+    .map_err(|e| AppError::OpdsTransport(e.to_string()))?;
+
+    let client = reqwest::Client::builder()
+        .timeout(std::time::Duration::from_secs(30))
+        .redirect(reqwest::redirect::Policy::none())
+        .use_rustls_tls()
+        .build()
+        .map_err(|e| AppError::OpdsTransport(format!("Failed to build HTTP client: {}", e)))?;
+
+    let context = DownloadContext::new(client, config.clone());
+
+    Ok(DownloadSetup {
+        url: parsed_url,
+        config,
+        context,
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn opds_transport_message(err: &AppError) -> &str {
+        match err {
+            AppError::OpdsTransport(msg) => msg,
+            other => panic!("expected OpdsTransport, got {other:?}"),
+        }
+    }
+
+    fn setup_error(catalog_url: &str) -> AppError {
+        match prepare_download_setup(catalog_url, "user", "pass") {
+            Err(e) => e,
+            Ok(_) => panic!("expected setup to fail for {catalog_url}"),
+        }
+    }
+
+    #[test]
+    fn valid_https_url_builds_setup() {
+        let setup = prepare_download_setup("https://example.com/opds", "user", "pass").unwrap();
+        assert_eq!(setup.url.as_str(), "https://example.com/opds");
+        assert_eq!(setup.config.origin(), "https://example.com");
+    }
+
+    #[test]
+    fn valid_http_url_builds_setup() {
+        let setup = prepare_download_setup("http://example.com:8080/opds", "user", "pass").unwrap();
+        assert_eq!(setup.config.origin(), "http://example.com:8080");
+    }
+
+    #[test]
+    fn setup_config_carries_provider_and_username() {
+        let setup = prepare_download_setup("https://example.com/opds", "alice", "s3cret").unwrap();
+        assert_eq!(setup.config.provider, "download");
+        assert_eq!(setup.config.username, "alice");
+        assert_eq!(setup.config.password, "s3cret");
+    }
+
+    #[test]
+    fn unparseable_url_rejected() {
+        let err = setup_error("not a url");
+        assert_eq!(opds_transport_message(&err), "Invalid URL: unable to parse");
+    }
+
+    #[test]
+    fn non_http_scheme_rejected() {
+        let err = setup_error("ftp://example.com/opds");
+        assert_eq!(
+            opds_transport_message(&err),
+            "Invalid URL: only HTTP and HTTPS schemes are allowed"
+        );
+    }
+
+    #[test]
+    fn credentials_embedded_in_url_rejected() {
+        let err = setup_error("https://user:pass@example.com/opds");
+        assert_eq!(
+            opds_transport_message(&err),
+            "Invalid URL: credentials must not be embedded in URL"
+        );
+    }
+
+    #[test]
+    fn setup_context_is_built_with_a_client() {
+        let setup = prepare_download_setup("https://example.com/opds", "user", "pass").unwrap();
+        // The context must carry the same provider and the configured max size.
+        assert_eq!(setup.context.config.provider, "download");
+    }
+}

src-tauri/src/commands/opds/mod.rs

@@ -1,5 +1,6 @@
 pub mod catalog;
 pub mod download;
+pub mod download_service;
 pub mod transport;
 
 pub use catalog::*;