feat(paste): precheck src existence before allocating a task

[lovehunter9]

Summary

• PasteMethod used to return a task id (HTTP 200) the instant request parsing succeeded; src existence was only ever discovered later, deep inside each task phase, where the failure modes varied per route and several looked like phantom Completed tasks to the client.
• Introduce pkg/drivers/precheck — a node-aware src-existence probe that runs immediately after PasteParam is fully resolved, covering sync, cloud, drive, cache, external/internal/smb/usb/hdd via local stat or a cross-pod /api/resources GET.
• Two related fixes batched in: pass dst basename through to seaserv.CopyFile / MoveFile so sync-to-sync rename works; tighten TrimShareId so trailing garbage on a share id no longer normalises back to a legitimate row.

Problem

Paste failure modes the client saw before this change:

Backend	Symptom for a missing src
Rsync / rclone	task surfaces "no such file" mid-phase
Sync (seafile)	GetFromSyncFileCount returns (0, nil), SyncCopy / DownloadFromSync "succeed" with zero bytes
Cross-node files-pod	DownloadFromFiles treats an empty tree stream as a clean completion

From the UI every variant looked the same: a phantom Completed (or briefly Running → Failed) task with zero bytes moved. There was no early signal that the operation could not possibly succeed.

Pre-validation (pkg/drivers/precheck)

Probes src existence per backend, with node-awareness baked in:

src.FileType	Probe
sync	seafile RPC GetRepo + GetFileIdByPath / GetDirIdByPath (file vs dir picked strictly from src.Path's trailing slash; no silent type coercion)
awss3 / tencent / google / dropbox	rclone GetFilesSize
drive (Home / Data)	local os.Stat (master node only by routing)
cache / external / internal / smb / usb / hdd	local os.Stat when src.Extend matches the current node; otherwise a GET against the owning files-pod's /api/resources/<fsType>/<extend><path> via the integration manager (same pod DownloadFromFiles already targets)

share=1 requests honour SrcOwner so the existence probe runs as the share grantor, mirroring the owner-rewrite the task layer applies downstream.

PasteMethod calls precheck.SourceExists right after PasteParam is fully populated (including resolved SrcSharePath / DstSharePath). All precheck failures collapse to a single

{ "code": 1, "msg": "..." }

at HTTP 500, using a new ErrorMessagePasteSrcNotExists constant whose phrasing matches the existing ErrorMessagePasteWrongSourceShare / ErrorMessagePasteSourceExpired. The raw Go error chain stays in klog.Warningf with src / owner / action for ops debugging.

The task pipeline below is unchanged and keeps its own defensive checks.

Related fixes

sync-to-sync rename

HandleBatchCopy / HandleBatchMove previously hard-coded the destination filename to equal the source's, silently dropping any caller-supplied rename target (and nullifying AddVersionSuffix's conflict-resolution suffix). The underlying seaserv.CopyFile / MoveFile already accept independent src/dst filenames; this wires the dst name through with a trailing dstDirents []string parameter that falls back to srcDirents when nil/empty — the no-rename path stays byte-for-byte identical for existing callers.

TrimShareId tightening

The previous implementation truncated any string longer than 36 chars to its first 36 chars, so URLs like ?path_id=<uuid>asdasd silently normalised back to <uuid> and hit the legitimate share_paths row.

Replaced with an isKnownNode lookup (production: global.GlobalNode.CheckNodeExists) that strips the suffix only when it is exactly _<a-real-cluster-node-name>. Bare UUIDs, trailing garbage, and unknown node names are returned untouched, so the downstream id = ? query either matches the real row or returns an empty set.

All 19 call sites updated (12 in share_service.go, 4 in router/middleware.go, 1 each in search_service.go, dynamic_hls_controller.go, streaming_helpers.go). Contract pinned with TestTrimShareId covering bare UUIDs, decorated ids with known / unknown / multi-underscore node names, the <uuid>asdasd regression case, lone trailing _, and a nil callback.

Test plan

• gofmt clean
• go vet ./...
• go test ./pkg/common/... — TestTrimShareId covers the regression
• go test ./pkg/drivers/precheck/... — structural tests pass without seafile/rclone/k8s wired up
• Manual: paste with a deleted src on each backend (drive / sync / cloud / external on another node / share) → request fails with 500 { "code": 1, "msg": ErrorMessagePasteSrcNotExists }, no task allocated, no phantom Completed entry in the task list
• Manual: paste a sync file/dir to itself under a new name → renamed copy/move lands with the new basename (and with AddVersionSuffix if there's a name conflict)
• Manual: hit ?path_id=<uuid>asdasd and ?path_id=<uuid>_<unknown-node> → both miss the real row instead of silently matching it; ?path_id=<uuid>_<known-node> still resolves
• Regression: existing in-cluster paste flows (drive → drive, sync → drive, drive → sync, cross-node external) — precheck passes and task completes as before