vtls: Refactor Curl_multissl_version to make the code clearer

Reported-by: Johannes Schindelin

Ref: https://github.com/curl/curl/pull/3863#pullrequestreview-241395121

Closes https://github.com/curl/curl/pull/4803

1 files changed, 21 insertions, 16 deletions

diff --git a/lib/vtls/vtls.c b/lib/vtls/vtls.c
index c493b1516..9d194f8ba 100644
--- a/lib/vtls/vtls.c
+++ b/lib/vtls/vtls.c
@@ -1236,7 +1236,7 @@ static size_t Curl_multissl_version(char *buffer, size_t size)
 {
   static const struct Curl_ssl *selected;
   static char backends[200];
-  static size_t total;
+  static size_t backends_len;
   const struct Curl_ssl *current;
 
   current = Curl_ssl == &Curl_ssl_multi ? available_backends[0] : Curl_ssl;
@@ -1248,27 +1248,32 @@ static size_t Curl_multissl_version(char *buffer, size_t size)
 
     selected = current;
 
-    for(i = 0; available_backends[i] && p < (end - 4); i++) {
-      if(i)
-        *(p++) = ' ';
-      if(selected != available_backends[i])
-        *(p++) = '(';
-      p += available_backends[i]->version(p, end - p - 2);
-      if(selected != available_backends[i])
-        *(p++) = ')';
+    backends[0] = '\0';
+
+    for(i = 0; available_backends[i]; ++i) {
+      char vb[200];
+      bool paren = (selected != available_backends[i]);
+
+      if(available_backends[i]->version(vb, sizeof(vb))) {
+        p += msnprintf(p, end - p, "%s%s%s%s", (p != backends ? " " : ""),
+                       (paren ? "(" : ""), vb, (paren ? ")" : ""));
+      }
     }
-    *p = '\0';
-    total = p - backends;
+
+    backends_len = p - backends;
   }
 
-  if(size > total)
-    memcpy(buffer, backends, total + 1);
-  else {
-    memcpy(buffer, backends, size - 1);
+  if(!size)
+    return 0;
+
+  if(size <= backends_len) {
+    strncpy(buffer, backends, size - 1);
     buffer[size - 1] = '\0';
+    return size - 1;
   }
 
-  return CURLMIN(size - 1, total);
+  strcpy(buffer, backends);
+  return backends_len;
 }
 
 static int multissl_init(const struct Curl_ssl *backend)