From d95163270e022fe87ece0c151c2987fd62274ba8 Mon Sep 17 00:00:00 2001
From: Dirk Engling <erdgeist@erdgeist.org>
Date: Sat, 24 Oct 2026 05:25:05 +0200
Subject: Add a dedicated ranged unsigned int scanner and a bencoded variant

---
 ot_scan.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
 ot_scan.h | 21 +++++++++++++++++++++
 2 files changed, 65 insertions(+)
 create mode 100644 ot_scan.c
 create mode 100644 ot_scan.h

diff --git a/ot_scan.c b/ot_scan.c
new file mode 100644
index 0000000..a96f82b
--- /dev/null
+++ b/ot_scan.c
@@ -0,0 +1,44 @@
+/* This software was written by Dirk Engling <erdgeist@erdgeist.org>
+   It is considered beerware. Prost. Skol. Cheers or whatever.
+
+   $id$ */
+
+/* System */
+#include <errno.h>
+#include <stdint.h>
+#include <stdlib.h>
+
+/* Opentracker */
+#include "ot_scan.h"
+
+size_t scan_udec(const char *src, uint64_t *dest, uint64_t max) {
+  unsigned long long value;
+  char              *end;
+
+  if (*src < '0' || *src > '9')
+    return 0;
+
+  errno = 0;
+  value = strtoull(src, &end, 10);
+
+  if (errno == ERANGE || value > (unsigned long long)max)
+    return 0;
+
+  *dest = (uint64_t)value;
+  return (size_t)(end - src);
+}
+
+size_t scan_udec_bencode(const char *src, uint64_t *dest, uint64_t max) {
+  uint64_t value;
+  size_t   consumed = scan_udec(src, &value, max);
+
+  /* bencode writes no leading zeros, so anything longer than a single digit
+     must not begin with one. */
+  if (consumed > 1 && *src == '0')
+    return 0;
+
+  if (consumed)
+    *dest = value;
+
+  return consumed;
+}
diff --git a/ot_scan.h b/ot_scan.h
new file mode 100644
index 0000000..860a088
--- /dev/null
+++ b/ot_scan.h
@@ -0,0 +1,21 @@
+/* This software was written by Dirk Engling <erdgeist@erdgeist.org>
+   It is considered beerware. Prost. Skol. Cheers or whatever.
+
+   $id$ */
+
+#ifndef OT_SCAN_H__
+#define OT_SCAN_H__
+
+#include <stddef.h>
+#include <stdint.h>
+
+/* Read an unsigned decimal number from src into dest and return how many
+   characters were consumed. Returns zero and leaves dest untouched when src
+   does not begin with a digit, or when the value would exceed max. */
+size_t scan_udec(const char *src, uint64_t *dest, uint64_t max);
+
+/* As scan_udec, but following the bencode integer grammar, which permits a
+   leading zero on zero alone. */
+size_t scan_udec_bencode(const char *src, uint64_t *dest, uint64_t max);
+
+#endif
-- 
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