<nss_action.h>: New abstraction for combining NSS modules and NSS actions

nss_action manages a set of lists of actions; these are the portions
of the lines in nsswitch.conf to the right of the colons, like
"dns [!UNAVAIL=return] files".  Each permutation of actions and
conditionals is cached for reuse, which limits memory growth, and
refers to the static list of modules managed by nss_modules.

Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

nss/nss_action_parse.c

@@ -0,0 +1,197 @@
+/* Parse a service line from nsswitch.conf.
+   Copyright (c) 1996-2020 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include "nss_action.h"
+#include "nss_module.h"
+
+#include <ctype.h>
+#include <string.h>
+#include <stdbool.h>
+
+/* Staging area during parsing.  */
+#define DYNARRAY_STRUCT action_list
+#define DYNARRAY_ELEMENT struct nss_action
+#define DYNARRAY_PREFIX action_list_
+#include <malloc/dynarray-skeleton.c>
+
+/* Skip whitespace in line[].  */
+#define SKIP_WS() \
+  while (line[0] != '\0' && isspace (line[0]))	\
+    ++line;
+
+/* Read the source names:
+        `( <source> ( "[" "!"? (<status> "=" <action> )+ "]" )? )*'
+   */
+static bool
+nss_action_parse (const char *line, struct action_list *result)
+{
+  while (1)
+    {
+      SKIP_WS ();
+      if (line[0] == '\0')
+        /* No more sources specified.  */
+        return true;
+
+      /* Read <source> identifier.  */
+      const char *name = line;
+      while (line[0] != '\0' && !isspace (line[0]) && line[0] != '[')
+        ++line;
+      if (name == line)
+        return true;
+
+      struct nss_action new_service
+        = { .module = __nss_module_allocate (name, line - name), };
+      if (new_service.module == NULL)
+        {
+          /* Memory allocation error.  */
+          action_list_mark_failed (result);
+          return false;
+        }
+      nss_action_set_all (&new_service, NSS_ACTION_CONTINUE);
+      nss_action_set (&new_service, NSS_STATUS_SUCCESS, NSS_ACTION_RETURN);
+      nss_action_set (&new_service, NSS_STATUS_RETURN, NSS_ACTION_RETURN);
+
+      SKIP_WS ();
+
+      if (line[0] == '[')
+        {
+          /* Read criterions.  */
+
+	  /* Skip the '['.  */
+	  ++line;
+	  SKIP_WS ();
+
+          do
+            {
+              int not;
+              enum nss_status status;
+              lookup_actions action;
+
+              /* Grok ! before name to mean all statuses but that one.  */
+              not = line[0] == '!';
+              if (not)
+                ++line;
+
+              /* Read status name.  */
+              name = line;
+              while (line[0] != '\0' && !isspace (line[0]) && line[0] != '='
+                     && line[0] != ']')
+                ++line;
+
+              /* Compare with known statuses.  */
+              if (line - name == 7)
+                {
+                  if (__strncasecmp (name, "SUCCESS", 7) == 0)
+                    status = NSS_STATUS_SUCCESS;
+                  else if (__strncasecmp (name, "UNAVAIL", 7) == 0)
+                    status = NSS_STATUS_UNAVAIL;
+                  else
+                    return false;
+                }
+              else if (line - name == 8)
+                {
+                  if (__strncasecmp (name, "NOTFOUND", 8) == 0)
+                    status = NSS_STATUS_NOTFOUND;
+                  else if (__strncasecmp (name, "TRYAGAIN", 8) == 0)
+                    status = NSS_STATUS_TRYAGAIN;
+                  else
+                    return false;
+                }
+              else
+		return false;
+
+	      SKIP_WS ();
+              if (line[0] != '=')
+                return false;
+
+	      /* Skip the '='.  */
+	      ++line;
+	      SKIP_WS ();
+              name = line;
+              while (line[0] != '\0' && !isspace (line[0]) && line[0] != '='
+                     && line[0] != ']')
+                ++line;
+
+              if (line - name == 6 && __strncasecmp (name, "RETURN", 6) == 0)
+                action = NSS_ACTION_RETURN;
+              else if (line - name == 8
+                       && __strncasecmp (name, "CONTINUE", 8) == 0)
+                action = NSS_ACTION_CONTINUE;
+              else if (line - name == 5
+                       && __strncasecmp (name, "MERGE", 5) == 0)
+                action = NSS_ACTION_MERGE;
+              else
+                return false;
+
+              if (not)
+                {
+                  /* Save the current action setting for this status,
+                     set them all to the given action, and reset this one.  */
+                  const lookup_actions save
+                    = nss_action_get (&new_service, status);
+                  nss_action_set_all (&new_service, action);
+                  nss_action_set (&new_service, status, save);
+                }
+              else
+                nss_action_set (&new_service, status, action);
+
+	      SKIP_WS ();
+            }
+          while (line[0] != ']');
+
+          /* Skip the ']'.  */
+          ++line;
+        }
+
+      action_list_add (result, new_service);
+    }
+}
+
+nss_action_list
+ __nss_action_parse (const char *line)
+{
+  struct action_list list;
+  action_list_init (&list);
+  if (nss_action_parse (line, &list))
+    {
+      size_t size = action_list_size (&list);
+      nss_action_list result
+        = malloc (sizeof (*result) * (size + 1));
+      if (result == NULL)
+        {
+          action_list_free (&list);
+          return NULL;
+        }
+      memcpy (result, action_list_begin (&list), sizeof (*result) * size);
+      /* Sentinel.  */
+      result[size].module = NULL;
+      return result;
+    }
+  else if (action_list_has_failed (&list))
+    {
+      /* Memory allocation error.  */
+      __set_errno (ENOMEM);
+      return NULL;
+    }
+  else
+    {
+      /* Parse error.  */
+      __set_errno (EINVAL);
+      return NULL;
+    }
+}