diff --git a/docs/README.md b/docs/README.md
index 7af02166..419d2e73 100644
--- a/docs/README.md
+++ b/docs/README.md
@@ -2657,7 +2657,7 @@ mg_snprintf(buf, sizeof(buf), "r: %M, %d", f,1,2,7);    // r: 3, 7
 size_t f(void (*out)(char, void *), void *ptr, va_list *ap) {
   int a = va_arg(*ap, int);
   int b = va_arg(*ap, int);
-  return mg_rprintf(out, ptr, "%d", a + b);
+  return mg_xprintf(out, ptr, "%d", a + b);
 }
 ```
 
@@ -2685,8 +2685,8 @@ free(msg);
 ### mg\_rprintf(), mg\_vrprintf()
 
 ```c
-size_t mg_rprintf(void (*out)(char, void *), void *param, const char *fmt, ...);
-size_t mg_vrprintf(void (*out)(char, void *), void *param, const char *fmt,
+size_t mg_xprintf(void (*out)(char, void *), void *param, const char *fmt, ...);
+size_t mg_vxprintf(void (*out)(char, void *), void *param, const char *fmt,
                    va_list *ap);
 ```
 
@@ -2704,7 +2704,7 @@ Usage example:
 ```c
 void myfn(char c, void *p);
 
-size_t len = mg_rprintf(myfn, myfn_p, "Double quoted string: %Q!", "hi");
+size_t len = mg_xprintf(myfn, myfn_p, "Double quoted string: %Q!", "hi");
 ```
 
 ### mg\_pfn\_iobuf()
@@ -2722,7 +2722,7 @@ Parameters:
 Usage example:
 
 ```c
-mg_rprintf(mg_pfn_iobuf, &c->send, "hi!");  // Append to the output buffer
+mg_xprintf(mg_pfn_iobuf, &c->send, "hi!");  // Append to the output buffer
 ```
 
 ### mg\_to64()
diff --git a/examples/huge-response/main.c b/examples/huge-response/main.c
index 66313a26..69e0b0cc 100644
--- a/examples/huge-response/main.c
+++ b/examples/huge-response/main.c
@@ -34,7 +34,7 @@ static size_t printdata(mg_pfn_t out, void *ptr, va_list *ap) {
   size_t n = 0;
   if (max > DATA_SIZE) max = DATA_SIZE;
   while (start < max) {
-    n += mg_rprintf(out, ptr, "%s%d", comma, s_data[start]);
+    n += mg_xprintf(out, ptr, "%s%d", comma, s_data[start]);
     comma = ",";
     start++;
   }
diff --git a/examples/webui-preact/main.c b/examples/webui-preact/main.c
deleted file mode 120000
index 5f0bdc78..00000000
--- a/examples/webui-preact/main.c
+++ /dev/null
@@ -1 +0,0 @@
-../webui-plain/main.c
\ No newline at end of file
diff --git a/examples/webui-preact/main.c b/examples/webui-preact/main.c
new file mode 100644
index 00000000..a80cf330
--- /dev/null
+++ b/examples/webui-preact/main.c
@@ -0,0 +1,63 @@
+// Copyright (c) 2022 Cesanta Software Limited
+// All rights reserved
+//
+// UI example
+// It implements the following endpoints:
+//    /api/config/get - respond with current config
+//    /api/config/set - POST a config change
+//    any other URI serves static files from s_root_dir
+// Data and results are JSON strings
+
+#include "mongoose.h"
+
+static const char *s_http_addr = "http://localhost:8000";  // HTTP port
+static const char *s_root_dir = "web_root";
+#define MQTT_SERVER "mqtt://broker.hivemq.com:1883"
+#define MQTT_PUBLISH_TOPIC "mg/my_device"
+#define MQTT_SUBSCRIBE_TOPIC "mg/#"
+
+static struct config { char *url, *pub, *sub; } s_config;
+
+// Try to update a single configuration value
+static void update_config(struct mg_str json, const char *path, char **value) {
+  char *jval;
+  if ((jval = mg_json_get_str(json, path)) != NULL) {
+    free(*value);
+    *value = strdup(jval);
+  }
+}
+
+static void fn(struct mg_connection *c, int ev, void *ev_data, void *fn_data) {
