Add error helpers (#10)

Author: Dean Karn

errors/retryable.go

@@ -0,0 +1,89 @@
+package errorsext
+
+import (
+	"errors"
+	"strings"
+	"syscall"
+)
+
+// IsRetryableHTTP returns if the provided error is considered retryable HTTP error. It also returns the
+// type, in string form, for optional logging and metrics use.
+func IsRetryableHTTP(err error) (retryType string, isRetryable bool) {
+	if retryType, isRetryable = IsRetryableNetwork(err); isRetryable {
+		return
+	}
+
+	errStr := err.Error()
+
+	if strings.Contains(errStr, "http2: server sent GOAWAY") {
+		return "goaway", true
+	}
+
+	// errServerClosedIdle is not seen by users for idempotent HTTP requests, but may be
+	// seen by a user if the server shuts down an idle connection and sends its FIN
+	// in flight with already-written POST body bytes from the client.
+	// See https://github.com/golang/go/issues/19943#issuecomment-355607646
+	//
+	// This will possibly get fixed in the upstream SDK's based on the ability to set an HTTP error in the future
+	// https://go-review.googlesource.com/c/go/+/191779/ but until then we should retry these.
+	//
+	if strings.Contains(errStr, "http: server closed idle connection") {
+		return "server_close_idle_connection", true
+	}
+	return "", false
+}
+
+// IsRetryableNetwork returns if the provided error is a retryable network related error. It also returns the
+// type, in string form, for optional logging and metrics use.
+func IsRetryableNetwork(err error) (retryType string, isRetryable bool) {
+	if IsTemporary(err) {
+		return "temporary", true
+	}
+	if IsTimeout(err) {
+		return "timeout", true
+	}
+	return IsTemporaryConnection(err)
+}
+
+// IsTemporary returns true if the provided error is considered retryable temporary error by testing if it
+// complies with an interface implementing `Temporary() bool` and calling the function.
+func IsTemporary(err error) bool {
+	var t interface{ Temporary() bool }
+	return errors.As(err, &t) && t.Temporary()
+}
+
+// IsTimeout returns true if the provided error is considered a retryable timeout error by testing if it
+// complies with an interface implementing `Timeout() bool` and calling the function.
+func IsTimeout(err error) bool {
+	var t interface{ Timeout() bool }
+	return errors.As(err, &t) && t.Timeout()
+}
+
+// IsTemporaryConnection returns if the provided error was a low level retryable connection error. It also returns the
+// type, in string form, for optional logging and metrics use.
+func IsTemporaryConnection(err error) (retryType string, isRetryable bool) {
+	if err != nil {
+		if errors.Is(err, syscall.ECONNRESET) {
+			return "econnreset", true
+		}
+		if errors.Is(err, syscall.ECONNABORTED) {
+			return "econnaborted", true
+		}
+		if errors.Is(err, syscall.ENOTCONN) {
+			return "enotconn", true
+		}
+		if errors.Is(err, syscall.EWOULDBLOCK) {
+			return "ewouldblock", true
+		}
+		if errors.Is(err, syscall.EAGAIN) {
+			return "eagain", true
+		}
+		if errors.Is(err, syscall.ETIMEDOUT) {
+			return "etimedout", true
+		}
+		if errors.Is(err, syscall.EINTR) {
+			return "eintr", true
+		}
+	}
+	return "", false
+}

net/http/retryable.go

@@ -0,0 +1,25 @@
+package httpext
+
+import (
+	"net/http"
+)
+
+var (
+	// retryableStatusCodes defines the common HTTP response codes that are considered retryable.
+	retryableStatusCodes = map[int]bool{
+		http.StatusServiceUnavailable: true,
+		http.StatusTooManyRequests:    true,
+		http.StatusBadGateway:         true,
+		http.StatusGatewayTimeout:     true,
+
+		// 524 is a Cloudflare specific error which indicates it connected to the origin server but did not receive
+		// response within 100 seconds and so times out.
+		// https://support.cloudflare.com/hc/en-us/articles/115003011431-Error-524-A-timeout-occurred#524error
+		524: true,
+	}
+)
+
+// IsRetryableStatusCode returns if the provided status code is considered retryable.
+func IsRetryableStatusCode(code int) bool {
+	return retryableStatusCodes[code]
+}