Refactor: Extract magic numbers as constants and reduce client code duplication

- Created internal/constants package with organized constant files:
  - timeouts.go: All time duration constants (timeouts, intervals, delays)
  - channels.go: Channel buffer size constants
  - limits.go: Numeric limits and configuration values
  - buffers.go: Buffer size constants in bytes

- Replaced all magic numbers throughout codebase with named constants:
  - Time durations (2s, 3s, 5s, 10s, 100ms, 24h) now use descriptive constants
  - Buffer sizes (8KB, 64KB, 1MB) extracted to constants
  - Channel buffer sizes and multipliers
  - Configuration limits (max connections, concurrency, etc.)
  - Health check status codes
  - Percentage calculations

- Reduced code duplication in client implementations:
  - Created CommonClient to share functionality between CatClient, GrepClient, and TailClient
  - All three clients now inherit from CommonClient
  - Eliminated duplicate makeHandler() and makeCommands() methods
  - Simplified client constructors

This refactoring improves code maintainability by centralizing configuration values
and reducing redundant code across similar client implementations.

32 files changed, 290 insertions, 140 deletions

diff --git a/internal/clients/baseclient.go b/internal/clients/baseclient.go
index 29a9cfc..0edae86 100644
--- a/internal/clients/baseclient.go
+++ b/internal/clients/baseclient.go
@@ -7,6 +7,7 @@ import (
 
 	"github.com/mimecast/dtail/internal/clients/connectors"
 	"github.com/mimecast/dtail/internal/config"
+	"github.com/mimecast/dtail/internal/constants"
 	"github.com/mimecast/dtail/internal/discovery"
 	"github.com/mimecast/dtail/internal/io/dlog"
 	"github.com/mimecast/dtail/internal/regex"
@@ -16,7 +17,7 @@ import (
 )
 
 // Reusable timer for retry delays - PBO optimization  
-var retryTimer = time.NewTimer(2 * time.Second)
+var retryTimer = time.NewTimer(constants.RetryTimerDuration)
 
 // This is the main client data structure.
 type baseClient struct {
@@ -135,7 +136,7 @@ func (c *baseClient) startConnection(ctx context.Context, i int,
 			default:
 			}
 		}
-		retryTimer.Reset(2 * time.Second)
+		retryTimer.Reset(constants.RetryTimerDuration)
 		select {
 		case <-retryTimer.C:
 		case <-ctx.Done():
diff --git a/internal/clients/catclient.go b/internal/clients/catclient.go
index bd65560..39f56d6 100644
--- a/internal/clients/catclient.go
+++ b/internal/clients/catclient.go
@@ -2,19 +2,14 @@ package clients
 
 import (
 	"errors"
-	"fmt"
-	"runtime"
-	"strings"
 
-	"github.com/mimecast/dtail/internal/clients/handlers"
 	"github.com/mimecast/dtail/internal/config"
-	"github.com/mimecast/dtail/internal/io/dlog"
 	"github.com/mimecast/dtail/internal/omode"
 )
 
 // CatClient is a client for returning a whole file from the beginning to the end.
 type CatClient struct {
-	baseClient
+	CommonClient
 }
 
 // NewCatClient returns a new cat client.
@@ -25,30 +20,10 @@ func NewCatClient(args config.Args) (*CatClient, error) {
 	args.Mode = omode.CatClient
 
 	c := CatClient{
-		baseClient: baseClient{
-			Args:       args,
-			throttleCh: make(chan struct{}, args.ConnectionsPerCPU*runtime.NumCPU()),
-			retry:      false,
-		},
+		CommonClient: NewCommonClient(args, false),
 	}
 
 	c.init()
 	c.makeConnections(c)
 	return &c, nil
 }
-
-func (c CatClient) makeHandler(server string) handlers.Handler {
-	return handlers.NewClientHandler(server)
-}
-
-func (c CatClient) makeCommands() (commands []string) {
-	regex, err := c.Regex.Serialize()
-	if err != nil {
-		dlog.Client.FatalPanic(err)
-	}
-	for _, file := range strings.Split(c.What, ",") {
-		commands = append(commands, fmt.Sprintf("%s:%s %s %s",
-			c.Mode.String(), c.Args.SerializeOptions(), file, regex))
-	}
-	return
-}
diff --git a/internal/clients/common.go b/internal/clients/common.go
new file mode 100644
index 0000000..2f35412
--- /dev/null
+++ b/internal/clients/common.go
@@ -0,0 +1,49 @@
+package clients
+
+import (
+	"fmt"
+	"runtime"
+	"strings"
+
+	"github.com/mimecast/dtail/internal/clients/handlers"
+	"github.com/mimecast/dtail/internal/config"
+	"github.com/mimecast/dtail/internal/io/dlog"
+	"github.com/mimecast/dtail/internal/omode"
+)
+
+// CommonClient provides shared functionality for CatClient, GrepClient, and TailClient
+type CommonClient struct {
+	baseClient
+}
+
+// NewCommonClient creates a new common client with the specified configuration
+func NewCommonClient(args config.Args, retry bool) CommonClient {
+	return CommonClient{
+		baseClient: baseClient{
+			Args:       args,
+			throttleCh: make(chan struct{}, args.ConnectionsPerCPU*runtime.NumCPU()),
+			retry:      retry,
+		},
+	}
+}
+
+// makeHandler returns a standard client handler
+func (c CommonClient) makeHandler(server string) handlers.Handler {
+	return handlers.NewClientHandler(server)
+}
+
+// makeCommands generates commands based on the client mode
+func (c CommonClient) makeCommands() (commands []string) {
+	regex, err := c.Regex.Serialize()
+	if err != nil {
+		dlog.Client.FatalPanic(err)
+	}
+	for _, file := range strings.Split(c.What, ",") {
+		commands = append(commands, fmt.Sprintf("%s:%s %s %s",
+			c.Mode.String(), c.Args.SerializeOptions(), file, regex))
+	}
+	if c.Mode == omode.TailClient {
+		dlog.Client.Debug(commands)
+	}
+	return
+}
\ No newline at end of file
diff --git a/internal/clients/grepclient.go b/internal/clients/grepclient.go
index 7521c67..71f0220 100644
--- a/internal/clients/grepclient.go
+++ b/internal/clients/grepclient.go
@@ -2,20 +2,15 @@ package clients
 
 import (
 	"errors"
-	"fmt"
-	"runtime"
-	"strings"
 
