encode: Configurable compression level for zstd (#6140)

* Add zstd compression level support

* Refactored zstd levels to string arguments

fastest, default, better, best

* Add comment with list of all available levels

* Corrected data types for config

---------

Co-authored-by: Evgeny Blinov <e.a.blinov@gmail.com>
Co-authored-by: Matt Holt <mholt@users.noreply.github.com>

modules/caddyhttp/encode/zstd/zstd.go

@@ -15,6 +15,8 @@
 package caddyzstd
 
 import (
+	"fmt"
+
 	"github.com/klauspost/compress/zstd"
 
 	"github.com/caddyserver/caddy/v2"
@@ -27,7 +29,13 @@ func init() {
 }
 
 // Zstd can create Zstandard encoders.
-type Zstd struct{}
+type Zstd struct {
+	// The compression level. Accepted values: fastest, better, best, default.
+	Level string `json:"level,omitempty"`
+
+	// Compression level refer to type constants value from zstd.SpeedFastest to zstd.SpeedBestCompression
+	level zstd.EncoderLevel
+}
 
 // CaddyModule returns the Caddy module information.
 func (Zstd) CaddyModule() caddy.ModuleInfo {
@@ -39,6 +47,37 @@ func (Zstd) CaddyModule() caddy.ModuleInfo {
 
 // UnmarshalCaddyfile sets up the handler from Caddyfile tokens.
 func (z *Zstd) UnmarshalCaddyfile(d *caddyfile.Dispenser) error {
+	d.Next() // consume option name
+	if !d.NextArg() {
+		return nil
+	}
+	levelStr := d.Val()
+	if ok, _ := zstd.EncoderLevelFromString(levelStr); !ok {
+		return d.Errf("unexpected compression level, use one of '%s', '%s', '%s', '%s'",
+			zstd.SpeedFastest,
+			zstd.SpeedBetterCompression,
+			zstd.SpeedBestCompression,
+			zstd.SpeedDefault,
+		)
+	}
+	z.Level = levelStr
+	return nil
+}
+
+// Provision provisions z's configuration.
+func (z *Zstd) Provision(ctx caddy.Context) error {
+	if z.Level == "" {
+		z.Level = zstd.SpeedDefault.String()
+	}
+	var ok bool
+	if ok, z.level = zstd.EncoderLevelFromString(z.Level); !ok {
+		return fmt.Errorf("unexpected compression level, use one of '%s', '%s', '%s', '%s'",
+			zstd.SpeedFastest,
+			zstd.SpeedDefault,
+			zstd.SpeedBetterCompression,
+			zstd.SpeedBestCompression,
+		)
+	}
 	return nil
 }
 
@@ -51,12 +90,19 @@ func (z Zstd) NewEncoder() encode.Encoder {
 	// The default of 8MB for the window is
 	// too large for many clients, so we limit
 	// it to 128K to lighten their load.
-	writer, _ := zstd.NewWriter(nil, zstd.WithWindowSize(128<<10), zstd.WithEncoderConcurrency(1), zstd.WithZeroFrames(true))
+	writer, _ := zstd.NewWriter(
+		nil,
+		zstd.WithWindowSize(128<<10),
+		zstd.WithEncoderConcurrency(1),
+		zstd.WithZeroFrames(true),
+		zstd.WithEncoderLevel(z.level),
+	)
 	return writer
 }
 
 // Interface guards
 var (
 	_ encode.Encoding       = (*Zstd)(nil)
 	_ caddyfile.Unmarshaler = (*Zstd)(nil)
+	_ caddy.Provisioner     = (*Zstd)(nil)
 )