[PATCH 11/11] avoid String#-@ call on request parsing under Ruby 2.6

[Eric Wong <e@80x24.org>]

Ruby 2.6 will unconditionally dedupe all hash key strings
thanks to Anmol Chopra at https://bugs.ruby-lang.org/issues/15251
---
 ext/kcar/extconf.rb | 11 +++++++++++
 ext/kcar/kcar.rl    |  5 +++--
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/ext/kcar/extconf.rb b/ext/kcar/extconf.rb
index b65846a..ba69c3c 100644
--- a/ext/kcar/extconf.rb
+++ b/ext/kcar/extconf.rb
@@ -22,4 +22,15 @@ rescue NoMethodError
   message("no, String#-@ not available\n")
 end
 
+message('checking if Hash#[]= (rb_hash_aset) dedupes... ')
+h = {}
+h[%w(m k m f).join('')] = :foo
+if 'mkmf'.freeze.equal?(h.keys[0])
+  $CPPFLAGS += ' -DHASH_ASET_DEDUPE=1 '
+  message("yes\n")
+else
+  $CPPFLAGS += ' -DHASH_ASET_DEDUPE=0 '
+  message("no, needs Ruby 2.6+\n")
+end
+
 create_makefile("kcar_ext")
diff --git a/ext/kcar/kcar.rl b/ext/kcar/kcar.rl
index 336af55..9d04dd8 100644
--- a/ext/kcar/kcar.rl
+++ b/ext/kcar/kcar.rl
@@ -489,7 +489,6 @@ static void write_response_value(struct http_parser *hp, VALUE hdr,
   }
 }
 
-/* TODO cache */
 static VALUE req_field(const char *ptr, size_t len)
 {
   size_t pfxlen = sizeof("HTTP_") - 1;
@@ -501,7 +500,7 @@ static VALUE req_field(const char *ptr, size_t len)
   assert(*(dst + RSTRING_LEN(str)) == '\0' &&
          "string didn't end with \\0"); /* paranoia */
 
-  return str_dd_freeze(str);
+  return str;
 }
 
 static void snake_upcase(char *ptr, size_t len)
@@ -570,6 +569,8 @@ static void write_request_value(struct http_parser *hp, VALUE env,
       hp->v.host = val;
   } else {
     key = req_field(fptr, flen);
+    if (!HASH_ASET_DEDUPE)
+      key = str_dd_freeze(key);
   }
   existing = rb_hash_aref(env, key);
   if (NIL_P(existing)) {