Ruby: Allow empty response headers.

If ruby/rack tried to send an empty header, e.g

  app = Proc.new do |env|
      ["200", {
          "Content-Type" => "text/plain",
          "X-Empty-Header" => nil,
      }, ["Hello World\n"]]
  end

  run app

you would get an error like

  2023/10/20 11:24:56 [error] 24829#24829 [unit] nginx#10: Ruby: Wrong header entry 'value' from application
  2023/10/20 11:24:56 [error] 24829#24829 [unit] nginx#10: Ruby: Failed to run ruby script

Empty headers are a thing, so we need to allow the ruby type T_NIL
(along with T_STRING) as a valid header value.

This factors out the setting of value & value_end into a macro as what
these get set to now depends on if we have a T_NIL or a T_STRING and
this prevents an increase in duplicated code.

Signed-off-by: Andrew Clayton <[email protected]>

src/ruby/nxt_ruby.c

@@ -874,6 +874,18 @@ nxt_ruby_rack_result_headers(nxt_unit_request_info_t *req, VALUE result,
 }
 
 
+#define NXT_RUBY_SET_HDR_VALUE(r_value, value, value_end)                     \
+    do {                                                                      \
+        if (TYPE(r_value) == T_STRING) {                                      \
+            value = RSTRING_PTR(r_value);                                     \
+            value_end = value + RSTRING_LEN(r_value);                         \
+        } else {                                                              \
+            value = "";                                                       \
+            value_end = value;                                                \
+        }                                                                     \
+    } while (0);
+
+
 static int
 nxt_ruby_hash_info(VALUE r_key, VALUE r_value, VALUE arg)
 {
@@ -889,16 +901,14 @@ nxt_ruby_hash_info(VALUE r_key, VALUE r_value, VALUE arg)
         goto fail;
     }
 
-    if (nxt_slow_path(TYPE(r_value) != T_STRING)) {
+    if (nxt_slow_path(TYPE(r_value) != T_STRING && TYPE(r_value) != T_NIL)) {
         nxt_unit_req_error(headers_info->req,
                            "Ruby: Wrong header entry 'value' from application");
 
         goto fail;
     }
 
-    value = RSTRING_PTR(r_value);
-    value_end = value + RSTRING_LEN(r_value);
-
+    NXT_RUBY_SET_HDR_VALUE(r_value, value, value_end);
     pos = value;
 
     for ( ;; ) {
@@ -941,11 +951,9 @@ nxt_ruby_hash_add(VALUE r_key, VALUE r_value, VALUE arg)
     headers_info = (void *) (uintptr_t) arg;
     rc = &headers_info->rc;
 
-    value = RSTRING_PTR(r_value);
-    value_end = value + RSTRING_LEN(r_value);
-
     key_len = RSTRING_LEN(r_key);
 
+    NXT_RUBY_SET_HDR_VALUE(r_value, value, value_end);
     pos = value;
 
     for ( ;; ) {