common/prpc, tools/cmd/cproto: prpc client

common/prpc/timeout.go

Index: common/prpc/timeout.go
diff --git a/server/prpc/timeout.go b/common/prpc/timeout.go
similarity index 51%
rename from server/prpc/timeout.go
rename to common/prpc/timeout.go
index 9811395ff985f533ca6a1d928e5715b37bb040f6..25d3aec9c05c004518f6af56b07cea340cadda87 100644
--- a/server/prpc/timeout.go
+++ b/common/prpc/timeout.go
@@ -10,10 +10,6 @@ import (
 	"time"
 )
 
-// headerTimeout is HTTP header used to set pRPC request timeout.
-// The single value should match regexp `\d+[HMSmun]`.
-const headerTimeout = "X-Prpc-Timeout"
-
 // The rest of this file is adapted from
 // https://github.com/grpc/grpc-go/blob/6a026b9f108b49838491178e5d9bf7a4dcf32cf2/transport/http_util.go#L295
 
@@ -47,7 +43,8 @@ func timeoutUnitToDuration(u timeoutUnit) (d time.Duration, ok bool) {
 	return
 }
 
-func decodeTimeout(s string) (time.Duration, error) {
+// DecodeTimeout decodes a gRPC/pRPC timeout header string into a time.Duration.
+func DecodeTimeout(s string) (time.Duration, error) {
 	size := len(s)
 	if size < 2 {
 		return 0, fmt.Errorf("too short: %q", s)
@@ -63,3 +60,39 @@ func decodeTimeout(s string) (time.Duration, error) {
 	}
 	return d * time.Duration(t), nil
 }
+
+const maxTimeoutValue int64 = 100000000 - 1
+
+// div does integer division and round-up the result. Note that this is
+// equivalent to (d+r-1)/r but has less chance to overflow.
+func div(d, r time.Duration) int64 {
+	if m := d % r; m > 0 {
+		return int64(d/r + 1)
+	}
+	return int64(d / r)
+}
+
+// EncodeTimeout encodes a gRPC/pRPC timeout into a timeout header
+// time.Duration.
+//
+// This rounds the time.Duration to the smallest time unit that can represent
+// it.
+func EncodeTimeout(t time.Duration) string {
+	if d := div(t, time.Nanosecond); d <= maxTimeoutValue {
+		return strconv.FormatInt(d, 10) + "n"
+	}
+	if d := div(t, time.Microsecond); d <= maxTimeoutValue {
+		return strconv.FormatInt(d, 10) + "u"
+	}
+	if d := div(t, time.Millisecond); d <= maxTimeoutValue {
+		return strconv.FormatInt(d, 10) + "m"
+	}
+	if d := div(t, time.Second); d <= maxTimeoutValue {
+		return strconv.FormatInt(d, 10) + "S"
+	}
+	if d := div(t, time.Minute); d <= maxTimeoutValue {
+		return strconv.FormatInt(d, 10) + "M"
+	}
+	// Note that maxTimeoutValue * time.Hour > MaxInt64.
+	return strconv.FormatInt(div(t, time.Hour), 10) + "H"
+}