From 7f7ff9f23778f5465fafc01687041d0f6bfdcd5f Mon Sep 17 00:00:00 2001
From: chronolaw <chrono_cpp@me.com>
Date: Wed, 14 Jun 2023 09:06:28 +0800
Subject: [PATCH 01/15] metric_data with string.buffer

---
 kong/plugins/prometheus/prometheus.lua | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/kong/plugins/prometheus/prometheus.lua b/kong/plugins/prometheus/prometheus.lua
index 0f8685ed3b0..88d61ee6be3 100644
--- a/kong/plugins/prometheus/prometheus.lua
+++ b/kong/plugins/prometheus/prometheus.lua
@@ -90,6 +90,9 @@ local TYPE_LITERAL = {
 -- Default metric name size for string.buffer.new()
 local NAME_BUFFER_SIZE_HINT = 256
 
+-- Default metric data size for string.buffer.new()
+local DATA_BUFFER_SIZE_HINT = 4096
+
 -- Default name for error metric incremented by this library.
 local DEFAULT_ERROR_METRIC_NAME = "nginx_metric_errors_total"
 
@@ -913,19 +916,19 @@ function Prometheus:metric_data(write_fn, local_only)
   table_sort(keys)
 
   local seen_metrics = {}
-  local output = {}
+
+  local output = buffer.new(DATA_BUFFER_SIZE_HINT)
   local output_count = 0
 
   local function buffered_print(data)
     if data then
       output_count = output_count + 1
-      output[output_count] = data
+      output:put(data)
     end
 
     if output_count >= 100 or not data then
-      write_fn(output)
+      write_fn(output:get())  -- cosume the whole buffer
       output_count = 0
-      tb_clear(output)
     end
   end
 

From 889140073ac41215ccf29c40822d5ef75c120a8a Mon Sep 17 00:00:00 2001
From: chronolaw <chrono_cpp@me.com>
Date: Wed, 14 Jun 2023 09:11:22 +0800
Subject: [PATCH 02/15] printable_metric_data in api.lua

---
 kong/plugins/prometheus/api.lua        | 9 ++++-----
 kong/plugins/prometheus/prometheus.lua | 2 +-
 2 files changed, 5 insertions(+), 6 deletions(-)

diff --git a/kong/plugins/prometheus/api.lua b/kong/plugins/prometheus/api.lua
index bf3e27d3ade..f73d03bc586 100644
--- a/kong/plugins/prometheus/api.lua
+++ b/kong/plugins/prometheus/api.lua
@@ -1,17 +1,16 @@
+local buffer = require("string.buffer")
 local exporter = require "kong.plugins.prometheus.exporter"
-local tbl_insert = table.insert
-local tbl_concat = table.concat
 
 
 local printable_metric_data = function(_)
-  local buffer = {}
+  local buf = buffer.new(4096)
   -- override write_fn, since stream_api expect response to returned
   -- instead of ngx.print'ed
   exporter.metric_data(function(new_metric_data)
-    tbl_insert(buffer, tbl_concat(new_metric_data, ""))
+    buf:put(new_metric_data)
   end)
 
-  return tbl_concat(buffer, "")
+  return buf:get()
 end
 
 
diff --git a/kong/plugins/prometheus/prometheus.lua b/kong/plugins/prometheus/prometheus.lua
index 88d61ee6be3..e9b4e9e12cb 100644
--- a/kong/plugins/prometheus/prometheus.lua
+++ b/kong/plugins/prometheus/prometheus.lua
@@ -70,7 +70,6 @@ local tostring = tostring
 local tonumber = tonumber
 local st_format = string.format
 local table_sort = table.sort
-local tb_clear = require("table.clear")
 local yield = require("kong.tools.utils").yield
 
 
@@ -917,6 +916,7 @@ function Prometheus:metric_data(write_fn, local_only)
 
   local seen_metrics = {}
 
+  -- the output is an integral string, not an array any more
   local output = buffer.new(DATA_BUFFER_SIZE_HINT)
   local output_count = 0
 

From e89bf62530a03b9ac661690bc1119406ba0b1ce8 Mon Sep 17 00:00:00 2001
From: chronolaw <chrono_cpp@me.com>
Date: Wed, 14 Jun 2023 09:18:55 +0800
Subject: [PATCH 03/15] seen_metrics

