Add PTY support to proc_open (again after 16 long years)

alexdowad · alexdowad · commit 6329dc97733e · 2020-05-04T22:55:59.000+02:00
Back in 2004, a feature was added to proc_open which allowed it to open a PTY, connecting specific FDs in the child process to the slave end of the PTY and returning the master end of the PTY (wrapped as a PHP stream) in the `$pipes` array. However, this feature was disabled just about a month later. Little information is available about why this was done, but from talking to the original implementer, it seems there were portability problems with some rare flavors of Unix. Re-enable this feature with a simplified implementation which uses openpty(). No attempt is made to support PTYs if the platform does not have openpty(). The configure script checks if linking with -lutil is necessary to use openpty(), but if anything else is required, like including some special header or linking with some other library, PTY support will be disabled. The original PTY support for proc_open automatically daemonized the child process (disassociating it from the TTY session and process group of the parent). However, I don't think this is a good idea. Just because a user opens a child process in a PTY, it doesn't mean they want it to continue running even when the parent process is killed. Of course, if the child process is some kind of server, it will likely daemonize itself; but we have no reason to preempt that decision. It turns out that since 2015, there has been one test case for PTY support in proc_open() in the test suite. This test was added in GitHub PR #1588 (#1588). That PR mentioned that the PHP binary in the Debian/Ubuntu repositories is patched to *enable* PTY support. Checking the Debian PHP repository (https://salsa.debian.org/php-team/php.git) shows that this is still true. Debian's patch does not modify the implementation from 2004 in any way; it just removes the #if 0 line which disables it. Naturally, the test case is skipped if PTY support is not enabled. This means that ever since it was added, every test run against the 'vanilla' PHP codebase has skipped it. Interestingly, the test case which was added in 2015 fails on my Linux Mint PC... both with this simplified implementation *and* when enabling the original implementation. Investigation reveals the reason: when the child process using the slave end of the PTY exits and its FDs are all closed, and all buffered data is read from the master end of the PTY, any further attempt to read from the master end fails with EIO. The test case seems to expect that reading from the master end will always return an empty string if no data is available. Could this mean that on the platform where this test case was originally developed, the PHP parent process ran *faster* than the child process, so that all the calls to fread() complete before the child process exits and closes its FDs? Or could something else about the platform have been different, such that read() in the parent does not fail with EIO even after the child process exits? Another question: Are the Debian packagers even running this test case every time they build PHP binaries? Intriguing questions, these! There may be another way out of this sticky dilemma: IF at least one FD referring to the slave end of the PTY is kept open *in the parent process*, the failure with EIO will not occur even after the child process exits. This might be a good approach, though we would need a way to ensure the FD will be closed eventually in long-running programs. Perhaps associate it with the proc resource and close it when the proc is freed or explicitly closed with proc_close? And the rabbit hole goes deeper. Although (for now) the test case from 2015 has been updated so it does not attempt to fread() multiple times from the PTY, it still fails intermittently. The reason? When the child process writes "foo\n" to the PTY, the parent sometimes receives "foo" (3 bytes) and sometimes "foo\r\n" (5 bytes). The "\r" is obviously from the TTY line discipline converting "\n" to "\r\n", but why on earth would the parent sometimes read the newline and sometimes not? What is more, strace clearly shows that this is happening *in the kernel*. The child process always executes a single write("foo\n") syscall, but when the blocking read() syscall issued by the parent process returns, sometimes it returns "foo" and sometimes "foo\r\n". This doesn't happen when I extract the test code and run it directly from the PHP CLI, only when the test case is run by run-tests.php. Thanks to Nikita Popov for suggesting that we should just use openpty() rather than grantpt(), unlockpt(), etc.
diff --git a/configure.ac b/configure.ac
@@ -566,7 +566,6 @@ getgrnam_r \
 getpwuid_r \
 getwd \
 glob \
-grantpt \
 inet_ntoa \
 inet_ntop \
 inet_pton \
@@ -578,7 +577,6 @@ mmap \
 nice \
 nl_langinfo \
 poll \
-ptsname \
 putenv \
 scandir \
 setitimer \
@@ -594,7 +592,6 @@ strptime \
 strtok_r \
 symlink \
 tzset \
-unlockpt \
 unsetenv \
 usleep \
 utime \
@@ -713,6 +710,9 @@ if test "$PHP_VALGRIND" != "no"; then
   fi
 fi
 
+dnl Check for openpty. It may require linking against libutil.
+PHP_CHECK_FUNC(openpty, util)
+
 dnl General settings.
 dnl ----------------------------------------------------------------------------
 PHP_CONFIGURE_PART(General settings)
diff --git a/ext/standard/proc_open.c b/ext/standard/proc_open.c
@@ -43,10 +43,8 @@
  * */
 #ifdef PHP_CAN_SUPPORT_PROC_OPEN
 
