Reduce memory allocated by var_export, json_encode, serialize, and other

NEWS

@@ -2,11 +2,16 @@ PHP                                                                        NEWS
 |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
 ?? ??? ????, PHP 8.2.0beta1
 
+- Core:
+  . Reduced the memory footprint of strings returned by var_export(),
+    json_encode(), serialize(), iconv_*(), mb_ereg*(), session_create_id(),
+    http_build_query(), strstr(), Reflection*::__toString(). (Arnaud)
+
 - CLI:
-   - Updated the mime-type table for the builtin-server. (Ayesh Karunaratne)
+  . Updated the mime-type table for the builtin-server. (Ayesh Karunaratne)
 
 - FPM:
-  - Added listen.setfib pool option to set route FIB on FreeBSD. (David Carlier)
+  . Added listen.setfib pool option to set route FIB on FreeBSD. (David Carlier)
 
 07 Jul 2022, PHP 8.2.0alpha3
 

UPGRADING.INTERNALS

@@ -39,6 +39,13 @@ PHP 8.2 INTERNALS UPGRADE NOTES
   - zend_object_do_operation_t
 * Added a new zero_position argument to php_stream_fopen_from_fd_rel to reflect
   if this a newly created file so the current file offset needs not to be checked.
+* Added smart_str_trim_to_size(). The function trims the memory allocated for the
+  string. This can considerably reduce the memory footprint of strings smaller
+  than approximately 4096 bytes.
+* smart_str_extract() and the spprintf family of functions now use
+  smart_str_trim_to_size() before returning the string.
+* It is recommended to use smart_str_extract() or smart_str_trim_to_size() when
+  using the smart_str API.
 
 ========================
 2. Build system changes

Zend/zend.c

@@ -272,8 +272,7 @@ ZEND_API zend_string *zend_vstrpprintf(size_t max_len, const char *format, va_li
 		ZSTR_LEN(buf.s) = max_len;
 	}
 
-	smart_str_0(&buf);
-	return buf.s;
+	return smart_str_extract(&buf);
 }
 /* }}} */
 

Zend/zend_smart_str.h

@@ -25,6 +25,10 @@
 	smart_str_appendl_ex((dest), (src), strlen(src), (what))
 #define smart_str_appends(dest, src) \
 	smart_str_appendl((dest), (src), strlen(src))
+#define smart_str_extract(dest) \
+	smart_str_extract_ex((dest), 0)
+#define smart_str_trim_to_size(dest) \
+	smart_str_trim_to_size_ex((dest), 0)
 #define smart_str_extend(dest, len) \
 	smart_str_extend_ex((dest), (len), 0)
 #define smart_str_appendc(dest, c) \
@@ -101,10 +105,19 @@ static zend_always_inline size_t smart_str_get_len(smart_str *str) {
 	return str->s ? ZSTR_LEN(str->s) : 0;
 }
 
-static zend_always_inline zend_string *smart_str_extract(smart_str *str) {
+static zend_always_inline void smart_str_trim_to_size_ex(smart_str *str, bool persistent)
+{
+	if (str->s && str->a > ZSTR_LEN(str->s)) {
+		str->s = zend_string_realloc(str->s, ZSTR_LEN(str->s), persistent);
+		str->a = ZSTR_LEN(str->s);
+	}
+}
+
+static zend_always_inline zend_string *smart_str_extract_ex(smart_str *str, bool persistent) {
 	if (str->s) {
 		zend_string *res;
 		smart_str_0(str);
+		smart_str_trim_to_size_ex(str, persistent);
 		res = str->s;
 		str->s = NULL;
 		return res;

Zend/zend_smart_str_public.h

@@ -18,6 +18,7 @@
 #define ZEND_SMART_STR_PUBLIC_H
 
 typedef struct {
+	/** See smart_str_extract() */
 	zend_string *s;
 	size_t a;
 } smart_str;

ext/dom/documenttype.c

@@ -188,8 +188,7 @@ int dom_documenttype_internal_subset_read(dom_object *obj, zval *retval)
 		}
 
 		if (ret_buf.s) {
-			smart_str_0(&ret_buf);
-			ZVAL_NEW_STR(retval, ret_buf.s);
+			ZVAL_STR(retval, smart_str_extract(&ret_buf));
 			return SUCCESS;
 		}
 	}

ext/filter/sanitizing_filters.c

@@ -46,9 +46,8 @@ static void php_filter_encode_html(zval *value, const unsigned char *chars)
 		s++;
 	}
 
