Log the rest of the request log's fields (closes #79)

Each request log line now has the fields "Request log" in SPEC.md lists
whose features are built: instance (SWWAF_INSTANCE_NAME), scheme,
request_id (a trusted proxy's X-Request-ID or a new one, sent on to the
app), forwarded_for, client_group, content_type, content_length, the
headers SWWAF_LOG_REQUEST_HEADERS names, has_authorization, has_cookie,
websocket, response_content_type, cache_control, location, counts,
duration_checks, duration_upstream_connect and
duration_upstream_first_byte. A field that does not apply is left out.
Authorization, Cookie and Set-Cookie values are never logged.

Deviation: counts has request totals only; byte totals come with the byte limits.
Deviation: SWWAF_INSTANCE_NAME is on request lines only, not yet on process lines or metrics.
Judgement call: the headers go under request_headers, a name SPEC.md does not give.

Model: opus-5-5

internal/config/config_test.go

@@ -6,6 +6,7 @@ import (
 	"log/slog"
 	"maps"
 	"net/netip"
+	"os"
 	"slices"
 	"strings"
 	"testing"
@@ -47,8 +48,14 @@ const (
 	stateCounterInterval    = "SWWAF_STATE_COUNTER_INTERVAL"
 	metricsToken            = "SWWAF_METRICS_TOKEN" //nolint:gosec // the setting's name
 	metricsTopN             = "SWWAF_METRICS_TOP_N"
+	instanceName            = "SWWAF_INSTANCE_NAME"
+	logRequestHeaders       = "SWWAF_LOG_REQUEST_HEADERS"
 )
 
+// defaultLogRequestHeaders is the default of SWWAF_LOG_REQUEST_HEADERS.
+const defaultLogRequestHeaders = "accept,accept-language,accept-encoding," +
+	"content-type,origin,range"
+
 // token is a token of 32 characters, the shortest allowed.
 const token = "0123456789abcdef0123456789abcdef"
 
@@ -120,6 +127,18 @@ func TestDefaults(t *testing.T) {
 	wantNetblocks(t, cfg.DenyNets)
 	wantCountries(t, deniedCountries, cfg.DeniedCountries)
 	wantCountries(t, allowedCountries, cfg.ExclusivelyAllowedCountries)
+
+	hostname, err := os.Hostname()
+	if err != nil || hostname == "" || cfg.InstanceName != hostname {
+		t.Errorf("%s is %q, want the host's name %q (%v)", instanceName,
+			cfg.InstanceName, hostname, err)
+	}
+
+	wantHeaders := strings.Split(defaultLogRequestHeaders, ",")
+	if !slices.Equal(cfg.LogRequestHeaders, wantHeaders) {
+		t.Errorf("%s gave %v, want %v", logRequestHeaders, cfg.LogRequestHeaders,
+			wantHeaders)
+	}
 }
 
 func TestValuesAsSet(t *testing.T) {
@@ -198,6 +217,21 @@ func TestValuesAsSet(t *testing.T) {
 	wantCountries(t, allowedCountries, cfg.ExclusivelyAllowedCountries, "DE")
 }
 
+func TestInstanceNameAndLoggedHeadersAsSet(t *testing.T) {
+	t.Parallel()
+
+	cfg := fromEnvironment(t, environment{
+		instanceName:      "fsn1app1/gitea",
+		logRequestHeaders: " Accept , X-Custom",
+	})
+
+	if cfg.InstanceName != "fsn1app1/gitea" ||
+		!slices.Equal(cfg.LogRequestHeaders, []string{"accept", "x-custom"}) {
+		t.Errorf("%s is %q and %s gives %v", instanceName, cfg.InstanceName,
+			logRequestHeaders, cfg.LogRequestHeaders)
+	}
+}
+
 func TestCodeOnBothCountryListsStopsTheStart(t *testing.T) {
 	t.Parallel()
 
@@ -361,6 +395,7 @@ func TestInvalidValueStopsTheStart(t *testing.T) {
 		{stateWriteDelay, off}, {stateWriteDelay, "0s"},
 		{stateCounterInterval, off}, {stateCounterInterval, "15"},
 		{metricsTopN, off}, {metricsTopN, "0"}, {metricsTopN, "-1"},
+		{logRequestHeaders, "accept,,origin"},
 	} {
 		t.Run(tc.name+"="+tc.value, func(t *testing.T) {
 			t.Parallel()
@@ -428,6 +463,8 @@ func TestLogsEachSettingWithItsValue(t *testing.T) {
 		t.Fatalf("decode %s: %v", out.Bytes(), err)
 	}
 
+	hostname, _ := os.Hostname()
+
 	want := map[string]string{
 		listenAddr:              ":8080",
 		upstreamURL:             "http://127.0.0.1:8081",
@@ -460,6 +497,8 @@ func TestLogsEachSettingWithItsValue(t *testing.T) {
 		stateCounterInterval:    "15m",
 		metricsToken:            "",
 		metricsTopN:             "50",
+		instanceName:            hostname,
+		logRequestHeaders:       defaultLogRequestHeaders,
 	}
 	if !maps.Equal(line.Settings, want) {
 		t.Errorf("logged settings\n%v\nwant\n%v", line.Settings, want)