Make HashContexts serializable.

* Modify php_hash_ops to contain the algorithm name and
  serialize and unserialize methods.
* Implement __serialize and __unserialize magic methods on
  HashContext.

Note that serialized HashContexts are not necessarily portable
between PHP versions or from architecture to architecture.
(Most are, but fast SHA3s are not necessarily.)

A ValueError is thrown when an unsupported serialization is
attempted.

Because of security concerns, HASH_HMAC contexts are not
currently serializable; attempting to serialize one throws
an error.

ext/hash/hash.c

@@ -23,9 +23,12 @@
 #include "php_hash.h"
 #include "ext/standard/info.h"
 #include "ext/standard/file.h"
+#include "ext/standard/php_var.h"
+#include "ext/spl/spl_exceptions.h"
 
 #include "zend_interfaces.h"
 #include "zend_exceptions.h"
+#include "zend_smart_str.h"
 
 #include "hash_arginfo.h"
 
@@ -111,6 +114,195 @@ PHP_HASH_API int php_hash_copy(const void *ops, void *orig_context, void *dest_c
 }
 /* }}} */
 
+
+static size_t parse_serialize_spec(const char **specp, size_t *pos, size_t *sz) {
+	size_t count;
+	const char *spec = *specp;
+	if (*spec == 's') {
+		*sz = 2;
+	} else if (*spec == 'l') {
+		*sz = 4;
+	} else if (*spec == 'q') {
+		*sz = 8;
+	} else if (*spec == 'i') {
+		*sz = sizeof(int);
+	} else {
+		*sz = 1;
+	}
+	++spec;
+	if (isdigit((unsigned char) *spec)) {
+		count = 0;
+		while (isdigit((unsigned char) *spec)) {
+			count = 10 * count + *spec - '0';
+			++spec;
+		}
+	} else {
+		count = 1;
+	}
+	*specp = spec;
+	// alignment
+	if (*sz > 1 && (*pos & (*sz - 1)) != 0) {
+		*pos += *sz - (*pos & (*sz - 1));
+	}
+	return count;
+}
+
+static uint64_t one_from_buffer(size_t sz, const unsigned char *buf) {
+	if (sz == 2) {
+		const uint16_t *x = (const uint16_t *) buf;
+		return *x;
+	} else if (sz == 4) {
+		const uint32_t *x = (const uint32_t *) buf;
+		return *x;
+	} else if (sz == 8) {
+		const uint64_t *x = (const uint64_t *) buf;
+		return *x;
+	} else {
+		return *buf;
+	}
+}
+
+static void one_to_buffer(size_t sz, unsigned char *buf, uint64_t val) {
+	if (sz == 2) {
+		uint16_t *x = (uint16_t *) buf;
+		*x = val;
+	} else if (sz == 4) {
+		uint32_t *x = (uint32_t *) buf;
+		*x = val;
+	} else if (sz == 8) {
+		uint64_t *x = (uint64_t *) buf;
+		*x = val;
+	} else {
+		*buf = val;
+	}
+}
+
+PHP_HASH_API int php_hash_serialize_spec(const php_hashcontext_object *hash, zend_long *magic, zval *zv, const char *spec) /* {{{ */
+{
+	size_t pos = 0, sz, count;
+	unsigned char *buf = (unsigned char *) hash->context;
+	zval tmp;
+	*magic = 2;
+	array_init(zv);
+	while (*spec != '\0' && *spec != '.') {
+		char specch = *spec;
+		count = parse_serialize_spec(&spec, &pos, &sz);
+		if (pos + count * sz > hash->ops->context_size) {
+			return FAILURE;
+		}
+		if (specch == '-') {
+			pos += count;
+		} else if (sz == 1 && count > 1) {
+			ZVAL_STRINGL(&tmp, (char *) buf + pos, count);
+			zend_hash_next_index_insert(Z_ARRVAL_P(zv), &tmp);
+			pos += count;
+		} else {
+			while (count > 0) {
