unpack() function accepts an additional optional argument $offset.

Author: dstogov

NEWS

@@ -53,5 +53,6 @@ PHP                                                                        NEWS
     (Ilia) (Julien)
   . Implemented FR #69359 (Provide a way to fetch the current environment
     variables). (Ferenc)
+  . unpack() function accepts an additional optional argument $offset. (Dmitry)
 
 <<< NOTE: Insert NEWS from last stable release here prior to actual release! >>>

UPGRADING

@@ -63,6 +63,9 @@ PHP 7.1 UPGRADE NOTES
   pg_fetch_row().
 - pg_select() accepts 4th optional result type parameter like pg_fetch_row().
 - parse_url() is more restrictive now and supports RFC3986.
+- unpack() accepts an additional optional $offset argument. '@' format code
+  (that specifes an absolute position) is applyed to input data after
+  the $offset argument.
 
 ========================================
 6. New Functions

ext/standard/pack.c

@@ -551,9 +551,10 @@ PHP_FUNCTION(unpack)
 	zend_string *formatarg, *inputarg;
 	zend_long formatlen, inputpos, inputlen;
 	int i;
+	zend_long offset = 0;
 
-	if (zend_parse_parameters(ZEND_NUM_ARGS(), "SS", &formatarg,
-		&inputarg) == FAILURE) {
+	if (zend_parse_parameters(ZEND_NUM_ARGS(), "SS|l", &formatarg,
+		&inputarg, &offset) == FAILURE) {
 		return;
 	}
 
@@ -563,6 +564,14 @@ PHP_FUNCTION(unpack)
 	inputlen = ZSTR_LEN(inputarg);
 	inputpos = 0;
 
+
+	if (offset < 0 || offset > inputlen) {
+		php_error_docref(NULL, E_WARNING, "Offset " ZEND_LONG_FMT " is out of input range" , offset);
+		RETURN_FALSE;
+	}
+	input += offset;
+	inputlen -= offset;
+
 	array_init(return_value);
 
 	while (formatlen-- > 0) {

ext/standard/tests/strings/unpack_error.phpt

@@ -15,7 +15,7 @@ var_dump( unpack() );
 
 echo "\n-- Testing unpack() function with more than expected no. of arguments --\n";
 $extra_arg = 10;
-var_dump(unpack("I", pack("I", 65534), $extra_arg));
+var_dump(unpack("I", pack("I", 65534), 0, $extra_arg));
 
 echo "\n-- Testing unpack() function with invalid format character --\n";
 $extra_arg = 10;
@@ -27,12 +27,12 @@ var_dump(unpack("G", pack("I", 65534)));
 
 -- Testing unpack() function with no arguments --
 
-Warning: unpack() expects exactly 2 parameters, 0 given in %s on line %d
+Warning: unpack() expects at least 2 parameters, 0 given in %s on line %d
 NULL
 
 -- Testing unpack() function with more than expected no. of arguments --
 
-Warning: unpack() expects exactly 2 parameters, 3 given in %s on line %d
+Warning: unpack() expects at most 3 parameters, 4 given in %s on line %d
 NULL
 
 -- Testing unpack() function with invalid format character --

ext/standard/tests/strings/unpack_offset.phpt

@@ -0,0 +1,17 @@
+--TEST--
+unpack() with offset
+--FILE--
+<?php
+$data = "pad" . pack("ll", 0x01020304, 0x05060708);
+
+$a = unpack("l2", $data, 3);
+printf("0x%08x 0x%08x\n", $a[1], $a[2]);
+
+printf("0x%08x 0x%08x\n",
+	unpack("l", $data, 3)[1],
+	unpack("@4/l", $data, 3)[1]);
+?>
+--EXPECT--
+0x01020304 0x05060708
+0x01020304 0x05060708
+