fix(PDK): fix response body repeated when kong.response.get_raw_body() called multiple times

CHANGELOG/unreleased/kong/11424.yaml

@@ -0,0 +1,7 @@
+message: Fix response body gets repeated when `kong.response.get_raw_body()` is called multiple times in a request lifecycle.
+type: bugfix
+scope: PDK
+prs:
+  - 11424
+jiras:
+  - "FTI-5296"

kong/pdk/response.lua

@@ -609,6 +609,7 @@ local function new(self, major_version)
       end
 
       arg[1] = body_buffer
+      ngx.ctx.KONG_BODY_BUFFER = nil
       return body_buffer
     end
 

t/01-pdk/08-response/14-get_raw_body.t

@@ -73,3 +73,37 @@ Enhanced by Body Filter
 Called 3 times
 --- no_error_log
 [error]
+
+
+
+=== TEST 3: response.get_raw_body() calls multiple times
+--- http_config eval: $t::Util::HttpConfig
+--- config
+    location = /t {
+        content_by_lua_block {
+            ngx.print("hello, world!\n")
+        }
+        body_filter_by_lua_block {
+            local PDK = require "kong.pdk"
+            local pdk = PDK.new()
+            -- call pdk.response.get_raw_body() multiple times
+            ngx.ctx.called = (ngx.ctx.called or 0) + 1
+            for i = 1, 3 do
+                ngx.ctx.called2 = (ngx.ctx.called2 or 0) + 1
+                local body = pdk.response.get_raw_body()
+                if body then
+                    assert("hello, world!\n" == body)
+                end
+            end
+        }
+        log_by_lua_block {
+            assert(ngx.ctx.called == 2)
+            assert(ngx.ctx.called2 == 6)
+        }
+    }
+--- request
+GET /t
+--- response_body
+hello, world!
+--- no_error_log
+[error]