Function validateInput

src/tools/FileReadTool/FileReadTool.ts:422–499

({ file_path, pages }, toolUseContext: ToolUseContext)

  },
  renderToolUseErrorMessage,
  async validateInput({ file_path, pages }, toolUseContext: ToolUseContext) {
    // Validate pages parameter (pure string parsing, no I/O)
    if (pages !== undefined) {
      const parsed = parsePDFPageRange(pages)
      if (!parsed) {
        return {
          result: false,
          message: `Invalid pages parameter: "${pages}". Use formats like "1-5", "3", or "10-20". Pages are 1-indexed.`,
          errorCode: 7,
        }
      }
      const rangeSize =
        parsed.lastPage === Infinity
          ? PDF_MAX_PAGES_PER_READ + 1
          : parsed.lastPage - parsed.firstPage + 1
      if (rangeSize > PDF_MAX_PAGES_PER_READ) {
        return {
          result: false,
          message: `Page range "${pages}" exceeds maximum of ${PDF_MAX_PAGES_PER_READ} pages per request. Please use a smaller range.`,
          errorCode: 8,
        }
      }
    }

    // Path expansion + deny rule check (no I/O)
    const fullFilePath = expandPath(file_path)

    const appState = toolUseContext.getAppState()
    const denyRule = matchingRuleForInput(
      fullFilePath,
      appState.toolPermissionContext,
      'read',
      'deny',
    )
    if (denyRule !== null) {
      return {
        result: false,
        message:
          'File is in a directory that is denied by your permission settings.',
        errorCode: 1,
      }
    }

    // SECURITY: UNC path check (no I/O) — defer filesystem operations
    // until after user grants permission to prevent NTLM credential leaks
    const isUncPath =
      fullFilePath.startsWith('\\\\') || fullFilePath.startsWith('//')
    if (isUncPath) {
      return { result: true }
    }

    // Binary extension check (string check on extension only, no I/O).
    // PDF, images, and SVG are excluded - this tool renders them natively.
    const ext = path.extname(fullFilePath).toLowerCase()
    if (
      hasBinaryExtension(fullFilePath) &&
      !isPDFExtension(ext) &&
      !IMAGE_EXTENSIONS.has(ext.slice(1))