Will Norris
3ec5be3f51
This file was never truly necessary and has never actually been used in the history of Tailscale's open source releases. A Brief History of AUTHORS files --- The AUTHORS file was a pattern developed at Google, originally for Chromium, then adopted by Go and a bunch of other projects. The problem was that Chromium originally had a copyright line only recognizing Google as the copyright holder. Because Google (and most open source projects) do not require copyright assignemnt for contributions, each contributor maintains their copyright. Some large corporate contributors then tried to add their own name to the copyright line in the LICENSE file or in file headers. This quickly becomes unwieldy, and puts a tremendous burden on anyone building on top of Chromium, since the license requires that they keep all copyright lines intact. The compromise was to create an AUTHORS file that would list all of the copyright holders. The LICENSE file and source file headers would then include that list by reference, listing the copyright holder as "The Chromium Authors". This also become cumbersome to simply keep the file up to date with a high rate of new contributors. Plus it's not always obvious who the copyright holder is. Sometimes it is the individual making the contribution, but many times it may be their employer. There is no way for the proejct maintainer to know. Eventually, Google changed their policy to no longer recommend trying to keep the AUTHORS file up to date proactively, and instead to only add to it when requested: https://opensource.google/docs/releasing/authors. They are also clear that: > Adding contributors to the AUTHORS file is entirely within the > project's discretion and has no implications for copyright ownership. It was primarily added to appease a small number of large contributors that insisted that they be recognized as copyright holders (which was entirely their right to do). But it's not truly necessary, and not even the most accurate way of identifying contributors and/or copyright holders. In practice, we've never added anyone to our AUTHORS file. It only lists Tailscale, so it's not really serving any purpose. It also causes confusion because Tailscalars put the "Tailscale Inc & AUTHORS" header in other open source repos which don't actually have an AUTHORS file, so it's ambiguous what that means. Instead, we just acknowledge that the contributors to Tailscale (whoever they are) are copyright holders for their individual contributions. We also have the benefit of using the DCO (developercertificate.org) which provides some additional certification of their right to make the contribution. The source file changes were purely mechanical with: git ls-files | xargs sed -i -e 's/\(Tailscale Inc &\) AUTHORS/\1 contributors/g' Updates #cleanup Change-Id: Ia101a4a3005adb9118051b3416f5a64a4a45987d Signed-off-by: Will Norris <will@tailscale.com>
107 lines
3.7 KiB
Go
107 lines
3.7 KiB
Go
// Copyright (c) Tailscale Inc & contributors
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// SPDX-License-Identifier: BSD-3-Clause
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package geo
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import (
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"math"
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"sync"
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)
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// MinSeparation is the minimum separation between two points after quantizing.
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// [Point.Quantize] guarantees that two points will either be snapped to exactly
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// the same point, which conflates multiple positions together, or that the two
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// points will be far enough apart that successfully performing most reverse
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// lookups would be highly improbable.
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const MinSeparation = 50_000 * Meter
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// Latitude
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var (
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// numSepsEquatorToPole is the number of separations between a point on
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// the equator to a point on a pole, that satisfies [minPointSep]. In
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// other words, the number of separations between 0° and +90° degrees
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// latitude.
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numSepsEquatorToPole = int(math.Floor(float64(
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earthPolarCircumference / MinSeparation / 4)))
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// latSep is the number of degrees between two adjacent latitudinal
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// points. In other words, the next point going straight north of
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// 0° would be latSep°.
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latSep = Degrees(90.0 / float64(numSepsEquatorToPole))
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)
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// snapToLat returns the number of the nearest latitudinal separation to
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// lat. A positive result is north of the equator, a negative result is south,
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// and zero is the equator itself. For example, a result of -1 would mean a
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// point that is [latSep] south of the equator.
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func snapToLat(lat Degrees) int {
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return int(math.Round(float64(lat / latSep)))
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}
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// lngSep is a lookup table for the number of degrees between two adjacent
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// longitudinal separations. where the index corresponds to the absolute value
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// of the latitude separation. The first value corresponds to the equator and
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// the last value corresponds to the separation before the pole. There is no
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// value for the pole itself, because longitude has no meaning there.
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//
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// [lngSep] is calculated on init, which is so quick and will be used so often
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// that the startup cost is negligible.
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var lngSep = sync.OnceValue(func() []Degrees {
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lut := make([]Degrees, numSepsEquatorToPole)
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// i ranges from the equator to a pole
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for i := range len(lut) {
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// lat ranges from [0°, 90°], because the southern hemisphere is
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// a reflection of the northern one.
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lat := Degrees(i) * latSep
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ratio := math.Cos(float64(lat.Radians()))
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circ := Distance(ratio) * earthEquatorialCircumference
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num := int(math.Floor(float64(circ / MinSeparation)))
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// We define lut[0] as 0°, lut[len(lut)] to be the north pole,
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// which means -lut[len(lut)] is the south pole.
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lut[i] = Degrees(360.0 / float64(num))
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}
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return lut
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})
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// snapToLatLng returns the number of the nearest latitudinal separation to lat,
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// and the nearest longitudinal separation to lng.
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func snapToLatLng(lat, lng Degrees) (Degrees, Degrees) {
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latN := snapToLat(lat)
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// absolute index into lngSep
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n := latN
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if n < 0 {
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n = -latN
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}
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lngSep := lngSep()
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if n < len(lngSep) {
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sep := lngSep[n]
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lngN := int(math.Round(float64(lng / sep)))
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return Degrees(latN) * latSep, Degrees(lngN) * sep
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}
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if latN < 0 { // south pole
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return -90 * Degree, 0 * Degree
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} else { // north pole
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return +90 * Degree, 0 * Degree
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}
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}
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// Quantize returns a new [Point] after throwing away enough location data in p
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// so that it would be difficult to distinguish a node among all the other nodes
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// in its general vicinity. One caveat is that if there’s only one point in an
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// obscure location, someone could triangulate the node using additional data.
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//
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// This method is stable: given the same p, it will always return the same
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// result. It is equivalent to snapping to points on Earth that are at least
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// [MinSeparation] apart.
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func (p Point) Quantize() Point {
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if p.IsZero() {
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return p
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}
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lat, lng := snapToLatLng(p.lat, p.lng180-180)
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return MakePoint(lat, lng)
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}
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