-	smart_str_0(&str);
 	zval_ptr_dtor(value);
-	ZVAL_NEW_STR(value, str.s);
+	ZVAL_STR(value, smart_str_extract(&str));
 }
 
 static const unsigned char hexchars[] = "0123456789ABCDEF";

ext/iconv/iconv.c

@@ -1845,7 +1845,7 @@ PHP_FUNCTION(iconv_substr)
 	_php_iconv_show_error(err, GENERIC_SUPERSET_NAME, charset);
 
 	if (err == PHP_ICONV_ERR_SUCCESS && retval.s != NULL) {
-		RETURN_NEW_STR(retval.s);
+		RETURN_STR(smart_str_extract(&retval));
 	}
 	smart_str_free(&retval);
 	RETURN_FALSE;
@@ -2038,11 +2038,7 @@ PHP_FUNCTION(iconv_mime_encode)
 	_php_iconv_show_error(err, out_charset, in_charset);
 
 	if (err == PHP_ICONV_ERR_SUCCESS) {
-		if (retval.s != NULL) {
-			RETVAL_STR(retval.s);
-		} else {
-			RETVAL_EMPTY_STRING();
-		}
+		RETVAL_STR(smart_str_extract(&retval));
 	} else {
 		smart_str_free(&retval);
 		RETVAL_FALSE;
@@ -2083,11 +2079,7 @@ PHP_FUNCTION(iconv_mime_decode)
 	_php_iconv_show_error(err, charset, "???");
 
 	if (err == PHP_ICONV_ERR_SUCCESS) {
-		if (retval.s != NULL) {
-			RETVAL_STR(retval.s);
-		} else {
-			RETVAL_EMPTY_STRING();
-		}
+		RETVAL_STR(smart_str_extract(&retval));
 	} else {
 		smart_str_free(&retval);
 		RETVAL_FALSE;

ext/json/json.c

@@ -212,11 +212,7 @@ PHP_FUNCTION(json_encode)
 		}
 	}
 
-	smart_str_0(&buf); /* copy? */
-	if (buf.s) {
-		RETURN_NEW_STR(buf.s);
-	}
-	RETURN_EMPTY_STRING();
+	RETURN_STR(smart_str_extract(&buf));
 }
 /* }}} */
 

ext/mbstring/php_mbregex.c

@@ -1144,13 +1144,10 @@ static void _php_mb_regex_ereg_replace_exec(INTERNAL_FUNCTION_PARAMETERS, OnigOp
 
 	if (err <= -2) {
 		smart_str_free(&out_buf);
-		RETVAL_FALSE;
-	} else if (out_buf.s) {
-		smart_str_0(&out_buf);
-		RETVAL_STR(out_buf.s);
-	} else {
-		RETVAL_EMPTY_STRING();
+		RETURN_FALSE;
 	}
+
+	RETURN_STR(smart_str_extract(&out_buf));
 }
 /* }}} */
 

ext/session/session.c

@@ -1464,7 +1464,7 @@ PHPAPI zend_result php_session_reset_id(void) /* {{{ */
 		smart_str_0(&var);
 		if (sid) {
 			zval_ptr_dtor_str(sid);
-			ZVAL_NEW_STR(sid, var.s);
+			ZVAL_STR(sid, smart_str_extract(&var));
 		} else {
 			REGISTER_STRINGL_CONSTANT("SID", ZSTR_VAL(var.s), ZSTR_LEN(var.s), 0);
 			smart_str_free(&var);
@@ -2362,8 +2362,7 @@ PHP_FUNCTION(session_create_id)
 		php_error_docref(NULL, E_WARNING, "Failed to create new ID");
 		RETURN_FALSE;
 	}
-	smart_str_0(&id);
-	RETVAL_NEW_STR(id.s);
+	RETVAL_STR(smart_str_extract(&id));
 }
 /* }}} */
 

