Adding http2 auto fallback - proxy compatible

client.go

@@ -3,13 +3,17 @@ package retryablehttp
 import (
 	"net/http"
 	"time"
+
+	"golang.org/x/net/http2"
 )
 
 // Client is used to make HTTP requests. It adds additional functionality
 // like automatic retries to tolerate minor outages.
 type Client struct {
-	// HTTPClient is the internal HTTP client.
+	// HTTPClient is the internal HTTP client (http1x + http2 via connection upgrade upgrade).
 	HTTPClient *http.Client
+	// HTTPClient is the internal HTTP client configured to fallback to native http2 at transport level
+	HTTPClient2 *http.Client
 
 	// RequestLogHook allows a user-supplied function to be called
 	// before each retry.
@@ -73,16 +77,22 @@ var DefaultOptionsSingle = Options{
 // NewClient creates a new Client with default settings.
 func NewClient(options Options) *Client {
 	httpclient := DefaultClient()
+	httpclient2 := DefaultClient()
+	if err := http2.ConfigureTransport(httpclient2.Transport.(*http.Transport)); err != nil {
+		return nil
+	}
+
 	// if necessary adjusts per-request timeout proportionally to general timeout (30%)
 	if options.Timeout > time.Second*15 {
 		httpclient.Timeout = time.Duration(options.Timeout.Seconds()*0.3) * time.Second
 	}
 
 	c := &Client{
-		HTTPClient: httpclient,
-		CheckRetry: DefaultRetryPolicy(),
-		Backoff:    DefaultBackoff(),
-		options:    options,
+		HTTPClient:  httpclient,
+		HTTPClient2: httpclient2,
+		CheckRetry:  DefaultRetryPolicy(),
+		Backoff:     DefaultBackoff(),
+		options:     options,
 	}
 
 	c.setKillIdleConnections()
@@ -91,10 +101,16 @@ func NewClient(options Options) *Client {
 
 // NewWithHTTPClient creates a new Client with default settings and provided http.Client
 func NewWithHTTPClient(client *http.Client, options Options) *Client {
+	httpclient2 := DefaultClient()
+	httpclient2.Transport = client.Transport.(*http.Transport).Clone()
+	if err := http2.ConfigureTransport(httpclient2.Transport.(*http.Transport)); err != nil {
+		return nil
+	}
 	c := &Client{
-		HTTPClient: client,
-		CheckRetry: DefaultRetryPolicy(),
-		Backoff:    DefaultBackoff(),
+		HTTPClient:  client,
+		HTTPClient2: httpclient2,
+		CheckRetry:  DefaultRetryPolicy(),
+		Backoff:     DefaultBackoff(),
 
 		options: options,
 	}

do.go

@@ -6,6 +6,7 @@ import (
 	"io"
 	"io/ioutil"
 	"net/http"
+	"strings"
 	"time"
 )
 
@@ -50,6 +51,12 @@ func (c *Client) Do(req *Request) (*http.Response, error) {
 		// Check if we should continue with retries.
 		checkOK, checkErr := c.CheckRetry(req.Context(), resp, err)
 
+		// if err is equal to missing minor protocol version retry with http/2
+		if err != nil && strings.Contains(err.Error(), "net/http: HTTP/1.x transport connection broken: malformed HTTP version \"HTTP/2\"") {
+			resp, err = c.HTTPClient2.Do(req.Request)
+			checkOK, checkErr = c.CheckRetry(req.Context(), resp, err)
+		}
+
 		if err != nil {
 			// Increment the failure counter as the request failed
 			req.Metrics.Failures++

go.mod

@@ -1,3 +1,5 @@
 module github.com/projectdiscovery/retryablehttp-go
 
 go 1.14
+
+require golang.org/x/net v0.0.0-20210521195947-fe42d452be8f

go.sum

@@ -0,0 +1,8 @@
+golang.org/x/net v0.0.0-20210521195947-fe42d452be8f h1:Si4U+UcgJzya9kpiEUJKQvjr512OLli+gL4poHrz93U=
+golang.org/x/net v0.0.0-20210521195947-fe42d452be8f/go.mod h1:9nx3DQGgdP8bBQD5qxJ1jj9UTztislL4KSBs9R2vV5Y=
+golang.org/x/sys v0.0.0-20201119102817-f84b799fce68/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20210423082822-04245dca01da/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
+golang.org/x/text v0.3.6 h1:aRYxNxv6iGQlyVaZmk6ZgYEDa+Jg18DxebPSrd6bg1M=
+golang.org/x/text v0.3.6/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
+golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=