bool fields always return `false`

[patryk4815]

bug - bool fields always return false
Your library somehow never executes Decoder.decodeBool, I put there @breakpoint(), but never hit.

I generated mmdb using this script:

package main

import (
	"log"
	"net"
	"os"

	"github.com/maxmind/mmdbwriter"
	"github.com/maxmind/mmdbwriter/mmdbtype"
)

func main() {
	writer, err := mmdbwriter.New(mmdbwriter.Options{
		DatabaseType: "example",
		RecordSize:   24,
		IncludeReservedNetworks: true,
	})
	if err != nil {
		log.Fatal(err)
	}

	{
		_, network, _ := net.ParseCIDR("1.2.3.0/24")
		data := mmdbtype.Map{
			"foo":       mmdbtype.Uint16(0xffa1),
			"is_foo":    mmdbtype.Bool(false),
			"is_bar": mmdbtype.Bool(true),
		}
		err = writer.Insert(network, data)
		if err != nil {
			log.Fatal(err)
		}
	}
	{
		_, network, _ := net.ParseCIDR("127.0.0.0/8")
		data := mmdbtype.Map{
			"foo":       mmdbtype.Uint16(0xfaf2),
			"is_foo":    mmdbtype.Bool(true),
			"is_bar": mmdbtype.Bool(false),
		}
		err = writer.Insert(network, data)
		if err != nil {
			log.Fatal(err)
		}
	}

	fh, err := os.Create("db.mmdb")
	if err != nil {
		log.Fatal(err)
	}
	defer fh.Close()
	writer.WriteTo(fh)
}

[patryk4815]

Repro:

test "bug" {
    const IpRow = struct {
        is_foo: bool = false,
        is_bar: bool = false,
        foo: u16 = 0x0,
    };
    var db = try maxminddb.Reader.mmap(
      std.testing.allocator,
      "/path/to/testdb.mmdb",
    );
    defer db.unmap();

    const ip = try std.net.Address.parseIp("127.0.0.1", 0);
    const got = try db.lookup(std.testing.allocator, IpRow, &ip);

    try std.testing.expectEqual(IpRow{
        .foo = 0xfaf2,
        .is_foo = true,
        .is_bar = false,
    }, got);
}

Result:

test
└─ run test 0/1 passed, 1 failed
error: 'foo.test.bug' failed: expected true, found false

/nix/store/6jjqcclq2zjgm2909qjj27d6ahzmazx4-zig-0.15.2/lib/zig/std/testing.zig:110:17: 0x1110837 in expectEqualInner__anon_32003 (test)
                return error.TestExpectedEqual;
                ^
/nix/store/6jjqcclq2zjgm2909qjj27d6ahzmazx4-zig-0.15.2/lib/zig/std/testing.zig:151:17: 0x11109e7 in expectEqualInner__anon_31998 (test)
                try expectEqual(@field(expected, field.name), @field(actual, field.name));
                ^
/Users/psondej/projekty/zigmmdb/src/foo.zig:95:5: 0x1110d4b in test.bug (test)
    try std.testing.expectEqual(IpRow{
    ^
error: while executing test 'foo.test.bug', the following test command failed:
./.zig-cache/o/47f0f98e823c539d9e17a2ceebc2082c/test --cache-dir=./.zig-cache --seed=0xbd6fedd4 --listen=-

Build Summary: 1/3 steps succeeded; 1 failed; 0/1 tests passed; 1 failed

[oschwald]

I think the issue is that decodeStruct appears to expect the values in the MMDB to be in the same order as the struct fields.

[patryk4815]

Soo it is required to have same order? Or this library limitation?

[oschwald]

Given that the keys in the database are not guaranteed to be in a particular order, this seems like an issue with the library to me.

[marselester]

This is a limitation of the library. I relied on the order of fields to implement optional fields, see https://github.com/marselester/maxminddb.zig/blob/master/src/decoder.zig#L109.

Struct fields must match the layout (names and order) in the database.
When the names don't match, the struct field is skipped.
This is useful for optional fields, e.g., some db records have city.is_in_european_union flag.

I didn't realize that keys could be in arbitrary order in the database. I will need to rethink the design then, sorry about that.