+  if (ev == MG_EV_OPEN && c->is_listening) {
+    s_config.url = strdup(MQTT_SERVER);
+    s_config.pub = strdup(MQTT_PUBLISH_TOPIC);
+    s_config.sub = strdup(MQTT_SUBSCRIBE_TOPIC);
+  } else if (ev == MG_EV_HTTP_MSG) {
+    struct mg_http_message *hm = (struct mg_http_message *) ev_data;
+    if (mg_http_match_uri(hm, "/api/config/get")) {
+      mg_http_reply(c, 200, "Content-Type: application/json\r\n",
+                    "{%Q:%Q,%Q:%Q,%Q:%Q}\n", "url", s_config.url, "pub",
+                    s_config.pub, "sub", s_config.sub);
+    } else if (mg_http_match_uri(hm, "/api/config/set")) {
+      struct mg_str json = hm->body;
+      update_config(json, "$.url", &s_config.url);
+      update_config(json, "$.pub", &s_config.pub);
+      update_config(json, "$.sub", &s_config.sub);
+      mg_http_reply(c, 200, "", "ok\n");
+    } else {
+      struct mg_http_serve_opts opts = {.root_dir = s_root_dir};
+      mg_http_serve_dir(c, ev_data, &opts);
+    }
+  }
+  (void) fn_data;
+}
+
+int main(void) {
+  struct mg_mgr mgr;                            // Event manager
+  mg_log_set(MG_LL_INFO);                       // Set to 3 to enable debug
+  mg_mgr_init(&mgr);                            // Initialise event manager
+  mg_http_listen(&mgr, s_http_addr, fn, NULL);  // Create HTTP listener
+  for (;;) mg_mgr_poll(&mgr, 1000);             // Infinite event loop
+  mg_mgr_free(&mgr);
+  return 0;
+}
diff --git a/examples/webui-push-rest/main.c b/examples/webui-push-rest/main.c
index 3933d8be..b9e44af4 100644
--- a/examples/webui-push-rest/main.c
+++ b/examples/webui-push-rest/main.c
@@ -30,7 +30,7 @@ static size_t printdata(void (*out)(char, void *), void *ptr, va_list *ap) {
   const char *comma = "";
   size_t n = 0;
   for (int i = 0; i < DATA_SIZE; ++i) {
-    n += mg_rprintf(out, ptr, "%s%d", comma, s_data[i]);
+    n += mg_xprintf(out, ptr, "%s%d", comma, s_data[i]);
     comma = ",";
   }
   return n;
diff --git a/mongoose.c b/mongoose.c
index c9395162..7410859d 100644
--- a/mongoose.c
+++ b/mongoose.c
@@ -412,6 +412,32 @@ void mg_error(struct mg_connection *c, const char *fmt, ...) {
 
 
 
+static void mg_pfn_iobuf_private(char ch, void *param, bool expand) {
+  struct mg_iobuf *io = (struct mg_iobuf *) param;
+  if (expand && io->len + 2 > io->size) mg_iobuf_resize(io, io->len + 2);
+  if (io->len + 2 <= io->size) {
+    io->buf[io->len++] = (uint8_t) ch;
+    io->buf[io->len] = 0;
+  } else if (io->len < io->size) {
+    io->buf[io->len++] = 0;  // Guarantee to 0-terminate
+  }
+}
+
+static void mg_putchar_iobuf_static(char ch, void *param) {
+  mg_pfn_iobuf_private(ch, param, false);
+}
+
+void mg_pfn_iobuf(char ch, void *param) {
+  mg_pfn_iobuf_private(ch, param, true);
+}
+
+size_t mg_vsnprintf(char *buf, size_t len, const char *fmt, va_list *ap) {
+  struct mg_iobuf io = {(uint8_t *) buf, len, 0, 0};
+  size_t n = mg_vxprintf(mg_putchar_iobuf_static, &io, fmt, ap);
+  if (n < len) buf[n] = '\0';
+  return n;
+}
+
 size_t mg_snprintf(char *buf, size_t len, const char *fmt, ...) {
   va_list ap;
   size_t n;
@@ -423,7 +449,7 @@ size_t mg_snprintf(char *buf, size_t len, const char *fmt, ...) {
 
 char *mg_vmprintf(const char *fmt, va_list *ap) {
   struct mg_iobuf io = {0, 0, 0, 256};
