Optimize memory allocations in ParseAccept

autoneg.go

@@ -35,9 +35,8 @@ DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
-
-
 */
+
 package goautoneg
 
 import (
@@ -53,16 +52,14 @@ type Accept struct {
 	Params        map[string]string
 }
 
-// For internal use, so that we can use the sort interface
-type accept_slice []Accept
+// acceptSlice is defined to implement sort interface.
+type acceptSlice []Accept
 
-func (accept accept_slice) Len() int {
-	slice := []Accept(accept)
+func (slice acceptSlice) Len() int {
 	return len(slice)
 }
 
-func (accept accept_slice) Less(i, j int) bool {
-	slice := []Accept(accept)
+func (slice acceptSlice) Less(i, j int) bool {
 	ai, aj := slice[i], slice[j]
 	if ai.Q > aj.Q {
 		return true
@@ -76,63 +73,93 @@ func (accept accept_slice) Less(i, j int) bool {
 	return false
 }
 
-func (accept accept_slice) Swap(i, j int) {
-	slice := []Accept(accept)
+func (slice acceptSlice) Swap(i, j int) {
 	slice[i], slice[j] = slice[j], slice[i]
 }
 
+func stringTrimSpaceCutset(r rune) bool {
+	return r == ' '
+}
+
+func nextSplitElement(s, sep string) (item string, remaining string) {
+	if index := strings.Index(s, sep); index != -1 {
+		return s[:index], s[index+1:]
+	}
+	return s, ""
+}
+
 // Parse an Accept Header string returning a sorted list
 // of clauses
-func ParseAccept(header string) (accept []Accept) {
-	parts := strings.Split(header, ",")
-	accept = make([]Accept, 0, len(parts))
-	for _, part := range parts {
-		part := strings.Trim(part, " ")
+func ParseAccept(header string) acceptSlice {
+	partsCount := 0
+	remaining := header
+	for len(remaining) > 0 {
+		partsCount++
+		_, remaining = nextSplitElement(remaining, ",")
+	}
+	accept := make(acceptSlice, 0, partsCount)
 
-		a := Accept{}
-		a.Params = make(map[string]string)
-		a.Q = 1.0
+	remaining = header
+	var part string
+	for len(remaining) > 0 {
+		part, remaining = nextSplitElement(remaining, ",")
+		part = strings.TrimFunc(part, stringTrimSpaceCutset)
+
+		a := Accept{
+			Q: 1.0,
+		}
 
-		mrp := strings.Split(part, ";")
+		sp, remainingPart := nextSplitElement(part, ";")
 
-		media_range := mrp[0]
-		sp := strings.Split(media_range, "/")
-		a.Type = strings.Trim(sp[0], " ")
+		sp0, spRemaining := nextSplitElement(sp, "/")
+		a.Type = strings.TrimFunc(sp0, stringTrimSpaceCutset)
 
 		switch {
-		case len(sp) == 1 && a.Type == "*":
-			a.SubType = "*"
-		case len(sp) == 2:
-			a.SubType = strings.Trim(sp[1], " ")
+		case len(spRemaining) == 0:
+			if a.Type == "*" {
+				a.SubType = "*"
+			} else {
+				continue
+			}
 		default:
-			continue
+			var sp1 string
+			sp1, spRemaining = nextSplitElement(spRemaining, "/")
+			if len(spRemaining) > 0 {
+				continue
+			}
+			a.SubType = strings.TrimFunc(sp1, stringTrimSpaceCutset)
 		}
 
-		if len(mrp) == 1 {
+		if len(remainingPart) == 0 {
 			accept = append(accept, a)
 			continue
 		}
 
-		for _, param := range mrp[1:] {
-			sp := strings.SplitN(param, "=", 2)
-			if len(sp) != 2 {
+		a.Params = make(map[string]string)
+		for len(remainingPart) > 0 {
+			sp, remainingPart = nextSplitElement(remainingPart, ";")
+			sp0, spRemaining = nextSplitElement(sp, "=")
+			if len(spRemaining) == 0 {
+				continue
+			}
+			var sp1 string
+			sp1, spRemaining = nextSplitElement(spRemaining, "=")
+			if len(spRemaining) != 0 {
 				continue
 			}
-			token := strings.Trim(sp[0], " ")
+			token := strings.TrimFunc(sp0, stringTrimSpaceCutset)
 			if token == "q" {
-				a.Q, _ = strconv.ParseFloat(sp[1], 32)
+				a.Q, _ = strconv.ParseFloat(sp1, 32)
 			} else {
-				a.Params[token] = strings.Trim(sp[1], " ")
+				a.Params[token] = strings.TrimFunc(sp1, stringTrimSpaceCutset)
 			}
 		}
 
 		accept = append(accept, a)
 	}
 
-	slice := accept_slice(accept)
-	sort.Sort(slice)
-
-	return
+	sort.Sort(accept)
+	return accept
 }
 
 // Negotiate the most appropriate content_type given the accept header