fix: setInputFiles() not working on Browserbase

[seanmcguire12]

why

• file uploads were failing on Browserbase. this is because setInputFiles() was not serializing the file payload

what changed

changed business logic of setInputFiles() to:

• call normalizeInputFiles(), which returns a serializable/base64 encoded file
• check if the browser is remote
• if remote, assignFilesViaPayloadInjection() is called, which then calls assignFilePayloadsToInputElement() (browser-side JS) and reconstructs the base64 back into a file, and directly assigns the reconstructed files to the input element
• if not remote (local), then the files are written to temp dirs, and those dirs are passed into DOM.setInputFiles (CDP command)

test plan

• added additional tests for various file input shapes
• regression evals

[changeset-bot]

🦋 Changeset detected

Latest commit: 6e1378c

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
@browserbasehq/stagehand	Patch
@browserbasehq/stagehand-evals	Patch

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[seanmcguire12]

@greptileai

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Greptile Overview

Greptile Summary

This PR fixes file uploads on Browserbase by implementing a dual-path strategy: remote browsers now serialize files to base64 and reconstruct them client-side via JavaScript injection, while local browsers continue using CDP's DOM.setFileInputFiles.

Key Changes:

• Created normalizeInputFiles() to standardize file inputs (paths/payloads) into in-memory buffers
• Added isBrowserRemote() check in Frame to detect Browserbase environments
• Implemented assignFilePayloadsToInputElement() browser-side script that reconstructs File objects from base64
• Added 50MB size limit for remote uploads (matching Playwright's limit)
• Expanded test coverage with fixtures for relative paths, absolute paths, payload objects, iframes, and multiple files

Implementation Quality:

• Clean separation between normalization logic (fileUploadUtils.ts) and execution paths
• Proper error handling with meaningful error messages
• Consistent with existing codebase patterns
• Good test coverage across different file input shapes

Confidence Score: 5/5

• This PR is safe to merge with minimal risk
• The implementation is well-structured with clear separation of concerns, comprehensive test coverage, proper error handling, and follows existing patterns. The approach mirrors Playwright's remote file upload strategy (including the 50MB limit), which is battle-tested. The changes are isolated to file upload functionality without affecting other features.
• No files require special attention

Important Files Changed

File Analysis

Filename	Score	Overview
packages/core/lib/v3/understudy/fileUploadUtils.ts	5/5	New utility file for normalizing file inputs - handles both file paths and buffer payloads correctly
packages/core/lib/v3/understudy/locator.ts	5/5	Updated setInputFiles to detect remote browsers and use payload injection method for Browserbase
packages/core/lib/v3/dom/locatorScripts/scripts.ts	5/5	Added assignFilePayloadsToInputElement function to reconstruct files from base64 in remote browsers
packages/core/lib/v3/tests/setinputfiles.spec.ts	5/5	Enhanced test coverage with fixtures and validation helpers for various file input scenarios

Sequence Diagram

sequenceDiagram
    participant User
    participant Locator
    participant FileUtils as normalizeInputFiles
    participant Frame
    participant CDP as CDP Session
    participant Browser as Browser/Page

    User->>Locator: setInputFiles(files)
    Locator->>CDP: Validate element is input[type=file]
    CDP-->>Locator: Validation OK
    
    Locator->>FileUtils: normalizeInputFiles(files)
    alt File path provided
        FileUtils->>FileUtils: Resolve absolute path
        FileUtils->>FileUtils: Read file from disk
        FileUtils-->>Locator: NormalizedFilePayload with buffer & path
    else Payload object provided
        FileUtils->>FileUtils: Convert buffer to Node Buffer
        FileUtils-->>Locator: NormalizedFilePayload with buffer
    end
    
    Locator->>Frame: isBrowserRemote()
    
    alt Remote Browser (Browserbase)
        Frame-->>Locator: true
        Locator->>Locator: Check file size < 50MB
        Locator->>Locator: Serialize files to base64
        Locator->>CDP: callFunctionOn(assignFilePayloadsToInputElement)
        CDP->>Browser: Execute in page context
        Browser->>Browser: Decode base64 to bytes
        Browser->>Browser: Create File objects via DataTransfer
        Browser->>Browser: Assign to input.files
        Browser->>Browser: Dispatch input/change events
        Browser-->>CDP: Success
        CDP-->>Locator: Upload complete
    else Local Browser
        Frame-->>Locator: false
        alt File has absolutePath
            Locator->>Locator: Use existing path
        else Payload without path
            Locator->>Locator: Write buffer to temp file
        end
        Locator->>CDP: DOM.setFileInputFiles(filePaths)
        CDP->>Browser: Set files via CDP
        Browser-->>CDP: Success
        CDP-->>Locator: Upload complete
        Locator->>Locator: Cleanup temp files
    end
    
    Locator-->>User: Success

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