-  mg_vrprintf(mg_pfn_iobuf, &io, fmt, ap);
+  mg_vxprintf(mg_pfn_iobuf, &io, fmt, ap);
   return (char *) io.buf;
 }
 
@@ -436,40 +462,15 @@ char *mg_mprintf(const char *fmt, ...) {
   return s;
 }
 
-size_t mg_rprintf(void (*out)(char, void *), void *ptr, const char *fmt, ...) {
+size_t mg_xprintf(void (*out)(char, void *), void *ptr, const char *fmt, ...) {
   size_t len = 0;
   va_list ap;
   va_start(ap, fmt);
-  len = mg_vrprintf(out, ptr, fmt, &ap);
+  len = mg_vxprintf(out, ptr, fmt, &ap);
   va_end(ap);
   return len;
 }
 
-static void mg_putchar_iobuf_static(char ch, void *param) {
-  struct mg_iobuf *io = (struct mg_iobuf *) param;
-  if (io->len + 2 <= io->size) {
-    io->buf[io->len++] = (uint8_t) ch;
-    io->buf[io->len] = 0;
-  }
-}
-
-void mg_pfn_iobuf(char ch, void *param) {
-  struct mg_iobuf *io = (struct mg_iobuf *) param;
-  if (io->len + 2 > io->size) mg_iobuf_resize(io, io->len + 2);
-  if (io->len + 2 <= io->size) {
-    io->buf[io->len++] = (uint8_t) ch;
-    io->buf[io->len] = 0;
-  }
-}
-
-size_t mg_vsnprintf(char *buf, size_t len, const char *fmt, va_list *ap) {
-  struct mg_iobuf io = {(uint8_t *) buf, len, 0, 0};
-  size_t n = mg_vrprintf(mg_putchar_iobuf_static, &io, fmt, ap);
-  if (n < len) buf[n] = '\0';
-  // if (len > 0) buf[len - 1] = '\0';  // Guarantee to 0-terminate
-  return n;
-}
-
 static bool is_digit(int c) {
   return c >= '0' && c <= '9';
 }
@@ -690,7 +691,7 @@ static size_t bcpy(void (*out)(char, void *), void *ptr, uint8_t *buf,
   return n;
 }
 
-size_t mg_vrprintf(void (*out)(char, void *), void *param, const char *fmt,
+size_t mg_vxprintf(void (*out)(char, void *), void *param, const char *fmt,
                    va_list *ap) {
   size_t i = 0, n = 0;
   while (fmt[i] != '\0') {
@@ -1647,7 +1648,7 @@ static void mg_http_vprintf_chunk(struct mg_connection *c, const char *fmt,
   va_list tmp;
   mg_send(c, "        \r\n", 10);
   va_copy(tmp, ap);
-  mg_vrprintf(mg_pfn_iobuf, &c->send, fmt, &tmp);
+  mg_vxprintf(mg_pfn_iobuf, &c->send, fmt, &tmp);
   va_end(tmp);
   if (c->send.len >= len + 10) {
     mg_snprintf((char *) c->send.buf + len, 9, "%08lx", c->send.len - len - 10);
@@ -1702,7 +1703,7 @@ void mg_http_reply(struct mg_connection *c, int code, const char *headers,
             mg_http_status_code_str(code), headers == NULL ? "" : headers);
   len = c->send.len;
   va_start(ap, fmt);
-  mg_vrprintf(mg_pfn_iobuf, &c->send, fmt, &ap);
+  mg_vxprintf(mg_pfn_iobuf, &c->send, fmt, &ap);
   va_end(ap);
   if (c->send.len > 15) {
     mg_snprintf((char *) &c->send.buf[len - 14], 11, "%010lu",
@@ -2741,7 +2742,7 @@ bool mg_log_prefix(int level, const char *file, int line, const char *fname) {
 void mg_log(const char *fmt, ...) {
   va_list ap;
   va_start(ap, fmt);
-  mg_vrprintf(s_log_func, s_log_func_param, fmt, &ap);
+  mg_vxprintf(s_log_func, s_log_func_param, fmt, &ap);
   va_end(ap);
   logc((unsigned char) '\n');
 }
@@ -3282,7 +3283,7 @@ size_t mg_vprintf(struct mg_connection *c, const char *fmt, va_list ap) {
   size_t old = c->send.len;
   va_list tmp;
   va_copy(tmp, ap);
-  mg_vrprintf(mg_pfn_iobuf, &c->send, fmt, &tmp);
+  mg_vxprintf(mg_pfn_iobuf, &c->send, fmt, &tmp);
   return c->send.len - old;
 }
 
@@ -3587,10 +3588,10 @@ void mg_rpc_process(struct mg_rpc_req *r) {
