Lua interface for discord webhooks. It needs no external libraries, but sends the webhook using os.execute and curl.

discord.lua

DiscordWebhook = {}
DiscordWebhook_metatable = { __index = DiscordWebhook }

function DiscordWebhook:new(webhook)
    return setmetatable({
        webhook = webhook,
        enableTTS = false,
        content = nil,
        username = nil,
        avatar_url = nil,
        embeds = {}
    }, DiscordWebhook_metatable)
end

function DiscordWebhook:enableTextToSpeech(newState)
    self.enableTTS = newState;
    return self;
end

function DiscordWebhook:withContent(newContent)
    self.content = newContent:gsub('"', '\\"');
    return self;
end

function DiscordWebhook:fromUsername(newName)
    self.username = newName:gsub('"', '\\"');
    return self;
end

function DiscordWebhook:withAvatarUrl(newUrl)
    self.avatar_url = newUrl:gsub('"', '\\"');
    return self;
end

function DiscordWebhook:withEmbed(newEmbed)
    table.insert(self.embeds, newEmbed)
    return self;
end

function DiscordWebhook:send()
    -- Build the complete string and send it
    local json = "{"
    json = json .. string.format('"tts":%s,', self.enableTTS and "true" or "false")
    if self.content ~= nil then
        json = json .. string.format('"content":"%s",', self.content)
    end
    if self.username ~= nil then
        json = json .. string.format('"username":"%s",', self.username)
    end
    if self.avatar_url ~= nil then
        json = json .. string.format('"avatar_url":"%s",', self.avatar_url)
    end

    -- if table.getn(self.embeds) > 0 then -- Lua < 5.2
    if #self.embeds > 0 then -- Lua >= 5.2
        json = json .. '"embeds": ['
        
        for key, value in ipairs(self.embeds) do
            json = json .. value
            -- if key < table.getn(self.embeds) then  -- Lua < 5.2
             if key < #self.embeds then -- Lua >= 5.2
                json = json .. ","
            end
        end
        
        json = json .. ']'
    end
    
    if json:sub(-1) == "," then
        json = json:sub(1, -2)
    end
    json = json .. "}"
    
    if json == '{"tts":false}' then
        return false
    else 
        local callStr = string.format('curl -H "Content-Type: application/json" -X POST -d \'%s\' \'%s\'', json, self.webhook)
        -- print(callStr)
        os.execute(callStr)
        return true
    end
end

DiscordEmbed = {}
DiscordEmbed_metatable = { __index = DiscordEmbed }

function DiscordEmbed:new(webhook)
    return setmetatable({
        title = nil,
        description = nil,
        color = nil,
        url = nil,
        image_url = nil,
        thumbnail_url = nil,
        fields = {},
        footer = {
            text = nil,
            icon_url = nil
        }
    }, DiscordEmbed_metatable)
end

function DiscordEmbed:withTitle(newTitle)
    self.title = newTitle:gsub('"', '\\"');
    return self;
end

function DiscordEmbed:withDescription(newDescription)
    self.description = newDescription:gsub('"', '\\"');
    return self;
end

function DiscordEmbed:withColor(newColor)
    self.color = newColor;
    return self;
end

function DiscordEmbed:withUrl(newUrl)
    self.url = newUrl:gsub('"', '\\"');
    return self;
end

function DiscordEmbed:withImage(newUrl)
    self.image_url = newUrl:gsub('"', '\\"');
    return self;
end

function DiscordEmbed:withThumbnail(newUrl)
    self.thumbnail_url = newUrl:gsub('"', '\\"');
    return self;
end

function DiscordEmbed:withField(title, value)
    table.insert(self.fields, {title = title:gsub('"', '\\"'), value = value:gsub('"', '\\"'), inline = false})
    return self;
end

function DiscordEmbed:withFieldInline(title, value)
    table.insert(self.fields, {title = title:gsub('"', '\\"'), value = value:gsub('"', '\\"'), inline = true})
    return self;
end

