diff --git a/include/ucore/dstr.h b/include/ucore/dstr.h
index 33f7be2..77e462d 100644
--- a/include/ucore/dstr.h
+++ b/include/ucore/dstr.h
@@ -2,6 +2,7 @@
 #define UC_DSTR_H_
 
 #include <stddef.h>
+#include <stdarg.h>
 
 #ifdef __cplusplus
 extern "C" {
@@ -134,6 +135,12 @@ size_t uc_dstr_replace(struct DStr *str, char f, char r);
  */
 void uc_dstr_trim(struct DStr *str);
 
+/** Append formatted string (just as sprintf)*/
+int uc_dstr_sprintf(struct DStr *str, const char *fmt, ...) __attribute__((format(printf,2,3)));
+
+/** va_list variant */
+int uc_dstr_vsprintf(struct DStr *str, const char *fmt, va_list ap_)__attribute__((format(printf,2,0)));
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/src/dstr.c b/src/dstr.c
index 101252d..59d4cbc 100644
--- a/src/dstr.c
+++ b/src/dstr.c
@@ -1,5 +1,7 @@
 #include <string.h>
 #include <stdlib.h>
+#include <stdarg.h>
+#include <stdio.h>
 #include "ucore/dstr.h"
 #include "ucore/utils.h"
 
@@ -26,7 +28,7 @@ int uc_dstr_ensure(struct DStr *str, size_t len)
         //allocate a minimum no. of bytes, and one
         //additional for the common case of nul terminating
         //the string
-        size_t new_len = str->len + UC_MAX(7U, len) + 1;
+        size_t new_len = UC_MAX(7U, len) + 1;
         char *new_str = realloc(str->str, new_len);
 
         if (new_str == NULL) {
@@ -204,4 +206,55 @@ void uc_dstr_trim(struct DStr *str)
     }
 }
 
+int uc_dstr_sprintf(struct DStr *str, const char *fmt, ...)
+{
+    va_list ap;
+    int rc;
+
+    va_start(ap, fmt);
+    rc = uc_dstr_vsprintf(str, fmt, ap);
+    va_end(ap);
+
+    return rc;
+}
+
+int uc_dstr_vsprintf(struct DStr *str, const char *fmt, va_list ap_)
+{
+    va_list ap;
+    int rc;
+    int available;
+    int needed;
+
+    rc = uc_dstr_ensure(str, str->len + 1);
+    if (rc != 0) {
+        return -1;
+    }
+
+    available = uc_dstr_available(str);
+
+    va_copy(ap, ap_);
+    needed = vsnprintf(str->str + str->len, available, fmt, ap);
+    va_end(ap);
+
+    if (needed <= 0) {
+        return needed;
+    }
+
+    if (needed >= available) {
+        rc = uc_dstr_ensure(str, str->len + needed);
+        if (rc != 0) {
+            return -1;
+        }
+
+        available = uc_dstr_available(str);
+
+        va_copy(ap, ap_);
+        needed = vsnprintf(str->str + str->len, available, fmt, ap);
+        va_end(ap);
+    }
+
+    str->len += needed;
+
+    return needed;
+}
 
diff --git a/test/test_dstr.c b/test/test_dstr.c
index 1d1a9d4..da5b625 100644
--- a/test/test_dstr.c
+++ b/test/test_dstr.c
@@ -31,7 +31,7 @@ START_TEST (test_dstr_basics)
     ck_assert_str_eq(uc_dstr_str(&str), "");
 
     uc_dstr_reset(&str);
-    ck_assert_int_ge(uc_dstr_available(&str), 0);
+    ck_assert_int_gt(uc_dstr_available(&str), 0);
 
     s = uc_dstr_put(&str, 2);
     fail_if(s == NULL);
@@ -123,6 +123,23 @@ START_TEST (test_dstr_filter)
 
 END_TEST
 
+START_TEST (test_dstr_sprintf)
+    struct DStr str;
+    size_t rc; 
+
+    uc_dstr_init(&str);
+    rc = uc_dstr_sprintf(&str, "%d-%d-%d", 1, 2, 3);
+    ck_assert_int_gt(rc, 0);
+    ck_assert_str_eq(uc_dstr_str(&str), "1-2-3");
+    
+    rc = uc_dstr_sprintf(&str, " Another, bigger %s.", "string");
+    ck_assert_int_gt(rc, 0);
+    ck_assert_str_eq(uc_dstr_str(&str), "1-2-3 Another, bigger string.");
+
+    uc_dstr_destroy(&str);
+
+END_TEST
+
 Suite *dstr_suite(void)
 {
     Suite *s = suite_create("dstr");
@@ -132,6 +149,7 @@ Suite *dstr_suite(void)
     tcase_add_test(tc, test_dstr_trim);
     tcase_add_test(tc, test_dstr_replace);
     tcase_add_test(tc, test_dstr_filter);
+    tcase_add_test(tc, test_dstr_sprintf);
 
     suite_add_tcase(s, tc);