refactor(input): don't use a ring for input

Since paste data is handled via a separate channel, the data processed via `input_buffer` is typically just explicit keys as typed in by the user. Therefore it should be fine to use `memmove()` to always put the remaining data in front when refilling the buffer.

src/nvim/api/vim.c

@@ -313,7 +313,7 @@ void nvim_feedkeys(String keys, String mode, Boolean escape_ks)
     keys_esc = keys.data;
   }
   if (lowlevel) {
-    input_enqueue_raw(cstr_as_string(keys_esc));
+    input_enqueue_raw(keys_esc, strlen(keys_esc));
   } else {
     ins_typebuf(keys_esc, (remap ? REMAP_YES : REMAP_NONE),
                 insert ? 0 : typebuf.tb_len, !typed, false);

src/nvim/main.c

@@ -154,7 +154,6 @@ void event_init(void)
   loop_init(&main_loop, NULL);
   resize_events = multiqueue_new_child(main_loop.events);
 
-  input_init();
   signal_init();
   // mspgack-rpc initialization
   channel_init();

src/nvim/memory.c

@@ -882,7 +882,6 @@ void free_all_mem(void)
 
   decor_free_all_mem();
   drawline_free_all_mem();
-  input_free_all_mem();
 
   if (ui_client_channel_id) {
     ui_client_free_all_mem();

src/nvim/os/input.c

@@ -33,7 +33,7 @@
 #include "nvim/state_defs.h"
 
 #define READ_BUFFER_SIZE 0xfff
-#define INPUT_BUFFER_SIZE (READ_BUFFER_SIZE * 4)
+#define INPUT_BUFFER_SIZE ((READ_BUFFER_SIZE * 4) + MAX_KEY_CODE_LEN)
 
 typedef enum {
   kInputNone,
@@ -42,7 +42,10 @@ typedef enum {
 } InbufPollResult;
 
 static RStream read_stream = { .s.closed = true };  // Input before UI starts.
-static RBuffer *input_buffer = NULL;
+static char input_buffer[INPUT_BUFFER_SIZE];
+static char *input_read_pos = input_buffer;
+static char *input_write_pos = input_buffer;
+
 static bool input_eof = false;
 static bool blocking = false;
 static int cursorhold_time = 0;  ///< time waiting for CursorHold event
@@ -52,11 +55,6 @@ static int cursorhold_tb_change_cnt = 0;  ///< tb_change_cnt when waiting starte
 # include "os/input.c.generated.h"
 #endif
 
-void input_init(void)
-{
-  input_buffer = rbuffer_new(INPUT_BUFFER_SIZE + MAX_KEY_CODE_LEN);
-}
-
 void input_start(void)
 {
   if (!read_stream.s.closed) {
@@ -78,13 +76,6 @@ void input_stop(void)
   rstream_may_close(&read_stream);
 }
 
-#ifdef EXITFREE
-void input_free_all_mem(void)
-{
-  rbuffer_free(input_buffer);
-}
-#endif
-
 static void cursorhold_event(void **argv)
 {
   event_T event = State & MODE_INSERT ? EVENT_CURSORHOLDI : EVENT_CURSORHOLD;
@@ -119,9 +110,12 @@ int os_inchar(uint8_t *buf, int maxlen, int ms, int tb_change_cnt, MultiQueue *e
     restart_cursorhold_wait(tb_change_cnt);
   }
 
-  if (maxlen && rbuffer_size(input_buffer)) {
+  if (maxlen && input_available()) {
     restart_cursorhold_wait(tb_change_cnt);
-    return (int)rbuffer_read(input_buffer, (char *)buf, (size_t)maxlen);
+    size_t to_read = MIN((size_t)maxlen, input_available());
+    memcpy(buf, input_read_pos, to_read);
+    input_read_pos += to_read;
+    return (int)to_read;
   }
 
   // No risk of a UI flood, so disable CTRL-C "interrupt" behavior if it's mapped.
@@ -161,11 +155,14 @@ int os_inchar(uint8_t *buf, int maxlen, int ms, int tb_change_cnt, MultiQueue *e
     return 0;
   }
 
-  if (maxlen && rbuffer_size(input_buffer)) {
+  if (maxlen && input_available()) {
     restart_cursorhold_wait(tb_change_cnt);
-    // Safe to convert rbuffer_read to int, it will never overflow since we use
-    // relatively small buffers.
-    return (int)rbuffer_read(input_buffer, (char *)buf, (size_t)maxlen);
+    // Safe to convert rbuffer_read to int, it will never overflow since
+    // INPUT_BUFFER_SIZE fits in an int
+    size_t to_read = MIN((size_t)maxlen, input_available());
+    memcpy(buf, input_read_pos, to_read);
+    input_read_pos += to_read;
+    return (int)to_read;
   }
 
   // If there are events, return the keys directly
@@ -247,11 +244,28 @@ bool os_isatty(int fd)
   return uv_guess_handle(fd) == UV_TTY;
 }
 
-void input_enqueue_raw(String keys)
+size_t input_available(void)
 {
-  if (keys.size > 0) {
-    rbuffer_write(input_buffer, keys.data, keys.size);
+  return (size_t)(input_write_pos - input_read_pos);
+}
+
+static size_t input_space(void)
+{
+  return (size_t)(input_buffer + INPUT_BUFFER_SIZE - input_write_pos);
+}
+
+void input_enqueue_raw(const char *data, size_t size)
+{
+  if (input_read_pos > input_buffer) {
+    size_t available = input_available();
+    memmove(input_buffer, input_read_pos, available);
+    input_read_pos = input_buffer;
+    input_write_pos = input_buffer + available;
   }
+
+  size_t to_write = MIN(size, input_space());
+  memcpy(input_write_pos, data, to_write);
+  input_write_pos += to_write;
 }
 
 size_t input_enqueue(String keys)
@@ -259,7 +273,7 @@ size_t input_enqueue(String keys)
   const char *ptr = keys.data;
   const char *end = ptr + keys.size;
 
