use coroutines for async/await bevavior (#2)

* use coroutines for async/await bevavior * add missing files * wip * working sync/await * tests * tests * use await as function arg * workign reject/error * interop test * rename * add error testcase * docs --------- Co-authored-by: BuckarooBanzay <[email protected]>
mt-mods · Jul 31, 2024 · bf75f46 · bf75f46
1 parent ccbd4c3
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diff --git a/async.lua b/async.lua
@@ -0,0 +1,60 @@
+
+local err_symbol = {}
+
+local function await(p)
+    assert(coroutine.running(), "running inside a Promise.async() call")
+    local result = nil
+    local err = nil
+    local finished = false
+
+    p:next(function(...)
+        result = {...}
+        finished = true
+    end):catch(function(e)
+        err = e
+        finished = true
+    end)
+
+    while true do
+        if finished then
+            if err then
+                return coroutine.yield({ err = err, err_symbol = err_symbol })
+            else
+                return unpack(result)
+            end
+        else
+            coroutine.yield()
+        end
+    end
+end
+
+function Promise.async(fn)
+    local t = coroutine.create(fn)
+    local p = Promise.new()
+
+    local step = nil
+    local result = nil
+    local cont = nil
+    local _ = nil
+    step = function()
+        if coroutine.status(t) == "suspended" then
+            cont, result = coroutine.resume(t, await)
+            if not cont then
+                -- error in first async() level
+                p:reject(result)
+            end
+            if type(result) == "table" and result.err_symbol == err_symbol then
+                -- error in await() call
+                p:reject(result.err)
+                return
+            end
+            minetest.after(0, step)
+        else
+            -- last result from resume was the return value
+            p:resolve(result)
+        end
+    end
+    step()
+
+    return p
+end
diff --git a/async.spec.lua b/async.spec.lua
@@ -0,0 +1,63 @@
+
+mtt.register("Promise.async", function(callback)
+    local p = Promise.async(function(await)
+        local v = await(Promise.after(0, 42))
+        assert(v == 42)
+        local v1 = await(Promise.resolved(666))
+        assert(v1 == 666)
+        return 99
+    end)
+
+    p:next(function(v)
+        assert(v == 99)
+        callback()
+    end)
+end)
+
+mtt.register("Promise.async interop", function()
+    return Promise.async(function(await)
+        return await(Promise.async(function()
+            local v = await(Promise.resolved(42))
+            assert(v == 42)
+        end))
+    end)
+end)
+
+mtt.register("Promise.async simple", function()
+    return Promise.async(function(await)
+        local v = await(Promise.resolved(42))
+        assert(v == 42)
+    end)
+end)
+
+mtt.register("Promise.async with handle_async", function()
+    return Promise.async(function(await)
+        local v = await(Promise.resolved(42))
+        assert(v == 42)
+        v = await(Promise.handle_async(function() return 100 end))
+        assert(v == 100)
+    end)
+end)
+
+mtt.register("Promise.async rejected", function(callback)
+    local p = Promise.async(function(await)
+        await(Promise.rejected("my-err"))
+    end)
+
+    p:catch(function(e)
+        assert(type(e) == "string")
+        callback()
+    end)
+end)
+
+mtt.register("Promise.async error", function(callback)
+    local p = Promise.async(function()
+        error("stuff")
+    end)
+
+    p:catch(function(e)
+        -- "/home/user/.minetest/mods/promise/async.spec.lua:55: stuff"
+        assert(type(e) == "string")
+        callback()
+    end)
+end)
diff --git a/http.spec.lua b/http.spec.lua
@@ -1,5 +1,7 @@
 local http = ...
 
+local toJson = function(res) return res.json() end
+
 mtt.register("Promise.http GET", function(callback)
     Promise.http(http, "https://api.chucknorris.io/jokes/random"):next(function(res)
         return res.json()
@@ -11,8 +13,14 @@ mtt.register("Promise.http GET", function(callback)
     end)
 end)
 
+mtt.register("Promise.http GET with async/await", function()
+    return Promise.async(function(await)
+        local joke = await(Promise.http(http, "https://api.chucknorris.io/jokes/random"):next(toJson))
+        assert(type(joke.value) == "string")
+    end)
+end)
+
 mtt.register("Promise.http/all GET", function(callback)
-    local toJson = function(res) return res.json() end
     local p1 = Promise.http(http, "https://api.chucknorris.io/jokes/random"):next(toJson)
     local p2 = Promise.http(http, "https://api.chucknorris.io/jokes/random"):next(toJson)
 

diff --git a/init.lua b/init.lua
@@ -8,13 +8,15 @@ dofile(MP.."/promise.lua")
 dofile(MP.."/util.lua")
 dofile(MP.."/http.lua")
 dofile(MP.."/formspec.lua")
+dofile(MP.."/async.lua")
 
 if minetest.get_modpath("mtt") and mtt.enabled then
 	local http = minetest.request_http_api()
 
 	dofile(MP .. "/promise.spec.lua")
 	dofile(MP .. "/formspec.spec.lua")
 	dofile(MP .. "/util.spec.lua")
+	dofile(MP .. "/async.spec.lua")
 	if http then
 		loadfile(MP .. "/http.spec.lua")(http)
 	end

diff --git a/readme.md b/readme.md
@@ -11,6 +11,7 @@ promise library for minetest
 Features:
 * Async event handling
 * Utilities for formspec, emerge_area, handle_async, http and minetest.after
+* async/await helpers (js example [here](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/async_function))
 
 # Examples
 
@@ -256,8 +257,47 @@ end)
 
 **NOTE**: experimental, only works if the `to_player` property is set
 
+# async/await with `Promise.async`
+
+Similar to [javascripts](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/async_function) implementation async/await can be used in lua too with the help of [coroutines](https://www.lua.org/pil/9.1.html)
+
+Example: fetch a joke with async/await
+```lua
+local toJson = function(res) return res.json() end
+
+Promise.async(function(await)
+    local joke = await(Promise.http(http, "https://api.chucknorris.io/jokes/random"):next(toJson))
+    assert(type(joke.value) == "string")
+    -- do stuff here with the joke
+end)
+```
+
+Example: sleep for a few seconds
+```lua
+Promise.async(function(await)
+    await(Promise.after(5))
+    -- 5 seconds passed
+end)
+```
+
+`Promise.async` returns a Promise that can be used with `:next` or `await` in another async function, for example:
+
+```lua
+local toJson = function(res) return res.json() end
+
+Promise.async(function(await)
+    local data = await(Promise.http(http, "https://my-api"):next(toJson))
+    return data.value * 200 -- "value" is a number
+end):next(function(n)
+    -- n is the result of the multiplication in the previous function
+end)
+```
+
 # License
 
 * Code: MIT (adapted from https://github.com/Billiam/promise.lua)
 
+<details>
+
 ![Yo dawg](yo.jpg)
+</details>