 void mg_rpc_vok(struct mg_rpc_req *r, const char *fmt, va_list *ap) {
   int len, off = mg_json_get(r->frame, "$.id", &len);
   if (off > 0) {
-    mg_rprintf(r->pfn, r->pfn_data, "{%Q:%.*s,%Q:", "id", len,
+    mg_xprintf(r->pfn, r->pfn_data, "{%Q:%.*s,%Q:", "id", len,
                &r->frame.ptr[off], "result");
-    mg_vrprintf(r->pfn, r->pfn_data, fmt == NULL ? "null" : fmt, ap);
-    mg_rprintf(r->pfn, r->pfn_data, "}");
+    mg_vxprintf(r->pfn, r->pfn_data, fmt == NULL ? "null" : fmt, ap);
+    mg_xprintf(r->pfn, r->pfn_data, "}");
   }
 }
 
@@ -3603,14 +3604,14 @@ void mg_rpc_ok(struct mg_rpc_req *r, const char *fmt, ...) {
 
 void mg_rpc_verr(struct mg_rpc_req *r, int code, const char *fmt, va_list *ap) {
   int len, off = mg_json_get(r->frame, "$.id", &len);
-  mg_rprintf(r->pfn, r->pfn_data, "{");
+  mg_xprintf(r->pfn, r->pfn_data, "{");
   if (off > 0) {
-    mg_rprintf(r->pfn, r->pfn_data, "%Q:%.*s,", "id", len, &r->frame.ptr[off]);
+    mg_xprintf(r->pfn, r->pfn_data, "%Q:%.*s,", "id", len, &r->frame.ptr[off]);
   }
-  mg_rprintf(r->pfn, r->pfn_data, "%Q:{%Q:%d,%Q:", "error", "code", code,
+  mg_xprintf(r->pfn, r->pfn_data, "%Q:{%Q:%d,%Q:", "error", "code", code,
              "message");
-  mg_vrprintf(r->pfn, r->pfn_data, fmt == NULL ? "null" : fmt, ap);
-  mg_rprintf(r->pfn, r->pfn_data, "}}");
+  mg_vxprintf(r->pfn, r->pfn_data, fmt == NULL ? "null" : fmt, ap);
+  mg_xprintf(r->pfn, r->pfn_data, "}}");
 }
 
 void mg_rpc_err(struct mg_rpc_req *r, int code, const char *fmt, ...) {
@@ -3624,7 +3625,7 @@ static size_t print_methods(mg_pfn_t pfn, void *pfn_data, va_list *ap) {
   struct mg_rpc *h, **head = (struct mg_rpc **) va_arg(*ap, void **);
   size_t len = 0;
   for (h = *head; h != NULL; h = h->next) {
-    len += mg_rprintf(pfn, pfn_data, "%s%.*Q", h == *head ? "" : ",",
+    len += mg_xprintf(pfn, pfn_data, "%s%.*Q", h == *head ? "" : ",",
                       (int) h->method.len, h->method.ptr);
   }
   return len;
@@ -5654,7 +5655,7 @@ struct ws_msg {
 size_t mg_ws_vprintf(struct mg_connection *c, int op, const char *fmt,
                      va_list *ap) {
   size_t len = c->send.len;
-  size_t n = mg_vrprintf(mg_pfn_iobuf, &c->send, fmt, ap);
+  size_t n = mg_vxprintf(mg_pfn_iobuf, &c->send, fmt, ap);
   mg_ws_wrap(c, c->send.len - len, op);
   return n;
 }
@@ -5680,13 +5681,13 @@ static void ws_handshake(struct mg_connection *c, const struct mg_str *wskey,
   mg_sha1_update(&sha_ctx, (unsigned char *) magic, 36);
   mg_sha1_final(sha, &sha_ctx);
   mg_base64_encode(sha, sizeof(sha), (char *) b64_sha);
-  mg_rprintf(mg_pfn_iobuf, &c->send,
+  mg_xprintf(mg_pfn_iobuf, &c->send,
              "HTTP/1.1 101 Switching Protocols\r\n"
              "Upgrade: websocket\r\n"
              "Connection: Upgrade\r\n"
              "Sec-WebSocket-Accept: %s\r\n",
              b64_sha);
-  if (fmt != NULL) mg_vrprintf(mg_pfn_iobuf, &c->send, fmt, ap);
+  if (fmt != NULL) mg_vxprintf(mg_pfn_iobuf, &c->send, fmt, ap);
   if (wsproto != NULL) {
     mg_printf(c, "Sec-WebSocket-Protocol: %.*s\r\n", (int) wsproto->len,
               wsproto->ptr);
@@ -5873,7 +5874,7 @@ struct mg_connection *mg_ws_connect(struct mg_mgr *mgr, const char *url,
     struct mg_str host = mg_url_host(url);