---
 kong/plugins/prometheus/prometheus.lua | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kong/plugins/prometheus/prometheus.lua b/kong/plugins/prometheus/prometheus.lua
index e9b4e9e12cb..f4e12933b29 100644
--- a/kong/plugins/prometheus/prometheus.lua
+++ b/kong/plugins/prometheus/prometheus.lua
@@ -70,6 +70,7 @@ local tostring = tostring
 local tonumber = tonumber
 local st_format = string.format
 local table_sort = table.sort
+local tb_new = require("table.new")
 local yield = require("kong.tools.utils").yield
 
 
@@ -914,7 +915,7 @@ function Prometheus:metric_data(write_fn, local_only)
   -- numerical order of their label values.
   table_sort(keys)
 
-  local seen_metrics = {}
+  local seen_metrics = tb_new(0, count)
 
   -- the output is an integral string, not an array any more
   local output = buffer.new(DATA_BUFFER_SIZE_HINT)

From 6da9c7b7d18cb6a6382ed71fce2097aa9577acab Mon Sep 17 00:00:00 2001
From: chronolaw <chrono_cpp@me.com>
Date: Wed, 14 Jun 2023 09:23:25 +0800
Subject: [PATCH 04/15] buffer:putf

---
 kong/plugins/prometheus/prometheus.lua | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/kong/plugins/prometheus/prometheus.lua b/kong/plugins/prometheus/prometheus.lua
index f4e12933b29..435b4a5842e 100644
--- a/kong/plugins/prometheus/prometheus.lua
+++ b/kong/plugins/prometheus/prometheus.lua
@@ -921,10 +921,10 @@ function Prometheus:metric_data(write_fn, local_only)
   local output = buffer.new(DATA_BUFFER_SIZE_HINT)
   local output_count = 0
 
-  local function buffered_print(data)
+  local function buffered_print(data, ...)
     if data then
       output_count = output_count + 1
-      output:put(data)
+      output:putf(data, ...)
     end
 
     if output_count >= 100 or not data then
@@ -954,12 +954,12 @@ function Prometheus:metric_data(write_fn, local_only)
       local m = self.registry[short_name]
       if m then
         if m.help then
-          buffered_print(st_format("# HELP %s%s %s\n",
-            self.prefix, short_name, m.help))
+          buffered_print("# HELP %s%s %s\n",
+            self.prefix, short_name, m.help)
         end
         if m.typ then
-          buffered_print(st_format("# TYPE %s%s %s\n",
-            self.prefix, short_name, TYPE_LITERAL[m.typ]))
+          buffered_print("# TYPE %s%s %s\n",
+            self.prefix, short_name, TYPE_LITERAL[m.typ])
         end
       end
       seen_metrics[short_name] = true
@@ -967,7 +967,7 @@ function Prometheus:metric_data(write_fn, local_only)
     if not is_local_metrics then -- local metrics is always a gauge
       key = fix_histogram_bucket_labels(key)
     end
-    buffered_print(st_format("%s%s %s\n", self.prefix, key, value))
+    buffered_print("%s%s %s\n", self.prefix, key, value)
 
     ::continue::
 

From e5520e5c50f4f3de46182c3990d1b5a60f13cf45 Mon Sep 17 00:00:00 2001
From: chronolaw <chrono_cpp@me.com>
Date: Wed, 14 Jun 2023 09:40:49 +0800
Subject: [PATCH 05/15] st_format

---
 kong/plugins/prometheus/prometheus.lua | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kong/plugins/prometheus/prometheus.lua b/kong/plugins/prometheus/prometheus.lua
index 435b4a5842e..bc8ee0f5b69 100644
--- a/kong/plugins/prometheus/prometheus.lua
+++ b/kong/plugins/prometheus/prometheus.lua
@@ -305,7 +305,7 @@ local function construct_bucket_format(buckets)
   for _, bucket in ipairs(buckets) do
     assert(type(bucket) == "number", "bucket boundaries should be numeric")
     -- floating point number with all trailing zeros removed
-    local as_string = string.format("%f", bucket):gsub("0*$", "")
+    local as_string = st_format("%f", bucket):gsub("0*$", "")
     local dot_idx = as_string:find(".", 1, true)
     max_order = math.max(max_order, dot_idx - 1)
     max_precision = math.max(max_precision, as_string:len() - dot_idx)
@@ -364,7 +364,7 @@ local function lookup_or_create(self, label_values)
   local cnt = label_values and #label_values or 0
   -- specially, if first element is nil, # will treat it as "non-empty"
   if cnt ~= self.label_count or (self.label_count > 0 and label_values[1] == nil) then
-    return nil, string.format("inconsistent labels count, expected %d, got %d",
+    return nil, st_format("inconsistent labels count, expected %d, got %d",
                               self.label_count, cnt)
   end
   local t = self.lookup
@@ -408,13 +408,13 @@ local function lookup_or_create(self, label_values)
     end
 
