Fix golangci-lint errcheck warnings

Handle unchecked error returns in CLN backend and tests:
- Wrap resp.Body.Close() in defer functions to acknowledge errors
- Add error checks for json.Decoder.Decode() calls
- Ignore non-critical errors with _ where appropriate (json.Encoder.Encode, w.Write in tests)

Signed-off-by: Gustavo Chain <me@qustavo.cc>

Author: qustavo

pkg/lightning/cln.go

@@ -87,7 +87,7 @@ func (b *CLNBackend) post(ctx context.Context, path string, body any) (*http.Res
 	}
 
 	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
-		defer resp.Body.Close()
+		defer func() { _ = resp.Body.Close() }()
 		body, _ := io.ReadAll(io.LimitReader(resp.Body, 512))
 		return nil, fmt.Errorf("POST %s: HTTP %d: %s", path, resp.StatusCode, string(body))
 	}
@@ -103,17 +103,16 @@ func (b *CLNBackend) Wait(ctx context.Context) error {
 		if err != nil {
 			return fmt.Errorf("getinfo: %w", err)
 		}
+		defer func() { _ = resp.Body.Close() }()
 
 		var info struct {
 			WarningBitcoindSync   string `json:"warning_bitcoind_sync"`
 			WarningLightningdSync string `json:"warning_lightningd_sync"`
 			BlockHeight           int64  `json:"blockheight"`
 		}
 		if err := json.NewDecoder(resp.Body).Decode(&info); err != nil {
-			resp.Body.Close()
 			return fmt.Errorf("decoding getinfo: %w", err)
 		}
-		resp.Body.Close()
 
 		// Synced when both warnings are absent/empty
 		if info.WarningBitcoindSync == "" && info.WarningLightningdSync == "" {
@@ -151,7 +150,7 @@ func (b *CLNBackend) CreateInvoice(ctx context.Context, amountMsat int64, memo s
 	if err != nil {
 		return nil, fmt.Errorf("invoice: %w", err)
 	}
-	defer resp.Body.Close()
+	defer func() { _ = resp.Body.Close() }()
 
 	var invResp struct {
 		PaymentHash string `json:"payment_hash"`
@@ -178,7 +177,7 @@ func (b *CLNBackend) VerifyPayment(ctx context.Context, paymentHash string) (boo
 	if err != nil {
 		return false, fmt.Errorf("listinvoices: %w", err)
 	}
-	defer resp.Body.Close()
+	defer func() { _ = resp.Body.Close() }()
 
 	var listResp struct {
 		Invoices []struct {

pkg/lightning/cln_test.go

@@ -15,7 +15,7 @@ func TestCLNBackend_Wait_NotSynced(t *testing.T) {
 			w.WriteHeader(http.StatusBadRequest)
 			return
 		}
-		json.NewEncoder(w).Encode(map[string]interface{}{
+		_ = json.NewEncoder(w).Encode(map[string]interface{}{
 			"warning_bitcoind_sync":   "syncing blocks",
 			"warning_lightningd_sync": "",
 			"blockheight":             100,
@@ -47,13 +47,13 @@ func TestCLNBackend_Wait_Synced(t *testing.T) {
 		}
 		callCount++
 		if callCount < 2 {
-			json.NewEncoder(w).Encode(map[string]interface{}{
+			_ = json.NewEncoder(w).Encode(map[string]interface{}{
 				"warning_bitcoind_sync":   "",
 				"warning_lightningd_sync": "syncing",
 				"blockheight":             100,
 			})
 		} else {
-			json.NewEncoder(w).Encode(map[string]interface{}{
+			_ = json.NewEncoder(w).Encode(map[string]interface{}{
 				"warning_bitcoind_sync":   "",
 				"warning_lightningd_sync": "",
 				"blockheight":             101,
@@ -87,14 +87,17 @@ func TestCLNBackend_CreateInvoice(t *testing.T) {
 		}
 
 		var req map[string]interface{}
-		json.NewDecoder(r.Body).Decode(&req)
+		if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+			w.WriteHeader(http.StatusBadRequest)
+			return
+		}
 
 		if req["amount_msat"].(float64) != 5000 || req["description"].(string) != "test memo" {
 			w.WriteHeader(http.StatusBadRequest)
 			return
 		}
 
-		json.NewEncoder(w).Encode(map[string]string{
+		_ = json.NewEncoder(w).Encode(map[string]string{
 			"payment_hash": "abcd1234567890ef",
 			"bolt11":       "lnbc50u1p...",
 		})
@@ -128,7 +131,7 @@ func TestCLNBackend_VerifyPayment_Unpaid(t *testing.T) {
 			w.WriteHeader(http.StatusBadRequest)
 			return
 		}
-		json.NewEncoder(w).Encode(map[string]interface{}{
+		_ = json.NewEncoder(w).Encode(map[string]interface{}{
 			"invoices": []map[string]string{
 				{"status": "unpaid"},
 			},
@@ -157,7 +160,7 @@ func TestCLNBackend_VerifyPayment_Paid(t *testing.T) {
 			w.WriteHeader(http.StatusBadRequest)
 			return
 		}
-		json.NewEncoder(w).Encode(map[string]interface{}{
+		_ = json.NewEncoder(w).Encode(map[string]interface{}{
 			"invoices": []map[string]string{
 				{"status": "paid"},
 			},
@@ -186,7 +189,7 @@ func TestCLNBackend_VerifyPayment_NotFound(t *testing.T) {
 			w.WriteHeader(http.StatusBadRequest)
 			return
 		}
-		json.NewEncoder(w).Encode(map[string]interface{}{
+		_ = json.NewEncoder(w).Encode(map[string]interface{}{
 			"invoices": []map[string]string{},
 		})
 	}))
@@ -210,7 +213,7 @@ func TestCLNBackend_VerifyPayment_NotFound(t *testing.T) {
 func TestCLNBackend_HTTPError(t *testing.T) {
 	server := httptest.NewTLSServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.WriteHeader(http.StatusUnauthorized)
-		w.Write([]byte("Invalid rune"))
+		_, _ = w.Write([]byte("Invalid rune"))
 	}))
 	defer server.Close()