[feature] S3 support (#674)

* feat: vendor minio client

* feat: introduce storage package with s3 support

* feat: serve s3 files directly

this saves a lot of bandwith as the files are fetched from the object
store directly

* fix: use explicit local storage in tests

* feat: integrate s3 storage with the main server

* fix: add s3 config to cli tests

* docs: explicitly set values in example config

also adds license header to the storage package

* fix: use better http status code on s3 redirect

HTTP 302 Found is the best fit, as it signifies that the resource
requested was found but not under its presumed URL

307/TemporaryRedirect would mean that this resource is usually located
here, not in this case

303/SeeOther indicates that the redirection does not link to the
requested resource but to another page

* refactor: use context in storage driver interface

vendor/github.com/dustin/go-humanize/comma.go

@@ -0,0 +1,116 @@
+package humanize
+
+import (
+	"bytes"
+	"math"
+	"math/big"
+	"strconv"
+	"strings"
+)
+
+// Comma produces a string form of the given number in base 10 with
+// commas after every three orders of magnitude.
+//
+// e.g. Comma(834142) -> 834,142
+func Comma(v int64) string {
+	sign := ""
+
+	// Min int64 can't be negated to a usable value, so it has to be special cased.
+	if v == math.MinInt64 {
+		return "-9,223,372,036,854,775,808"
+	}
+
+	if v < 0 {
+		sign = "-"
+		v = 0 - v
+	}
+
+	parts := []string{"", "", "", "", "", "", ""}
+	j := len(parts) - 1
+
+	for v > 999 {
+		parts[j] = strconv.FormatInt(v%1000, 10)
+		switch len(parts[j]) {
+		case 2:
+			parts[j] = "0" + parts[j]
+		case 1:
+			parts[j] = "00" + parts[j]
+		}
+		v = v / 1000
+		j--
+	}
+	parts[j] = strconv.Itoa(int(v))
+	return sign + strings.Join(parts[j:], ",")
+}
+
+// Commaf produces a string form of the given number in base 10 with
+// commas after every three orders of magnitude.
+//
+// e.g. Commaf(834142.32) -> 834,142.32
+func Commaf(v float64) string {
+	buf := &bytes.Buffer{}
+	if v < 0 {
+		buf.Write([]byte{'-'})
+		v = 0 - v
+	}
+
+	comma := []byte{','}
+
+	parts := strings.Split(strconv.FormatFloat(v, 'f', -1, 64), ".")
+	pos := 0
+	if len(parts[0])%3 != 0 {
+		pos += len(parts[0]) % 3
+		buf.WriteString(parts[0][:pos])
+		buf.Write(comma)
+	}
+	for ; pos < len(parts[0]); pos += 3 {
+		buf.WriteString(parts[0][pos : pos+3])
+		buf.Write(comma)
+	}
+	buf.Truncate(buf.Len() - 1)
+
+	if len(parts) > 1 {
+		buf.Write([]byte{'.'})
+		buf.WriteString(parts[1])
+	}
+	return buf.String()
+}
+
+// CommafWithDigits works like the Commaf but limits the resulting
+// string to the given number of decimal places.
+//
+// e.g. CommafWithDigits(834142.32, 1) -> 834,142.3
+func CommafWithDigits(f float64, decimals int) string {
+	return stripTrailingDigits(Commaf(f), decimals)
+}
+
+// BigComma produces a string form of the given big.Int in base 10
+// with commas after every three orders of magnitude.
+func BigComma(b *big.Int) string {
+	sign := ""
+	if b.Sign() < 0 {
+		sign = "-"
+		b.Abs(b)
+	}
+
+	athousand := big.NewInt(1000)
+	c := (&big.Int{}).Set(b)
+	_, m := oom(c, athousand)
+	parts := make([]string, m+1)
+	j := len(parts) - 1
+
+	mod := &big.Int{}
+	for b.Cmp(athousand) >= 0 {
+		b.DivMod(b, athousand, mod)
+		parts[j] = strconv.FormatInt(mod.Int64(), 10)
+		switch len(parts[j]) {
+		case 2:
+			parts[j] = "0" + parts[j]
+		case 1:
+			parts[j] = "00" + parts[j]
+		}
+		j--
+	}
+	parts[j] = strconv.Itoa(int(b.Int64()))
+	return sign + strings.Join(parts[j:], ",")
+}