Convert duration to string supporting days and weeks

README.md

@@ -84,3 +84,5 @@ func main() {
         }
 }
 ```
+
+Also, you can convert to string the duration using `String(t time.Duration)` function. This support weeks and days and not return the ugly decimals from golang standard `t.String()` function. Units with 0 values aren't returned. For example: `1d1ms` means 1 day 1 millisecond.

str2duration.go

@@ -182,3 +182,150 @@ func leadingFraction(s string) (x int64, scale float64, rem string) {
 	}
 	return x, scale, s[i:]
 }
+
+// String returns a string representing the duration in the form "1w4d2h3m5s".
+// Units with 0 values aren't returned, for example: 1d1ms is 1 day 1 milliseconds
+func String(d time.Duration) string {
+	if d == 0 {
+		return "0s"
+	}
+
+	// Largest time is 15250w1d23h47m16s854ms775us807ns
+	var buf [32]byte
+	w := len(buf)
+	var sign string
+
+	u := uint64(d)
+	neg := d < 0
+	if neg {
+		u = -u
+		sign = "-"
+	}
+
+	// u is nanoseconds (ns)
+	if u > 0 {
+		w--
+
+		if u%1000 > 0 {
+			buf[w] = 's'
+			w--
+			buf[w] = 'n'
+			w = fmtInt(buf[:w], u%1000)
+		} else {
+			w++
+		}
+
+		u /= 1000
+
+		// u is now integer microseconds (us)
+		if u > 0 {
+			w--
+			if u%1000 > 0 {
+				buf[w] = 's'
+				w--
+				buf[w] = 'u'
+				w = fmtInt(buf[:w], u%1000)
+			} else {
+				w++
+			}
+			u /= 1000
+
+			// u is now integer milliseconds (ms)
+			if u > 0 {
+				w--
+				if u%1000 > 0 {
+					buf[w] = 's'
+					w--
+					buf[w] = 'm'
+					w = fmtInt(buf[:w], u%1000)
+				} else {
+					w++
+				}
+				u /= 1000
+
+				// u is now integer seconds (s)
+				if u > 0 {
+					w--
+					if u%60 > 0 {
+						buf[w] = 's'
+						w = fmtInt(buf[:w], u%60)
+					} else {
+						w++
+					}
+					u /= 60
+
+					// u is now integer minutes (m)
+					if u > 0 {
+						w--
+
+						if u%60 > 0 {
+							buf[w] = 'm'
+							w = fmtInt(buf[:w], u%60)
+						} else {
+							w++
+						}
+
+						u /= 60
+
+						// u is now integer hours (h)
+						if u > 0 {
+							w--
+
+							if u%24 > 0 {
+								buf[w] = 'h'
+								w = fmtInt(buf[:w], u%24)
+							} else {
+								w++
+							}
+
+							u /= 24
+
+							// u is now integer days (d)
+							if u > 0 {
+								w--
+
+								if u%7 > 0 {
+									buf[w] = 'd'
+									w = fmtInt(buf[:w], u%7)
+								} else {
+									w++
+								}
+
+								u /= 7
+
+								// u is now integer weeks (w)
+								if u > 0 {
+									w--
+									buf[w] = 'w'
+									w = fmtInt(buf[:w], u)
+								}
+
+							}
+
+						}
+					}
+				}
+			}
+		}
+
+	}
+
+	return sign + string(buf[w:])
+}
+
+// fmtInt formats v into the tail of buf.
+// It returns the index where the output begins.
