failed to unmarshal input edges graph to graph: %s

Error message

failed to unmarshal input edges graph to graph: %s

What it means

The plugin's RouteEdges RPC receives a serialized edges graph from the host process. d2graph.DeserializeGraph failed to decode in.GEdges into a d2graph.Graph, so the plugin cannot reconstruct the edges to route. This guards the plugin against malformed or incompatible serialized graph payloads.

Source

Thrown at d2plugin/serve.go:180

	inRaw, err := io.ReadAll(ms.Stdin)
	if err != nil {
		return err
	}

	var in routeEdgesInput
	err = json.Unmarshal(inRaw, &in)
	if err != nil {
		return err
	}

	var g d2graph.Graph
	if err := d2graph.DeserializeGraph(in.G, &g); err != nil {
		return fmt.Errorf("failed to unmarshal input graph to graph: %s", in)
	}

	var gedges d2graph.Graph
	if err := d2graph.DeserializeGraph(in.GEdges, &gedges); err != nil {
		return fmt.Errorf("failed to unmarshal input edges graph to graph: %s", in)
	}

	err = p.RouteEdges(ctx, &g, gedges.Edges)
	if err != nil {
		return err
	}

	b, err := d2graph.SerializeGraph(&g)
	if err != nil {
		return err
	}
	_, err = ms.Stdout.Write(b)
	if err != nil {
		return err
	}
	return nil
}

View on GitHub (pinned to 0d69dca6f5)

Solutions

Regenerate the GEdges payload with d2graph.SerializeGraph from the same d2 version as the plugin
Verify the plugin and host use the same terrastruct/d2 module version (go.mod alignment)
Inspect in.GEdges and confirm it is a valid serialized d2graph.Graph, not the DSL source or the main diagram
If writing a custom caller, serialize the edges graph exactly as the d2 plugin host does

Example fix

// before
req.GEdges = string(diagramJSON) // wrong payload
// after
var gedges d2graph.Graph
gedges.Edges = g.Edges
b, _ := d2graph.SerializeGraph(&gedges)
req.GEdges = b

Defensive patterns

Strategy: validation

Validate before calling

var check d2graph.Graph
if err := d2graph.DeserializeGraph(in.GEdges, &check); err != nil {
	return fmt.Errorf("invalid GEdges payload: %w", err)
}

Prevention

Keep host and plugin on the same terrastruct/d2 version
Always produce GEdges with d2graph.SerializeGraph
Never hand-construct plugin request payloads
Add a smoke test that round-trips Serialize/DeserializeGraph

When it happens

Trigger: Calling a routing plugin (via serve-handler) with an input whose GEdges field is not valid serialized d2graph JSON, or was produced by a different d2 version with an incompatible schema.

Common situations: Host and plugin built from different terrastruct/d2 versions; GEdges accidentally left nil/empty or overwritten with wrong JSON; custom plugin callers hand-constructing the request struct with an invalid GEdges blob.

Related errors

AI-assisted analysis of d2lang/d2@0d69dca6f5 (2026-08-31). Data as JSON: /api/errors/cd1f417ee403f0ad. Report an issue: GitHub.