Merge de17f182bb into 7121983c45

Avoids some table allocations.
In a quick test over 50000 iterations it reduces the time from 130ms to
74 ms

For the test setup details see:

https://github.com/mfussenegger/nvim-dap/pull/1394#issue-2725352391

runtime/lua/vim/lsp/rpc.lua

@@ -16,34 +16,21 @@ local function format_message_with_content_length(message)
   })
 end
 
----@class (private) vim.lsp.rpc.Headers: {string: any}
----@field content_length integer
-
---- Parses an LSP Message's header
+--- Extract content-length from the msg header
 ---
----@param header string The header to parse.
----@return vim.lsp.rpc.Headers#parsed headers
-local function parse_headers(header)
-  assert(type(header) == 'string', 'header must be a string')
-  --- @type vim.lsp.rpc.Headers
-  local headers = {}
-  for line in vim.gsplit(header, '\r\n', { plain = true }) do
+---@param header string The header to parse
+---@return integer?
+local function get_content_length(header)
+  for line in header:gmatch('(.-)\r\n') do
     if line == '' then
       break
     end
-    --- @type string?, string?
-    local key, value = line:match('^%s*(%S+)%s*:%s*(.+)%s*$')
-    if key then
-      key = key:lower():gsub('%-', '_') --- @type string
-      headers[key] = value
-    else
-      log.error('invalid header line %q', line)
-      error(string.format('invalid header line %q', line))
+    local key, value = line:match('^%s*(%S+)%s*:%s*(%d+)%s*$')
+    if key and key:lower() == 'content-length' then
+      return tonumber(value)
     end
   end
-  headers.content_length = tonumber(headers.content_length)
-    or error(string.format('Content-Length not found in headers. %q', header))
-  return headers
+  error('Content-Length not found in header: ' .. header)
 end
 
 -- This is the start of any possible header patterns. The gsub converts it to a
@@ -52,15 +39,45 @@ local header_start_pattern = ('content'):gsub('%w', function(c)
   return '[' .. c .. c:upper() .. ']'
 end)
 
+
+local has_strbuffer, strbuffer = pcall(require, "string.buffer")
+
 --- The actual workhorse.
-local function request_parser_loop()
+---@type function
+local request_parser_loop
+
+if has_strbuffer then
+  request_parser_loop = function()
+    local buf = strbuffer.new()
+    while true do
+      local msg = buf:tostring()
+      local header_end = msg:find('\r\n\r\n', 1, true)
+      if header_end then
+        local header = buf:get(header_end + 1)
+        buf:skip(2) -- skip past header boundary
+        local content_length = get_content_length(header)
+        while #buf < content_length do
+          local chunk = coroutine.yield()
+          buf:put(chunk)
+        end
+        local body = buf:get(content_length)
+        local chunk = coroutine.yield(body)
+        buf:put(chunk)
+      else
+        local chunk = coroutine.yield()
+        buf:put(chunk)
+      end
+    end
+  end
+else
+  request_parser_loop = function()
     local buffer = '' -- only for header part
     while true do
       -- A message can only be complete if it has a double CRLF and also the full
       -- payload, so first let's check for the CRLFs
-    local start, finish = buffer:find('\r\n\r\n', 1, true)
+      local header_end, body_start = buffer:find('\r\n\r\n', 1, true)
       -- Start parsing the headers
-    if start then
+      if header_end then
         -- This is a workaround for servers sending initial garbage before
         -- sending headers, such as if a bash script sends stdout. It assumes
         -- that we know all of the headers ahead of time. At this moment, the
@@ -76,13 +93,13 @@ local function request_parser_loop()
             )
           )
         end
-      local headers = parse_headers(buffer:sub(buffer_start, start - 1))
-      local content_length = headers.content_length
+        local header = buffer:sub(buffer_start, header_end + 1)
+        local content_length = get_content_length(header)
         -- Use table instead of just string to buffer the message. It prevents
         -- a ton of strings allocating.
         -- ref. http://www.lua.org/pil/11.6.html
         ---@type string[]
-      local body_chunks = { buffer:sub(finish + 1) }
+        local body_chunks = { buffer:sub(body_start + 1) }
         local body_length = #body_chunks[1]
         -- Keep waiting for data until we have enough.
         while body_length < content_length do
@@ -103,7 +120,7 @@ local function request_parser_loop()
         -- Yield our data.
 
         --- @type string
-      local data = coroutine.yield(headers, body)
+        local data = coroutine.yield(body)
           or error('Expected more data for the body. The server may have died.')
         buffer = rest .. data
       else
@@ -114,8 +131,10 @@ local function request_parser_loop()
         buffer = buffer .. data
       end
     end
+  end
 end
 
+
 local M = {}
 
 --- Mapping of error codes used by the client
@@ -237,7 +256,7 @@ local default_dispatchers = {
 --- @param on_exit? fun()
 --- @param on_error fun(err: any)
 function M.create_read_loop(handle_body, on_exit, on_error)
-  local parse_chunk = coroutine.wrap(request_parser_loop) --[[@as fun(chunk: string?): vim.lsp.rpc.Headers?, string?]]
+  local parse_chunk = coroutine.wrap(request_parser_loop) --[[@as fun(chunk: string?): string]]
   parse_chunk()
   return function(err, chunk)
     if err then
@@ -253,9 +272,9 @@ function M.create_read_loop(handle_body, on_exit, on_error)
     end
 
     while true do
-      local headers, body = parse_chunk(chunk)
-      if headers then
-        handle_body(assert(body))
+      local body = parse_chunk(chunk)
+      if body then
+        handle_body(body)
         chunk = ''
       else
         break