config: add sanity check to prevent non-negative worker counts

config.go

@@ -990,6 +990,12 @@ func loadConfig() (*config, error) {
 			"minbackoff")
 	}
 
+	// Assert that all worker pools will have a positive number of
+	// workers, otherwise the pools will rendered useless.
+	if err := cfg.Workers.Validate(); err != nil {
+		return nil, err
+	}
+
 	// Finally, ensure that the user's color is correctly formatted,
 	// otherwise the server will not be able to start after the unlocking
 	// the wallet.

lncfg/workers.go

@@ -1,5 +1,7 @@
 package lncfg
 
+import "fmt"
+
 const (
 	// DefaultReadWorkers is the default maximum number of concurrent
 	// workers used by the daemon's read pool.
@@ -26,3 +28,22 @@ type Workers struct {
 	// Sig is the maximum number of concurrent sig pool workers.
 	Sig int `long:"sig" description:"Maximum number of concurrent sig pool workers."`
 }
+
+// Validate checks the Workers configuration to ensure that the input values are
+// sane.
+func (w *Workers) Validate() error {
+	if w.Read <= 0 {
+		return fmt.Errorf("number of read workers (%d) must be "+
+			"positive", w.Read)
+	}
+	if w.Write <= 0 {
+		return fmt.Errorf("number of write workers (%d) must be "+
+			"positive", w.Write)
+	}
+	if w.Sig <= 0 {
+		return fmt.Errorf("number of sig workers (%d) must be "+
+			"positive", w.Sig)
+	}
+
+	return nil
+}

lncfg/workers_test.go

@@ -0,0 +1,102 @@
+package lncfg_test
+
+import (
+	"testing"
+
+	"github.com/lightningnetwork/lnd/lncfg"
+)
+
+const (
+	maxUint = ^uint(0)
+	maxInt  = int(maxUint >> 1)
+	minInt  = -maxInt - 1
+)
+
+// TestValidateWorkers asserts that validating the Workers config only succeeds
+// if all fields specify a positive number of workers.
+func TestValidateWorkers(t *testing.T) {
+	tests := []struct {
+		name  string
+		cfg   *lncfg.Workers
+		valid bool
+	}{
+		{
+			name: "min valid",
+			cfg: &lncfg.Workers{
+				Read:  1,
+				Write: 1,
+				Sig:   1,
+			},
+			valid: true,
+		},
+		{
+			name: "max valid",
+			cfg: &lncfg.Workers{
+				Read:  maxInt,
+				Write: maxInt,
+				Sig:   maxInt,
+			},
+			valid: true,
+		},
+		{
+			name: "read max invalid",
+			cfg: &lncfg.Workers{
+				Read:  0,
+				Write: 1,
+				Sig:   1,
+			},
+		},
+		{
+			name: "write max invalid",
+			cfg: &lncfg.Workers{
+				Read:  1,
+				Write: 0,
+				Sig:   1,
+			},
+		},
+		{
+			name: "sig max invalid",
+			cfg: &lncfg.Workers{
+				Read:  1,
+				Write: 1,
+				Sig:   0,
+			},
+		},
+		{
+			name: "read min invalid",
+			cfg: &lncfg.Workers{
+				Read:  minInt,
+				Write: 1,
+				Sig:   1,
+			},
+		},
+		{
+			name: "write min invalid",
+			cfg: &lncfg.Workers{
+				Read:  1,
+				Write: minInt,
+				Sig:   1,
+			},
+		},
+		{
+			name: "sig min invalid",
+			cfg: &lncfg.Workers{
+				Read:  1,
+				Write: 1,
+				Sig:   minInt,
+			},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			err := test.cfg.Validate()
+			switch {
+			case test.valid && err != nil:
+				t.Fatalf("valid config was invalid: %v", err)
+			case !test.valid && err == nil:
+				t.Fatalf("invalid config was valid")
+			}
+		})
+	}
+}