fix: retry preflight HEAD and prefer catalog size when downloading models (ATO-302)#182
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…dels (ATO-302) The preflight HEAD request that resolves a model's file size ran exactly once, while the download stream itself retries up to 5 times. A single transient network blip (TLS handshake EOF, timeout) during HEAD therefore produced an immediate, unrecoverable 'Download failed'. - Skip the HEAD request entirely when the catalog already provides the file size (item.size), so it cannot fail the download at all. - When the size is unknown, retry the HEAD with the same policy as the stream (5 attempts, exponential backoff, cancel-aware), classifying transport errors and 408/429/5xx as retryable. - Make a preflight failure non-fatal: fall back to an unknown size and let the GET path (which has its own retries) surface the real error.
… ATO-302 - preflight_head_retries_dropped_connections: the server tears down the first two TCP connections before responding (the 'unexpected EOF during handshake' class of failure from the original report) and the preflight still resolves the size on the third attempt. - download_succeeds_when_preflight_head_always_fails: full _download_files_internal regression test — HEAD returns 500 on every attempt, yet the download completes via GET. Fails with 'Failed to get file size: HTTP status 500' on the pre-fix code.
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Problem
The preflight
HEADrequest that resolves a model's file size before download ran exactly once, while the download stream itself retries up to 5 times (MAX_STREAM_RETRIES, exponential backoff). A single transient network blip during HEAD — TLS handshake EOF, connection reset, timeout — produced an immediate, unrecoverable "Download failed", even though the actual download would have succeeded after a retry.Models are served from
huggingface.co, so this hit anyone with a flaky path to HF (DPI, VPN, HTTPS-inspecting antivirus, flapping ISP). Origin: Discord report (Windows 11, qwen35) withunexpected EOF during handshakein the logs.Fixes ATO-302.
Changes
src-tauri/src/core/downloads/helpers.rs:item.size) — no network round-trip at preflight, so nothing to fail.Tests
Six new tests in
src-tauri/src/core/downloads/tests.rs, all against real local HTTP/TCP servers:download_succeeds_when_preflight_head_always_fails— end-to-end regression test through_download_files_internal: HEAD returns 500 on every attempt, download still completes via GET. Verified to fail on pre-fixmainwith the exact bug (Failed to get file size: HTTP status 500).preflight_head_retries_dropped_connections— server tears down the first two TCP connections before responding (the handshake-EOF failure class from the report); size resolves on the third attempt.preflight_head_retries_transient_failures— two 500s, then success.preflight_uses_catalog_size_without_a_head_request— known catalog size ⇒ zero requests to the server.preflight_head_failure_is_not_fatal— permanent 500s ⇒ falls back to size 0 after 6 attempts, no error.preflight_head_does_not_retry_fatal_status— 404 is not retried.Full crate suite: 157 passed, 0 failed.