-#if 0 && HAVE_PTSNAME && HAVE_GRANTPT && HAVE_UNLOCKPT && HAVE_SYS_IOCTL_H && HAVE_TERMIOS_H
-# include <sys/ioctl.h>
-# include <termios.h>
-# define PHP_CAN_DO_PTS	1
+#if HAVE_OPENPTY
+#include <pty.h>
 #endif
 
 #include "proc_open.h"
@@ -592,6 +590,27 @@ static int set_proc_descriptor_to_blackhole(struct php_proc_open_descriptor_item
 	return SUCCESS;
 }
 
+static int set_proc_descriptor_to_pty(struct php_proc_open_descriptor_item *desc, int *master_fd, int *slave_fd)
+{
+#if HAVE_OPENPTY
+	if (*master_fd == -1) {
+		if (openpty(master_fd, slave_fd, NULL, NULL, NULL)) {
+			php_error_docref(NULL, E_WARNING, "Could not open PTY (pseudoterminal) - %s", strerror(errno));
+			return FAILURE;
+		}
+	}
+
+	desc->is_pipe    = 1;
+	desc->childend   = dup(*slave_fd);
+	desc->parentend  = dup(*master_fd);
+	desc->mode_flags = O_RDWR;
+	return SUCCESS;
+#else
+	php_error_docref(NULL, E_WARNING, "PTY (pseudoterminal) not supported on this system");
+	return FAILURE;
+#endif
+}
+
 static int set_proc_descriptor_to_pipe(struct php_proc_open_descriptor_item *desc, zend_string *zmode)
 {
 	php_file_descriptor_t newpipe[2];
@@ -708,9 +727,9 @@ static int redirect_proc_descriptor(struct php_proc_open_descriptor_item *desc,
 	return dup_proc_descriptor(redirect_to, &desc->childend, nindex);
 }
 
-
 int set_proc_descriptor_from_array(
-		zval *descitem, struct php_proc_open_descriptor_item *descriptors, int ndesc, int nindex) {
+		zval *descitem, struct php_proc_open_descriptor_item *descriptors, int ndesc,
+		int nindex, int *pty_master_fd, int *pty_slave_fd) {
 	zend_string *ztype = get_string_parameter(descitem, 0, "handle qualifier");
 	if (!ztype) {
 		return FAILURE;
@@ -749,32 +768,7 @@ int set_proc_descriptor_from_array(
 	} else if (zend_string_equals_literal(ztype, "null")) {
 		retval = set_proc_descriptor_to_blackhole(&descriptors[ndesc]);
 	} else if (zend_string_equals_literal(ztype, "pty")) {
-#if PHP_CAN_DO_PTS
-		if (dev_ptmx == -1) {
-			/* open things up */
-			dev_ptmx = open("/dev/ptmx", O_RDWR);
-			if (dev_ptmx == -1) {
-				php_error_docref(NULL, E_WARNING, "Failed to open /dev/ptmx, errno %d", errno);
-				goto finish;
-			}
-			grantpt(dev_ptmx);
-			unlockpt(dev_ptmx);
-			slave_pty = open(ptsname(dev_ptmx), O_RDWR);
-
-			if (slave_pty == -1) {
-				php_error_docref(NULL, E_WARNING, "Failed to open slave pty, errno %d", errno);
-				goto finish;
-			}
-		}
-		descriptors[ndesc].is_pipe = 1;
-		descriptors[ndesc].childend = dup(slave_pty);
-		descriptors[ndesc].parentend = dup(dev_ptmx);
-		descriptors[ndesc].mode_flags = O_RDWR;
-		retval = SUCCESS;
-#else
-		php_error_docref(NULL, E_WARNING, "PTY pseudo terminal not supported on this system");
-		goto finish;
-#endif
+		retval = set_proc_descriptor_to_pty(&descriptors[ndesc], pty_master_fd, pty_slave_fd);
 	} else {
 		php_error_docref(NULL, E_WARNING, "%s is not a valid descriptor spec/mode", ZSTR_VAL(ztype));
 		goto finish;
@@ -867,14 +861,10 @@ PHP_FUNCTION(proc_open)
 #else
 	char **argv = NULL;
 #endif
+	int pty_master_fd = -1, pty_slave_fd = -1;
 	php_process_id_t child;
 	struct php_process_handle *proc;
 