-	"github.com/mimecast/dtail/internal/clients/handlers"
 	"github.com/mimecast/dtail/internal/config"
-	"github.com/mimecast/dtail/internal/io/dlog"
 	"github.com/mimecast/dtail/internal/omode"
 )
 
 // GrepClient searches a remote file for all lines matching a regular
 // expression. Only the matching lines are displayed.
 type GrepClient struct {
-	baseClient
+	CommonClient
 }
 
 // NewGrepClient creates a new grep client.
@@ -26,30 +21,10 @@ func NewGrepClient(args config.Args) (*GrepClient, error) {
 	args.Mode = omode.GrepClient
 
 	c := GrepClient{
-		baseClient: baseClient{
-			Args:       args,
-			throttleCh: make(chan struct{}, args.ConnectionsPerCPU*runtime.NumCPU()),
-			retry:      false,
-		},
+		CommonClient: NewCommonClient(args, false),
 	}
 
 	c.init()
 	c.makeConnections(c)
 	return &c, nil
 }
-
-func (c GrepClient) makeHandler(server string) handlers.Handler {
-	return handlers.NewClientHandler(server)
-}
-
-func (c GrepClient) makeCommands() (commands []string) {
-	regex, err := c.Regex.Serialize()
-	if err != nil {
-		dlog.Client.FatalPanic(err)
-	}
-	for _, file := range strings.Split(c.What, ",") {
-		commands = append(commands, fmt.Sprintf("%s:%s %s %s",
-			c.Mode.String(), c.Args.SerializeOptions(), file, regex))
-	}
-	return
-}
diff --git a/internal/clients/handlers/basehandler.go b/internal/clients/handlers/basehandler.go
index 6f637a7..20e5fe3 100644
--- a/internal/clients/handlers/basehandler.go
+++ b/internal/clients/handlers/basehandler.go
@@ -9,6 +9,7 @@ import (
 	"time"
 
 	"github.com/mimecast/dtail/internal"
+	"github.com/mimecast/dtail/internal/constants"
 	"github.com/mimecast/dtail/internal/io/dlog"
 	"github.com/mimecast/dtail/internal/protocol"
 )
@@ -47,7 +48,7 @@ func (h *baseHandler) SendMessage(command string) error {
 
 	select {
 	case h.commands <- fmt.Sprintf("protocol %s base64 %v;", protocol.ProtocolCompat, encoded):
-	case <-time.After(time.Second * 5):
+	case <-time.After(constants.HandlerTimeout):
 		return fmt.Errorf("Timed out sending command '%s' (base64: '%s')", command, encoded)
 	case <-h.Done():
 		return nil
diff --git a/internal/clients/handlers/healthhandler.go b/internal/clients/handlers/healthhandler.go
index 47b594e..e602c39 100644
--- a/internal/clients/handlers/healthhandler.go
+++ b/internal/clients/handlers/healthhandler.go
@@ -4,6 +4,7 @@ import (
 	"strings"
 
 	"github.com/mimecast/dtail/internal"
+	"github.com/mimecast/dtail/internal/constants"
 	"github.com/mimecast/dtail/internal/io/dlog"
 	"github.com/mimecast/dtail/internal/protocol"
 )
@@ -22,7 +23,7 @@ func NewHealthHandler(server string) *HealthHandler {
 			server:       server,
 			shellStarted: false,
 			commands:     make(chan string),
-			status:       2, // Assume CRITICAL status by default.
+			status:       constants.HealthCriticalStatus, // Assume CRITICAL status by default.
 			done:         internal.NewDone(),
 		},
 	}
@@ -51,6 +52,6 @@ func (h *HealthHandler) handleMessage(message string) {
 	s := strings.Split(message, protocol.FieldDelimiter)
 	message = s[len(s)-1]
 	if message == "OK" {
-		h.baseHandler.status = 0
+		h.baseHandler.status = constants.HealthOKStatus
 	}
 }
diff --git a/internal/clients/maprclient.go b/internal/clients/maprclient.go
index 6362028..1f587ce 100644
--- a/internal/clients/maprclient.go
+++ b/internal/clients/maprclient.go
@@ -11,6 +11,7 @@ import (
 	"github.com/mimecast/dtail/internal/clients/handlers"
 	"github.com/mimecast/dtail/internal/color"
 	"github.com/mimecast/dtail/internal/config"
+	"github.com/mimecast/dtail/internal/constants"
 	"github.com/mimecast/dtail/internal/io/dlog"
 	"github.com/mimecast/dtail/internal/mapr"
 	"github.com/mimecast/dtail/internal/omode"
@@ -164,12 +165,12 @@ func (c *MaprClient) printResults() {
 	var result string
 	var err error
 	var numRows int
-	rowsLimit := -1
+	rowsLimit := constants.MapReduceUnlimited
 