     for i, buc in ipairs(self.buckets) do
-      full_name[i+2] = string.format("%sle=\"%s\"}", bucket_pref, self.bucket_format:format(buc))
+      full_name[i+2] = st_format("%sle=\"%s\"}", bucket_pref, self.bucket_format:format(buc))
     end
     -- Last bucket. Note, that the label value is "Inf" rather than "+Inf"
     -- required by Prometheus. This is necessary for this bucket to be the last
     -- one when all metrics are lexicographically sorted. "Inf" will get replaced
     -- by "+Inf" in Prometheus:metric_data().
-    full_name[self.bucket_count+3] = string.format("%sle=\"Inf\"}", bucket_pref)
+    full_name[self.bucket_count+3] = st_format("%sle=\"Inf\"}", bucket_pref)
   else
     full_name = full_metric_name(self.name, self.label_names, label_values)
   end

From 97eab6de86a9176e9c0ffea2c2049b018fb491a2 Mon Sep 17 00:00:00 2001
From: chronolaw <chrono_cpp@me.com>
Date: Wed, 14 Jun 2023 09:46:00 +0800
Subject: [PATCH 06/15] param fmt

---
 kong/plugins/prometheus/prometheus.lua | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kong/plugins/prometheus/prometheus.lua b/kong/plugins/prometheus/prometheus.lua
index bc8ee0f5b69..f3becba740c 100644
--- a/kong/plugins/prometheus/prometheus.lua
+++ b/kong/plugins/prometheus/prometheus.lua
@@ -921,13 +921,13 @@ function Prometheus:metric_data(write_fn, local_only)
   local output = buffer.new(DATA_BUFFER_SIZE_HINT)
   local output_count = 0
 
-  local function buffered_print(data, ...)
-    if data then
+  local function buffered_print(fmt, ...)
+    if fmt then
       output_count = output_count + 1
-      output:putf(data, ...)
+      output:putf(fmt, ...)
     end
 
-    if output_count >= 100 or not data then
+    if output_count >= 100 or not fmt then
       write_fn(output:get())  -- cosume the whole buffer
       output_count = 0
     end

From fcc35b51e271c01275b71d05638a8213532b4aed Mon Sep 17 00:00:00 2001
From: chronolaw <chrono_cpp@me.com>
Date: Wed, 14 Jun 2023 09:48:06 +0800
Subject: [PATCH 07/15] dont use iparis

---
 kong/plugins/prometheus/prometheus.lua | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kong/plugins/prometheus/prometheus.lua b/kong/plugins/prometheus/prometheus.lua
index f3becba740c..e443f50d407 100644
--- a/kong/plugins/prometheus/prometheus.lua
+++ b/kong/plugins/prometheus/prometheus.lua
@@ -933,9 +933,11 @@ function Prometheus:metric_data(write_fn, local_only)
     end
   end
 
-  for _, key in ipairs(keys) do
+  for i = 1, count do
     yield()
 
+    key = keys[i]
+
     local value, err
     local is_local_metrics = true
     value = self.local_metrics[key]

From 65a9617f61161546c9c738d2c41c8c3ea213b9fa Mon Sep 17 00:00:00 2001
From: chronolaw <chrono_cpp@me.com>
Date: Wed, 14 Jun 2023 10:07:29 +0800
Subject: [PATCH 08/15] string.sub with -2

---
 kong/plugins/prometheus/prometheus.lua | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kong/plugins/prometheus/prometheus.lua b/kong/plugins/prometheus/prometheus.lua
index e443f50d407..f57da6d86aa 100644
--- a/kong/plugins/prometheus/prometheus.lua
+++ b/kong/plugins/prometheus/prometheus.lua
@@ -402,7 +402,7 @@ local function lookup_or_create(self, label_values)
     local bucket_pref
     if self.label_count > 0 then
       -- strip last }
-      bucket_pref = self.name .. "_bucket" .. string.sub(labels, 1, #labels-1) .. ","
+      bucket_pref = self.name .. "_bucket" .. string.sub(labels, 1, -2) .. ","
     else
       bucket_pref = self.name .. "_bucket{"
     end

