initial commit

range.go

@@ -0,0 +1,106 @@
+package main
+
+import (
+	"errors"
+	"net/textproto"
+	"strconv"
+	"strings"
+)
+
+// errNoOverlap is returned by serveContent's parseRange if first-byte-pos of
+// all of the byte-range-spec values is greater than the content size.
+var errInvalidRange = errors.New("invalid range")
+
+// httpRange specifies the byte range to be sent to the client.
+type httpRange struct {
+	start, length int64
+}
+
+// parseRange parses a Range header string as per RFC 7233.
+// errNoOverlap is returned if none of the ranges overlap.
+func parseRange(s string, size int64) ([]httpRange, error) {
+	if s == "" {
+		return nil, nil // header not present
+	}
+	const b = "bytes="
+	if !strings.HasPrefix(s, b) {
+		return nil, errInvalidRange
+	}
+	var ranges []httpRange
+	noOverlap := false
+	for _, ra := range strings.Split(s[len(b):], ",") {
+		ra = textproto.TrimString(ra)
+		if ra == "" {
+			continue
+		}
+		start, end, ok := Cut(ra, "-")
+		if !ok {
+			return nil, errInvalidRange
+		}
+		start, end = textproto.TrimString(start), textproto.TrimString(end)
+		var r httpRange
+		if start == "" {
+			// If no start is specified, end specifies the
+			// range start relative to the end of the file,
+			// and we are dealing with <suffix-length>
+			// which has to be a non-negative integer as per
+			// RFC 7233 Section 2.1 "Byte-Ranges".
+			if end == "" || end[0] == '-' {
+				return nil, errInvalidRange
+			}
+			i, err := strconv.ParseInt(end, 10, 64)
+			if i < 0 || err != nil {
+				return nil, errInvalidRange
+			}
+			if i > size {
+				i = size
+			}
+			r.start = size - i
+			r.length = size - r.start
+		} else {
+			i, err := strconv.ParseInt(start, 10, 64)
+			if err != nil || i < 0 {
+				return nil, errInvalidRange
+			}
+			if i >= size {
+				// If the range begins after the size of the content,
+				// then it does not overlap.
+				noOverlap = true
+				continue
+			}
+			r.start = i
+			if end == "" {
+				// If no end is specified, range extends to end of the file.
+				r.length = size - r.start
+			} else {
+				i, err := strconv.ParseInt(end, 10, 64)
+				if err != nil || r.start > i {
+					return nil, errInvalidRange
+				}
+				if i >= size {
+					i = size - 1
+				}
+				r.length = i - r.start + 1
+			}
+		}
+		ranges = append(ranges, r)
+	}
+	if noOverlap && len(ranges) == 0 {
+		// The specified ranges did not overlap with the content.
+		return nil, errInvalidRange
+	}
+	return ranges, nil
+}
+
+// Cut slices s around the first instance of sep,
+// returning the text before and after sep.
+// The found result reports whether sep appears in s.
+// If sep does not appear in s, cut returns s, nil, false.
+//
+// Cut returns slices of the original slice s, not copies.
+func Cut(s, sep string) (before, after string, found bool) {
+	if i := strings.Index(s, sep); i >= 0 {
+		return s[:i], s[i+len(sep):], true
+	}
+	return s, "", false
+}