     mg_random(nonce, sizeof(nonce));
     mg_base64_encode((unsigned char *) nonce, sizeof(nonce), key);
-    mg_rprintf(mg_pfn_iobuf, &c->send,
+    mg_xprintf(mg_pfn_iobuf, &c->send,
                "GET %s HTTP/1.1\r\n"
                "Upgrade: websocket\r\n"
                "Host: %.*s\r\n"
@@ -5884,10 +5885,10 @@ struct mg_connection *mg_ws_connect(struct mg_mgr *mgr, const char *url,
     if (fmt != NULL) {
       va_list ap;
       va_start(ap, fmt);
-      mg_vrprintf(mg_pfn_iobuf, &c->send, fmt, &ap);
+      mg_vxprintf(mg_pfn_iobuf, &c->send, fmt, &ap);
       va_end(ap);
     }
-    mg_rprintf(mg_pfn_iobuf, &c->send, "\r\n");
+    mg_xprintf(mg_pfn_iobuf, &c->send, "\r\n");
     c->pfn = mg_ws_cb;
     c->pfn_data = NULL;
   }
diff --git a/mongoose.h b/mongoose.h
index 2cf9349d..19f3dbce 100644
--- a/mongoose.h
+++ b/mongoose.h
@@ -791,8 +791,8 @@ size_t mg_lld(char *buf, int64_t val, bool is_signed, bool is_hex);
 double mg_atod(const char *buf, int len, int *numlen);
 size_t mg_dtoa(char *buf, size_t len, double d, int width);
 
-size_t mg_vrprintf(void (*)(char, void *), void *, const char *fmt, va_list *);
-size_t mg_rprintf(void (*fn)(char, void *), void *, const char *fmt, ...);
+size_t mg_vxprintf(void (*)(char, void *), void *, const char *fmt, va_list *);
+size_t mg_xprintf(void (*fn)(char, void *), void *, const char *fmt, ...);
 size_t mg_vsnprintf(char *buf, size_t len, const char *fmt, va_list *ap);
 size_t mg_snprintf(char *, size_t, const char *fmt, ...);
 char *mg_vmprintf(const char *fmt, va_list *ap);
diff --git a/src/fmt.c b/src/fmt.c
index 121df2fc..fa7ccdbe 100644
--- a/src/fmt.c
+++ b/src/fmt.c
@@ -1,6 +1,32 @@
 #include "fmt.h"
 #include "iobuf.h"
 
+static void mg_pfn_iobuf_private(char ch, void *param, bool expand) {
+  struct mg_iobuf *io = (struct mg_iobuf *) param;
+  if (expand && io->len + 2 > io->size) mg_iobuf_resize(io, io->len + 2);
+  if (io->len + 2 <= io->size) {
+    io->buf[io->len++] = (uint8_t) ch;
+    io->buf[io->len] = 0;
+  } else if (io->len < io->size) {
+    io->buf[io->len++] = 0;  // Guarantee to 0-terminate
+  }
+}
+
+static void mg_putchar_iobuf_static(char ch, void *param) {
+  mg_pfn_iobuf_private(ch, param, false);
+}
+
+void mg_pfn_iobuf(char ch, void *param) {
+  mg_pfn_iobuf_private(ch, param, true);
+}
+
+size_t mg_vsnprintf(char *buf, size_t len, const char *fmt, va_list *ap) {
+  struct mg_iobuf io = {(uint8_t *) buf, len, 0, 0};
+  size_t n = mg_vxprintf(mg_putchar_iobuf_static, &io, fmt, ap);
+  if (n < len) buf[n] = '\0';
+  return n;
+}
+
 size_t mg_snprintf(char *buf, size_t len, const char *fmt, ...) {
   va_list ap;
   size_t n;
@@ -12,7 +38,7 @@ size_t mg_snprintf(char *buf, size_t len, const char *fmt, ...) {
 
 char *mg_vmprintf(const char *fmt, va_list *ap) {
   struct mg_iobuf io = {0, 0, 0, 256};
-  mg_vrprintf(mg_pfn_iobuf, &io, fmt, ap);
+  mg_vxprintf(mg_pfn_iobuf, &io, fmt, ap);
   return (char *) io.buf;
 }
 
@@ -25,40 +51,15 @@ char *mg_mprintf(const char *fmt, ...) {
   return s;
 }
 
-size_t mg_rprintf(void (*out)(char, void *), void *ptr, const char *fmt, ...) {
+size_t mg_xprintf(void (*out)(char, void *), void *ptr, const char *fmt, ...) {
   size_t len = 0;
   va_list ap;
   va_start(ap, fmt);
