Fix array out of bounds during using http-set-header (#627)

Happens for example when payload stops at a '-' and we are searching for
Accept-Encoding.The method has been simplified and now does full case
insensitivity. Performance checking, on x64, it is ever so slightly
faster than the original.

proto/proto.go

@@ -42,87 +42,23 @@ func MIMEHeadersStartPos(payload []byte) int {
 	return bytes.Index(payload, CLRF) + 2 // Find first line end
 }
 
-func isLower(b byte) bool {
-	if 'a' <= b && b <= 'z' {
-		return true
-	}
-
-	return false
-}
-
-func toUpper(b byte) byte {
-	if 'a' <= b && b <= 'z' {
-		b -= 'a' - 'A'
-	}
-	return b
-}
-
-func toLower(b byte) byte {
-	if 'A' <= b && b <= 'Z' {
-		b += 'a' - 'A'
-	}
-	return b
-}
-
 func headerIndex(payload []byte, name []byte) int {
-	isLower := isLower(name[0])
 	i := 0
-
 	for {
-		if i >= len(payload) {
+		// we need enough space for at least '\n' and the header name
+		if i >= (len(payload) - len(name) - 1) {
 			return -1
 		}
 
 		if payload[i] == '\n' {
 			i++
-
-			// We are at the end
-			if i == len(payload) {
-				return -1
-			}
-
-			if payload[i] == name[0] ||
-				(!isLower && payload[i] == toLower(name[0])) ||
-				(isLower && payload[i] == toUpper(name[0])) {
-
-				i++
-				j := 1
-				for {
-					if j == len(name) {
-						// Matched, and return start of the header
-						return i - len(name)
-					}
-
-					// We are at the end
-					if i == len(payload) {
-						return -1
-					}
-
-					if payload[i] != name[j] {
-						break
-					}
-
-					// If compound header name do one more case check: Content-Length or Transfer-Encoding
-					if name[j] == '-' {
-						i++
-						j++
-
-						if !(payload[i] == name[j] ||
-							(!isLower && payload[i] == toLower(name[j])) ||
-							(isLower && payload[i] == toUpper(name[j]))) {
-							break
-						}
-					}
-
-					j++
-					i++
-				}
+			if bytes.EqualFold(name, payload[i:i+len(name)]) {
+				return i
 			}
 		}
-
 		i++
-	}
 
+	}
 	return -1
 }