feat(pprof): add pprof HTTP server (#807)

- `PPROF_ENABLED=no`
- `PPROF_BLOCK_PROFILE_RATE=0`
- `PPROF_MUTEX_PROFILE_RATE=0`
- `PPROF_HTTP_SERVER_ADDRESS=":6060"`

internal/httpserver/settings.go

@@ -0,0 +1,111 @@
+package httpserver
+
+import (
+	"errors"
+	"fmt"
+	"net/http"
+	"os"
+	"strings"
+	"time"
+
+	"github.com/qdm12/gluetun/internal/configuration/settings/helpers"
+	"github.com/qdm12/gotree"
+	"github.com/qdm12/govalid/address"
+)
+
+type Settings struct {
+	// Name is the server name to use in logs.
+	// It defaults to the empty string.
+	Name *string
+	// Address is the server listening address.
+	// It defaults to :8000.
+	Address string
+	// Handler is the HTTP Handler to use.
+	// It must be set and cannot be left to nil.
+	Handler http.Handler
+	// Logger is the logger to use.
+	// It must be set and cannot be left to nil.
+	Logger Logger
+	// ShutdownTimeout is the shutdown timeout duration
+	// of the HTTP server. It defaults to 3 seconds.
+	ShutdownTimeout *time.Duration
+}
+
+func (s *Settings) SetDefaults() {
+	s.Name = helpers.DefaultStringPtr(s.Name, "")
+	s.Address = helpers.DefaultString(s.Address, ":8000")
+	const defaultShutdownTimeout = 3 * time.Second
+	s.ShutdownTimeout = helpers.DefaultDuration(s.ShutdownTimeout, defaultShutdownTimeout)
+}
+
+func (s Settings) Copy() Settings {
+	return Settings{
+		Name:            helpers.CopyStringPtr(s.Name),
+		Address:         s.Address,
+		Handler:         s.Handler,
+		Logger:          s.Logger,
+		ShutdownTimeout: helpers.CopyDurationPtr(s.ShutdownTimeout),
+	}
+}
+
+func (s *Settings) MergeWith(other Settings) {
+	s.Name = helpers.MergeWithStringPtr(s.Name, other.Name)
+	s.Address = helpers.MergeWithString(s.Address, other.Address)
+	s.Handler = helpers.MergeWithHTTPHandler(s.Handler, other.Handler)
+	if s.Logger == nil {
+		s.Logger = other.Logger
+	}
+	s.ShutdownTimeout = helpers.MergeWithDuration(s.ShutdownTimeout, other.ShutdownTimeout)
+}
+
+func (s *Settings) OverrideWith(other Settings) {
+	s.Name = helpers.OverrideWithStringPtr(s.Name, other.Name)
+	s.Address = helpers.OverrideWithString(s.Address, other.Address)
+	s.Handler = helpers.OverrideWithHTTPHandler(s.Handler, other.Handler)
+	if other.Logger != nil {
+		s.Logger = other.Logger
+	}
+	s.ShutdownTimeout = helpers.OverrideWithDuration(s.ShutdownTimeout, other.ShutdownTimeout)
+}
+
+var (
+	ErrHandlerIsNotSet         = errors.New("HTTP handler cannot be left unset")
+	ErrLoggerIsNotSet          = errors.New("logger cannot be left unset")
+	ErrShutdownTimeoutTooSmall = errors.New("shutdown timeout is too small")
+)
+
+func (s Settings) Validate() (err error) {
+	uid := os.Getuid()
+	_, err = address.Validate(s.Address, address.OptionListening(uid))
+	if err != nil {
+		return err
+	}
+
+	if s.Handler == nil {
+		return ErrHandlerIsNotSet
+	}
+
+	if s.Logger == nil {
+		return ErrLoggerIsNotSet
+	}
+
+	const minShutdownTimeout = 5 * time.Millisecond
+	if *s.ShutdownTimeout < minShutdownTimeout {
+		return fmt.Errorf("%w: %s must be at least %s",
+			ErrShutdownTimeoutTooSmall,
+			*s.ShutdownTimeout, minShutdownTimeout)
+	}
+
+	return nil
+}
+
+func (s Settings) ToLinesNode() (node *gotree.Node) {
+	node = gotree.New("%s HTTP server settings:", strings.Title(*s.Name))
+	node.Appendf("Listening address: %s", s.Address)
+	node.Appendf("Shutdown timeout: %s", *s.ShutdownTimeout)
+	return node
+}
+
+func (s Settings) String() string {
+	return s.ToLinesNode().String()
+}