1 files changed, 31 insertions, 0 deletions
diff --git a/src/base/string/appendf.c b/src/base/string/appendf.c
new file mode 100644
index 0000000..4b8d76c
--- /dev/null
+++ b/src/base/string/appendf.c
@@ -0,0 +1,31 @@
+#include "internal.h"
+
+/*
+ * appendf will append the given formatted string to our buffer.
+ * returns the newly minted string
+ */
+
+int
+str·appendf(string *s, const byte* fmt, ...)
+{
+    va_list args;
+    va_start(args, fmt);
+    int remain = str·cap(*s) - str·len(*s);
+    int n      = vsnprintf(*s + str·len(*s), remain + 1, fmt, args);
+    va_end(args);
+
+    if(n > remain){
+        // If the first write was incomplete, we overwite the data again.
+        str·grow(s, n);
+        va_list args;
+        va_start(args, fmt);
+        n = vsnprintf(*s + str·len(*s), n + 1, fmt, args);
+        assert(n - remain <= str·cap(*s));
+        va_end(args);
+    }
+
+    Hdr* h = (Hdr*)(*s - sizeof(Hdr));
+    h->len += n;
+
+    return n;
+}