function DiscordEmbed:withFooterText(newText)
    self.footer.text = newText:gsub('"', '\\"');
    return self;
end

function DiscordEmbed:withFooterIcon(newUrl)
    self.footer.icon_url = newUrl:gsub('"', '\\"');
    return self;
end

function DiscordEmbed:build()
    local json =  '{'
    
    if self.title ~= nil then
        json = json .. string.format('"title":"%s",', self.title)
    end
    if self.description ~= nil then
        json = json .. string.format('"description":"%s",', self.description)
    end
    if self.url ~= nil then
        json = json .. string.format('"url":"%s",', self.url)
    end
    if self.color ~= nil then
        json = json .. string.format('"color":"%s",', self.color)
    end
    if self.image_url ~= nil then
        json = json .. string.format('"image":{"url":"%s"},', self.image_url)
    end
    if self.thumbnail_url ~= nil then
        json = json .. string.format('"thumbnail":{"url":"%s"},', self.thumbnail_url)
    end
    if (self.footer.text ~= nil) then
        json = json .. '"footer": {'
        if (self.footer.icon_url ~= nil) then
            json = json .. string.format('"icon_url":"%s",', self.footer.icon_url)
        end
        if (self.footer.text ~= nil) then
            json = json .. string.format('"text":"%s"', self.footer.text)
        end
        json = json .. '},'
    end
    
    -- if table.getn(self.fields) > 0 then -- Lua < 5.2
    if #self.fields > 0 then -- Lua >= 5.2
        json = json .. '"fields": ['
        
        for key, value in ipairs(self.fields) do
            json = json .. string.format(
                '{"name":"%s", "value":"%s", "inline":%s}', 
                value.title, 
                value.value,
                value.inline and "true" or "false"
            )
            --- if key < table.getn(self.fields) then -- Lua < 5.2
            if key < #self.fields then -- Lua >= 5.2
                json = json .. ","
            end
        end
        
        json = json .. ']'
    end
    
    
    if json:sub(-1) == "," then
        json = json:sub(1, -2)
    end
    json = json .. '}'
    return json
end

example1.lua

-- Send a simple text message.
DiscordWebhook
    :new("https://discordapp.com/api/webhooks/yourwebhook/xxx-yyy-zzz")
    :withContent("Hello World!")
    :send()

-- Send TTS-message with username and avatar image
DiscordWebhook
    :new("https://discordapp.com/api/webhooks/yourwebhook/xxx-yyy-zzz")
    :fromUsername("TestUser")
    :withContent("Hello World!")
    :withAvatarUrl("https://www.chip.de/ii/7/5/7/9/6/5/4/f783c7a2253da84f.jpg")
    :enableTextToSpeech(true)
    :send()

-- Add one or more Embeds!
DiscordWebhook
    :new("https://discordapp.com/api/webhooks/yourwebhook/xxx-yyy-zzz")
    :fromUsername("TestUser")
    :withContent("Hello World!")
    :withAvatarUrl("https://www.chip.de/ii/7/5/7/9/6/5/4/f783c7a2253da84f.jpg")
    :withEmbed(DiscordEmbed:new() -- A very simple embed
        :withTitle("Embed Test")
        :withDescription("Gread stuff!!")
        :build())
    :withEmbed(DiscordEmbed:new() -- And you can add multiple embeds!
        :withTitle("Embed Test")
        :withDescription("Gread stuff!!")
        :withUrl("https://google.com/")
        :withColor(1337331)
        :withField("Field A", "Text A")
        :withFieldInline("Field B", "Text B") -- Yes, inline fields are also working!
        :withFieldInline("Field C", "Text C")
        :withField("Field D", "Text D")
        :withImage("https://www.gstatic.com/images/branding/product/2x/photos_96dp.png")
        :withThumbnail("https://www.gstatic.com/images/branding/product/2x/photos_96dp.png")
        :withFooterText("Footer Text!")
        :withFooterIcon("https://www.gstatic.com/images/branding/product/2x/photos_96dp.png")
        :build())
    :send()