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Catch infinite loop when passing sweep line over endpoints (#95) #97

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merged 2 commits into from
Jun 29, 2020
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Catch infinite loop when passing sweep line over endpoints (#95) #97

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44a36ac
Catch infinite loop when passing sweep line over endpoints (#95)
OliverColeman Jun 17, 2020
0ad7c01
Add env vars for setting iterative process limits.
OliverColeman Jun 22, 2020
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6 changes: 6 additions & 0 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -69,6 +69,12 @@ The tests are broken up into unit tests and end-to-end tests. The end-to-end tes

The Martinez-Rueda-Feito polygon clipping algorithm is used to compute the result in `O((n+k)*log(n))` time, where `n` is the total number of edges in all polygons involved and `k` is the number of intersections between edges.

## Settings

Global settings are set via environment variables.

* **POLYGON_CLIPPING_MAX_QUEUE_SIZE** and **POLYGON_CLIPPING_MAX_SWEEPLINE_SEGMENTS**: Aims to prevent infinite loops - usually caused by floating-point math round-off errors. Defaults are 1,000,000.

## Changelog

This project adheres to [Semantic Versioning](https://semver.org/).
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29 changes: 29 additions & 0 deletions src/operation.js
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Expand Up @@ -6,6 +6,10 @@ import rounder from './rounder'
import SweepEvent from './sweep-event'
import SweepLine from './sweep-line'

// Limits on iterative processes to prevent infinite loops - usually caused by floating-point math round-off errors.
const POLYGON_CLIPPING_MAX_QUEUE_SIZE = process.env.POLYGON_CLIPPING_MAX_QUEUE_SIZE || 1000000
const POLYGON_CLIPPING_MAX_SWEEPLINE_SEGMENTS = process.env.POLYGON_CLIPPING_MAX_SWEEPLINE_SEGMENTS || 1000000

export class Operation {
run (type, geom, moreGeoms) {
operation.type = type
Expand Down Expand Up @@ -52,6 +56,14 @@ export class Operation {
const sweepEvents = multipolys[i].getSweepEvents()
for (let j = 0, jMax = sweepEvents.length; j < jMax; j++) {
queue.insert(sweepEvents[j])

if (queue.size > POLYGON_CLIPPING_MAX_QUEUE_SIZE) {
// prevents an infinite loop, an otherwise common manifestation of bugs
throw new Error(
'Infinite loop when putting segment endpoints in a priority queue ' +
'(queue size too big). Please file a bug report.'
)
}
}
}

Expand All @@ -72,6 +84,23 @@ export class Operation {
'Please file a bug report.'
)
}

if (queue.size > POLYGON_CLIPPING_MAX_QUEUE_SIZE) {
// prevents an infinite loop, an otherwise common manifestation of bugs
throw new Error(
'Infinite loop when passing sweep line over endpoints ' +
'(queue size too big). Please file a bug report.'
)
}

if (sweepLine.segments.length > POLYGON_CLIPPING_MAX_SWEEPLINE_SEGMENTS) {
// prevents an infinite loop, an otherwise common manifestation of bugs
throw new Error(
'Infinite loop when passing sweep line over endpoints ' +
'(too many sweep line segments). Please file a bug report.'
)
}

const newEvents = sweepLine.process(evt)
for (let i = 0, iMax = newEvents.length; i < iMax; i++) {
const evt = newEvents[i]
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