-	if c.query.Limit == -1 {
+	if c.query.Limit == constants.MapReduceUnlimited {
 		// Limit output to 10 rows when the result is printed to stdout.
 		// This can be overriden with the limit clause though.
-		rowsLimit = 10
+		rowsLimit = constants.DefaultMapReduceRowsLimit
 	}
 
 	if c.cumulative {
diff --git a/internal/clients/stats.go b/internal/clients/stats.go
index 9a17899..7160357 100644
--- a/internal/clients/stats.go
+++ b/internal/clients/stats.go
@@ -10,12 +10,13 @@ import (
 
 	"github.com/mimecast/dtail/internal/color"
 	"github.com/mimecast/dtail/internal/config"
+	"github.com/mimecast/dtail/internal/constants"
 	"github.com/mimecast/dtail/internal/io/dlog"
 	"github.com/mimecast/dtail/internal/protocol"
 )
 
 // Reusable timer to reduce allocations - PBO optimization
-var statsTimer = time.NewTimer(3 * time.Second)
+var statsTimer = time.NewTimer(constants.StatsTimerDuration)
 
 // Used to collect and display various client stats.
 type stats struct {
@@ -55,7 +56,7 @@ func (s *stats) Start(ctx context.Context, throttleCh <-chan struct{},
 			default:
 			}
 		}
-		statsTimer.Reset(3 * time.Second)
+		statsTimer.Reset(constants.StatsTimerDuration)
 		
 		select {
 		case message := <-statsCh:
@@ -104,7 +105,7 @@ func (s *stats) printStatsDueInterrupt(messages []string) {
 		}
 		fmt.Println(fmt.Sprintf(" %s", message))
 	}
-	time.Sleep(time.Second * time.Duration(config.InterruptTimeoutS))
+	time.Sleep(time.Second * time.Duration(constants.InterruptTimeoutSeconds))
 	dlog.Client.Resume()
 }
 
@@ -149,7 +150,7 @@ func (s *stats) numConnected() int {
 
 func percentOf(total float64, value float64) float64 {
 	if total == 0 || total == value {
-		return 100
+		return constants.PercentageMultiplier
 	}
-	return value / (total / 100.0)
+	return value / (total / constants.PercentageMultiplier)
 }
diff --git a/internal/clients/tailclient.go b/internal/clients/tailclient.go
index 35c01d4..f71da41 100644
--- a/internal/clients/tailclient.go
+++ b/internal/clients/tailclient.go
@@ -1,50 +1,23 @@
 package clients
 
 import (
-	"fmt"
-	"runtime"
-	"strings"
-
-	"github.com/mimecast/dtail/internal/clients/handlers"
 	"github.com/mimecast/dtail/internal/config"
-	"github.com/mimecast/dtail/internal/io/dlog"
 	"github.com/mimecast/dtail/internal/omode"
 )
 
 // TailClient is used for tailing remote log files (opening, seeking to the end and returning only new incoming lines).
 type TailClient struct {
-	baseClient
+	CommonClient
 }
 
 // NewTailClient returns a new TailClient.
 func NewTailClient(args config.Args) (*TailClient, error) {
 	args.Mode = omode.TailClient
 	c := TailClient{
-		baseClient: baseClient{
-			Args:       args,
-			throttleCh: make(chan struct{}, args.ConnectionsPerCPU*runtime.NumCPU()),
-			retry:      true,
-		},
+		CommonClient: NewCommonClient(args, true),
 	}
 
 	c.init()
 	c.makeConnections(c)
 	return &c, nil
 }
-
-func (c TailClient) makeHandler(server string) handlers.Handler {
-	return handlers.NewClientHandler(server)
-}
-
-func (c TailClient) makeCommands() (commands []string) {
-	regex, err := c.Regex.Serialize()
-	if err != nil {
-		dlog.Client.FatalPanic(err)
-	}
-	for _, file := range strings.Split(c.What, ",") {
-		commands = append(commands, fmt.Sprintf("%s:%s %s %s",
-			c.Mode.String(), c.Args.SerializeOptions(), file, regex))
-	}
-	dlog.Client.Debug(commands)
-	return
-}
diff --git a/internal/config/config.go b/internal/config/config.go
index ee23829..8cc6287 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -1,6 +1,9 @@
 package config
 
-import "github.com/mimecast/dtail/internal/source"
+import (
+	"github.com/mimecast/dtail/internal/constants"
+	"github.com/mimecast/dtail/internal/source"
+)
 
 const (
 	// HealthUser is used for the health check
@@ -10,11 +13,11 @@ const (
 	// ContinuousUser is used for non-interactive continuous mapreduce queries.
 	ContinuousUser string = "DTAIL-CONTINUOUS"
 	// InterruptTimeoutS specifies the Ctrl+C log pause interval.
-	InterruptTimeoutS int = 3
+	InterruptTimeoutS int = constants.InterruptTimeoutSeconds
 	// DefaultConnectionsPerCPU controls how many connections are established concurrently.
-	DefaultConnectionsPerCPU int = 10
+	DefaultConnectionsPerCPU int = constants.DefaultConnectionsPerCPU
 	// DefaultSSHPort is the default DServer port.
-	DefaultSSHPort int = 2222
+	DefaultSSHPort int = constants.DefaultSSHPort
 	// DefaultLogLevel specifies the default log level (obviously)
 	DefaultLogLevel string = "info"
 	// DefaultClientLogger specifies the default logger for the client commands.
diff --git a/internal/config/initializer.go b/internal/config/initializer.go
index 9724902..825f612 100644
--- a/internal/config/initializer.go
+++ b/internal/config/initializer.go
@@ -8,6 +8,7 @@ import (
 	"os"
 	"strings"
 
+	"github.com/mimecast/dtail/internal/constants"
 	"github.com/mimecast/dtail/internal/source"
 )
 