-  while (rbuffer_space(input_buffer) >= 19 && ptr < end) {
+  while (input_space() >= 19 && ptr < end) {
     // A "<x>" form occupies at least 1 characters, and produces up
     // to 19 characters (1 + 5 * 3 for the char and 3 for a modifier).
     // In the case of K_SPECIAL (0x80), 3 bytes are escaped and needed,
@@ -272,7 +286,7 @@ size_t input_enqueue(String keys)
 
     if (new_size) {
       new_size = handle_mouse_event(&ptr, buf, new_size);
-      rbuffer_write(input_buffer, (char *)buf, new_size);
+      input_enqueue_raw((char *)buf, new_size);
       continue;
     }
 
@@ -293,11 +307,11 @@ size_t input_enqueue(String keys)
 
     // copy the character, escaping K_SPECIAL
     if ((uint8_t)(*ptr) == K_SPECIAL) {
-      rbuffer_write(input_buffer, (char *)&(uint8_t){ K_SPECIAL }, 1);
-      rbuffer_write(input_buffer, (char *)&(uint8_t){ KS_SPECIAL }, 1);
-      rbuffer_write(input_buffer, (char *)&(uint8_t){ KE_FILLER }, 1);
+      input_enqueue_raw((char *)&(uint8_t){ K_SPECIAL }, 1);
+      input_enqueue_raw((char *)&(uint8_t){ KS_SPECIAL }, 1);
+      input_enqueue_raw((char *)&(uint8_t){ KE_FILLER }, 1);
     } else {
-      rbuffer_write(input_buffer, ptr, 1);
+      input_enqueue_raw(ptr, 1);
     }
     ptr++;
   }
@@ -422,7 +436,7 @@ static unsigned handle_mouse_event(const char **ptr, uint8_t *buf, unsigned bufs
   return bufsize;
 }
 
-size_t input_enqueue_mouse(int code, uint8_t modifier, int grid, int row, int col)
+void input_enqueue_mouse(int code, uint8_t modifier, int grid, int row, int col)
 {
   modifier |= check_multiclick(code, grid, row, col);
   uint8_t buf[7];
@@ -442,8 +456,7 @@ size_t input_enqueue_mouse(int code, uint8_t modifier, int grid, int row, int co
   mouse_col = col;
 
   size_t written = 3 + (size_t)(p - buf);
-  rbuffer_write(input_buffer, (char *)buf, written);
-  return written;
+  input_enqueue_raw((char *)buf, written);
 }
 
 /// @return true if the main loop is blocked and waiting for input.
@@ -484,20 +497,15 @@ static InbufPollResult inbuf_poll(int ms, MultiQueue *events)
   return input_eof ? kInputEof : kInputNone;
 }
 
-bool input_available(void)
-{
-  return rbuffer_size(input_buffer) != 0;
-}
-
 static void input_read_cb(RStream *stream, RBuffer *buf, size_t c, void *data, bool at_eof)
 {
   if (at_eof) {
     input_eof = true;
   }
 
-  assert(rbuffer_space(input_buffer) >= rbuffer_size(buf));
+  assert(input_space() >= rbuffer_size(buf));
   RBUFFER_UNTIL_EMPTY(buf, ptr, len) {
-    (void)rbuffer_write(input_buffer, ptr, len);
+    input_enqueue_raw(ptr, len);
     rbuffer_consumed(buf, len);
   }
 }
@@ -508,23 +516,24 @@ static void process_ctrl_c(void)
     return;
   }
 
-  size_t consume_count = 0;
-  RBUFFER_EACH_REVERSE(input_buffer, c, i) {
-    if ((uint8_t)c == Ctrl_C
-        || ((uint8_t)c == 'C' && i >= 3
-            && (uint8_t)(*rbuffer_get(input_buffer, i - 3)) == K_SPECIAL
-            && (uint8_t)(*rbuffer_get(input_buffer, i - 2)) == KS_MODIFIER
-            && (uint8_t)(*rbuffer_get(input_buffer, i - 1)) == MOD_MASK_CTRL)) {
-      *rbuffer_get(input_buffer, i) = Ctrl_C;
+  size_t available = input_available();
+  ssize_t i;
+  for (i = (ssize_t)available - 1; i >= 0; i--) {
+    uint8_t c = (uint8_t)input_read_pos[i];
+    if (c == Ctrl_C
+        || (c == 'C' && i >= 3
+            && (uint8_t)input_read_pos[i - 3] == K_SPECIAL
+            && (uint8_t)input_read_pos[i - 2] == KS_MODIFIER
+            && (uint8_t)input_read_pos[i - 1] == MOD_MASK_CTRL)) {
+      input_read_pos[i] = Ctrl_C;
       got_int = true;
-      consume_count = i;
       break;
     }
   }
 
-  if (got_int && consume_count) {
+  if (got_int && i > 0) {
     // Remove all unprocessed input (typeahead) before the CTRL-C.
-    rbuffer_consumed(input_buffer, consume_count);
+    input_read_pos += i;
   }
 }
 
@@ -548,7 +557,7 @@ static int push_event_key(uint8_t *buf, int maxlen)
 bool os_input_ready(MultiQueue *events)
 {
   return (typebuf_was_filled             // API call filled typeahead
-          || rbuffer_size(input_buffer)  // Input buffer filled
+          || input_available()           // Input buffer filled
           || pending_events(events));    // Events must be processed
 }