Runtime: Add a last_error function to the miniz bindings

This is a bit questionable, but without it there's no way to actually test the error messages (since Lua doesn't have access to the archive userdata, and it likely shouldn't). The map is just to guard against multithreaded access even if I don't really consider this supported...

The previous approach of hardcoding errors doesn't work reliably.

Runtime/Bindings/lminiz.cpp

@@ -1,5 +1,8 @@
 #include "lminiz.hpp"
 
+#include <unordered_map>
+#include <string>
+
 extern "C" {
 #include "luv.h"
 
@@ -38,6 +41,18 @@ static int lmz_check_compression_level(lua_State* L, int index) {
 	return level;
 }
 
+static std::unordered_map<lua_State*, std::string> error_messages;
+static int lmz_last_error(lua_State* L) {
+	auto iter = error_messages.find(L);
+	if(iter == error_messages.end()) {
+		lua_pushnil(L);
+	} else {
+		lua_pushstring(L, iter->second.c_str());
+		error_messages.erase(iter);
+	}
+	return 1;
+}
+
 static int lmz_reader_init(lua_State* L) {
 	const char* path = luaL_checkstring(L, 1);
 	mz_uint32 flags = luaL_optinteger(L, 2, 0);
@@ -55,8 +70,10 @@ static int lmz_reader_init(lua_State* L) {
 	archive->m_pIO_opaque = zip;
 	if(!mz_zip_reader_init(archive, size, flags)) {
 		lua_pushnil(L);
+		const char* error_string = mz_zip_get_error_string(mz_zip_get_last_error(archive));
+		error_messages[L] = error_string;
 		lua_pushfstring(L, "Failed to initialize miniz reader for archive %s (Last error: %s)", path,
-			mz_zip_get_error_string(mz_zip_get_last_error(archive)));
+			error_string);
 		return 2;
 	}
 	return 1;
@@ -474,6 +491,7 @@ static const luaL_Reg lminiz_f[] = {
 	{ "version", lmz_version },
 	{ "new_deflator", lmz_deflator_init },
 	{ "new_inflator", lmz_inflator_init },
+	{ "last_error", lmz_last_error },
 	{ NULL, NULL }
 };
 

Tests/BDD/miniz-library.spec.lua

@@ -12,6 +12,7 @@ describe("miniz", function()
 		"uncompress",
 		"new_deflator",
 		"new_inflator",
+		"last_error",
 	}
 
 	it("should export all miniz functions", function()
@@ -169,12 +170,23 @@ describe("miniz", function()
 
 	describe("new_reader", function()
 		it("should fail if an invalid file path was passed", function()
-			assertFailure(
-				function()
-					return miniz.new_reader("asdf-does-not-exist.zip")
-				end,
-				"Failed to initialize miniz reader for archive asdf-does-not-exist.zip (Last error: failed finding central directory)"
+			local success, failureMessage = miniz.new_reader("asdf-does-not-exist.zip")
+			-- Can't use assertFailure here because the message is only available after new_reader exits
+			assertNil(success)
+			assertEquals(
+				failureMessage,
+				format(
+					"Failed to initialize miniz reader for archive asdf-does-not-exist.zip (Last error: %s)",
+					miniz.last_error()
+				)
 			)
 		end)
 	end)
+
+	describe("last_error", function()
+		it("should return nil if no error has been set", function()
+			-- Technically, an error may have been set (and not cleared) by a previous test, but that's a no-no and should be caught
+			assertNil(miniz.last_error())
+		end)
+	end)
 end)