@@ -83,7 +84,7 @@ func (in *initializer) transformConfig(sourceProcess source.Source, args *Args,
 func (in *initializer) processEnvVars(args *Args) {
 	if Env("DTAIL_INTEGRATION_TEST_RUN_MODE") {
 		os.Setenv("DTAIL_HOSTNAME_OVERRIDE", "integrationtest")
-		in.Server.MaxLineLength = 1024
+		in.Server.MaxLineLength = constants.DefaultMaxLineLength
 	}
 	sshPrivateKeyPathFile := os.Getenv("DTAIL_SSH_PRIVATE_KEYFILE_PATH")
 	if len(sshPrivateKeyPathFile) > 0 && args.SSHPrivateKeyFilePath == "" {
diff --git a/internal/config/server.go b/internal/config/server.go
index cb9ca2b..38186fd 100644
--- a/internal/config/server.go
+++ b/internal/config/server.go
@@ -2,6 +2,8 @@ package config
 
 import (
 	"errors"
+
+	"github.com/mimecast/dtail/internal/constants"
 )
 
 // Permissions map. Each SSH user has a list of permissions which log files it
@@ -74,13 +76,13 @@ func newDefaultServerConfig() *ServerConfig {
 	defaultPermissions := []string{"^/.*"}
 	defaultBindAddress := "0.0.0.0"
 	return &ServerConfig{
-		HostKeyBits:        4096,
+		HostKeyBits:        constants.HostKeyBits,
 		HostKeyFile:        "./cache/ssh_host_key",
 		MapreduceLogFormat: "default",
-		MaxConcurrentCats:  2,
-		MaxConcurrentTails: 50,
-		MaxConnections:     10,
-		MaxLineLength:      1024 * 1024,
+		MaxConcurrentCats:  constants.MaxConcurrentCats,
+		MaxConcurrentTails: constants.MaxConcurrentTails,
+		MaxConnections:     constants.MaxConnections,
+		MaxLineLength:      constants.ServerMaxLineLength,
 		SSHBindAddress:     defaultBindAddress,
 		Permissions: Permissions{
 			Default: defaultPermissions,
diff --git a/internal/constants/buffers.go b/internal/constants/buffers.go
new file mode 100644
index 0000000..b80586a
--- /dev/null
+++ b/internal/constants/buffers.go
@@ -0,0 +1,19 @@
+package constants
+
+// Buffer size constants in bytes
+const (
+	// StatsArraySize is the size of arrays for tracking stats
+	StatsArraySize = 100
+
+	// LineBufferInitialCapacity is the initial capacity for line buffers (8KB)
+	LineBufferInitialCapacity = 8192
+
+	// ReadBufferSize is the size of read buffers (8KB)
+	ReadBufferSize = 8192
+
+	// DefaultChunkSize is the default chunk size for reading (64KB)
+	DefaultChunkSize = 64 * 1024
+
+	// InitialBufferSize is the initial buffer size for processors (64KB)
+	InitialBufferSize = 64 * 1024
+)
\ No newline at end of file
diff --git a/internal/constants/channels.go b/internal/constants/channels.go
new file mode 100644
index 0000000..9f2d619
--- /dev/null
+++ b/internal/constants/channels.go
@@ -0,0 +1,14 @@
+package constants
+
+// Channel buffer size constants
+const (
+	// DefaultLinesChannelSize is the default buffer size for lines channels
+	DefaultLinesChannelSize = 100
+
+	// DefaultServerMessagesChannelSize is the default buffer size for server messages
+	DefaultServerMessagesChannelSize = 10
+
+	// LoggerBufferChannelSize is the buffer size for logger channels
+	// Calculated as runtime.NumCPU() * 100 at runtime
+	LoggerBufferChannelMultiplier = 100
+)
\ No newline at end of file
diff --git a/internal/constants/limits.go b/internal/constants/limits.go
new file mode 100644
index 0000000..5b871ce
--- /dev/null
+++ b/internal/constants/limits.go
@@ -0,0 +1,55 @@
+package constants
+
+// Numeric limits and configuration values
+const (
+	// MaxFlushRetries is the maximum number of flush retry attempts
+	MaxFlushRetries = 10
+
+	// MaxReadCommandRetries is the maximum number of read command retries
+	MaxReadCommandRetries = 5
+
+	// DefaultConnectionsPerCPU is the default number of connections per CPU
+	DefaultConnectionsPerCPU = 10
+
+	// DefaultSSHPort is the default SSH server port
+	DefaultSSHPort = 2222
+
+	// InterruptTimeoutSeconds is the timeout for interrupt handling
+	InterruptTimeoutSeconds = 3
+
+	// MaxConcurrentCats is the maximum number of concurrent cat operations
+	MaxConcurrentCats = 2
+
+	// MaxConcurrentTails is the maximum number of concurrent tail operations
+	MaxConcurrentTails = 50
+
+	// MaxConnections is the maximum total number of connections
+	MaxConnections = 10
+
+	// HostKeyBits is the number of bits for SSH host keys
+	HostKeyBits = 4096
+
+	// DefaultMaxLineLength is the default maximum line length (1KB)
+	DefaultMaxLineLength = 1024
+
+	// ServerMaxLineLength is the server maximum line length (1MB)
+	ServerMaxLineLength = 1024 * 1024
+
+	// MaxSymlinkDepth is the maximum depth for following symlinks
+	MaxSymlinkDepth = 100
+
+	// DefaultMapReduceRowsLimit is the default limit for MapReduce output rows
+	DefaultMapReduceRowsLimit = 10
+
+	// MapReduceUnlimited indicates no limit on MapReduce rows
+	MapReduceUnlimited = -1
+
+	// HealthOKStatus is the status code for healthy service
+	HealthOKStatus = 0
+
+	// HealthCriticalStatus is the status code for critical health issues
+	HealthCriticalStatus = 2
+
+	// PercentageMultiplier is used for percentage calculations
+	PercentageMultiplier = 100.0
+)
\ No newline at end of file
diff --git a/internal/constants/timeouts.go b/internal/constants/timeouts.go
new file mode 100644
index 0000000..9373b23
--- /dev/null
+++ b/internal/constants/timeouts.go
@@ -0,0 +1,60 @@
+package constants
+
+import "time"
+
+// Timeout constants used throughout the application
+const (
+	// ReadTimeout is the timeout for read operations
+	ReadTimeout = 1 * time.Second
+
+	// WriteTimeout is the timeout for write operations
+	WriteTimeout = 10 * time.Second
+
+	// HandlerTimeout is the timeout for handler operations
+	HandlerTimeout = 5 * time.Second
+
+	// SSHConnectionTimeout is the timeout for SSH connection attempts
+	SSHConnectionTimeout = 30 * time.Second
+
+	// ReconnectSleepDuration is how long to wait before reconnecting
+	ReconnectSleepDuration = 2 * time.Second
+
+	// StatsTimerDuration is the interval for client stats reporting
+	StatsTimerDuration = 3 * time.Second
+
+	// ServerStatsTimerDuration is the interval for server stats reporting
+	ServerStatsTimerDuration = 10 * time.Second
+
+	// DefaultMapReduceInterval is the default interval for MapReduce operations
+	DefaultMapReduceInterval = 5 * time.Second
+
+	// ProcessorSleepDuration is the sleep duration for processors
+	ProcessorSleepDuration = 10 * time.Millisecond
+
+	// ProcessorTimeoutDuration is the timeout for processor operations
+	ProcessorTimeoutDuration = 100 * time.Millisecond
+
+	// MapReduceSleepDuration is the sleep duration in MapReduce aggregation
+	MapReduceSleepDuration = 100 * time.Millisecond
+
+	// ContinuousJobsStartDelay is the delay before starting continuous jobs
+	ContinuousJobsStartDelay = 2 * time.Second
+
+	// SchedulerStartDelay is the delay before starting the scheduler
+	SchedulerStartDelay = 2 * time.Second
+
+	// RetryTimerDuration is the duration for retry operations
+	RetryTimerDuration = 2 * time.Second
+
+	// SSHDialTimeout is the timeout for SSH dial operations
+	SSHDialTimeout = 2 * time.Second
+
+	// KnownHostsCallbackTimeout is the timeout for known hosts callback
+	KnownHostsCallbackTimeout = 2 * time.Second
+
+	// ReadCommandRetryInterval is the interval between read command retries
+	ReadCommandRetryInterval = 5 * time.Second
+
+	// DayDuration represents 24 hours for date calculations
+	DayDuration = 24 * time.Hour
+)
\ No newline at end of file
diff --git a/internal/io/dlog/loggers/file.go b/internal/io/dlog/loggers/file.go
index 6a09353..b183843 100644
--- a/internal/io/dlog/loggers/file.go
+++ b/internal/io/dlog/loggers/file.go
@@ -10,6 +10,7 @@ import (
 	"time"
 