+				uint64_t val = one_from_buffer(sz, buf + pos);
+				pos += sz;
+				ZVAL_LONG(&tmp, val);
+				zend_hash_next_index_insert(Z_ARRVAL_P(zv), &tmp);
+#if SIZEOF_ZEND_LONG == 4
+				if (sz == 8) {
+					ZVAL_LONG(&tmp, val >> 32);
+					zend_hash_next_index_insert(Z_ARRVAL_P(zv), &tmp);
+				}
+#endif
+				--count;
+			}
+		}
+	}
+	if (*spec == '.' && pos != hash->ops->context_size) {
+		return FAILURE;
+	}
+	return SUCCESS;
+}
+/* }}} */
+
+PHP_HASH_API int php_hash_unserialize_spec(php_hashcontext_object *hash, zend_long magic, const zval *zv, const char *spec) /* {{{ */
+{
+	size_t pos = 0, sz, count, j = 0;
+	unsigned char *buf = (unsigned char *) hash->context;
+	zval *elt;
+	if (magic != 2 || Z_TYPE_P(zv) != IS_ARRAY) {
+		return FAILURE;
+	}
+	while (*spec != '\0' && *spec != '.') {
+		char specch = *spec;
+		count = parse_serialize_spec(&spec, &pos, &sz);
+		if (pos + count * sz > hash->ops->context_size) {
+			return FAILURE;
+		}
+		if (specch == '-') {
+			pos += count;
+		} else if (sz == 1 && count > 1) {
+			elt = zend_hash_index_find(Z_ARRVAL_P(zv), j);
+			if (!elt || Z_TYPE_P(elt) != IS_STRING || Z_STRLEN_P(elt) != count) {
+				return FAILURE;
+			}
+			++j;
+			memcpy(buf + pos, Z_STRVAL_P(elt), count);
+			pos += count;
+		} else {
+			while (count > 0) {
+				uint64_t val;
+				elt = zend_hash_index_find(Z_ARRVAL_P(zv), j);
+				if (!elt || Z_TYPE_P(elt) != IS_LONG) {
+					return FAILURE;
+				}
+				++j;
+				val = zval_get_long(elt);
+#if SIZEOF_ZEND_LONG == 4
+				if (sz == 8) {
+					elt = zend_hash_index_find(Z_ARRVAL_P(zv), j);
+					if (!elt || Z_TYPE_P(elt) != IS_LONG) {
+						return FAILURE;
+					}
+					++j;
+					val += ((uint64_t) zval_get_long(elt)) << 32;
+				}
+#endif
+				one_to_buffer(sz, buf + pos, val);
+				pos += sz;
+				--count;
+			}
+		}
+	}
+	if (*spec == '.' && pos != hash->ops->context_size) {
+		return FAILURE;
+	}
+	return SUCCESS;
+}
+/* }}} */
+
+PHP_HASH_API int php_hash_serialize(const php_hashcontext_object *hash, zend_long *magic, zval *zv) /* {{{ */
+{
+	if (hash->ops->serialize_spec) {
+		return php_hash_serialize_spec(hash, magic, zv, hash->ops->serialize_spec);
+	} else {
+		*magic = PHP_HASH_SERIALIZE_MAGIC;
+		ZVAL_STRINGL(zv, (const char *) hash->context, hash->ops->context_size);
+		return SUCCESS;
+	}
+}
+/* }}} */
+
+PHP_HASH_API int php_hash_unserialize(php_hashcontext_object *hash, zend_long magic, const zval *zv) /* {{{ */
+{
+	if (hash->ops->serialize_spec) {
+		return php_hash_unserialize_spec(hash, magic, zv, hash->ops->serialize_spec);
+	} else {
+		if (Z_TYPE_P(zv) != IS_STRING
+			|| Z_STRLEN_P(zv) != hash->ops->context_size
+			|| magic != PHP_HASH_SERIALIZE_MAGIC) {
+			return FAILURE;
+		}
+		memcpy(hash->context, Z_STRVAL_P(zv), hash->ops->context_size);
+		return SUCCESS;
+	}
+}
+/* }}} */
+
 /* Userspace */
 
 static void php_hash_do_hash(INTERNAL_FUNCTION_PARAMETERS, int isfilename, zend_bool raw_output_default) /* {{{ */
@@ -1170,6 +1362,138 @@ static zend_object *php_hashcontext_clone(zend_object *zobj) {
 }
 /* }}} */
 
