From c862d84d0b6827106a53bc571c81eb523b05c50f Mon Sep 17 00:00:00 2001
From: Xavier Del Campo Romero <xavi.dcr@tutanota.com>
Date: Thu, 8 Oct 2020 08:41:22 +0200
Subject: [PATCH] Add dynstr_vprepend

---
 dynstr.c         | 73 +++++++++++++++++++++++-------------------------
 include/dynstr.h | 13 +++++++++
 2 files changed, 48 insertions(+), 38 deletions(-)

diff --git a/dynstr.c b/dynstr.c
index e9ef185..92930f2 100644
--- a/dynstr.c
+++ b/dynstr.c
@@ -60,49 +60,46 @@ enum dynstr_err dynstr_append(struct dynstr *const d, const char *const format,
     return dynstr_vappend(d, format, ap);
 }
 
+enum dynstr_err dynstr_vprepend(struct dynstr *const d, const char *const format, va_list ap)
+{
+    const size_t src_len = vsnprintf(NULL, 0, format, ap);
+    const size_t new_len = d->len + src_len + 1;
+
+    d->str = realloc(d->str, new_len * sizeof *d->str);
+
+    if (d->str && d->len)
+    {
+        /* Keep byte that will be removed by later call to vsprintf. */
+        const char c = *d->str;
+
+        for (size_t i = new_len - 1, j = d->len; j <= d->len; i--, j--)
+        {
+            d->str[i] = d->str[j];
+        }
+
+        vsprintf(d->str, format, ap);
+        d->str[src_len] = c;
+    }
+    else if (!d->len)
+    {
+        vsprintf(d->str + d->len, format, ap);
+    }
+    else
+    {
+        return DYNSTR_ERR_ALLOC;
+    }
+
+    va_end(ap);
+    d->len += src_len;
+    return DYNSTR_OK;
+}
+
 enum dynstr_err dynstr_prepend(struct dynstr *const d, const char *const format, ...)
 {
     va_list ap;
 
     va_start(ap, format);
-
-    {
-        const size_t src_len = vsnprintf(NULL, 0, format, ap);
-        const size_t new_len = d->len + src_len + 1;
-        va_end(ap);
-
-        d->str = realloc(d->str, new_len * sizeof *d->str);
-
-        if (d->str && d->len)
-        {
-            /* Keep byte that will be removed by later call to vsprintf. */
-            const char c = *d->str;
-
-            for (size_t i = new_len - 1, j = d->len; j <= d->len; i--, j--)
-            {
-                d->str[i] = d->str[j];
-            }
-
-            va_start(ap, format);
-            vsprintf(d->str, format, ap);
-            va_end(ap);
-            d->str[src_len] = c;
-        }
-        else if (!d->len)
-        {
-            va_start(ap, format);
-            vsprintf(d->str + d->len, format, ap);
-            va_end(ap);
-        }
-        else
-        {
-            return DYNSTR_ERR_ALLOC;
-        }
-
-        d->len += src_len;
-    }
-
-    return DYNSTR_OK;
+    return dynstr_vprepend(d, format, ap);
 }
 
 enum dynstr_err dynstr_dup(struct dynstr *const dst, const struct dynstr *const src)
diff --git a/include/dynstr.h b/include/dynstr.h
index 2c36865..38c05c5 100644
--- a/include/dynstr.h
+++ b/include/dynstr.h
@@ -134,6 +134,19 @@ enum dynstr_err dynstr_vappend(struct dynstr *d, const char *format, va_list ap)
  */
 enum dynstr_err dynstr_prepend(struct dynstr *d, const char *format, ...);
 
+/**
+ * This function takes a string literal in printf format and a variable
+ * argument list, calculates its size and prepends it into the beginning of the
+ * dynamic string.
+ * @param d Dynamic string where new string will be prepended.
+ * @param format String literal in printf format.
+ * @param ap Variable argument list.
+ * @return Returns one of the following error codes:
+ *    # DYNSTR_OK if successful.
+ *    # DYNSTR_ERR_ALLOC if no more memory is available.
+ */
+enum dynstr_err dynstr_vprepend(struct dynstr *d, const char *format, va_list ap);
+
 /**
  * This function duplicates a dynamic string to another instance.
  * @attention Destination instance must be initialized before calling