From 25de6f366bd220200ad6951bbb79eacd88e8a12f Mon Sep 17 00:00:00 2001
From: chronolaw <chrono_cpp@me.com>
Date: Wed, 14 Jun 2023 10:08:21 +0800
Subject: [PATCH 09/15] ngx.get_phase

---
 kong/plugins/prometheus/prometheus.lua | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kong/plugins/prometheus/prometheus.lua b/kong/plugins/prometheus/prometheus.lua
index f57da6d86aa..e9ba5119b36 100644
--- a/kong/plugins/prometheus/prometheus.lua
+++ b/kong/plugins/prometheus/prometheus.lua
@@ -704,8 +704,9 @@ end
 -- Returns:
 --   an object that should be used to register metrics.
 function Prometheus.init(dict_name, options_or_prefix)
-  if ngx.get_phase() ~= 'init' and ngx.get_phase() ~= 'init_worker' and
-      ngx.get_phase() ~= 'timer' then
+  local phase = ngx.get_phase()
+  if phase ~= 'init' and phase ~= 'init_worker' and
+     phase ~= 'timer' then
     error('Prometheus.init can only be called from ' ..
       'init_by_lua_block, init_worker_by_lua_block or timer' , 2)
   end

From 83abc7adfa3d3c7b7ae03cd2a93ec85c24acde3f Mon Sep 17 00:00:00 2001
From: chronolaw <chrono_cpp@me.com>
Date: Wed, 14 Jun 2023 10:12:34 +0800
Subject: [PATCH 10/15] ngx.shared[shm]

---
 kong/plugins/prometheus/exporter.lua | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kong/plugins/prometheus/exporter.lua b/kong/plugins/prometheus/exporter.lua
index 358d7597ce4..40a45a6b685 100644
--- a/kong/plugins/prometheus/exporter.lua
+++ b/kong/plugins/prometheus/exporter.lua
@@ -90,7 +90,7 @@ end
 
 local function init()
   local shm = "prometheus_metrics"
-  if not ngx.shared.prometheus_metrics then
+  if not ngx.shared[shm] then
     kong.log.err("prometheus: ngx shared dict 'prometheus_metrics' not found")
     return
   end

From 2eb32398356d7a747dbc1a9894947544bf58ef87 Mon Sep 17 00:00:00 2001
From: chronolaw <chrono_cpp@me.com>
Date: Wed, 14 Jun 2023 10:14:00 +0800
Subject: [PATCH 11/15] lint fix

---
 kong/plugins/prometheus/prometheus.lua | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kong/plugins/prometheus/prometheus.lua b/kong/plugins/prometheus/prometheus.lua
index e9ba5119b36..60872f4a522 100644
--- a/kong/plugins/prometheus/prometheus.lua
+++ b/kong/plugins/prometheus/prometheus.lua
@@ -937,7 +937,7 @@ function Prometheus:metric_data(write_fn, local_only)
   for i = 1, count do
     yield()
 
-    key = keys[i]
+    local key = keys[i]
 
     local value, err
     local is_local_metrics = true

From 250e372b0a5f539658c60892815a9f232c2a850c Mon Sep 17 00:00:00 2001
From: chronolaw <chrono_cpp@me.com>
Date: Wed, 14 Jun 2023 10:26:36 +0800
Subject: [PATCH 12/15] changelog

---
 CHANGELOG.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index a598d51bd47..d068a65551d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -54,6 +54,7 @@
 - The Prometheus plugin has been optimized to reduce proxy latency impacts during scraping.
   [#10949](https://github.com/Kong/kong/pull/10949)
   [#11040](https://github.com/Kong/kong/pull/11040)
+  [#11065](https://github.com/Kong/kong/pull/11065)
 
 ### Fixes
 

From 29b9ded5b1c9934a0b7be051fb78ed0fa748c706 Mon Sep 17 00:00:00 2001
From: chronolaw <chrono_cpp@me.com>
Date: Wed, 14 Jun 2023 13:41:25 +0800
Subject: [PATCH 13/15] remove st_format

