[performance] Don't retry/backoff invalid http requests that will never succeed (#609)

* add httpguts (ew)

* add ValidateRequest err wrapping logic

* don't retry on unrecoverable errors

* i am very clever

internal/httpclient/client.go

@@ -28,6 +28,9 @@ import (
 	"time"
 )
 
+// ErrInvalidRequest is returned if a given HTTP request is invalid and cannot be performed.
+var ErrInvalidRequest = errors.New("invalid http request")
+
 // ErrReservedAddr is returned if a dialed address resolves to an IP within a blocked or reserved net.
 var ErrReservedAddr = errors.New("dial within blocked / reserved IP range")
 
@@ -164,6 +167,11 @@ func (c *Client) Do(req *http.Request) (*http.Response, error) {
 		defer func() { <-c.queue }()
 	}
 
+	// Firstly, ensure this is a valid request
+	if err := ValidateRequest(req); err != nil {
+		return nil, err
+	}
+
 	// Perform the HTTP request
 	rsp, err := c.client.Do(req)
 	if err != nil {