Detect which PHP SAPI the CLI binary uses during setup

Summary:
  - PHP uses a SAPI ("server API") to determine how it interacts with the caller
(e.g., how to read the environment, how to read flags, what code to execute).
  - There are several different SAPIs: cli, cgi, cgi-fcgi, apache, etc.
  - Each SAPI has different behavior -- for instance, the "cgi" SAPI emits some
CGI headers unless told not to, so a script like 'echo "x"' actually echoes some
headers and then 'x' as an HTTP body.
  - In some setups, "php" may be php-cgi.
  - If you run php-cgi as "php scriptname.php" and your ENV has an existing CGI
request in it, it runs that CGI request instead of the script. This causes an
infinite loop.
  - Add checks to verify that "php" is the "cli" SAPI binary, not some other
SAPI.
  - In particular, cPanel uses suphp and is affected by this configuration
issue. See this thread:
https://lists.marsching.com/pipermail/suphp/2008-September/002036.html

Test Plan:
  - On a cPanel + suphp machine, ran setup and was stopped for having the
"cgi-fcgi" SAPI instead of throw into an infinite loop.
  - Applied the suggested remedy, setup now runs fine.

Reviewers: btrahan, jungejason

Reviewed By: btrahan

CC: aran, btrahan, epriestley

Differential Revision: https://secure.phabricator.com/D1390

src/infrastructure/setup/PhabricatorSetup.php

@@ -147,19 +147,63 @@ class PhabricatorSetup {
       }
     }
 
-    list($err, $stdout, $stderr) = exec_manual(
+    list($err, $stdout, $stderr) = exec_manual('which php');
-      '/usr/bin/env php -r %s',
-      'exit;');
     if ($err) {
       self::writeFailure();
-      self::write("Unable to execute 'php' on the command line from the web ".
+      self::write("Unable to locate 'php' on the command line from the web ".
                   "server. Verify that 'php' is in the webserver's PATH.\n".
                   "   err: {$err}\n".
                   "stdout: {$stdout}\n".
                   "stderr: {$stderr}\n");
       return;
+    } else {
+      self::write(" okay  PHP binary found on the command line.\n");
+      $php_bin = trim($stdout);
+    }
+
+    // NOTE: In cPanel + suphp installs, 'php' may be the PHP CGI SAPI, not the
+    // PHP CLI SAPI. proc_open() will pass the environment to the child process,
+    // which will re-execute the webpage (causing an infinite number of
+    // processes to spawn). To test that the 'php' binary is safe to execute,
+    // we call php_sapi_name() using "env -i" to wipe the environment so it
+    // doesn't execute another reuqest if it's the wrong binary. We can't use
+    // "-r" because php-cgi doesn't support that flag.
+
+    $tmp_file = new TempFile('sapi.php');
+    Filesystem::writeFile($tmp_file, '<?php echo php_sapi_name();');
+
+    list($err, $stdout, $stderr) = exec_manual(
+      '/usr/bin/env -i %s -f %s',
+      $php_bin,
+      $tmp_file);
+    if ($err) {
+      self::writeFailure();
+      self::write("Unable to execute 'php' on the command line from the web ".
+                  "server.\n".
+                  "   err: {$err}\n".
+                  "stdout: {$stdout}\n".
+                  "stderr: {$stderr}\n");
+      return;
     } else {
       self::write(" okay  PHP is available from the command line.\n");
+
+      $sapi = trim($stdout);
+      if ($sapi != 'cli') {
+        self::writeFailure();
+        self::write(
+          "The 'php' binary on this system uses the '{$sapi}' SAPI, but the ".
+          "'cli' SAPI is expected. Replace 'php' with the php-cli SAPI ".
+          "binary, or edit your webserver configuration so the first 'php' ".
+          "in PATH is the 'cli' SAPI.\n\n".
+          "If you're running cPanel with suphp, the easiest way to fix this ".
+          "is to add '/usr/local/bin' before '/usr/bin' for 'env_path' in ".
+          "suconf.php:\n\n".
+          '  env_path="/bin:/usr/local/bin:/usr/bin"'.
+          "\n\n");
+        return;
+      } else {
+        self::write(" okay  'php' is CLI SAPI.\n");
+      }
     }
 
     $root = dirname(phutil_get_library_root('phabricator'));