e2e: get_random

Allocate a blob of memory and fill it with random data.
(There must be some existing portable function for this?!)

Signed-off-by: Dr. David Alan Gilbert <dave@treblig.org>

1 files changed, 20 insertions, 0 deletions

diff --git a/matrix-e2e.c b/matrix-e2e.c
index dbd7dd1..2e3acd9 100644
--- a/matrix-e2e.c
+++ b/matrix-e2e.c
@@ -22,6 +22,7 @@
 #include "matrix-api.h"
 #include "matrix-e2e.h"
 #include "matrix-json.h"
+#include "debug.h"
 
 /* json-glib */
 #include <json-glib/json-glib.h>
@@ -50,6 +51,25 @@ static void clear_mem(volatile char *data, size_t len)
 #endif
 }
 
+/* Returns a pointer to a freshly allocated buffer of 'n' bytes of random data.
+ * If it fails it returns NULL.
+ * TODO: There must be some portable function we can call to do this.
+ */
+static void *get_random(size_t n)
+{
+    FILE *urandom = fopen("/dev/urandom", "rb");
+    if (!urandom) {
+        return NULL;
+    }
+    void *buffer = g_malloc(n);
+    if (fread(buffer, 1, n, urandom) != n) {
+        g_free(buffer);
+        buffer = NULL;
+    }
+    fclose(urandom);
+    return buffer;
+}
+
 /* Sign the JsonObject with olm_account_sign and add it to the object
  * as a 'signatures' member of the top level object.
  * 0 on success