Add http.LogRoundTripper helper for request debugging

Signed-off-by: Knut Ahlers <knut@ahlers.me>

http/logRoundTrip.go

@@ -0,0 +1,61 @@
+package http
+
+import (
+	"fmt"
+	"io"
+	"net/http"
+	"net/http/httputil"
+
+	"github.com/pkg/errors"
+)
+
+type (
+	// LogRoundTripper is a drop-in for the Transport of a http.Client
+	// which then will log requests and responses to the given writer
+	// (os.Stdout / os.Stderr / logrus writer / ...)
+	LogRoundTripper struct {
+		next   http.RoundTripper
+		output io.Writer
+	}
+)
+
+var _ http.RoundTripper = LogRoundTripper{}
+
+// NewLogRoundTripper creates a new LogRoundTripper with the given
+// next transport and output writer. If no next transport is given
+// (next == nil) the http.DefaultTransport is used. If no writer
+// is given the io.Discard writer is used.
+func NewLogRoundTripper(next http.RoundTripper, out io.Writer) LogRoundTripper {
+	if next == nil {
+		next = http.DefaultTransport
+	}
+
+	if out == nil {
+		// Makes no sense but ensures we don't fail writing to nil
+		out = io.Discard
+	}
+
+	return LogRoundTripper{next, out}
+}
+
+// RoundTrip implements http.RoundTripper interface
+func (l LogRoundTripper) RoundTrip(req *http.Request) (*http.Response, error) {
+	dump, err := httputil.DumpRequest(req, true)
+	if err != nil {
+		return nil, errors.Wrap(err, "dumping request")
+	}
+
+	fmt.Fprintf(l.output, "---- 8< REQ >8 ----\n%s", dump)
+
+	resp, err := l.next.RoundTrip(req)
+	if err != nil {
+		return resp, err
+	}
+	if dump, err = httputil.DumpResponse(resp, true); err != nil {
+		return nil, errors.Wrap(err, "dumping response")
+	}
+
+	fmt.Fprintf(l.output, "---- 8< RES >8 ----\n%s---- 8< END >8 ----\n", dump)
+
+	return resp, err
+}