Freika/dawarich · warning

Failed to parse track segments:

Error message

Failed to parse track segments:

What it means

When a track is clicked, the handler fetches the full track with segments and expects properties.segments to be either an already-parsed array or a JSON string. If it is a string, JSON.parse() runs inside a try/catch; malformed or truncated JSON throws and logs this warning. segments stays [] so the track still renders, but per-segment colors and hover callbacks show nothing.

Source

Thrown at app/javascript/controllers/maps/maplibre/event_handlers.js:714

  /**
   * Load track segments from API (lazy loading)
   * @private
   */
  async _loadTrackSegments(trackId, fullFeature) {
    try {
      const trackFeature =
        await this.controller.api.fetchTrackWithSegments(trackId)
      if (!trackFeature) return

      let segments = []
      try {
        const props = trackFeature.properties
        segments =
          typeof props.segments === "string"
            ? JSON.parse(props.segments)
            : props.segments || []
      } catch (err) {
        console.warn("Failed to parse track segments:", err)
      }

      const tracksLayer = this.controller.layerManager.getLayer("tracks")
      if (tracksLayer?.showSegments) {
        tracksLayer.showSegments(fullFeature, segments)
        tracksLayer.setSegmentHoverCallback((segmentIndex) => {
          this._highlightSegmentOnMap(segmentIndex)
          this._dispatchSegmentHover(trackId, segments[segmentIndex]?.id)
        })
        tracksLayer.setSegmentLeaveCallback(() => {
          this._clearSegmentHighlight()
          this._dispatchSegmentUnhover(trackId)
        })
      }

      this._createTrackSegmentMarkers(trackId, fullFeature, segments)
    } catch (error) {
      console.error("Failed to load track segments:", error)

View on GitHub (pinned to 97fad417c5)

Solutions

1. Log props.segments (typeof plus first 200 chars) to see whether it is malformed, double-encoded, or an unexpected shape
2. Fix the backend serializer to emit valid JSON or a native array — arrays avoid the parse entirely
3. Validate the parsed value is an array before using it: Array.isArray(segments) ? segments : []
4. Add a serializer regression test covering a track with many segments

Example fix

// before
segments =
  typeof props.segments === "string"
    ? JSON.parse(props.segments)
    : props.segments || []
// after
if (typeof props.segments === "string") {
  try {
    const parsed = JSON.parse(props.segments)
    segments = Array.isArray(parsed) ? parsed : []
  } catch (err) {
    console.warn("Failed to parse track segments:", err)
    segments = []
  }
} else {
  segments = Array.isArray(props.segments) ? props.segments : []
}

function safeParseSegments(raw) {
  if (Array.isArray(raw)) return raw
  if (typeof raw !== "string" || raw.length === 0) return []
  try {
    const parsed = JSON.parse(raw)
    return Array.isArray(parsed) ? parsed : []
  } catch {
    return []
  }
}
const segments = safeParseSegments(props.segments)

/** @param {unknown} value @returns {value is Array} */
function isSegmentArray(value) {
  return Array.isArray(value)
}

try {
  segments = safeParseSegments(props.segments)
} catch (err) {
  console.warn("Failed to parse track segments:", err)
  segments = [] // degrade to no-segment rendering, keep the track visible
}

When it happens

Trigger: The tracks serializer emitting invalid JSON in properties.segments (truncated by a response size limit, double-encoded string, NaN serialized by to_json); a backend change wrapping segments in a new shape so the parsed value is not an array; very large segment arrays clipped by a proxy or cache.

Common situations: Long tracks with thousands of points where serialized segments exceed response limits; serializer refactors switching between string and array; caching layers that re-encode JSON; hand-written fixtures with malformed segment strings.

Understand the failure class

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• Failed to parse track segments for marker update:
• Failed to add photos layer:
• Failed to apply speed colors to route:
• Could not classify zip contents -- file may be corrupted
• [EventHandlers] Failed to highlight track:

AI-assisted analysis of Freika/dawarich@97fad417c5 (2026-08-21). Data as JSON: /api/errors/e2b66392cf5efa46. Report an issue: GitHub.