Fix #62004: SplFileObject: fgets after seek returns wrong line

As it is, `::seek(0)` sets the file pointer to the beginning of the
file, but `::seek($n)` where `$n > 0` sets the file pointer to the
beginning of the following line, having line `$n` already read into the
line buffer.  This is pretty inconsistent; we fix it by always seeking
to the beginning of the line.

We also add a test case for the duplicate bug #46569.

Closes GH-6434.

Author: cmb69

NEWS

@@ -33,6 +33,9 @@ PHP                                                                        NEWS
 - Phpdbg:
   . Fixed bug #76813 (Access violation near NULL on source operand). (cmb)
 
+- SPL:
+  . Fixed #62004 (SplFileObject: fgets after seek returns wrong line). (cmb)
+
 - Standard:
   . Fixed bug #80366 (Return Value of zend_fstat() not Checked). (sagpant, cmb)
 

UPGRADING

@@ -516,6 +516,8 @@ PHP 8.0 UPGRADE NOTES
 
 - SPL:
   . SplFileObject::fgetss() has been removed.
+  . SplFileObject::seek() now always seeks to the beginning of the line.
+    Previously, positions >=1 sought to the beginning of the next line.
   . SplHeap::compare($a, $b) now specifies a method signature. Inheriting
     classes implementing this method will now have to use a compatible
     method signature.

ext/spl/spl_directory.c

@@ -2727,7 +2727,7 @@ PHP_METHOD(SplFileObject, ftruncate)
 PHP_METHOD(SplFileObject, seek)
 {
 	spl_filesystem_object *intern = Z_SPLFILESYSTEM_P(ZEND_THIS);
-	zend_long line_pos;
+	zend_long line_pos, i;
 
 	if (zend_parse_parameters(ZEND_NUM_ARGS(), "l", &line_pos) == FAILURE) {
 		RETURN_THROWS();
@@ -2742,11 +2742,15 @@ PHP_METHOD(SplFileObject, seek)
 
 	spl_filesystem_file_rewind(ZEND_THIS, intern);
 
-	while(intern->u.file.current_line_num < line_pos) {
+	for (i = 0; i < line_pos; i++) {
 		if (spl_filesystem_file_read_line(ZEND_THIS, intern, 1) == FAILURE) {
-			break;
+			return;
 		}
 	}
+	if (line_pos > 0) {
+		intern->u.file.current_line_num++;
+		spl_filesystem_file_free_line(intern);
+	}
 } /* }}} */
 
 /* {{{ PHP_MINIT_FUNCTION(spl_directory) */

ext/spl/tests/SplFileObject_key_error001.phpt

@@ -12,11 +12,11 @@ Erwin Poeze <erwin.poeze@gmail.com>
 //line 5
 $s = new SplFileObject(__FILE__);
 
-$s->seek(12);
+$s->seek(13);
 $s->next();
 var_dump($s->key());
 var_dump($s->valid());
 ?>
 --EXPECT--
-int(13)
+int(14)
 bool(false)

ext/spl/tests/SplFileObject_next_variation002.phpt

@@ -26,5 +26,5 @@ echo $s->current();
 --EXPECT--
 //line 3
 //line 4
-//line 3
 //line 4
+//line 5

ext/spl/tests/bug46569.csv

@@ -0,0 +1,5 @@
+first,line
+second,line
+third,line
+fourth,line
+fifth,line

ext/spl/tests/bug46569.phpt

@@ -0,0 +1,14 @@
+--TEST--
+Bug #46569 (SplFileObject: fgetcsv after seek returns wrong line)
+--FILE--
+<?php
+$file = new SplFileObject(__DIR__ . '/bug46569.csv');
+$file->seek(1);
+print_r($file->fgetcsv());
+?>
+--EXPECT--
+Array
+(
+    [0] => second
+    [1] => line
+)

ext/spl/tests/bug62004.phpt

@@ -0,0 +1,17 @@
+--TEST--
+Bug #62004 (SplFileObject: fgets after seek returns wrong line)
+--FILE--
+<?php
+$f = new SplFileObject(__DIR__ . '/bug62004.txt');
+$f->setFlags(SplFileObject::SKIP_EMPTY);
+$f->seek(0);
+echo $f->fgets();
+$f->seek(1);
+echo $f->fgets();
+$f->seek(2);
+echo $f->fgets();
+?>
+--EXPECT--
+Line 1
+Line 2
+Line 3

ext/spl/tests/bug62004.txt

@@ -0,0 +1,4 @@
+Line 1
+Line 2
+Line 3
+Line 4

ext/spl/tests/fileobject_getcurrentline_basic.phpt

@@ -15,5 +15,5 @@ echo $s->getCurrentLine();
 echo $s->getCurrentLine();
 ?>
 --EXPECT--
+//line 2
 //line 3
-//line 4