bug: 'global_rule' is a boolean value

[membphis]

Steps to reproduce:

1. Add global routes (such as prometheus)
2. Delete some global routes
3. User request, we can see the response 500 error.

One photo from community:

This patch should be fine, and we need to add test case for confirming.

[proxychains] DLL init
diff --git a/apisix/init.lua b/apisix/init.lua
index aa8598e8..1e6b1efb 100644
--- a/apisix/init.lua
+++ b/apisix/init.lua
@@ -264,14 +264,16 @@ function _M.http_access_phase()
        and #router.global_rules.values > 0 then
         local plugins = core.tablepool.fetch("plugins", 32, 0)
         for _, global_rule in ipairs(router.global_rules.values) do
-            api_ctx.conf_type = "global_rule"
-            api_ctx.conf_version = global_rule.modifiedIndex
-            api_ctx.conf_id = global_rule.value.id
-
-            core.table.clear(plugins)
-            api_ctx.plugins = plugin.filter(global_rule, plugins)
-            run_plugin("rewrite", plugins, api_ctx)
-            run_plugin("access", plugins, api_ctx)
+            if type(global_rule) == "table" then
+                api_ctx.conf_type = "global_rule"
+                api_ctx.conf_version = global_rule.modifiedIndex
+                api_ctx.conf_id = global_rule.value.id
+
+                core.table.clear(plugins)
+                api_ctx.plugins = plugin.filter(global_rule, plugins)
+                run_plugin("rewrite", plugins, api_ctx)
+                run_plugin("access", plugins, api_ctx)
+            end
         end

         core.tablepool.release("plugins", plugins)

[spacewander]

I guess the problem happens there:
https://github.com/apache/incubator-apisix/blob/7440192f8fdf679dadc3e816767762e6047d0893/apisix/core/config_etcd.lua#L284

I am not quite understand the tombstone mechanism. Is the memory footprint so high that we need to use some trick? Can we implement an iterator to hide the detail?

[membphis]

@spacewander you are right.

If the original data is deleted, it is marked as "false".

This is why we need to check the data type first.

Can we implement an iterator to hide the detail?

can you provide an example? I can't imagine it.

[spacewander]

In Lua, we can implement custom iterator to iterate table, for instance:

local t = {{"a"}, false, {"b"}}

local function _iterate_values(self, tab)
    while true do
        self.idx = self.idx + 1
        local v = tab[self.idx]
        if type(v) == "table" then
            return self.idx, v
        end
        if v == nil then
            return nil, nil
        end
        -- skip other type of values
    end
end

local function iterate_values(tab)
    local iter = setmetatable({idx = 0}, {__call = _iterate_values})
    return iter, tab, 0
end

local j = 0
for k = 1, 1e5 do
    for i, v in iterate_values(t) do
        j = j + i
    end
end

[membphis]

Well done, a very good solution. We can use this method to iterate over all values.