 	"github.com/mimecast/dtail/internal/config"
+	"github.com/mimecast/dtail/internal/constants"
 )
 
 type fileWriter struct{}
@@ -36,7 +37,7 @@ type file struct {
 
 func newFile(strategy Strategy) *file {
 	return &file{
-		bufferCh: make(chan *fileMessageBuf, runtime.NumCPU()*100),
+		bufferCh: make(chan *fileMessageBuf, runtime.NumCPU()*constants.LoggerBufferChannelMultiplier),
 		pauseCh:  make(chan struct{}),
 		resumeCh: make(chan struct{}),
 		rotateCh: make(chan struct{}),
diff --git a/internal/io/fs/aggregateprocessor.go b/internal/io/fs/aggregateprocessor.go
index 98d0c31..809f298 100644
--- a/internal/io/fs/aggregateprocessor.go
+++ b/internal/io/fs/aggregateprocessor.go
@@ -5,6 +5,7 @@ import (
 	"context"
 	"time"
 
+	"github.com/mimecast/dtail/internal/constants"
 	"github.com/mimecast/dtail/internal/io/line"
 	"github.com/mimecast/dtail/internal/lcontext"
 	"github.com/mimecast/dtail/internal/regex"
@@ -69,7 +70,7 @@ func (p *AggregateLineProcessor) Flush() []byte {
 	if !p.isTailing {
 		// Close the lines channel to signal end of input
 		// Add a small delay to ensure all lines are processed before closing
-		time.Sleep(10 * time.Millisecond)
+		time.Sleep(constants.ProcessorSleepDuration)
 		close(p.linesCh)
 	}
 	return nil
diff --git a/internal/io/fs/chunkedreader.go b/internal/io/fs/chunkedreader.go
index ab78ba1..7775a58 100644
--- a/internal/io/fs/chunkedreader.go
+++ b/internal/io/fs/chunkedreader.go
@@ -6,12 +6,13 @@ import (
 	"io"
 	"time"
 
+	"github.com/mimecast/dtail/internal/constants"
 	"github.com/mimecast/dtail/internal/io/dlog"
 	"github.com/mimecast/dtail/internal/io/pool"
 )
 
 // Reusable timer to reduce allocations - PBO optimization
-var sharedTimer = time.NewTimer(10 * time.Millisecond)
+var sharedTimer = time.NewTimer(constants.ProcessorSleepDuration)
 
