[Tarantool-patches] [PATCH] lua: handle uri.format empty input properly

[olegrok@tarantool.org]

From: Oleg Babin <babinoleg@mail.ru>

After 7fd6c8096343ca254fec10c2ce8a8233ebe47028
(buffer: port static allocator to Lua) uri started to use
static_allocator - cyclic buffer that also is used in
several modules.

However situation then uri.format output is zero-length
string was not handled properly and ffi.string could
return data that was previously written in static buffer
because use as string terminator the first zero byte.

To prevent such situation let's pass result length explicitly.

Closes #4779
---
Issue: https://github.com/tarantool/tarantool/issues/4779
Branch: https://github.com/tarantool/tarantool/tree/olegrok/4779-uri-format-junk-output
 src/lua/uri.lua           |  4 ++--
 test/app-tap/uri.test.lua | 18 +++++++++++++++++-
 2 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/src/lua/uri.lua b/src/lua/uri.lua
index 5967c8bf2..e08e20675 100644
--- a/src/lua/uri.lua
+++ b/src/lua/uri.lua
@@ -77,8 +77,8 @@ local function format(uri, write_password)
     uribuf.fragment = uri.fragment
     uribuf.fragment_len = string.len(uri.fragment or '')
     local str = static_alloc('char', 1024)
-    builtin.uri_format(str, 1024, uribuf, write_password and 1 or 0)
-    return ffi.string(str)
+    local len = builtin.uri_format(str, 1024, uribuf, write_password and 1 or 0)
+    return ffi.string(str, len)
 end
 
 return {
diff --git a/test/app-tap/uri.test.lua b/test/app-tap/uri.test.lua
index 5405b0873..27efe6bc6 100755
--- a/test/app-tap/uri.test.lua
+++ b/test/app-tap/uri.test.lua
@@ -2,6 +2,8 @@
 
 local tap = require('tap')
 local uri = require('uri')
+local ffi = require('ffi')
+local static_alloc = require('buffer').static_alloc
 
 local function test_parse(test)
     -- Tests for uri.parse() Lua bindings.
@@ -64,8 +66,22 @@ local function test_format(test)
     test:is(uri.format(u, true), "user:password@localhost", "password kept")
 end
 
+local function test_static_alloc(test)
+    -- gh-4779 uri.format returns junk output
+    local buffer_size = 12288
+    local buf = static_alloc('char', buffer_size)
+    ffi.fill(buf, 512, string.byte('x'))
+
+    local iterations = 10
+    test:plan(iterations)
+    for _ = 1, iterations do
+        test:is(uri.format({}), '')
+    end
+end
+
 tap.test("uri", function(test)
-    test:plan(2)
+    test:plan(3)
     test:test("parse", test_parse)
     test:test("format", test_format)
+    test:test("static_alloc", test_static_alloc)
 end)
-- 
2.23.0