-  len = mg_vrprintf(out, ptr, fmt, &ap);
+  len = mg_vxprintf(out, ptr, fmt, &ap);
   va_end(ap);
   return len;
 }
 
-static void mg_putchar_iobuf_static(char ch, void *param) {
-  struct mg_iobuf *io = (struct mg_iobuf *) param;
-  if (io->len + 2 <= io->size) {
-    io->buf[io->len++] = (uint8_t) ch;
-    io->buf[io->len] = 0;
-  }
-}
-
-void mg_pfn_iobuf(char ch, void *param) {
-  struct mg_iobuf *io = (struct mg_iobuf *) param;
-  if (io->len + 2 > io->size) mg_iobuf_resize(io, io->len + 2);
-  if (io->len + 2 <= io->size) {
-    io->buf[io->len++] = (uint8_t) ch;
-    io->buf[io->len] = 0;
-  }
-}
-
-size_t mg_vsnprintf(char *buf, size_t len, const char *fmt, va_list *ap) {
-  struct mg_iobuf io = {(uint8_t *) buf, len, 0, 0};
-  size_t n = mg_vrprintf(mg_putchar_iobuf_static, &io, fmt, ap);
-  if (n < len) buf[n] = '\0';
-  // if (len > 0) buf[len - 1] = '\0';  // Guarantee to 0-terminate
-  return n;
-}
-
 static bool is_digit(int c) {
   return c >= '0' && c <= '9';
 }
@@ -279,7 +280,7 @@ static size_t bcpy(void (*out)(char, void *), void *ptr, uint8_t *buf,
   return n;
 }
 
-size_t mg_vrprintf(void (*out)(char, void *), void *param, const char *fmt,
+size_t mg_vxprintf(void (*out)(char, void *), void *param, const char *fmt,
                    va_list *ap) {
   size_t i = 0, n = 0;
   while (fmt[i] != '\0') {
diff --git a/src/fmt.h b/src/fmt.h
index b41ad67c..1afc1bf0 100644
--- a/src/fmt.h
+++ b/src/fmt.h
@@ -11,8 +11,8 @@ size_t mg_lld(char *buf, int64_t val, bool is_signed, bool is_hex);
 double mg_atod(const char *buf, int len, int *numlen);
 size_t mg_dtoa(char *buf, size_t len, double d, int width);
 
-size_t mg_vrprintf(void (*)(char, void *), void *, const char *fmt, va_list *);
-size_t mg_rprintf(void (*fn)(char, void *), void *, const char *fmt, ...);
+size_t mg_vxprintf(void (*)(char, void *), void *, const char *fmt, va_list *);
+size_t mg_xprintf(void (*fn)(char, void *), void *, const char *fmt, ...);
 size_t mg_vsnprintf(char *buf, size_t len, const char *fmt, va_list *ap);
 size_t mg_snprintf(char *, size_t, const char *fmt, ...);
 char *mg_vmprintf(const char *fmt, va_list *ap);
diff --git a/src/http.c b/src/http.c
index 02024b35..b5c87b1b 100644
--- a/src/http.c
+++ b/src/http.c
@@ -272,7 +272,7 @@ static void mg_http_vprintf_chunk(struct mg_connection *c, const char *fmt,
   va_list tmp;
   mg_send(c, "        \r\n", 10);
   va_copy(tmp, ap);
-  mg_vrprintf(mg_pfn_iobuf, &c->send, fmt, &tmp);
+  mg_vxprintf(mg_pfn_iobuf, &c->send, fmt, &tmp);
   va_end(tmp);
   if (c->send.len >= len + 10) {
     mg_snprintf((char *) c->send.buf + len, 9, "%08lx", c->send.len - len - 10);
@@ -327,7 +327,7 @@ void mg_http_reply(struct mg_connection *c, int code, const char *headers,
             mg_http_status_code_str(code), headers == NULL ? "" : headers);
   len = c->send.len;
   va_start(ap, fmt);
-  mg_vrprintf(mg_pfn_iobuf, &c->send, fmt, &ap);
+  mg_vxprintf(mg_pfn_iobuf, &c->send, fmt, &ap);
   va_end(ap);
   if (c->send.len > 15) {
     mg_snprintf((char *) &c->send.buf[len - 14], 11, "%010lu",
diff --git a/src/log.c b/src/log.c
index 295bb962..40e9b781 100644
--- a/src/log.c
+++ b/src/log.c
@@ -51,7 +51,7 @@ bool mg_log_prefix(int level, const char *file, int line, const char *fname) {