-#if PHP_CAN_DO_PTS
-	php_file_descriptor_t dev_ptmx = -1;	/* master */
-	php_file_descriptor_t slave_pty = -1;
-#endif
-
 	ZEND_PARSE_PARAMETERS_START(3, 6)
 		Z_PARAM_ZVAL(command_zv)
 		Z_PARAM_ARRAY(descriptorspec)
@@ -957,7 +947,8 @@ PHP_FUNCTION(proc_open)
 				goto exit_fail;
 			}
 		} else if (Z_TYPE_P(descitem) == IS_ARRAY) {
-			if (set_proc_descriptor_from_array(descitem, descriptors, ndesc, nindex) == FAILURE) {
+			if (set_proc_descriptor_from_array(descitem, descriptors, ndesc, nindex,
+				                                 &pty_master_fd, &pty_slave_fd) == FAILURE) {
 				goto exit_fail;
 			}
 		} else {
@@ -1044,27 +1035,6 @@ PHP_FUNCTION(proc_open)
 	if (child == 0) {
 		/* this is the child process */
 
-#if PHP_CAN_DO_PTS
-		if (dev_ptmx >= 0) {
-			int my_pid = getpid();
-
-#ifdef TIOCNOTTY
-			/* detach from original tty. Might only need this if isatty(0) is true */
-			ioctl(0,TIOCNOTTY,NULL);
-#else
-			setsid();
-#endif
-			/* become process group leader */
-			setpgid(my_pid, my_pid);
-			tcsetpgrp(0, my_pid);
-		}
-
-		if (dev_ptmx >= 0) {
-			close(dev_ptmx);
-			close(slave_pty);
-		}
-#endif
-
 		if (close_parent_ends_of_pipes_in_child(descriptors, ndesc) == FAILURE) {
 			/* We are already in child process and can't do anything to make
 			 *   proc_open() return an error in the parent
@@ -1121,13 +1091,6 @@ PHP_FUNCTION(proc_open)
 #endif
 	proc->env = env;
 
-#if PHP_CAN_DO_PTS
-	if (dev_ptmx >= 0) {
-		close(dev_ptmx);
-		close(slave_pty);
-	}
-#endif
-
 	/* clean up all the child ends and then open streams on the parent
 	 * ends, where appropriate */
 	for (i = 0; i < ndesc; i++) {
@@ -1191,7 +1154,14 @@ PHP_FUNCTION(proc_open)
 #else
 	efree_argv(argv);
 #endif
-
+#if HAVE_OPENPTY
+	if (pty_master_fd != -1) {
+		close(pty_master_fd);
+	}
+	if (pty_slave_fd != -1) {
+		close(pty_slave_fd);
+	}
+#endif
 	efree(descriptors);
 	ZVAL_RES(return_value, zend_register_resource(proc, le_proc_open));
 	return;
@@ -1211,12 +1181,12 @@ PHP_FUNCTION(proc_open)
 #else
 	efree_argv(argv);
 #endif
-#if PHP_CAN_DO_PTS
-	if (dev_ptmx >= 0) {
-		close(dev_ptmx);
+#if HAVE_OPENPTY
+	if (pty_master_fd != -1) {
+		close(pty_master_fd);
 	}
-	if (slave_pty >= 0) {
-		close(slave_pty);
+	if (pty_slave_fd != -1) {
+		close(pty_slave_fd);
 	}
 #endif
 	RETURN_FALSE;
diff --git a/ext/standard/tests/file/bug69442.phpt b/ext/standard/tests/file/bug69442.phpt
@@ -17,7 +17,7 @@ EOC;
     $output = join("\n", $output);
     unlink($tmpFile);
 
-    if (strstr($output, "PTY pseudo terminal not supported on this system") !== false) {
+    if (strstr($output, "PTY (pseudoterminal) not supported on this system") !== false) {
         die("skip PTY pseudo terminals are not supported");
     }
 --FILE--
@@ -28,17 +28,18 @@ $pipes = array();
 
 $process = proc_open($cmd, $descriptors, $pipes);
 
-foreach ($pipes as $type => $pipe) {
-    $data = fread($pipe, 999);
-    echo 'type ' . $type . ' ';
-    var_dump($data);
-    fclose($pipe);
-}
+$data0 = fread($pipes[0], 100);
+echo 'read from pipe 0: ';
+var_dump($data0);
+fclose($pipes[0]);
+
+$data3 = fread($pipes[3], 100);
+echo 'read from pipe 3: ';
+var_dump($data3);
+fclose($pipes[3]);
+
 proc_close($process);
 --EXPECT--
-type 0 string(5) "foo
-"
-type 1 string(0) ""
-type 2 string(0) ""
-type 3 string(3) "42
+read from pipe 0: string(3) "foo"
+read from pipe 3: string(3) "42
 "
