implement the gossip api with Spear.cluster_info/2 #21
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the-mikedavis
commented
Apr 19, 2021
lib/spear/uuid.ex
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| @doc """ | ||
| Reproduces a UUID from a pair of most and least-significant bits | ||
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| This function is an adaptation of the OpenJDK 8 source for turning | ||
| the `java.util.UUID` into a typical string The java source code is as | ||
| follows: | ||
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| ```java | ||
| public String toString() { | ||
| return (digits(mostSigBits >> 32, 8) + "-" + | ||
| digits(mostSigBits >> 16, 4) + "-" + | ||
| digits(mostSigBits, 4) + "-" + | ||
| digits(leastSigBits >> 48, 4) + "-" + | ||
| digits(leastSigBits, 12)); | ||
| } | ||
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| private static String digits(long val, int digits) { | ||
| long hi = 1L << (digits * 4); | ||
| return Long.toHexString(hi | (val & (hi - 1))).substring(1); | ||
| } | ||
| ``` | ||
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| ## Examples | ||
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| iex> Spear.Uuid.from_structured(-1466833724069688543, -8694761462116790879) | ||
| "eba4c27f-e443-4b21-8756-00845bc5cda1" | ||
| """ | ||
| @doc since: "0.5.0" | ||
| @spec from_structured(integer(), integer()) :: String.t() | ||
| def from_structured(most_sig_bits, least_sig_bits) do | ||
| [ | ||
| digits(most_sig_bits >>> 32, 8), | ||
| digits(most_sig_bits >>> 16, 4), | ||
| digits(most_sig_bits, 4), | ||
| digits(least_sig_bits >>> 48, 4), | ||
| digits(least_sig_bits, 12) | ||
| ] | ||
| |> Enum.intersperse(?-) | ||
| |> IO.iodata_to_binary() | ||
| end | ||
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| defp digits(val, digits) do | ||
| hi = 1 <<< (digits * 4) | ||
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| <<_drop_first_byte, rest::binary>> = | ||
| (hi ||| (val &&& hi - 1)) | ||
| |> Integer.to_string(16) | ||
| |> String.downcase() | ||
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| rest | ||
| end |
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there's a nice big time 🐉 thread on the stand board for this thing
apparently you can describe a uuid with just two 64bit longs which is nice because a string uuid takes up many more bits (288 I think?)
it's used by object oriented languages for their UUID objects so it's not surprising that I didn't find an implementation for this scanning over the most popular erlang & elixir uuid generators
had to dig into the java source code and translate
tonyvanriet
reviewed
Apr 19, 2021
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+96
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| # I'll say "this code is not novel and probably belongs to Ecto" but I've | ||
| # heard that laywers generally don't like the term "probably." |
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I think "probably"s fine if it only ends up as a civil lawsuit :)
tonyvanriet
approved these changes
Apr 19, 2021
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dunno exactly how one uses this yet but seems useful
connects #7