 // ChunkedReader reads data in large chunks and processes it line by line
 // This replaces the byte-by-byte reading approach for better performance
@@ -29,14 +30,14 @@ type ChunkedReader struct {
 // NewChunkedReader creates a new chunked reader with the specified chunk size
 func NewChunkedReader(reader io.Reader, chunkSize int) *ChunkedReader {
 	if chunkSize <= 0 {
-		chunkSize = 64 * 1024 // Default 64KB chunks
+		chunkSize = constants.DefaultChunkSize // Default 64KB chunks
 	}
 	return &ChunkedReader{
 		reader:     reader,
 		buffer:     make([]byte, chunkSize),
 		chunkSize:  chunkSize,
 		// PBO optimization: Pre-allocate line buffer
-		lineBuffer: make([]byte, 0, 8192), // 8KB initial capacity
+		lineBuffer: make([]byte, 0, constants.LineBufferInitialCapacity), // 8KB initial capacity
 	}
 }
 
@@ -76,7 +77,7 @@ func (cr *ChunkedReader) ProcessLines(ctx context.Context, rawLines chan *bytes.
 							default:
 							}
 						}
-						sharedTimer.Reset(10 * time.Millisecond)
+						sharedTimer.Reset(constants.ProcessorSleepDuration)
 						select {
 						case <-ctx.Done():
 							return ctx.Err()
diff --git a/internal/io/fs/directprocessor.go b/internal/io/fs/directprocessor.go
index 84b78bb..312ac9c 100644
--- a/internal/io/fs/directprocessor.go
+++ b/internal/io/fs/directprocessor.go
@@ -9,6 +9,7 @@ import (
 	"time"
 
 	"github.com/mimecast/dtail/internal/config"
+	"github.com/mimecast/dtail/internal/constants"
 	"github.com/mimecast/dtail/internal/lcontext"
 )
 
@@ -77,7 +78,7 @@ func (dp *DirectProcessor) ProcessReader(ctx context.Context, reader io.Reader,
 
 	// Set buffer size respecting MaxLineLength configuration
 	maxLineLength := config.Server.MaxLineLength
-	initialBufSize := 64 * 1024
+	initialBufSize := constants.InitialBufferSize
 	if maxLineLength < initialBufSize {
 		initialBufSize = maxLineLength
 	}
@@ -337,7 +338,7 @@ func (dp *DirectProcessor) followFile(ctx context.Context, filePath string) erro
 		select {
 		case <-ctx.Done():
 			return ctx.Err()
-		case <-time.After(100 * time.Millisecond):
+		case <-time.After(constants.ProcessorTimeoutDuration):
 			// Check if file has grown
 			fileInfo, err := os.Stat(filePath)
 			if err != nil {
diff --git a/internal/io/fs/stats.go b/internal/io/fs/stats.go
index 4121ff7..1990e53 100644
--- a/internal/io/fs/stats.go
+++ b/internal/io/fs/stats.go
@@ -1,14 +1,16 @@
 package fs
 
+import "github.com/mimecast/dtail/internal/constants"
+
 // Used to calculate how many log lines matched the regular expression
 // and how many log files could be transmitted from the server to the client.
 // Hit and transmit percentage takes only the last 100 log lines into calculation.
 type stats struct {
 	pos           int
 	lineCount     uint64
-	matched       [100]bool
+	matched       [constants.StatsArraySize]bool
 	matchCount    uint64
-	transmitted   [100]bool
+	transmitted   [constants.StatsArraySize]bool
 	transmitCount int
 }
 
@@ -25,7 +27,7 @@ func (f *stats) transmittedPerc() int {
 // Update bucket position. We only take into consideration the last 100
 // lines for stats.
 func (f *stats) updatePosition() {
-	f.pos = (f.pos + 1) % 100
+	f.pos = (f.pos + 1) % constants.StatsArraySize
 	f.lineCount++
 }
 
@@ -63,7 +65,7 @@ func (f *stats) updateLineNotTransmitted() {
 
 func percentOf(total float64, value float64) float64 {
 	if total == 0 || total == value {
-		return 100
+		return constants.PercentageMultiplier
 	}
-	return value / (total / 100.0)
+	return value / (total / constants.PercentageMultiplier)
 }
diff --git a/internal/io/fs/tailprocessor.go b/internal/io/fs/tailprocessor.go
index 3bc9029..55934ce 100644
--- a/internal/io/fs/tailprocessor.go
+++ b/internal/io/fs/tailprocessor.go
@@ -7,6 +7,7 @@ import (
 	"time"
 
 	"github.com/mimecast/dtail/internal/config"
+	"github.com/mimecast/dtail/internal/constants"
 	"github.com/mimecast/dtail/internal/lcontext"
 	"github.com/mimecast/dtail/internal/regex"
 )
@@ -163,7 +164,7 @@ func (ftp *FollowingTailProcessor) followFile(ctx context.Context, filePath stri
 func (ftp *FollowingTailProcessor) followReader(ctx context.Context, file *os.File, filePath string) error {
 	// Set buffer size respecting MaxLineLength configuration
 	maxLineLength := config.Server.MaxLineLength
-	initialBufSize := 64 * 1024
+	initialBufSize := constants.InitialBufferSize
 	if maxLineLength < initialBufSize {
 		initialBufSize = maxLineLength
 	}
@@ -259,7 +260,7 @@ func (ftp *FollowingTailProcessor) followReader(ctx context.Context, file *os.Fi
 		select {
 		case <-ctx.Done():
 			return ctx.Err()
-		case <-time.After(100 * time.Millisecond):
+		case <-time.After(constants.ProcessorTimeoutDuration):
 			// Continue the loop to check for new content
 		}
 	}
diff --git a/internal/mapr/query.go b/internal/mapr/query.go
index ddcbc90..dc1a1c2 100644
--- a/internal/mapr/query.go
+++ b/internal/mapr/query.go
@@ -6,6 +6,8 @@ import (
 	"strconv"
 	"strings"
 	"time"
+
+	"github.com/mimecast/dtail/internal/constants"
 )
 
 const (
@@ -70,8 +72,8 @@ func NewQuery(queryStr string) (*Query, error) {
 	q := Query{
 		RawQuery: queryStr,
 		tokens:   tokens,
-		Interval: time.Second * 5,
-		Limit:    -1,
+		Interval: constants.DefaultMapReduceInterval,
+		Limit:    constants.MapReduceUnlimited,
 	}
 