ext/soap/php_sdl.c

@@ -3261,8 +3261,7 @@ sdlPtr get_sdl(zval *this_ptr, char *uri, zend_long cache_wsdl)
 			smart_str_appends(&proxy,Z_STRVAL_P(proxy_host));
 			smart_str_appends(&proxy,":");
 			smart_str_append_long(&proxy,Z_LVAL_P(proxy_port));
-			smart_str_0(&proxy);
-			ZVAL_NEW_STR(&str_proxy, proxy.s);
+			ZVAL_STR(&str_proxy, smart_str_extract(&proxy));
 
 			if (!context) {
 				context = php_stream_context_alloc();
@@ -3304,8 +3303,7 @@ sdlPtr get_sdl(zval *this_ptr, char *uri, zend_long cache_wsdl)
 			http_context_headers(context, has_authorization, has_proxy_authorization, 0, &headers);
 		}
 
-		smart_str_0(&headers);
-		ZVAL_NEW_STR(&str_headers, headers.s);
+		ZVAL_STR(&str_headers, smart_str_extract(&headers));
 		php_stream_context_set_option(context, "http", "header", &str_headers);
 		zval_ptr_dtor(&str_headers);
 	}

ext/spl/spl_array.c

@@ -1554,7 +1554,7 @@ PHP_METHOD(ArrayObject, serialize)
 	/* done */
 	PHP_VAR_SERIALIZE_DESTROY(var_hash);
 
-	RETURN_NEW_STR(buf.s);
+	RETURN_STR(smart_str_extract(&buf));
 } /* }}} */
 
 /* {{{ unserialize the object */

ext/spl/spl_dllist.c

@@ -1032,12 +1032,10 @@ PHP_METHOD(SplDoublyLinkedList, serialize)
 		current = next;
 	}
 
-	smart_str_0(&buf);
-
 	/* done */
 	PHP_VAR_SERIALIZE_DESTROY(var_hash);
 
-	RETURN_NEW_STR(buf.s);
+	RETURN_STR(smart_str_extract(&buf));
 } /* }}} */
 
 /* {{{ Unserializes storage */

ext/spl/spl_observer.c

@@ -808,7 +808,7 @@ PHP_METHOD(SplObjectStorage, serialize)
 	/* done */
 	PHP_VAR_SERIALIZE_DESTROY(var_hash);
 
-	RETURN_NEW_STR(buf.s);
+	RETURN_STR(smart_str_extract(&buf));
 } /* }}} */
 
 /* {{{ Unserializes storage */

ext/standard/http.c

@@ -238,12 +238,6 @@ PHP_FUNCTION(http_build_query)
 
 	php_url_encode_hash_ex(HASH_OF(formdata), &formstr, prefix, prefix_len, NULL, 0, NULL, 0, (Z_TYPE_P(formdata) == IS_OBJECT ? formdata : NULL), arg_sep, (int)enc_type);
 
-	if (!formstr.s) {
-		RETURN_EMPTY_STRING();
-	}
-
-	smart_str_0(&formstr);
-
-	RETURN_NEW_STR(formstr.s);
+	RETURN_STR(smart_str_extract(&formstr));
 }
 /* }}} */

ext/standard/string.c

@@ -2891,8 +2891,7 @@ static void php_strtr_array(zval *return_value, zend_string *input, HashTable *p
 
 	if (result.s) {
 		smart_str_appendl(&result, str + old_pos, slen - old_pos);
-		smart_str_0(&result);
-		RETVAL_NEW_STR(result.s);
+		RETVAL_STR(smart_str_extract(&result));
 	} else {
 		smart_str_free(&result);
 		RETVAL_STR_COPY(input);

ext/standard/var.c

@@ -645,7 +645,7 @@ PHP_FUNCTION(var_export)
 	smart_str_0 (&buf);
 
 	if (return_output) {
-		RETURN_NEW_STR(buf.s);
+		RETURN_STR(smart_str_extract(&buf));
 	} else {
 		PHPWRITE(ZSTR_VAL(buf.s), ZSTR_LEN(buf.s));
 		smart_str_free(&buf);
@@ -1318,11 +1318,7 @@ PHP_FUNCTION(serialize)
 		RETURN_THROWS();
 	}
 
-	if (buf.s) {
-		RETURN_NEW_STR(buf.s);
-	} else {
-		RETURN_EMPTY_STRING();
-	}
+	RETURN_STR(smart_str_extract(&buf));
 }
 /* }}} */