optimize: log parser

add: fast text reader to log parser

27-functional-programming/log-parser-exp/textreaderfast.go

@@ -0,0 +1,106 @@
+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+package main
+
+import (
+	"bufio"
+	"bytes"
+	"errors"
+	"fmt"
+	"io"
+)
+
+// this could be made faster.
+// currently, it's 30-35% faster.
+//
+// so, what's different than the textreader?
+//
+// + creates the buffers specific to the input file/stdin size
+// + manually parses the fields: instead of strings.Fields
+// + gets the lines using scanner's Bytes() method: instead of Text()
+// + uses a manual atoi
+// +
+
+func fastTextReader(r io.Reader) inputFunc {
+	return func() ([]result, error) {
+		// first: count the lines, so the parseText can create
+		// enough buffer.
+		var buf bytes.Buffer
+		l, err := countLines(io.TeeReader(r, &buf))
+		if err != nil {
+			return nil, err
+		}
+
+		return fastParseText(bufio.NewScanner(&buf), l)
+	}
+}
+
+func fastParseText(in *bufio.Scanner, nlines int) ([]result, error) {
+	// needs to know the number of total lines in the file
+	res := make([]result, 0, nlines)
+
+	for l := 0; in.Scan(); l++ {
+		r, err := fastParseFields(in.Bytes())
+
+		if err != nil {
+			return nil, fmt.Errorf("line %d: %v", l, err)
+		}
+		res = append(res, r)
+	}
+
+	return res, in.Err()
+}
+
+func fastParseFields(data []byte) (res result, err error) {
+	var field int
+
+	for i, last := 0, 0; i < len(data); i++ {
+		done := len(data) == i+1
+
+		if c := data[i]; c == ' ' || done {
+			if done {
+				i = len(data)
+			}
+
+			switch field {
+			case 0:
+				res.domain = string(data[last:i])
+			case 1:
+				res.page = string(data[last:i])
+			case 2:
+				res.visits, err = atoi(data[last:i])
+			case 3:
+				res.uniques, err = atoi(data[last:i])
+			}
+
+			if err != nil {
+				return res, err
+			}
+
+			last = i + 1
+			field++
+		}
+	}
+
+	if field != 4 {
+		return result{}, errors.New("wrong number of fields")
+	}
+	return res, nil
+}
+
+func atoi(input []byte) (int, error) {
+	val := 0
+	for i := 0; i < len(input); i++ {
+		char := input[i]
+		if char < '0' || char > '9' {
+			return 0, errors.New("invalid number")
+		}
+		val = val*10 + int(char) - '0'
+	}
+	return val, nil
+}