GetRail fails for raw FIL (payer-is-operator) Rails

[JAG-UK]

What I did:

I called GetRail() on a native FIL rail (where payment contract is 0x0 and payer-is-operator). Specifically I did this:

`// FindActiveFILRail returns a rail ID where payer pays payee in native FIL, rail not terminated and not past end epoch.
func (c *Client) FindActiveFILRail(ctx context.Context, payer, payee common.Address) (*big.Int, error) {

    [...]

for {
	results, nextOff, total, err := c.payments.GetRailsForPayerAndToken(ctx, payer, filToken, offset, limit)
	
             [... bunch of checks ...]

	for _, ri := range results {
		view, err := c.payments.GetRail(ctx, ri.RailId)
		
                     [... bunch of checks ...]

		return ri.RailId, nil
	}
}
c.payInfo("no matching FIL rail", "payer", payer.Hex(), "payee", payee.Hex())
return nil, fmt.Errorf("filpay: no active native-FIL rail from %s to %s", payer.Hex(), payee.Hex())

}`

What I expected to happen:

Either a valid rail returned with nice inspectable info, or a clean error

What actually happened:

It panicked:

2026/03/24 10:43:36 http: panic serving 127.0.0.1:62322: reflect: call of reflect.Value.Len on struct Value goroutine 37 [running]: net/http.(*conn).serve.func1() /opt/homebrew/Cellar/go/1.24.4/libexec/src/net/http/server.go:1947 +0xb0 panic({0x100caace0?, 0x140004988a0?}) /opt/homebrew/Cellar/go/1.24.4/libexec/src/runtime/panic.go:792 +0x124 reflect.Value.lenNonSlice({0x14000121b00?, 0x14000020bb0?, 0x140002f7250?}) /opt/homebrew/Cellar/go/1.24.4/libexec/src/reflect/value.go:1782 +0x20c reflect.Value.Len(...) /opt/homebrew/Cellar/go/1.24.4/libexec/src/reflect/value.go:1761 github.com/ethereum/go-ethereum/accounts/abi.setArray({0x100d2c300?, 0x14000020a50?, 0x100d2c300?}, {0x14000121b00?, 0x14000020bb0?, 0x100d73fc0?}) /Users/jag/go/pkg/mod/github.com/ethereum/go-ethereum@v1.14.12/accounts/abi/reflect.go:145 +0xbc github.com/ethereum/go-ethereum/accounts/abi.set({0x100d2c300?, 0x14000020a50?, 0x140003002a0?}, {0x14000121b00?, 0x14000020bb0?, 0x0?}) /Users/jag/go/pkg/mod/github.com/ethereum/go-ethereum@v1.14.12/accounts/abi/reflect.go:114 +0x3e4 github.com/ethereum/go-ethereum/accounts/abi.Arguments.copyAtomic({0x0?, 0x1400029a090?, 0x14000035f18?}, {0x100c6e500?, 0x14000020a50?}, {0x14000121b00, 0x14000020bb0}) /Users/jag/go/pkg/mod/github.com/ethereum/go-ethereum@v1.14.12/accounts/abi/argument.go:136 +0x114 github.com/ethereum/go-ethereum/accounts/abi.Arguments.Copy({0x1400022a5a0?, 0x0?, 0x0?}, {0x100c6e500?, 0x14000020a50?}, {0x14000298040?, 0x0?, 0x0?}) /Users/jag/go/pkg/mod/github.com/ethereum/go-ethereum@v1.14.12/accounts/abi/argument.go:127 +0xb8 github.com/ethereum/go-ethereum/accounts/abi.ABI.UnpackIntoInterface({{{0x0, 0x0}, {0x0, 0x0}, 0x0, {0x0, 0x0}, 0x0, 0x0, {0x0, ...}, ...}, ...}, ...) /Users/jag/go/pkg/mod/github.com/ethereum/go-ethereum@v1.14.12/accounts/abi/abi.go:125 +0xc8 github.com/data-preservation-programs/go-synapse/contracts.(*PaymentsContract).GetRail(0x140001dd208, {0x100d6bc58, 0x140003cc140}, 0x14000036ae8?) /Users/jag/go/pkg/mod/github.com/data-preservation-programs/go-synapse@v0.0.0-20260310124115-0faeb6924d36/contracts/payments.go:358 +0x1fc github.com/fidlabs/paid-retrievals/internal/filpay.(*Client).FindActiveFILRail(0x1400003ee40, {0x100d6bc58, 0x140003cc140}, {0x20, 0x15, 0x45, 0xe0, 0x4c, 0xc9, 0x79, ...}, ...) /Users/jag/repos/filecoin_stuff/paid-retrievals/internal/filpay/settlement.go:385 +0x7e8 github.com/fidlabs/paid-retrievals/internal/filpay.(*Client).SettleIfFunded(0x1400003ee40, {0x100d6bc58, 0x140003cc140}, {0x20, 0x15, 0x45, 0xe0, 0x4c, 0xc9, 0x79, ...}, ...) /Users/jag/repos/filecoin_stuff/paid-retrievals/internal/filpay/settlement.go:423 +0x224 github.com/fidlabs/paid-retrievals/internal/spproxy.handlePaid({0x100d6ad68, 0x140003d00e0}, 0x1400031c140, 0x140001a4260, {{0x16f98f5eb, 0x4}, {0x100ae73b0, 0x6}, {0x100aee940, 0x10}, ...}, ...) /Users/jag/repos/filecoin_stuff/paid-retrievals/internal/spproxy/proxy.go:227 +0xd10 github.com/fidlabs/paid-retrievals/internal/spproxy.NewHandler.func1({0x100d6ad68, 0x140003d00e0}, 0x1400031c140) /Users/jag/repos/filecoin_stuff/paid-retrievals/internal/spproxy/proxy.go:95 +0x52c net/http.HandlerFunc.ServeHTTP(0x0?, {0x100d6ad68?, 0x140003d00e0?}, 0x14000037b60?) /opt/homebrew/Cellar/go/1.24.4/libexec/src/net/http/server.go:2294 +0x38 net/http.serverHandler.ServeHTTP({0x140002306c0?}, {0x100d6ad68?, 0x140003d00e0?}, 0x1?) /opt/homebrew/Cellar/go/1.24.4/libexec/src/net/http/server.go:3301 +0xbc net/http.(*conn).serve(0x14000554000, {0x100d6bc20, 0x140001e9e90}) /opt/homebrew/Cellar/go/1.24.4/libexec/src/net/http/server.go:2102 +0x52c created by net/http.(*Server).Serve in goroutine 1 /opt/homebrew/Cellar/go/1.24.4/libexec/src/net/http/server.go:3454 +0x3d8

System:

MacOS, go-synapse main head commit 0faeb69

[JAG-UK]

I have a patch for this and go test passes, just want to make sure it still works with non-tupled output before raising PR

[parkan]

fixed by #9 (but feel free to re-open if you disagree/observe otherwise)