---
 kong/plugins/prometheus/prometheus.lua | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/kong/plugins/prometheus/prometheus.lua b/kong/plugins/prometheus/prometheus.lua
index 60872f4a522..1757a2c7c85 100644
--- a/kong/plugins/prometheus/prometheus.lua
+++ b/kong/plugins/prometheus/prometheus.lua
@@ -68,7 +68,6 @@ local ipairs = ipairs
 local pairs = pairs
 local tostring = tostring
 local tonumber = tonumber
-local st_format = string.format
 local table_sort = table.sort
 local tb_new = require("table.new")
 local yield = require("kong.tools.utils").yield
@@ -305,7 +304,7 @@ local function construct_bucket_format(buckets)
   for _, bucket in ipairs(buckets) do
     assert(type(bucket) == "number", "bucket boundaries should be numeric")
     -- floating point number with all trailing zeros removed
-    local as_string = st_format("%f", bucket):gsub("0*$", "")
+    local as_string = string.format("%f", bucket):gsub("0*$", "")
     local dot_idx = as_string:find(".", 1, true)
     max_order = math.max(max_order, dot_idx - 1)
     max_precision = math.max(max_precision, as_string:len() - dot_idx)
@@ -364,7 +363,7 @@ local function lookup_or_create(self, label_values)
   local cnt = label_values and #label_values or 0
   -- specially, if first element is nil, # will treat it as "non-empty"
   if cnt ~= self.label_count or (self.label_count > 0 and label_values[1] == nil) then
-    return nil, st_format("inconsistent labels count, expected %d, got %d",
+    return nil, string.format("inconsistent labels count, expected %d, got %d",
                               self.label_count, cnt)
   end
   local t = self.lookup
@@ -408,13 +407,13 @@ local function lookup_or_create(self, label_values)
     end
 
     for i, buc in ipairs(self.buckets) do
-      full_name[i+2] = st_format("%sle=\"%s\"}", bucket_pref, self.bucket_format:format(buc))
+      full_name[i+2] = string.format("%sle=\"%s\"}", bucket_pref, self.bucket_format:format(buc))
     end
     -- Last bucket. Note, that the label value is "Inf" rather than "+Inf"
     -- required by Prometheus. This is necessary for this bucket to be the last
     -- one when all metrics are lexicographically sorted. "Inf" will get replaced
     -- by "+Inf" in Prometheus:metric_data().
-    full_name[self.bucket_count+3] = st_format("%sle=\"Inf\"}", bucket_pref)
+    full_name[self.bucket_count+3] = string.format("%sle=\"Inf\"}", bucket_pref)
   else
     full_name = full_metric_name(self.name, self.label_names, label_values)
   end

From 1bc473dc6912071ef1873a91b273fd1b225a2bb2 Mon Sep 17 00:00:00 2001
From: chronolaw <chrono_cpp@me.com>
Date: Wed, 14 Jun 2023 13:43:42 +0800
Subject: [PATCH 14/15] typo fix

---
 kong/plugins/prometheus/prometheus.lua | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kong/plugins/prometheus/prometheus.lua b/kong/plugins/prometheus/prometheus.lua
index 1757a2c7c85..a04805b16af 100644
--- a/kong/plugins/prometheus/prometheus.lua
+++ b/kong/plugins/prometheus/prometheus.lua
@@ -928,7 +928,7 @@ function Prometheus:metric_data(write_fn, local_only)
     end
 
     if output_count >= 100 or not fmt then
-      write_fn(output:get())  -- cosume the whole buffer
+      write_fn(output:get())  -- consume the whole buffer
       output_count = 0
     end
   end

From 44899311bcadf144161b6d0b7ba432d708be6d40 Mon Sep 17 00:00:00 2001
From: chronolaw <chrono_cpp@me.com>
Date: Wed, 21 Jun 2023 10:39:11 +0800
Subject: [PATCH 15/15] buffer free

---
 kong/plugins/prometheus/api.lua        | 6 +++++-
 kong/plugins/prometheus/prometheus.lua | 2 ++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/kong/plugins/prometheus/api.lua b/kong/plugins/prometheus/api.lua
index f73d03bc586..72762bfe034 100644
--- a/kong/plugins/prometheus/api.lua
+++ b/kong/plugins/prometheus/api.lua
@@ -10,7 +10,11 @@ local printable_metric_data = function(_)
     buf:put(new_metric_data)
   end)
 
-  return buf:get()
+  local str = buf:get()
+
+  buf:free()
+
+  return str
 end
 
 
diff --git a/kong/plugins/prometheus/prometheus.lua b/kong/plugins/prometheus/prometheus.lua
index a04805b16af..e837de1cdc3 100644
--- a/kong/plugins/prometheus/prometheus.lua
+++ b/kong/plugins/prometheus/prometheus.lua
@@ -976,6 +976,8 @@ function Prometheus:metric_data(write_fn, local_only)
   end
 
   buffered_print(nil)
+
+  output:free()
 end
 
 -- Present all metrics in a text format compatible with Prometheus.