1 files changed, 77 insertions, 0 deletions
diff --git a/modules/http/http_trace.lua b/modules/http/http_trace.lua
new file mode 100644
index 0000000..123cd52
--- /dev/null
+++ b/modules/http/http_trace.lua
@@ -0,0 +1,77 @@
+-- SPDX-License-Identifier: GPL-3.0-or-later
+local ffi = require('ffi')
+local condition = require('cqueues.condition')
+
+-- Trace execution of DNS queries
+local function serve_trace(h, _)
+	local path = h:get(':path')
+	local qname, qtype_str = path:match('/trace/([^/]+)/?([^/]*)')
+	if not qname then
+		return 400, 'expected /trace/<query name>/<query type>'
+	end
+
+	-- Parse query type (or default to A)
+	if not qtype_str or #qtype_str == 0 then
+		qtype_str = 'A'
+	end
+
+	local qtype = kres.type[qtype_str]
+	if not qtype then
+		return 400, string.format('unexpected query type: %s', qtype_str)
+	end
+
+	-- Create logging handler callback
+	local buffer = {}
+	local buffer_log_cb = ffi.cast('trace_log_f', function (_, msg)
+		jit.off(true, true) -- JIT for (C -> lua)^2 nesting isn't allowed
+		table.insert(buffer, ffi.string(msg))
+	end)
+
+	-- Wait for the result of the query
+	-- Note: We can't do non-blocking write to stream directly from resolve callbacks
+	-- because they don't run inside cqueue.
+	local cond = condition.new()
+	local waiting, done = false, false
+	local finish_cb = ffi.cast('trace_callback_f', function (req)
+		jit.off(true, true) -- JIT for (C -> lua)^2 nesting isn't allowed
+		table.insert(buffer, req:selected_tostring())
+		if waiting then
+			cond:signal()
+		end
+		done = true
+	end)
+
+	-- Resolve query and buffer logs into table
+	resolve {
+		name = qname,
+		type = qtype,
+		options = {'TRACE'},
+		init = function (req)
+			req:trace_chain_callbacks(buffer_log_cb, finish_cb)
+		end
+	}
+
+	-- Wait for asynchronous query and free callbacks
+	if not done then
+		waiting = true
+		cond:wait()
+	end
+
+	buffer_log_cb:free()
+	finish_cb:free()
+
+	-- Build the result
+	local result = table.concat(buffer, '')
+	-- Return buffered data
+	if not done then
+		return 504, result
+	end
+	return result
+end
+
+-- Export endpoints
+return {
+	endpoints = {
+		['/trace']   = {'text/plain', serve_trace},
+	}
+}