+func fmtInt(buf []byte, v uint64) int {
+	w := len(buf)
+	if v == 0 {
+		w--
+		buf[w] = '0'
+	} else {
+		for v > 0 {
+			w--
+			buf[w] = byte(v%10) + '0'
+			v /= 10
+		}
+	}
+	return w
+}

str2duration_test.go

@@ -49,7 +49,7 @@ func TestParseString(t *testing.T) {
 	}
 }
 
-//TestParseDuration test if string returned by a duration is equal to string returned with the package
+// TestParseDuration test if string returned by a duration is equal to string returned with the package
 func TestParseDuration(t *testing.T) {
 
 	for i, duration := range []time.Duration{
@@ -89,3 +89,63 @@ func TestParseDuration(t *testing.T) {
 		}
 	}
 }
+
+func TestString(t *testing.T) {
+
+	for i, tt := range []struct {
+		dur      time.Duration
+		expected string
+	}{
+		//This times are returned with time.Duration string
+		{time.Duration(0), "0s"},
+		{time.Duration(time.Hour), "1h"},
+		{time.Duration(time.Minute), "1m"},
+		{time.Duration(time.Second), "1s"},
+		{time.Duration(time.Millisecond), "1ms"},
+		{time.Duration(time.Microsecond), "1us"},
+		{time.Duration(time.Nanosecond), "1ns"},
+		{time.Duration(4*time.Second + time.Nanosecond), "4s1ns"},
+		{time.Duration(time.Hour + 4*time.Second + time.Nanosecond), "1h4s1ns"},
+		{time.Duration(61*time.Minute + 10*time.Millisecond), "1h1m10ms"},
+		{time.Duration(61*time.Minute + 123456789*time.Nanosecond), "1h1m123ms456us789ns"},
+		{time.Duration(time.Millisecond + 20*time.Nanosecond), "1ms20ns"},
+		{time.Duration(time.Second + 20*time.Nanosecond), "1s20ns"},
+		{time.Duration(693 * time.Nanosecond), "693ns"},
+		{time.Duration(10*time.Second + time.Microsecond + 693*time.Nanosecond), "10s1us693ns"},
+		{time.Duration(time.Millisecond + 1*time.Nanosecond), "1ms1ns"},
+		{time.Duration(time.Second + 20*time.Nanosecond), "1s20ns"},
+		{time.Duration(60*time.Hour + 8*time.Millisecond), "2d12h8ms"},
+		{time.Duration(96*time.Hour + 63*time.Second), "4d1m3s"},
+		{time.Duration(48*time.Hour + 3*time.Second + 96*time.Nanosecond), "2d3s96ns"},
+		{time.Duration(168*time.Hour + 48*time.Hour + 3*time.Second + 96*time.Nanosecond), "1w2d3s96ns"},
+		{time.Duration(168*time.Hour + 48*time.Hour + 3*time.Second + 3*time.Microsecond + 96*time.Nanosecond), "1w2d3s3us96ns"},
+
+		// this is the maximum supported by golang std: 2540400h10m10.000000000s
+		{time.Duration(2540400*time.Hour + 10*time.Minute + 10*time.Second), "15121w3d10m10s"},
+
+		// this is max int64, the max duration supported to convert
+		{time.Duration(9_223_372_036_854_775_807 * time.Nanosecond), "15250w1d23h47m16s854ms775us807ns"},
+
+		// this is max int64 in negative, the max negative duration supported to convert
+		{time.Duration(-9_223_372_036_854_775_807 * time.Nanosecond), "-15250w1d23h47m16s854ms775us807ns"},
+
+		// negatives
+		{time.Duration(-time.Hour), "-1h"},
+		{time.Duration(-time.Minute), "-1m"},
+		{time.Duration(-time.Second), "-1s"},
+		{time.Duration(-time.Millisecond), "-1ms"},
+		{time.Duration(-time.Microsecond), "-1us"},
+		{time.Duration(-time.Nanosecond), "-1ns"},
+		{time.Duration(-4*time.Second - time.Nanosecond), "-4s1ns"},
+	} {
+		stringDuration := String(tt.dur)
+		if tt.expected != stringDuration {
+			t.Errorf("index %d -> in: %s returned: %s\tnot equal to %s", i, tt.dur, stringDuration, tt.expected)
+		}
+
+		durationParsed, _ := ParseDuration(stringDuration)
+		if durationParsed != tt.dur {
+			t.Errorf("error converting string to duration: index %d -> in: %s returned: %s", i, tt.dur, durationParsed)
+		}
+	}
+}