 	// If log format is CSV, then use "." as the table. It means, that
diff --git a/internal/mapr/server/aggregate.go b/internal/mapr/server/aggregate.go
index 4f14751..8fabfc9 100644
--- a/internal/mapr/server/aggregate.go
+++ b/internal/mapr/server/aggregate.go
@@ -7,6 +7,7 @@ import (
 
 	"github.com/mimecast/dtail/internal"
 	"github.com/mimecast/dtail/internal/config"
+	"github.com/mimecast/dtail/internal/constants"
 	"github.com/mimecast/dtail/internal/io/dlog"
 	"github.com/mimecast/dtail/internal/io/line"
 	"github.com/mimecast/dtail/internal/mapr"
@@ -167,7 +168,7 @@ func (a *Aggregate) fieldsFromLines(ctx context.Context) <-chan map[string]strin
 				if noMoreChannels {
 					return
 				}
-				time.Sleep(time.Millisecond * 100)
+				time.Sleep(constants.MapReduceSleepDuration)
 				continue
 			}
 
diff --git a/internal/server/continuous.go b/internal/server/continuous.go
index ac5c686..0a218d4 100644
--- a/internal/server/continuous.go
+++ b/internal/server/continuous.go
@@ -8,6 +8,7 @@ import (
 
 	"github.com/mimecast/dtail/internal/clients"
 	"github.com/mimecast/dtail/internal/config"
+	"github.com/mimecast/dtail/internal/constants"
 	"github.com/mimecast/dtail/internal/io/dlog"
 	"github.com/mimecast/dtail/internal/omode"
 	gossh "golang.org/x/crypto/ssh"
@@ -21,7 +22,7 @@ func newContinuous() *continuous {
 
 func (c *continuous) start(ctx context.Context) {
 	dlog.Server.Info("Starting continuous job runner after 2s")
-	time.Sleep(time.Second * 2)
+	time.Sleep(constants.ContinuousJobsStartDelay)
 	c.runJobs(ctx)
 }
 
diff --git a/internal/server/filldates.go b/internal/server/filldates.go
index a6b0ba8..e7489ca 100644
--- a/internal/server/filldates.go
+++ b/internal/server/filldates.go
@@ -3,21 +3,23 @@ package server
 import (
 	"strings"
 	"time"
+
+	"github.com/mimecast/dtail/internal/constants"
 )
 
 func fillDates(str string) string {
-	yyyesterday := time.Now().Add(3 * -24 * time.Hour).Format("20060102")
+	yyyesterday := time.Now().Add(-3 * constants.DayDuration).Format("20060102")
 	str = strings.ReplaceAll(str, "$yyyesterday", yyyesterday)
 
-	yyesterday := time.Now().Add(2 * -24 * time.Hour).Format("20060102")
+	yyesterday := time.Now().Add(-2 * constants.DayDuration).Format("20060102")
 	str = strings.ReplaceAll(str, "$yyesterday", yyesterday)
 
-	yesterday := time.Now().Add(1 * -24 * time.Hour).Format("20060102")
+	yesterday := time.Now().Add(-1 * constants.DayDuration).Format("20060102")
 	str = strings.ReplaceAll(str, "$yesterday", yesterday)
 
 	today := time.Now().Format("20060102")
 	str = strings.ReplaceAll(str, "$today", today)
 
-	tomorrow := time.Now().Add(1 * 24 * time.Hour).Format("20060102")
+	tomorrow := time.Now().Add(1 * constants.DayDuration).Format("20060102")
 	return strings.ReplaceAll(str, "$tomorrow", tomorrow)
 }
diff --git a/internal/server/handlers/basehandler.go b/internal/server/handlers/basehandler.go
index e8ce19a..19096bf 100644
--- a/internal/server/handlers/basehandler.go
+++ b/internal/server/handlers/basehandler.go
@@ -15,6 +15,7 @@ import (
 
 	"github.com/mimecast/dtail/internal"
 	"github.com/mimecast/dtail/internal/config"
+	"github.com/mimecast/dtail/internal/constants"
 	"github.com/mimecast/dtail/internal/io/dlog"
 	"github.com/mimecast/dtail/internal/io/line"
 	"github.com/mimecast/dtail/internal/io/pool"
@@ -117,7 +118,7 @@ func (h *baseHandler) Read(p []byte) (n int, err error) {
 		pool.RecycleBytesBuffer(line.Content)
 		line.Recycle()
 
