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.

1 files changed, 3 insertions, 2 deletions

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
 		}
 	}