Flow Network Monitor Window

Flow is a dockable network throughput meter available in classic and modern UI.

Source Project

• Upstream reference/source project: https://github.com/programmersd21/flow
• Relationship: clean-room Swift/AppKit reimplementation (upstream flow is a Go terminal app); no flow code is bundled. Credited via a courtesy notice at Sources/NullPlayer/Resources/ThirdPartyLicenses/flow_NOTICE.txt (flow is MIT upstream).
• Third-party notice registration: scripts/third_party_components.tsv entry flow
• NullPlayer's implementation is a Swift/AppKit integration adapted for the classic and modern window stacks; keep user-facing credits in the third-party notices rather than duplicating them in window chrome.

User Behavior

• Open from the Windows menu or the main-window context menu as Flow.
• Shows one direction at a time: download or upload.
• Double-click anywhere in the window body to toggle download/upload.
• The entire non-control face drags the window; see the ui-guide window-dragging requirement.
• Right-click opens the Flow menu:
  • Network interfaces, with the selected interface checked
  • Next Interface
  • Show Upload View or Show Download View
  • Close
• The selected download/upload view persists in UserDefaults under NetworkMonitorDisplayDirection.
• The selected network interface persists via NetworkThroughputMonitor.selectedInterfaceDefaultsKey.

Window Layout

• Flow participates in the center window stack managed by WindowManager.
• It is a single-height stack window, matching the Spectrum/Waveform baseline height.
• PeppyMeter uses a taller 1.75x landscape stack height; do not reuse PeppyMeter sizing for Flow.
• Classic uses SkinElements.SpectrumWindow.windowSize / minSize.
• Modern uses ModernSkinElements.spectrumWindowSize / spectrumMinSize.
• Restored Flow frames are normalized to at least the current single-height stack height, but user-stretched heights above that floor are preserved.
• The Cava spectrum window (cava) is another single-height center-stack window built on this same pattern (same sizing constants, whole-face drag, classic/modern chrome) — a good reference when threading a new center-stack window through WindowManager.

Key Source Files

File	Purpose
Utilities/NetworkThroughputMonitor.swift	Network byte counters, interface selection, history, daily totals, snapshots
Windows/NetworkMonitor/NetworkMonitorDrawing.swift	Shared Flow content renderer and download/upload view persistence
Windows/NetworkMonitor/NetworkMonitorView.swift	Classic chrome, hit testing, context menu, double-click direction toggle
Windows/NetworkMonitor/NetworkMonitorWindowController.swift	Classic window lifecycle, monitor start/stop, default frame
Windows/ModernNetworkMonitor/ModernNetworkMonitorView.swift	Modern chrome, docking masks, context menu, double-click direction toggle
Windows/ModernNetworkMonitor/ModernNetworkMonitorWindowController.swift	Modern window lifecycle, monitor start/stop
App/NetworkMonitorWindowProviding.swift	Classic/modern provider abstraction
App/WindowManager.swift	Show/toggle Flow, center-stack sizing, restored-frame normalization

Rendering Notes

• NetworkMonitorRenderState smooths displayed download/upload values toward the latest snapshot.
• NetworkMonitorDrawing.drawContent advances both directions every frame, but draws only the selected direction.
• Flow intentionally does not draw an inner rounded panel border. The outer window chrome is the only border.
• Do not shrink the modern Flow content rect with an additional outer padding/gutter. That creates the old heavy-border appearance. Keep the content rect at the shared chrome inset and put any spacing inside NetworkMonitorDrawing instead.
• Classic Flow uses tighter content insets than modern so the meter fills the classic skin interior.
• Modern Flow uses the standard auxiliary chrome inset without an extra window-specific gutter. The modern content rect expands through adjacent joined chrome strips (via NSRect.expandingThroughJoinedEdges) in every render style — not just Metal — so no ~1px seam shows on a docked edge (issue #364). The helper must not expand across a visible title bar gap; Flow's body content must never paint over the title bar or close button.
• Flow's animated content reaches the bottom/joined edge, unlike PeppyMeter's padded meter art. Do not use a broad Peppy-style setNeedsDisplay(contentAreaRect()) fast path for timer redraws; it can flicker the bottom edge when Flow is locked above another window. Timer redraws should invalidate a guarded animation rect that excludes the bottom strip, while NetworkMonitorDrawing.drawContent still receives the full content rect so graph layout remains stable. Full-window paints should draw content first and chrome/borders after it.
• Tiny mode renders a compact single-line rate for the selected direction.

Monitoring Lifecycle

• showWindow starts the monitor and refreshes interfaces.
• Occlusion, miniaturize, and deminiaturize notifications keep monitoring active only while visible.
• prepareForUITeardown() calls tearDownMonitoring() through NetworkMonitorWindowProviding.
• Interface refreshes are done on demand before menu display to avoid unnecessary per-frame interface enumeration on the main thread.

Implementation Checks

• Keep classic and modern behavior paired; both views should support the same Flow-specific menu items and double-click toggle.
• Do not add Flow to audio-consumer or render-loop systems; it reads network counters only.
• When changing stack height rules, verify centerStackHeightMultiplier(for:), applyCenterStackSizingConstraints, and normalizedCenterStackRestoredFrame.
• Build with swift build.