Read a node's build capacity from the build module's own setting at every pull, defaulting to the builder's values, so the control-node pulls nothing (issue 1887 A7, ADR 0525 §5)

go/buildstep/askrun_test.go

@@ -92,7 +92,9 @@ build {"artifact":"lib","module":"modules/m","publish":true,"workspace":"/w/1"}`
 func TestRunAskRefusesAnotherToolchain(t *testing.T) {
 	r := &recorder{fetch: map[string]any{"workspace": "/w"}}
 	s := r.steps()
-	s.Toolchain = func(context.Context) (delivery.ToolchainUsed, error) { return delivery.ToolchainUsed{Version: "go1.27", Recipe: "3"}, nil }
+	s.Toolchain = func(context.Context) (delivery.ToolchainUsed, error) {
+		return delivery.ToolchainUsed{Version: "go1.27", Recipe: "3"}, nil
+	}
 	_, err := RunAsk(context.Background(), s, ask(delivery.BuildJob{Module: "m", Path: ".", Fetch: map[string]any{"repository": "novox/x", "commit": runCommit},
 		Artifacts: []delivery.AskArtifact{{Artifact: "bundle"}}, Toolchain: &delivery.ToolchainUsed{Version: "go1.26", Recipe: "3"}}))
 	var ref *Refusal

go/buildstep/capacity.go

@@ -0,0 +1,52 @@
+package buildstep
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery/buildrun"
+)
+
+// CapacitySetting is the build modules' setting of each node's build capacity (novox/hq ADR 0525 §5): `<node>=<asks at
+// once>` pairs separated by commas, as the builder's was (ADR 0485 §1). Each build module declares it with
+// DefaultCapacities as its default, and the controller lays it into the module's settings file.
+const CapacitySetting = "capacity"
+
+// DefaultCapacities is the setting's default, the builder's before R4g: the control-node (novox) and the laptop (g14)
+// build nothing.
+const DefaultCapacities = "shanks=3,ace=2,g14=0,novox=0"
+
+// NodeCapacity is node's build capacity, read from the module's settings file at path at every call, so a change takes
+// effect at the next pull; with no path it reads fallback. A node the setting does not name runs one ask at a time (as
+// the builder's did). A file or a setting that cannot be read gives 0 and says why: pulling on a setting nobody can read
+// could build on a node that must not.
+func NodeCapacity(path, fallback, node string, logf func(string, ...any)) func() int {
+	say := func(format string, args ...any) {
+		if logf != nil {
+			logf(format, args...)
+		}
+	}
+	return func() int {
+		setting := fallback
+		if path != "" {
+			raw, err := os.ReadFile(path)
+			if err != nil {
+				say("the build capacity cannot be read, so %s pulls nothing: %v", node, err)
+				return 0
+			}
+			var s map[string]any
+			if err := json.Unmarshal(raw, &s); err != nil {
+				say("the settings file %s is not JSON, so %s pulls nothing: %v", path, node, err)
+				return 0
+			}
+			setting, _ = s[CapacitySetting].(string)
+		}
+		caps, err := buildrun.ParseCapacity(setting)
+		if err != nil {
+			say("%v, so %s pulls nothing", fmt.Errorf("the build capacity: %w", err), node)
+			return 0
+		}
+		return (&buildrun.Places{Capacity: caps}).CapacityOf(node)
+	}
+}

go/buildstep/capacity_test.go

@@ -0,0 +1,38 @@
+package buildstep
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+// 1887/A7: the node's build capacity is the build module's setting, read at every pull: the control-node at 0 pulls
+// nothing, a change takes effect at the next read, and a setting that cannot be read pulls nothing.
+func TestNodeCapacity(t *testing.T) {
+	if got := NodeCapacity("", DefaultCapacities, "novox", nil)(); got != 0 {
+		t.Errorf("novox = %d by default, want 0", got)
+	}
+	if got := NodeCapacity("", DefaultCapacities, "shanks", nil)(); got != 3 {
+		t.Errorf("shanks = %d by default, want 3", got)
+	}
+	file := filepath.Join(t.TempDir(), "settings.json")
+	os.WriteFile(file, []byte(`{"capacity":"shanks=1,ace=2"}`), 0o600)
+	capacity := NodeCapacity(file, DefaultCapacities, "shanks", nil)
+	if got := capacity(); got != 1 {
+		t.Errorf("shanks = %d from the file, want 1", got)
+	}
+	os.WriteFile(file, []byte(`{"capacity":"shanks=4"}`), 0o600)
+	if got := capacity(); got != 4 {
+		t.Errorf("shanks = %d after the change, want 4", got)
+	}
+	if got := NodeCapacity(file, "", "pi", nil)(); got != 1 {
+		t.Errorf("a node not named = %d, want 1", got)
+	}
+	os.WriteFile(file, []byte(`{"capacity":"shanks=lots"}`), 0o600)
+	if got := capacity(); got != 0 {
+		t.Errorf("an unreadable setting = %d, want 0", got)
+	}
+	if got := NodeCapacity(filepath.Join(t.TempDir(), "none"), DefaultCapacities, "shanks", nil)(); got != 0 {
+		t.Errorf("a missing file = %d, want 0", got)
+	}
+}