Add strbuf_tohex() primitive

strbuf.c

@@ -69,6 +69,24 @@ strbuf strbuf_puts(strbuf sb, const char *text)
   return sb;
 }
 
+strbuf strbuf_tohex(strbuf sb, const unsigned char *data, size_t len)
+{
+  static char hexdigit[16] = {'0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F'};
+  char *p = sb->current;
+  sb->current += len * 2;
+  if (sb->start) {
+    char *e = sb->current < sb->end ? sb->current : sb->end;
+    // The following loop could overwrite the '\0' at *sp->end.
+    for (; p < e; ++data) {
+      *p++ = hexdigit[*data >> 4];
+      *p++ = hexdigit[*data & 0xf];
+    }
+    // This will restore the '\0' at *sp->end if it was overwritten.
+    *e = '\0';
+  }
+  return sb;
+}
+
 strbuf strbuf_putc(strbuf sb, char ch)
 {
   if (sb->start && sb->current < sb->end) {

strbuf.h

@@ -254,6 +254,23 @@ strbuf strbuf_ncat(strbuf sb, const char *text, size_t len);
 strbuf strbuf_puts(strbuf sb, const char *text);
 
 
+/** Append binary data strbuf, in uppercase hexadecimal format, truncating if
+ * necessary to avoid buffer overrun.  Return a pointer to the strbuf.
+ *
+ * After these operations:
+ *      n = strbuf_len(sb);
+ *      c = strbuf_count(sb);
+ *      strbuf_tohex(data, len);
+ * the following invariants hold:
+ *      strbuf_count(sb) == c + len * 2
+ *      strbuf_len(sb) >= n
+ *      strbuf_len(sb) <= n + len * 2
+ *
+ * @author Andrew Bettison <andrew@servalproject.com>
+ */
+strbuf strbuf_tohex(strbuf sb, const unsigned char *data, size_t len);
+
+
 /** Append a single character to the strbuf if there is space, and place a
  * terminating nul after it.  Return a pointer to the strbuf so that
  * concatenations can be chained in a single line.