 void mg_log(const char *fmt, ...) {
   va_list ap;
   va_start(ap, fmt);
-  mg_vrprintf(s_log_func, s_log_func_param, fmt, &ap);
+  mg_vxprintf(s_log_func, s_log_func_param, fmt, &ap);
   va_end(ap);
   logc((unsigned char) '\n');
 }
diff --git a/src/net.c b/src/net.c
index 24d953c1..6f7e95da 100644
--- a/src/net.c
+++ b/src/net.c
@@ -9,7 +9,7 @@ size_t mg_vprintf(struct mg_connection *c, const char *fmt, va_list ap) {
   size_t old = c->send.len;
   va_list tmp;
   va_copy(tmp, ap);
-  mg_vrprintf(mg_pfn_iobuf, &c->send, fmt, &tmp);
+  mg_vxprintf(mg_pfn_iobuf, &c->send, fmt, &tmp);
   return c->send.len - old;
 }
 
diff --git a/src/rpc.c b/src/rpc.c
index 53175868..c513a555 100644
--- a/src/rpc.c
+++ b/src/rpc.c
@@ -40,10 +40,10 @@ void mg_rpc_process(struct mg_rpc_req *r) {
 void mg_rpc_vok(struct mg_rpc_req *r, const char *fmt, va_list *ap) {
   int len, off = mg_json_get(r->frame, "$.id", &len);
   if (off > 0) {
-    mg_rprintf(r->pfn, r->pfn_data, "{%Q:%.*s,%Q:", "id", len,
+    mg_xprintf(r->pfn, r->pfn_data, "{%Q:%.*s,%Q:", "id", len,
                &r->frame.ptr[off], "result");
-    mg_vrprintf(r->pfn, r->pfn_data, fmt == NULL ? "null" : fmt, ap);
-    mg_rprintf(r->pfn, r->pfn_data, "}");
+    mg_vxprintf(r->pfn, r->pfn_data, fmt == NULL ? "null" : fmt, ap);
+    mg_xprintf(r->pfn, r->pfn_data, "}");
   }
 }
 
@@ -56,14 +56,14 @@ void mg_rpc_ok(struct mg_rpc_req *r, const char *fmt, ...) {
 
 void mg_rpc_verr(struct mg_rpc_req *r, int code, const char *fmt, va_list *ap) {
   int len, off = mg_json_get(r->frame, "$.id", &len);
-  mg_rprintf(r->pfn, r->pfn_data, "{");
+  mg_xprintf(r->pfn, r->pfn_data, "{");
   if (off > 0) {
-    mg_rprintf(r->pfn, r->pfn_data, "%Q:%.*s,", "id", len, &r->frame.ptr[off]);
+    mg_xprintf(r->pfn, r->pfn_data, "%Q:%.*s,", "id", len, &r->frame.ptr[off]);
   }
-  mg_rprintf(r->pfn, r->pfn_data, "%Q:{%Q:%d,%Q:", "error", "code", code,
+  mg_xprintf(r->pfn, r->pfn_data, "%Q:{%Q:%d,%Q:", "error", "code", code,
              "message");
-  mg_vrprintf(r->pfn, r->pfn_data, fmt == NULL ? "null" : fmt, ap);
-  mg_rprintf(r->pfn, r->pfn_data, "}}");
+  mg_vxprintf(r->pfn, r->pfn_data, fmt == NULL ? "null" : fmt, ap);
+  mg_xprintf(r->pfn, r->pfn_data, "}}");
 }
 
 void mg_rpc_err(struct mg_rpc_req *r, int code, const char *fmt, ...) {
@@ -77,7 +77,7 @@ static size_t print_methods(mg_pfn_t pfn, void *pfn_data, va_list *ap) {
   struct mg_rpc *h, **head = (struct mg_rpc **) va_arg(*ap, void **);
   size_t len = 0;
   for (h = *head; h != NULL; h = h->next) {
-    len += mg_rprintf(pfn, pfn_data, "%s%.*Q", h == *head ? "" : ",",
+    len += mg_xprintf(pfn, pfn_data, "%s%.*Q", h == *head ? "" : ",",
                       (int) h->method.len, h->method.ptr);
   }
   return len;
diff --git a/src/ws.c b/src/ws.c
index 6a6c6a4e..cb5807b4 100644
--- a/src/ws.c
+++ b/src/ws.c
@@ -17,7 +17,7 @@ struct ws_msg {
 size_t mg_ws_vprintf(struct mg_connection *c, int op, const char *fmt,
                      va_list *ap) {
   size_t len = c->send.len;
-  size_t n = mg_vrprintf(mg_pfn_iobuf, &c->send, fmt, ap);
+  size_t n = mg_vxprintf(mg_pfn_iobuf, &c->send, fmt, ap);
   mg_ws_wrap(c, c->send.len - len, op);
   return n;
 }
@@ -43,13 +43,13 @@ static void ws_handshake(struct mg_connection *c, const struct mg_str *wskey,