+/* Serialization format: 5- or 6-element array
+   Index 0: hash algorithm (string)
+   Index 1: options (long, 0)
+   Index 2: hash-determined serialization of internal state (mixed, usually string)
+   Index 3: magic number defining layout of internal state (long)
+   Index 4: properties (array)
+
+   HashContext serializations are not necessarily portable between architectures or
+   PHP versions. If the format of a serialized hash context changes, that should
+   be reflected in either a different value of `magic` or a different length of
+   the serialized context string. A particular hash algorithm can make its
+   HashContext serialization portable by parsing different representations in
+   its custom `hash_unserialize` method.
+
+   Currently HASH_HMAC contexts cannot be serialized, because serializing them
+   would require serializing the HMAC key in plaintext. */
+
+/* {{{ proto array HashContext::__serialize()
+   Serialize the object */
+PHP_METHOD(HashContext, __serialize)
+{
+	zval *object = ZEND_THIS;
+	php_hashcontext_object *hash = php_hashcontext_from_object(Z_OBJ_P(object));
+	zend_long magic = 0;
+	zval tmp;
+
+	if (zend_parse_parameters_none() == FAILURE) {
+		RETURN_THROWS();
+	}
+
+	array_init(return_value);
+
+	if (!hash->ops->hash_serialize) {
+		goto serialize_failure;
+	} else if (hash->options & PHP_HASH_HMAC) {
+		zend_value_error("HashContext with HASH_HMAC option cannot be serialized");
+		RETURN_THROWS();
+	}
+
+	ZVAL_STRING(&tmp, hash->ops->algo);
+	zend_hash_next_index_insert(Z_ARRVAL_P(return_value), &tmp);
+
+	ZVAL_LONG(&tmp, hash->options);
+	zend_hash_next_index_insert(Z_ARRVAL_P(return_value), &tmp);
+
+	if (hash->ops->hash_serialize(hash, &magic, &tmp) != SUCCESS) {
+		goto serialize_failure;
+	}
+	zend_hash_next_index_insert(Z_ARRVAL_P(return_value), &tmp);
+
+	ZVAL_LONG(&tmp, magic);
+	zend_hash_next_index_insert(Z_ARRVAL_P(return_value), &tmp);
+
+	/* members */
+	ZVAL_ARR(&tmp, zend_std_get_properties(&hash->std));
+	Z_TRY_ADDREF(tmp);
+	zend_hash_next_index_insert(Z_ARRVAL_P(return_value), &tmp);
+
+	return;
+
+serialize_failure:
+	zend_value_error("HashContext for algorithm '%s' cannot be serialized", hash->ops->algo);
+	RETURN_THROWS();
+}
+/* }}} */
+
+/* {{{ proto void HashContext::__unserialize(array serialized)
+ * unserialize the object
+ */
+PHP_METHOD(HashContext, __unserialize)
+{
+	zval *object = ZEND_THIS;
+	php_hashcontext_object *hash = php_hashcontext_from_object(Z_OBJ_P(object));
+	HashTable *data;
+	zval *algo_zv, *magic_zv, *options_zv, *hash_zv, *members_zv;
+	zend_long magic, options;
+	const php_hash_ops *ops;
+
+	if (zend_parse_parameters(ZEND_NUM_ARGS(), "h", &data) == FAILURE) {
+		RETURN_THROWS();
+	}
+
+	if (hash->context) {
+		zend_throw_exception(spl_ce_LogicException, "HashContext::__unserialize called on initialized object", 0);
