Bound file previews and offer download for unpreviewable files

[kirangadhave]

📝 Summary

Open every selected file in FileViewer while preventing oversized files from being fully read, base64-encoded, and shipped through JSON.

The /api/files/file_details endpoint bounds a read only when the caller passes maxBytes, so the file preview stays capped at 10 MiB while every other consumer (AI attachments, ACP reads, vimrc) reads in full as before. Metadata lookup is split from content retrieval, and reads stop at the limit without opening oversized files. The frontend classifies each response into text, CSV, media, or unsupported, and renders file metadata with a download action instead of mounting an empty editor or dumping base64 for oversized or unsupported files. Native downloads use the streaming GET endpoint; the explicit WASM download stays full-content.

Closes MO-6275

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Project	Deployment	Actions	Updated (UTC)
marimo-docs	Ready	Preview, Comment	Jul 23, 2026 5:31pm

[Copilot]

Pull request overview

This PR improves file preview behavior in marimo’s file explorer by bounding preview reads (to avoid sending large/binary payloads through JSON), adding file-size metadata, and offering a download-first UX when previewing isn’t feasible.

Changes:

• Backend: Add FileInfo.size, introduce FileSystem.get_info() for metadata-only operations, and support bounded reads via maxBytes + isTooLarge in file-details responses.
• Frontend: Request bounded previews (10 MiB), classify responses by render mode (text/csv/media/unsupported), and render metadata + download action for oversized/unsupported files.
• Tests/OpenAPI: Extend API schema and add coverage across server, Pyodide bridge, and frontend rendering behavior.

Reviewed changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/_server/files/test_os_file_system.py	Adds tests for get_info() size reporting and bounded get_details() behavior.
tests/_server/api/endpoints/test_file_explorer.py	Verifies maxBytes behavior (bounded vs unbounded) and negative-limit rejection.
tests/_pyodide/test_pyodide_session.py	Adds tests ensuring Pyodide bridge honors bounded vs unbounded file_details.
packages/openapi/src/api.ts	Updates generated TS types for maxBytes, isTooLarge, and FileInfo.size.
packages/openapi/api.yaml	Updates OpenAPI schema for maxBytes, isTooLarge, and size.
marimo/_server/models/files.py	Adds size, max_bytes, and is_too_large to models.
marimo/_server/files/os_file_system.py	Implements metadata-only get_info() and bounded read logic in get_details().
marimo/_server/files/file_system.py	Adds get_info() abstraction and max_bytes parameter to get_details().
marimo/_server/api/endpoints/file_explorer.py	Adds maxBytes validation and switches validation calls to get_info().
marimo/_pyodide/pyodide_session.py	Plumbs max_bytes through the Pyodide bridge.
frontend/src/core/network/types.ts	Updates sendFileDetails signature to accept FileDetailsRequest.
frontend/src/components/editor/file-tree/file-viewer.tsx	Requests bounded previews and renders metadata/download for oversized/unsupported files.
frontend/src/components/editor/file-tree/file-render-mode.ts	Adds central render-mode classification helper.
frontend/src/components/editor/file-tree/file-preview-metadata.tsx	New metadata-only preview UI with optional download action.
frontend/src/components/editor/file-tree/tests/file-viewer.test.tsx	Adds UI tests for bounded previews and unsupported/oversized behavior.
frontend/src/components/editor/file-tree/tests/file-render-mode.test.ts	Adds unit tests for render-mode mapping.

[cubic-dev-ai]

All reported issues were addressed across 16 files

Architecture diagram

sequenceDiagram
    participant Client as FileViewer (Frontend)
    participant API as Frontend API Client
    participant Server as file_details Endpoint
    participant FS as OSFileSystem
    participant Disk as File on Disk
    participant Download as /download Endpoint

    Note over Client,Download: NEW: Bounded file preview + download fallback

    Client->>API: sendFileDetails({path, maxBytes: 10 MB})
    API->>Server: POST /api/files/file_details<br/>with maxBytes
    Server->>FS: get_details(path, max_bytes=10 MB)
    
    Note over FS,Disk: NEW: Separate metadata path for other operations
    FS->>Disk: stat(path) → size, mime_type
    Disk-->>FS: file info

    alt size > maxBytes (or file content exceeds limit after reading)
        FS->>FS: is_too_large = True, contents = None
    else size <= maxBytes
        Note over FS: Reads at most maxBytes+1 bytes
        FS->>Disk: open and read bounded content
        Disk-->>FS: raw bytes (≤ maxBytes+1)
        FS->>FS: decode as text or base64-encode binary
    end
    FS-->>Server: FileDetailsResponse<br/>(is_too_large, contents, mime_type, ...)
    Server-->>API: HTTP 200
    API-->>Client: FileDetailsResponse

    Client->>Client: getFileRenderMode(mime_type, isBase64)

    alt is_too_large OR renderMode === "unsupported"
        Client->>Client: Show FilePreviewMetadata<br/>(path, type, size, message)
        Note over Client,Download: Download button triggers streaming GET
        Client->>Download: GET /download?path=...
        Download-->>Client: file stream
    else text / csv / media
        Client->>Client: Render FileContentRenderer<br/>(editor or media viewer)
    end

    Note over Server,FS: CHANGED: delete/copy/move/update endpoints now use<br/>get_info() instead of get_details() to avoid content reads

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[github-actions]

Coverage Report for ./frontend

Status	Category	Percentage	Covered / Total
🔵	Lines	77%	77222 / 100277
🔵	Statements	77%	77222 / 100277
🔵	Functions	71.21%	653 / 917
🔵	Branches	79.47%	4524 / 5692

File Coverage

File	Stmts	Branches	Functions	Lines	Uncovered Lines
Changed Files
frontend/src/components/editor/file-tree/file-preview-metadata.tsx	100%	100%	100%	100%
frontend/src/components/editor/file-tree/file-render-mode.ts	100%	100%	100%	100%
frontend/src/components/editor/file-tree/file-viewer.tsx	89.01%	63.88%	0%	89.01%	126-130, 161-169, 220-226, 238-240, 244
frontend/src/core/network/types.ts	0%	0%	0%	0%

Generated in workflow #19870 for commit ed0b602 by the Vitest Coverage Report Action