-	case <-time.After(time.Second):
+	case <-time.After(constants.ReadTimeout):
 		select {
 		case <-h.done.Done():
 			err = io.EOF
@@ -288,13 +289,13 @@ func (h *baseHandler) flush() {
 	numUnsentMessages := func() int {
 		return len(h.lines) + len(h.serverMessages) + len(h.maprMessages)
 	}
-	for i := 0; i < 10; i++ {
+	for i := 0; i < constants.MaxFlushRetries; i++ {
 		if numUnsentMessages() == 0 {
 			dlog.Server.Debug(h.user, "ALL lines sent", fmt.Sprintf("%p", h))
 			return
 		}
 		dlog.Server.Debug(h.user, "Still lines to be sent")
-		time.Sleep(time.Millisecond * 10)
+		time.Sleep(constants.ProcessorSleepDuration)
 	}
 	dlog.Server.Warn(h.user, "Some lines remain unsent", numUnsentMessages())
 }
@@ -312,7 +313,7 @@ func (h *baseHandler) shutdown() {
 
 	select {
 	case <-h.ackCloseReceived:
-	case <-time.After(time.Second * 5):
+	case <-time.After(constants.HandlerTimeout):
 		dlog.Server.Debug(h.user, "Shutdown timeout reached, enforcing shutdown")
 	case <-h.done.Done():
 	}
diff --git a/internal/server/handlers/readcommand.go b/internal/server/handlers/readcommand.go
index c75b9fc..f7568a5 100644
--- a/internal/server/handlers/readcommand.go
+++ b/internal/server/handlers/readcommand.go
@@ -8,6 +8,7 @@ import (
 	"strings"
 	"time"
 
+	"github.com/mimecast/dtail/internal/constants"
 	"github.com/mimecast/dtail/internal/io/dlog"
 	"github.com/mimecast/dtail/internal/io/fs"
 	"github.com/mimecast/dtail/internal/io/line"
@@ -106,7 +107,7 @@ func (r *readCommand) start(ctx context.Context, ltx lcontext.LContext,
 func (r *readCommand) readGlob(ctx context.Context, ltx lcontext.LContext,
 	glob string, re regex.Regex, retries int, queryStr string) {
 
-	retryInterval := time.Second * 5
+	retryInterval := constants.ReadCommandRetryInterval
 	glob = filepath.Clean(glob)
 
 	for retryCount := 0; retryCount < retries; retryCount++ {
diff --git a/internal/server/scheduler.go b/internal/server/scheduler.go
index cc51b7e..1f89ef5 100644
--- a/internal/server/scheduler.go
+++ b/internal/server/scheduler.go
@@ -10,6 +10,7 @@ import (
 
 	"github.com/mimecast/dtail/internal/clients"
 	"github.com/mimecast/dtail/internal/config"
+	"github.com/mimecast/dtail/internal/constants"
 	"github.com/mimecast/dtail/internal/io/dlog"
 	"github.com/mimecast/dtail/internal/omode"
 
@@ -24,8 +25,8 @@ func newScheduler() *scheduler {
 
 func (s *scheduler) start(ctx context.Context) {
 	dlog.Server.Info("Starting scheduled job runner after 2s")
-	// First run after just 10s!
-	time.Sleep(time.Second * 2)
+	// First run after just 2s!
+	time.Sleep(constants.SchedulerStartDelay)
 	s.runJobs(ctx)
 	for {
 		select {
diff --git a/internal/server/stats.go b/internal/server/stats.go
index 99a644a..cdf3f03 100644
--- a/internal/server/stats.go
+++ b/internal/server/stats.go
@@ -7,6 +7,7 @@ import (
 	"time"
 
 	"github.com/mimecast/dtail/internal/config"
+	"github.com/mimecast/dtail/internal/constants"
 	"github.com/mimecast/dtail/internal/io/dlog"
 )
 
@@ -67,7 +68,7 @@ func (s *stats) serverLimitExceeded() error {
 func (s *stats) start(ctx context.Context) {
 	for {
 		select {
-		case <-time.NewTimer(time.Second * 10).C:
+		case <-time.NewTimer(constants.ServerStatsTimerDuration).C:
 			s.logServerStats()
 		case <-ctx.Done():
 			return
@@ -78,7 +79,7 @@ func (s *stats) start(ctx context.Context) {
 func (s *stats) waitForConnections() {
 	for {
 		select {
-		case <-time.NewTimer(time.Second).C:
+		case <-time.NewTimer(constants.ReadTimeout).C:
 			if !s.hasConnections() {
 				return
 			}
diff --git a/internal/ssh/client/knownhostscallback.go b/internal/ssh/client/knownhostscallback.go
index 393c4c7..d5f605f 100644
--- a/internal/ssh/client/knownhostscallback.go
+++ b/internal/ssh/client/knownhostscallback.go
@@ -10,6 +10,7 @@ import (
 	"sync"
 	"time"
 
+	"github.com/mimecast/dtail/internal/constants"
 	"github.com/mimecast/dtail/internal/io/dlog"
 	"github.com/mimecast/dtail/internal/io/prompt"
 
@@ -125,7 +126,7 @@ func (c KnownHostsCallback) PromptAddHosts(ctx context.Context) {
 				c.promptAddHosts(hosts)
 				hosts = []unknownHost{}
 			}
-		case <-time.After(2 * time.Second):
+		case <-time.After(constants.KnownHostsCallbackTimeout):
 			// Or ask when after 2 seconds no new unknown hosts were added.
 			if len(hosts) > 0 {
 				c.promptAddHosts(hosts)
diff --git a/internal/user/server/user.go b/internal/user/server/user.go
index abf74f3..2b2d720 100644
--- a/internal/user/server/user.go
+++ b/internal/user/server/user.go
@@ -8,11 +8,12 @@ import (
 	"strings"
 
 	"github.com/mimecast/dtail/internal/config"
+	"github.com/mimecast/dtail/internal/constants"
 	"github.com/mimecast/dtail/internal/io/dlog"
 	"github.com/mimecast/dtail/internal/io/fs/permissions"
 )
 
-const maxLinkDepth int = 100
+const maxLinkDepth int = constants.MaxSymlinkDepth
 
 // User represents an end-user which connected to the server via the DTail client.
 type User struct {