1 files changed, 93 insertions, 0 deletions
diff --git a/src/basic/replace-var.c b/src/basic/replace-var.c
new file mode 100644
index 0000000..01c26ce
--- /dev/null
+++ b/src/basic/replace-var.c
@@ -0,0 +1,93 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include <errno.h>
+#include <stddef.h>
+#include <stdlib.h>
+
+#include "alloc-util.h"
+#include "macro.h"
+#include "replace-var.h"
+#include "string-util.h"
+
+/*
+ * Generic infrastructure for replacing @FOO@ style variables in
+ * strings. Will call a callback for each replacement.
+ */
+
+static int get_variable(const char *b, char **r) {
+        size_t k;
+        char *t;
+
+        assert(b);
+        assert(r);
+
+        if (*b != '@')
+                return 0;
+
+        k = strspn(b + 1, UPPERCASE_LETTERS "_");
+        if (k <= 0 || b[k+1] != '@')
+                return 0;
+
+        t = strndup(b + 1, k);
+        if (!t)
+                return -ENOMEM;
+
+        *r = t;
+        return 1;
+}
+
+char *replace_var(const char *text, char *(*lookup)(const char *variable, void *userdata), void *userdata) {
+        char *r, *t;
+        const char *f;
+        size_t l;
+
+        assert(text);
+        assert(lookup);
+
+        l = strlen(text);
+        r = new(char, l+1);
+        if (!r)
+                return NULL;
+
+        f = text;
+        t = r;
+        while (*f) {
+                _cleanup_free_ char *v = NULL, *n = NULL;
+                char *a;
+                int k;
+                size_t skip, d, nl;
+
+                k = get_variable(f, &v);
+                if (k < 0)
+                        goto oom;
+                if (k == 0) {
+                        *(t++) = *(f++);
+                        continue;
+                }
+
+                n = lookup(v, userdata);
+                if (!n)
+                        goto oom;
+
+                skip = strlen(v) + 2;
+
+                d = t - r;
+                nl = l - skip + strlen(n);
+                a = realloc(r, nl + 1);
+                if (!a)
+                        goto oom;
+
+                l = nl;
+                r = a;
+                t = r + d;
+
+                t = stpcpy(t, n);
+                f += skip;
+        }
+
+        *t = 0;
+        return r;
+
+oom:
+        return mfree(r);
+}