diff --git a/runtime/doc/news.txt b/runtime/doc/news.txt
index ea340105d3..6eaa69cb64 100644
--- a/runtime/doc/news.txt
+++ b/runtime/doc/news.txt
@@ -177,6 +177,8 @@ PERFORMANCE
   Lua.
 • The table holding LSP data is now cleared using `table.clear`,
   thus reducing GC and memory reallocation during each data reset.
+• When parsing the received Content-Length messages,
+  the RPC client will no longer allocate extra strings.
 
 PLUGINS
 
diff --git a/runtime/lua/vim/_core/stringbuffer.lua b/runtime/lua/vim/_core/stringbuffer.lua
index 0241784a9b..e789f7b003 100644
--- a/runtime/lua/vim/_core/stringbuffer.lua
+++ b/runtime/lua/vim/_core/stringbuffer.lua
@@ -22,21 +22,22 @@ if has_strbuffer then
   return M
 end
 
+--- @class vim._core.stringbuffer.ptr
+--- @field [integer] integer
+
 --- @class vim._core.stringbuffer
+--- @field private ptr vim._core.stringbuffer.ptr
 --- @field private buf string[]
 --- @field package len integer absolute length of the `buf`
 --- @field package skip_ptr integer
 local StrBuffer = {}
 StrBuffer.__index = StrBuffer
 
---- @return string
-function StrBuffer:tostring()
+function StrBuffer:_normalize()
   if #self.buf > 1 then
     self.buf = { table.concat(self.buf) }
   end
 
-  -- assert(self.len == #(self.buf[1] or ''), 'len mismatch')
-
   if self.skip_ptr > 0 then
     if self.buf[1] then
       self.buf[1] = self.buf[1]:sub(self.skip_ptr + 1)
@@ -45,18 +46,21 @@ function StrBuffer:tostring()
     self.skip_ptr = 0
   end
 
-  -- assert(self.len == #(self.buf[1] or ''), 'len mismatch')
+  return self
+end
 
-  return self.buf[1] or ''
+--- @return string
+function StrBuffer:tostring()
+  return self:_normalize().buf[1] or ''
 end
 
 StrBuffer.__tostring = StrBuffer.tostring
 
 --- @private
---- Efficiently peak at the first `n` characters of the buffer.
+--- Efficiently peek at the first `n` characters of the buffer.
 --- @param n integer
 --- @return string
-function StrBuffer:_peak(n)
+function StrBuffer:_peek(n)
   local skip, buf1 = self.skip_ptr, self.buf[1]
   if buf1 and (n + skip) < #buf1 then
     return buf1:sub(skip + 1, skip + n)
@@ -81,7 +85,7 @@ end
 --- @return string
 function StrBuffer:get(n)
   n = n or self.len
-  local r = self:_peak(n)
+  local r = self:_peek(n)
   self:skip(n)
   return r
 end
@@ -99,8 +103,27 @@ function StrBuffer:reset()
   return self
 end
 
+--- Efficiently read the character at the 0-based index `k` in the buffer.
+--- @param k integer
+--- @return integer
+function StrBuffer:_index(k)
+  return self:_normalize().buf[1]:byte(k + 1)
+end
+
+--- @return vim._core.stringbuffer.ptr, integer
+function StrBuffer:ref()
+  return self.ptr, self.len - self.skip_ptr
+end
+
 function M.new()
-  return setmetatable({}, StrBuffer):reset()
+  local self = setmetatable({}, StrBuffer):reset()
+  ---@diagnostic disable-next-line: invisible
+  self.ptr = setmetatable({}, {
+    __index = function(_, k)
+      return StrBuffer._index(self, k)
+    end,
+  })
+  return self
 end
 
 --- @param buf vim._core.stringbuffer
diff --git a/runtime/lua/vim/lsp/rpc.lua b/runtime/lua/vim/lsp/rpc.lua
index 7d85be89c9..6739073cd3 100644
--- a/runtime/lua/vim/lsp/rpc.lua
+++ b/runtime/lua/vim/lsp/rpc.lua
@@ -191,22 +191,30 @@ local default_dispatchers = {
 }
 
 --- @async
-local function request_parser_loop()
-  local buf = strbuffer.new()
+local function parse_content_length()
+  local strbuf = 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 strbuffer.len(buf) < content_length do
-        buf:put(coroutine.yield())
+    local header_len ---@type integer?
+    local ptr, len = strbuf:ref()
+    for i = 0, len - 4 do
+      -- Find the header boundary "\r\n\r\n"
+      -- (compare bytes instead of string.find(), to avoid a string alloc).
+      if ptr[i] == 13 and ptr[i + 1] == 10 and ptr[i + 2] == 13 and ptr[i + 3] == 10 then
+        header_len = i + 2
+        break
       end
-      local body = buf:get(content_length)
-      buf:put(coroutine.yield(body))
+    end
+    if header_len then
+      local header = strbuf:get(header_len)
+      strbuf:skip(2) -- skip past header boundary
+      local content_length = get_content_length(header)
+      while strbuffer.len(strbuf) < content_length do
+        strbuf:put(coroutine.yield())
+      end
+      local body = strbuf:get(content_length)
+      strbuf:put(coroutine.yield(body))
     else
-      buf:put(coroutine.yield())
+      strbuf:put(coroutine.yield())
     end
   end
 end
@@ -218,7 +226,7 @@ end
 function M.create_read_loop(handle_body, on_exit, on_error)
   on_exit = on_exit or function() end
   on_error = on_error or function() end
-  local co = coroutine.create(request_parser_loop)
+  local co = coroutine.create(parse_content_length)
   coroutine.resume(co)
   return function(err, chunk)
     if err then