prosody
439cf3bbe5f3
util/promise.lua

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util/promise.lua @ 9512:439cf3bbe5f3

util.promise: Also support automatic resolution by returning a promise from an on_reject handler Originally unimplemented because it wasn't clear to me what the correct behaviour was, but the A+ spec is clear that both onFulfilled and onRejected may return a promise.
author Matthew Wild <mwild1@gmail.com>
date Thu, 18 Oct 2018 12:11:50 +0100
parent 9510:8ef46d09386a
child 9513:4f4f9823bd1d
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1 local promise_methods = {};
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2 local promise_mt = { __name = "promise", __index = promise_methods };
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3
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4 local function is_promise(o)
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5 local mt = getmetatable(o);
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6 return mt == promise_mt;
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7 end
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8
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9 local function next_pending(self, on_fulfilled, on_rejected)
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10 table.insert(self._pending_on_fulfilled, on_fulfilled);
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11 table.insert(self._pending_on_rejected, on_rejected);
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12 end
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13
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14 local function next_fulfilled(promise, on_fulfilled, on_rejected) -- luacheck: ignore 212/on_rejected
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15 on_fulfilled(promise.value);
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16 end
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17
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18 local function next_rejected(promise, on_fulfilled, on_rejected) -- luacheck: ignore 212/on_fulfilled
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19 on_rejected(promise.reason);
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20 end
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21
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22 local function promise_settle(promise, new_state, new_next, cbs, value)
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23 if promise._state ~= "pending" then
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24 return;
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25 end
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26 promise._state = new_state;
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27 promise._next = new_next;
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28 for _, cb in ipairs(cbs) do
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29 cb(value);
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30 end
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31 return true;
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32 end
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33
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34 local function new_resolve_functions(p)
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35 local resolved = false;
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36 local function _resolve(v)
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37 if resolved then return; end
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38 resolved = true;
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39 if is_promise(v) then
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40 v:next(new_resolve_functions(p));
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41 elseif promise_settle(p, "fulfilled", next_fulfilled, p._pending_on_fulfilled, v) then
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42 p.value = v;
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43 end
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44
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45 end
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46 local function _reject(e)
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47 if resolved then return; end
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48 resolved = true;
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49 if is_promise(e) then
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50 e:next(new_resolve_functions(p));
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51 elseif promise_settle(p, "rejected", next_rejected, p._pending_on_rejected, e) then
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52 p.reason = e;
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53 end
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54 end
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55 return _resolve, _reject;
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56 end
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57
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58 local function new(f)
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59 local p = setmetatable({ _state = "pending", _next = next_pending, _pending_on_fulfilled = {}, _pending_on_rejected = {} }, promise_mt);
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60 if f then
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61 local resolve, reject = new_resolve_functions(p);
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62 local ok, ret = pcall(f, resolve, reject);
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63 if not ok and p._state == "pending" then
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64 reject(ret);
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65 end
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66 end
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67 return p;
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68 end
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69
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70 local function wrap_handler(f, resolve, reject)
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71 return function (param)
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72 local ok, ret = pcall(f, param);
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73 if ok then
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74 resolve(ret);
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75 else
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76 reject(ret);
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77 end
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78 end;
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79 end
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80
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81 function promise_methods:next(on_fulfilled, on_rejected)
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82 return new(function (resolve, reject)
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83 self:_next(
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84 on_fulfilled and wrap_handler(on_fulfilled, resolve, reject) or nil,
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85 on_rejected and wrap_handler(on_rejected, resolve, reject) or nil
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86 );
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87 end);
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88 end
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89
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90 function promise_methods:catch(on_rejected)
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91 return self:next(nil, on_rejected);
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92 end
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93
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94 local function all(promises)
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95 return new(function (resolve, reject)
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96 local count, total, results = 0, #promises, {};
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97 for i = 1, total do
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98 promises[i]:next(function (v)
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99 results[i] = v;
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100 count = count + 1;
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101 if count == total then
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102 resolve(results);
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103 end
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104 end, reject);
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105 end
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106 end);
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107 end
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108
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109 local function race(promises)
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110 return new(function (resolve, reject)
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111 for i = 1, #promises do
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112 promises[i]:next(resolve, reject);
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113 end
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114 end);
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115 end
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116
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117 local function resolve(v)
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118 return new(function (_resolve)
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119 _resolve(v);
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120 end);
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121 end
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122
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123 local function reject(v)
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124 return new(function (_, _reject)
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125 _reject(v);
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126 end);
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127 end
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128
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129 return {
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130 new = new;
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131 resolve = resolve;
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132 reject = reject;
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133 all = all;
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134 race = race;
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135 }