util: add creds-util.[ch] with helpers for dealing with credentials

src/basic/creds-util.c

@@ -0,0 +1,54 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include "creds-util.h"
+#include "fd-util.h"
+#include "fileio.h"
+#include "path-util.h"
+
+bool credential_name_valid(const char *s) {
+        /* We want that credential names are both valid in filenames (since that's our primary way to pass
+         * them around) and as fdnames (which is how we might want to pass them around eventually) */
+        return filename_is_valid(s) && fdname_is_valid(s);
+}
+
+int get_credentials_dir(const char **ret) {
+        const char *e;
+
+        assert(ret);
+
+        e = secure_getenv("CREDENTIALS_DIRECTORY");
+        if (!e)
+                return -ENXIO;
+
+        if (!path_is_absolute(e) || !path_is_normalized(e))
+                return -EINVAL;
+
+        *ret = e;
+        return 0;
+}
+
+int read_credential(const char *name, void **ret, size_t *ret_size) {
+        _cleanup_free_ char *fn = NULL;
+        const char *d;
+        int r;
+
+        assert(ret);
+
+        if (!credential_name_valid(name))
+                return -EINVAL;
+
+        r = get_credentials_dir(&d);
+        if (r < 0)
+                return r;
+
+        fn = path_join(d, name);
+        if (!fn)
+                return -ENOMEM;
+
+        return read_full_file_full(
+                        AT_FDCWD, fn,
+                        UINT64_MAX, SIZE_MAX,
+                        READ_FULL_FILE_SECURE,
+                        NULL,
+                        (char**) ret, ret_size);
+}

src/basic/creds-util.h

@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+#pragma once
+
+#include <inttypes.h>
+#include <stdbool.h>
+#include <sys/types.h>
+
+bool credential_name_valid(const char *s);
+
+int get_credentials_dir(const char **ret);
+
+int read_credential(const char *name, void **ret, size_t *ret_size);

src/basic/meson.build

@@ -35,6 +35,8 @@ basic_sources = files('''
         conf-files.h
         copy.c
         copy.h
+        creds-util.c
+        creds-util.h
         def.h
         device-nodes.c
         device-nodes.h

src/basic/path-util.c

@@ -1190,9 +1190,3 @@ bool prefixed_path_strv_contains(char **l, const char *path) {
 
         return false;
 }
-
-bool credential_name_valid(const char *s) {
-        /* We want that credential names are both valid in filenames (since that's our primary way to pass
-         * them around) and as fdnames (which is how we might want to pass them around eventually) */
-        return filename_is_valid(s) && fdname_is_valid(s);
-}

src/basic/path-util.h

@@ -183,5 +183,3 @@ static inline const char *empty_to_root(const char *path) {
 
 bool path_strv_contains(char **l, const char *path);
 bool prefixed_path_strv_contains(char **l, const char *path);
-
-bool credential_name_valid(const char *s);