Fix bugs in strbuf_ncat(), strbuf_puts() and strbuf_putc()

Were not advancing the 'current' pointer the entire length of the appended text

strbuf.c

@@ -45,9 +45,11 @@ strbuf strbuf_ncat(strbuf sb, const char *text, size_t len)
 {
   if (sb->start && sb->current < sb->end) {
     register size_t n = min(sb->end - sb->current, len);
-    while (n-- && (*sb->current = *text++))
-      ++sb->current;
+    char *c;
+    for (c = sb->current; n-- && (*c = *text); ++c, ++text)
+      ;
   }
+  sb->current += len;
   return sb;
 }
 
@@ -55,8 +57,14 @@ strbuf strbuf_puts(strbuf sb, const char *text)
 {
   if (sb->start && sb->current < sb->end) {
     register size_t n = sb->end - sb->current;
-    while (n-- && (*sb->current = *text++))
+    while (n-- && (*sb->current = *text)) {
       ++sb->current;
+      ++text;
+    }
+  }
+  while (*text) {
+    ++sb->current;
+    ++text;
   }
   return sb;
 }
@@ -66,7 +74,8 @@ strbuf strbuf_putc(strbuf sb, char ch)
   if (sb->start && sb->current < sb->end) {
     *sb->current++ = ch;
     *sb->current = '\0';
-  }
+  } else
+    ++sb->current;
   return sb;
 }
 
@@ -111,16 +120,15 @@ char *strbuf_substr(const_strbuf sb, int offset)
 
 strbuf strbuf_trunc(strbuf sb, int offset)
 {
-  char *s;
   if (offset < 0) {
-    s = (sb->current < sb->end ? sb->current : sb->end) + offset;
-    if (s < sb->start)
-      s = sb->start;
+    char *e = sb->current < sb->end ? sb->current : sb->end;
+    sb->current = offset <= sb->start - e ? sb->start : e + offset;
   } else {
-    s = sb->start + offset;
-    if (s > sb->end)
-      s = sb->end;
+    char *s = sb->start + offset;
+    if (s < sb->current)
+      sb->current = s;
   }
-  sb->current = s;
+  if (sb->start && sb->current < sb->end)
+    *sb->current = '\0';
   return sb;
 }

strbuf.h

@@ -318,21 +318,26 @@ char *strbuf_substr(const_strbuf sb, int offset);
  * and the string's length truncated accordingly.  Return a pointer to the
  * strbuf so that operations can be chained in a single line.
  *
- * After the operation:
+ * After the operations:
+ *      count = strbuf_count(sb);
  *      len = strbuf_len(sb);
  *      strbuf_trunc(sb, off);
  * the following invariants hold:
- * where len <= off, sb is unchanged;
- * where 0 <= off < len:
+ *  if count <= off, sb is unchanged:
+ *      strbuf_count(sb) == count
+ *      strbuf_len(sb) == len
+ *  if len <= off < count:
+ *      strbuf_count(sb) == off
+ *      strbuf_len(sb) == len
+ *  if 0 <= off < len:
  *      strbuf_count(sb) == off
  *      strbuf_len(sb) == off
- * where -len <= off < 0:
+ *  if -len <= off < 0:
  *      strbuf_count(sb) == len + off
  *      strbuf_len(sb) == len + off
- * where off < -len:
+ *  if off < -len:
  *      strbuf_count(sb) == 0
  *      strbuf_len(sb) == 0
- *      strbuf_str(sb)[0] == '\0'
  *
  * @author Andrew Bettison <andrew@servalproject.com>
  */