   mg_sha1_update(&sha_ctx, (unsigned char *) magic, 36);
   mg_sha1_final(sha, &sha_ctx);
   mg_base64_encode(sha, sizeof(sha), (char *) b64_sha);
-  mg_rprintf(mg_pfn_iobuf, &c->send,
+  mg_xprintf(mg_pfn_iobuf, &c->send,
              "HTTP/1.1 101 Switching Protocols\r\n"
              "Upgrade: websocket\r\n"
              "Connection: Upgrade\r\n"
              "Sec-WebSocket-Accept: %s\r\n",
              b64_sha);
-  if (fmt != NULL) mg_vrprintf(mg_pfn_iobuf, &c->send, fmt, ap);
+  if (fmt != NULL) mg_vxprintf(mg_pfn_iobuf, &c->send, fmt, ap);
   if (wsproto != NULL) {
     mg_printf(c, "Sec-WebSocket-Protocol: %.*s\r\n", (int) wsproto->len,
               wsproto->ptr);
@@ -236,7 +236,7 @@ struct mg_connection *mg_ws_connect(struct mg_mgr *mgr, const char *url,
     struct mg_str host = mg_url_host(url);
     mg_random(nonce, sizeof(nonce));
     mg_base64_encode((unsigned char *) nonce, sizeof(nonce), key);
-    mg_rprintf(mg_pfn_iobuf, &c->send,
+    mg_xprintf(mg_pfn_iobuf, &c->send,
                "GET %s HTTP/1.1\r\n"
                "Upgrade: websocket\r\n"
                "Host: %.*s\r\n"
@@ -247,10 +247,10 @@ struct mg_connection *mg_ws_connect(struct mg_mgr *mgr, const char *url,
     if (fmt != NULL) {
       va_list ap;
       va_start(ap, fmt);
-      mg_vrprintf(mg_pfn_iobuf, &c->send, fmt, &ap);
+      mg_vxprintf(mg_pfn_iobuf, &c->send, fmt, &ap);
       va_end(ap);
     }
-    mg_rprintf(mg_pfn_iobuf, &c->send, "\r\n");
+    mg_xprintf(mg_pfn_iobuf, &c->send, "\r\n");
     c->pfn = mg_ws_cb;
     c->pfn_data = NULL;
   }
diff --git a/test/unit_test.c b/test/unit_test.c
index 2434d05a..79bb5dc4 100644
--- a/test/unit_test.c
+++ b/test/unit_test.c
@@ -1414,13 +1414,13 @@ static bool sccmp(const char *s1, const char *s2, int expected) {
 static size_t pf1(void (*out)(char, void *), void *ptr, va_list *ap) {
   int a = va_arg(*ap, int);
   int b = va_arg(*ap, int);
-  return mg_rprintf(out, ptr, "%d", a + b);
+  return mg_xprintf(out, ptr, "%d", a + b);
 }
 
 static size_t pf2(void (*out)(char, void *), void *ptr, va_list *ap) {
   int cnt = va_arg(*ap, int);
   size_t n = 0;
-  while (cnt-- > 0) n += mg_rprintf(out, ptr, "%d", cnt);
+  while (cnt-- > 0) n += mg_xprintf(out, ptr, "%d", cnt);
   return n;
 }
 
@@ -1510,6 +1510,14 @@ static void test_str(void) {
     mg_snprintf(buf, sizeof(buf), "%Q", "");
     ASSERT(strcmp(buf, expected) == 0);
 
+    expected = "";
+    mg_snprintf(buf, 1, "%s", "abc");
+    ASSERT(strcmp(buf, expected) == 0);
+
+    expected = "a";
+    mg_snprintf(buf, 2, "%s", "abc");
+    ASSERT(strcmp(buf, expected) == 0);
+
     expected = "\"hi, \\\"\"";
     mg_snprintf(buf, sizeof(buf), "\"hi, %q\"", "\"");
     MG_INFO(("[%s] [%s]", buf, expected));
@@ -1535,9 +1543,9 @@ static void test_str(void) {
     ASSERT(strcmp(p, "[9876543210,7]") == 0);
     free(p);
 
-    mg_rprintf(mg_pfn_iobuf, &io, "[%M", pf2, 10);
-    mg_rprintf(mg_pfn_iobuf, &io, ",");
-    mg_rprintf(mg_pfn_iobuf, &io, "%d]", 7);
+    mg_xprintf(mg_pfn_iobuf, &io, "[%M", pf2, 10);
+    mg_xprintf(mg_pfn_iobuf, &io, ",");
+    mg_xprintf(mg_pfn_iobuf, &io, "%d]", 7);
     ASSERT(strcmp((char *) io.buf, "[9876543210,7]") == 0);
     mg_iobuf_free(&io);
   }