+		RETURN_THROWS();
+	}
+
+	algo_zv = zend_hash_index_find(data, 0);
+	options_zv = zend_hash_index_find(data, 1);
+	hash_zv = zend_hash_index_find(data, 2);
+	magic_zv = zend_hash_index_find(data, 3);
+	members_zv = zend_hash_index_find(data, 4);
+
+	if (!algo_zv || Z_TYPE_P(algo_zv) != IS_STRING
+		|| !magic_zv || Z_TYPE_P(magic_zv) != IS_LONG
+		|| !options_zv || Z_TYPE_P(options_zv) != IS_LONG
+		|| !hash_zv
+		|| !members_zv || Z_TYPE_P(members_zv) != IS_ARRAY) {
+		zend_value_error("Incomplete or ill-formed serialization data");
+		RETURN_THROWS();
+	}
+
+	magic = zval_get_long(magic_zv);
+	options = zval_get_long(options_zv);
+	if (options & PHP_HASH_HMAC) {
+		zend_value_error("HashContext with HASH_HMAC option cannot be serialized");
+		RETURN_THROWS();
+	}
+
+	ops = php_hash_fetch_ops(Z_STR_P(algo_zv));
+	if (!ops) {
+		zend_value_error("Unknown hash algorithm");
+		RETURN_THROWS();
+	} else if (!ops->hash_unserialize) {
+		zend_value_error("Hash algorithm '%s' cannot be unserialized", ops->algo);
+		RETURN_THROWS();
+	}
+
+	hash->ops = ops;
+	hash->context = emalloc(ops->context_size);
+	ops->hash_init(hash->context);
+	hash->options = options;
+
+	if (ops->hash_unserialize(hash, magic, hash_zv) != SUCCESS) {
+		zend_value_error("HashContext for algorithm '%s' cannot be unserialized, format may be non-portable", ops->algo);
+		RETURN_THROWS();
+	}
+
+	object_properties_load(&hash->std, Z_ARRVAL_P(members_zv));
+}
+/* }}} */
+
 /* {{{ PHP_MINIT_FUNCTION
  */
 PHP_MINIT_FUNCTION(hash)
@@ -1241,8 +1565,6 @@ PHP_MINIT_FUNCTION(hash)
 	php_hashcontext_ce = zend_register_internal_class(&ce);
 	php_hashcontext_ce->ce_flags |= ZEND_ACC_FINAL;
 	php_hashcontext_ce->create_object = php_hashcontext_create;
-	php_hashcontext_ce->serialize = zend_class_serialize_deny;
-	php_hashcontext_ce->unserialize = zend_class_unserialize_deny;
 
 	memcpy(&php_hashcontext_handlers, &std_object_handlers,
 	       sizeof(zend_object_handlers));

ext/hash/hash.stub.php

@@ -53,4 +53,8 @@ function mhash(int $hash, string $data, string $key = UNKNOWN): string|false {}
 final class HashContext
 {
     private function __construct() {}
+
+    public function __serialize(): array {}
+
+    public function __unserialize(array $serialized): void {}
 }

ext/hash/hash_adler32.c

@@ -59,10 +59,14 @@ PHP_HASH_API int PHP_ADLER32Copy(const php_hash_ops *ops, PHP_ADLER32_CTX *orig_
 }
 
 const php_hash_ops php_hash_adler32_ops = {
+	"adler32",
 	(php_hash_init_func_t) PHP_ADLER32Init,
 	(php_hash_update_func_t) PHP_ADLER32Update,
 	(php_hash_final_func_t) PHP_ADLER32Final,
 	(php_hash_copy_func_t) PHP_ADLER32Copy,
+	php_hash_serialize,
+	php_hash_unserialize,
+	PHP_ADLER32_SPEC,
 	4, /* what to say here? */
 	4,
 	sizeof(PHP_ADLER32_CTX),