fix(loggly): fix the error caused by the missing /bin/hostname

1. Refactor the PDK's get_hostname to use only the gethostname system call to retrieve the hostname.
2. Loggly uses the PDK's get_hostname to retrieve the hostname.

FTI-6046

changelog/unreleased/kong/fix-loggly-hostname-notfound.yml

@@ -0,0 +1,2 @@
+message: "**loggly**: fixed the error caused by the missing `/bin/hostname`."
+type: bugfix

kong/pdk/node.lua

@@ -252,15 +252,15 @@ local function new(self)
     local buf = ffi_new("unsigned char[?]", SIZE)
     local res = C.gethostname(buf, SIZE)
 
-    if res == 0 then
-      local hostname = ffi_str(buf, SIZE)
-      return gsub(hostname, "%z+$", "")
+    if res ~= 0 then
+      -- Return an empty string "" instead of nil and error message,
+      -- because strerror is not thread-safe and the behavior of strerror_r
+      -- is inconsistent across different systems.
+      return ""
     end
 
-    local f = io.popen("/bin/hostname")
-    local hostname = f:read("*a") or ""
-    f:close()
-    return gsub(hostname, "\n$", "")
+    local hostname = ffi_str(buf, SIZE)
+    return gsub(hostname, "%z+$", "")
   end
 
 

kong/plugins/loggly/handler.lua

@@ -1,6 +1,7 @@
 local cjson = require "cjson"
 local sandbox = require "kong.tools.sandbox".sandbox
 local kong_meta = require "kong.meta"
+local get_host_name = require "kong.pdk.node".get_hostname
 
 
 local kong = kong
@@ -16,15 +17,6 @@ local insert = table.insert
 local sandbox_opts = { env = { kong = kong, ngx = ngx } }
 
 
-local function get_host_name()
-  local f = io.popen("/bin/hostname")
-  local hostname = f:read("*a") or ""
-  f:close()
-  hostname = string.gsub(hostname, "\n$", "")
-  return hostname
-end
-
-
 local HOSTNAME = get_host_name()
 local SENDER_NAME = "kong"
 local LOG_LEVELS = {