add: download and default client for gvm

cli/client.go

@@ -0,0 +1,54 @@
+package cli
+
+import (
+	"context"
+	"net"
+	"net/http"
+	"runtime"
+	"time"
+)
+
+const _defaultConcurrentDialsPerCPU = 5 << 1
+
+var (
+	_defaultTimeOut   = 30 * time.Second
+	_defaultKeepAlive = 30 * time.Second
+)
+
+type dialRateLimiter struct {
+	dialer *net.Dialer
+	sem    chan struct{}
+}
+
+func DownloadClient(maxIdleConnsPerHost int) *http.Client {
+	transport := http.DefaultTransport.(*http.Transport).Clone()
+	dialer := rateLimiter(&net.Dialer{
+		Timeout:   _defaultTimeOut,
+		KeepAlive: _defaultKeepAlive,
+	})
+
+	transport.DialContext = dialer.DialContext
+	transport.MaxIdleConns = 0 // not limit
+	transport.MaxIdleConnsPerHost = maxIdleConnsPerHost
+	transport.DisableCompression = true
+	return &http.Client{
+		Transport: transport,
+	}
+}
+
+func DefaultClient() *http.Client {
+	return http.DefaultClient
+}
+
+func rateLimiter(dialer *net.Dialer) *dialRateLimiter {
+	return &dialRateLimiter{
+		dialer: dialer,
+		sem:    make(chan struct{}, _defaultConcurrentDialsPerCPU*runtime.NumCPU()),
+	}
+}
+
+func (d *dialRateLimiter) DialContext(ctx context.Context, network, address string) (net.Conn, error) {
+	d.sem <- struct{}{}
+	defer func() { <-d.sem }()
+	return d.dialer.DialContext(ctx, network, address)
+}