1 files changed, 109 insertions, 0 deletions
diff --git a/modules/http/http_trace.lua b/modules/http/http_trace.lua
new file mode 100644
index 0000000..9e4d466
--- /dev/null
+++ b/modules/http/http_trace.lua
@@ -0,0 +1,109 @@
+local ffi = require('ffi')
+local bit = require('bit')
+local condition = require('cqueues.condition')
+
+-- Buffer selected record information to a table
+local function add_selected_records(dst, records)
+	for _, rec in ipairs(records) do
+		local rank = rec.rank
+		-- Separate the referral chain verified flag
+		local verified = bit.band(rec.rank, kres.rank.AUTH)
+		if verified then
+			rank = bit.band(rank, bit.bnot(kres.rank.AUTH))
+		end
+		local rank_name = kres.tostring.rank[rank] or tostring(rank)
+		-- Write out each individual RR
+		for rr in tostring(rec.rr):gmatch('[^\n]+\n?') do
+			local row = string.format('cached: %s, rank: %s, record: %s',
+				rec.cached, rank_name:lower(), rr)
+			table.insert(dst, row)
+		end
+	end
+end
+
+local function format_selected_records(header, records)
+	if #records == 0 then return '' end
+	return string.format('%s\n%s\n', header, string.rep('-', #header))
+	       .. table.concat(records, '') .. '\n'
+end
+
+-- 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 (query, source, msg)
+		local message = string.format('[%5s] [%s] %s',
+			query.id, ffi.string(source), ffi.string(msg))
+		table.insert(buffer, message)
+	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 answers, authority = {}, {}
+	local cond = condition.new()
+	local waiting, done = false, false
+	local finish_cb = ffi.cast('trace_callback_f', function (req)
+		req = kres.request_t(req)
+		add_selected_records(answers, req.answ_selected)
+		add_selected_records(authority, req.auth_selected)
+		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 = kres.request_t(req)
+			req.trace_log = buffer_log_cb
+			req.trace_finish = 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, '') .. '\n'
+	               .. format_selected_records('Used records from answer:', answers)
+	               .. format_selected_records('Used records from authority:', authority)
+	-- Return buffered data
+	if not done then
+		return 504, result
+	end
+	return result
+end
+
+-- Export endpoints
+return {
+	endpoints = {
+		['/trace']   = {'text/plain', serve_trace},
+	}
+}
+\ No newline at end of file