Problem with several subqueries in one query

[oizgagin]

Hi! Thanks for such a great project!

Problem

promxy v0.0.57 panics when given e.g. the folowing metric

deriv(avg_over_time(sum(node_cpu)[5m:1m])[5m:1m]) * 60

with traceback

goroutine 136 [running]:
github.com/jacksontj/promxy/pkg/proxystorage.(*ProxyStorage).NodeReplacer(0xc00021ca10, 0x273c8e0, 0xc000810100, 0xc0004d2320, 0x26e5cc0, 0xc0007e0cc0, 0xc0000a81e0, 0x0, 0xc000810100, 0x26e0000)
        /go/src/github.com/jacksontj/promxy/pkg/proxystorage/proxy.go:262 +0x31f2
github.com/jacksontj/promxy/vendor/github.com/prometheus/prometheus/promql.Walk(0x273c8e0, 0xc000810100, 0x26e8320, 0xc000810040, 0xc0004d2320, 0x26e5cc0, 0xc0007e0cc0, 0xc0008101c0, 0x3, 0x4, ...)
        /go/src/github.com/jacksontj/promxy/vendor/github.com/prometheus/prometheus/promql/ast.go:275 +0x186f
github.com/jacksontj/promxy/vendor/github.com/prometheus/prometheus/promql.Walk(0x273c8e0, 0xc000810100, 0x26e8320, 0xc000810040, 0xc0004d2320, 0x26e8300, 0xc000330a40, 0xc0008101c0, 0x3, 0x4, ...)
        /go/src/github.com/jacksontj/promxy/vendor/github.com/prometheus/prometheus/promql/ast.go:300 +0x430
github.com/jacksontj/promxy/vendor/github.com/prometheus/prometheus/promql.Walk(0x273c8e0, 0xc000810100, 0x26e8320, 0xc000810040, 0xc0004d2320, 0x26e5be0, 0xc0007de400, 0xc000330a20, 0x2, 0x2, ...)
        /go/src/github.com/jacksontj/promxy/vendor/github.com/prometheus/prometheus/promql/ast.go:355 +0x1518
github.com/jacksontj/promxy/vendor/github.com/prometheus/prometheus/promql.Walk.func1(0x273c8e0, 0xc000810100, 0x26e8320, 0xc000810040, 0xc0004d2320, 0xc00008d180, 0xc00021d240, 0xc0000d8a20, 0xc0000781e0, 0x1, ...)
        /go/src/github.com/jacksontj/promxy/vendor/github.com/prometheus/prometheus/promql/ast.go:328 +0xf1
created by github.com/jacksontj/promxy/vendor/github.com/prometheus/prometheus/promql.Walk
        /go/src/github.com/jacksontj/promxy/vendor/github.com/prometheus/prometheus/promql/ast.go:327 +0xd10

Possible solution

From my understanding, it should be ok to add another case to switch here:

diff --git a/pkg/proxystorage/proxy.go b/pkg/proxystorage/proxy.go
index 11386ba6..1e46139c 100644
--- a/pkg/proxystorage/proxy.go
+++ b/pkg/proxystorage/proxy.go
@@ -258,6 +258,8 @@ func (p *ProxyStorage) NodeReplacer(ctx context.Context, s *promql.EvalStmt, nod
                        n.Expr = promql.NewRawMatrixFromMatrix(subNodeTyped)
                case *promql.VectorSelector:
                        n.Expr = promql.NewRawMatrixFromVector(subNodeTyped)
+               case nil:
+                       break
                default:
                        panic(fmt.Sprintf("Unhandled SubqueryExpr return type: %T", subNode))
                }

[oizgagin]

@jacksontj is there anything I can help you with?

[jacksontj]

@oizgagin Thanks for the report, debug, and fix! I've opened #278 with the fix (it looks correct to me), so once CI passes that'll get merged in.

[oizgagin]

Thanks!