tests/lapi: add io tests

The functions below are not covered:
`io.close()`, `io.flush()`, `io.input()`, `io.open()`,
`io.output()`, `io.tmpfile()`, `io.type()`, `io.write()`,
`file:close()`, `file:flush()`, `file:lines()`, `file:read()`,
`file:seek()`, `file:setvbuf()`, `file:write()`.

Author: ligurio

tests/lapi/io_lines_test.lua

@@ -0,0 +1,35 @@
+--[[
+SPDX-License-Identifier: ISC
+Copyright (c) 2023-2025, Sergey Bronnikov.
+
+5.7 – Input and Output Facilities
+https://www.lua.org/manual/5.1/manual.html#5.7
+https://www.lua.org/pil/21.1.html
+
+Does io.lines() stream or slurp the file?
+https://stackoverflow.com/questions/43005068/does-io-lines-stream-or-slurp-the-file
+
+io.lines does not check maximum number of options,
+https://www.lua.org/bugs.html#5.3.1-1
+
+Synopsis: io.lines([filename, ...])
+]]
+
+local luzer = require("luzer")
+local test_lib = require("lib")
+
+local function TestOneInput(buf)
+    local fdp = luzer.FuzzedDataProvider(buf)
+    local str = fdp:consume_string(test_lib.MAX_STR_LEN)
+    local lua_chunk = ("io.write([[%s]])"):format(str)
+    local lua_cmd = ("%s -e '%s'"):format(test_lib.luabin(arg), lua_chunk)
+    local fh = assert(io.popen(lua_cmd))
+    fh:lines("*all")
+    fh:flush()
+    fh:close()
+end
+
+local args = {
+    artifact_prefix = "io_lines_",
+}
+luzer.Fuzz(TestOneInput, nil, args)

tests/lapi/io_popen_test.lua

@@ -0,0 +1,34 @@
+--[[
+SPDX-License-Identifier: ISC
+Copyright (c) 2023-2025, Sergey Bronnikov.
+
+5.7 – Input and Output Facilities
+https://www.lua.org/manual/5.1/manual.html#5.7
+
+'popen' can crash if called with an invalid mode,
+https://github.com/lua/lua/commit/1ecfbfa1a1debd2258decdf7c1954ac6f9761699
+
+On some machines, closing a "piped file" (created with io.popen) may crash Lua,
+https://www.lua.org/bugs.html#5.0.2-8
+
+Synopsis: io.popen(prog [, mode])
+]]
+
+local luzer = require("luzer")
+local test_lib = require("lib")
+
+local function TestOneInput(buf)
+    local fdp = luzer.FuzzedDataProvider(buf)
+    local str = fdp:consume_string(test_lib.MAX_STR_LEN)
+    local lua_chunk = ("io.write([[%s]])"):format(str)
+    local lua_cmd = ("%s -e '%s'"):format(test_lib.luabin(arg), lua_chunk)
+    local fh = assert(io.popen(lua_cmd))
+    fh:lines("*all")
+    fh:flush()
+    fh:close()
+end
+
+local args = {
+    artifact_prefix = "io_popen_",
+}
+luzer.Fuzz(TestOneInput, nil, args)

tests/lapi/io_read_test.lua

@@ -0,0 +1,34 @@
+--[[
+SPDX-License-Identifier: ISC
+Copyright (c) 2023-2025, Sergey Bronnikov.
+
+5.7 – Input and Output Facilities
+https://www.lua.org/manual/5.1/manual.html#5.7
+https://www.lua.org/pil/21.3.html
+
+Synopsis: io.read(...)
+]]
+
+local luzer = require("luzer")
+local test_lib = require("lib")
+
+local READ_MODE = { "*n", "*a", "*l" }
+
+local function TestOneInput(buf)
+    local fdp = luzer.FuzzedDataProvider(buf)
+    local str = fdp:consume_string(test_lib.MAX_STR_LEN)
+    local lua_cmd = ("%s -e '%s'"):format(test_lib.luabin(arg), str)
+    local fh = io.popen(lua_cmd, "w")
+    local mode = fdp:oneof(READ_MODE)
+    local cur_pos = fh:seek()
+    fh:seek("end")
+    fh:seek("set", cur_pos)
+    fh:read(mode)
+    fh:flush()
+    fh:close()
+end
+
+local args = {
+    artifact_prefix = "io_read_",
+}
+luzer.Fuzz(TestOneInput, nil, args)

tests/lapi/lib.lua

@@ -96,9 +96,19 @@ local function random_locale(fdp)
     return fdp:oneof(locales)
 end
 
+local function luabin(argv)
+    -- arg[-1] is guaranteed to be not nil.
+    local idx = -2
+    while argv[idx] do
+        idx = idx - 1
+    end
+    return argv[idx + 1]
+end
+
 return {
     approx_equal = approx_equal,
     bitwise_op = bitwise_op,
+    luabin = luabin,
     lua_version = lua_version,
     lua_current_version_ge_than = lua_current_version_ge_than,
     lua_current_version_lt_than = lua_current_version_lt_than,