From 400a92fa0461d128cc0a74e9a0f6fde48854850f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20Ekl=C3=B6f?= <daniel@ekloef.se>
Date: Mon, 7 Jan 2019 18:26:48 +0100
Subject: [PATCH] tag: rename and rewrite sbuf_strcat()

In particular, don't use strncat() with a length derived from the
source.
---
 tag.c | 30 ++++++++++++++----------------
 1 file changed, 14 insertions(+), 16 deletions(-)

diff --git a/tag.c b/tag.c
index 86b8406..5a3e40e 100644
--- a/tag.c
+++ b/tag.c
@@ -373,27 +373,25 @@ struct sbuf {
 };
 
 static void
-sbuf_strncat(struct sbuf *s1, const char *s2, size_t n)
+sbuf_append_at_most(struct sbuf *s1, const char *s2, size_t n)
 {
-    size_t s2_actual_len = strlen(s2);
-    size_t s2_len = s2_actual_len < n ? s2_actual_len : n;
-
-    if (s1->len + s2_len >= s1->size) {
-        size_t required_size = s1->len + s2_len + 1;
+    if (s1->len + n >= s1->size) {
+        size_t required_size = s1->len + n + 1;
         s1->size = 2 * required_size;
 
         s1->s = realloc(s1->s, s1->size);
-        s1->s[s1->len] = '\0';
+        //s1->s[s1->len] = '\0';
     }
 
-    strncat(s1->s, s2, s2_len);
-    s1->len += s2_len;
+    memcpy(&s1->s[s1->len], s2, n);
+    s1->len += n;
+    s1->s[s1->len] = '\0';
 }
 
 static void
-sbuf_strcat(struct sbuf *s1, const char *s2)
+sbuf_append(struct sbuf *s1, const char *s2)
 {
-    sbuf_strncat(s1, s2, strlen(s2));
+    sbuf_append_at_most(s1, s2, strlen(s2));
 }
 
 char *
@@ -409,7 +407,7 @@ tags_expand_template(const char *template, const struct tag_set *tags)
 
         if (begin == NULL) {
             /* No more tags, copy remaining characters */
-            sbuf_strcat(&formatted, template);
+            sbuf_append(&formatted, template);
             break;
         }
 
@@ -417,7 +415,7 @@ tags_expand_template(const char *template, const struct tag_set *tags)
         const char *end = strchr(begin, '}');
         if (end == NULL) {
             /* Wasn't actually a tag, copy as-is instead */
-            sbuf_strncat(&formatted, template, begin - template + 1);
+            sbuf_append_at_most(&formatted, template, begin - template + 1);
             template = begin + 1;
             continue;
         }
@@ -431,17 +429,17 @@ tags_expand_template(const char *template, const struct tag_set *tags)
         const struct tag *tag = tag_for_name(tags, tag_name);
         if (tag == NULL) {
             /* No such tag, copy as-is instead */
-            sbuf_strncat(&formatted, template, begin - template + 1);
+            sbuf_append_at_most(&formatted, template, begin - template + 1);
             template = begin + 1;
             continue;
         }
 
         /* Copy characters preceeding the tag (name) */
-        sbuf_strncat(&formatted, template, begin - template);
+        sbuf_append_at_most(&formatted, template, begin - template);
 
         /* Copy tag value */
         const char *value = tag->as_string(tag);
-        sbuf_strcat(&formatted, value);
+        sbuf_append(&formatted, value);
 
         /* Skip past tag name + closing '}' */
         template = end + 1;