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/* Exercise: Loops and Functions #43 */ | |
package main | |
import ( | |
"fmt" | |
"math" | |
) | |
func Sqrt(x float64) float64 { | |
z := float64(2.) | |
s := float64(0) | |
for { | |
z = z - (z*z - x)/(2*z) | |
if math.Abs(s-z) < 1e-15 { | |
break | |
} | |
s = z | |
} | |
return s | |
} | |
func main() { | |
fmt.Println(Sqrt(2)) | |
fmt.Println(math.Sqrt(2)) | |
} | |
/******************************************************************************************************/ | |
/* Exercise: Maps #44 */ | |
package main | |
import ( | |
"tour/wc" | |
"strings" | |
) | |
func WordCount(s string) map[string]int { | |
ss := strings.Fields(s) | |
num := len(ss) | |
ret := make(map[string]int) | |
for i := 0; i < num; i++ { | |
(ret[ss[i]])++ | |
} | |
return ret | |
} | |
func main() { | |
wc.Test(WordCount) | |
} | |
/******************************************************************************************************/ | |
/* Exercise: Slices #45 */ | |
package main | |
import "tour/pic" | |
func Pic(dx, dy int) [][]uint8 { | |
ret := make([][]uint8, dy) | |
for i := 0; i < dy; i++ { | |
ret[i] = make([]uint8, dx) | |
for j := 0; j < dx; j++ { | |
ret[i][j] = uint8(i^j+(i+j)/2) | |
} | |
} | |
return ret | |
} | |
func main() { | |
pic.Show(Pic) | |
} | |
/******************************************************************************************************/ | |
/* Exercise: Fibonacci closure #46 */ | |
package main | |
import "fmt" | |
// fibonacci is a function that returns | |
// a function that returns an int. | |
func fibonacci() func() int { | |
var x, y = 0, 1 | |
return func() (z int) { | |
z, x, y = x, y, x+y | |
return | |
} | |
} | |
func main() { | |
f := fibonacci() | |
for i := 0; i < 10; i++ { | |
fmt.Println(f()) | |
} | |
} | |
/******************************************************************************************************/ | |
/* Advanced Exercise: Complex cube roots #47 */ | |
package main | |
import ( | |
"fmt" | |
"math/cmplx" | |
) | |
func Cbrt(x complex128) complex128 { | |
z := complex128(2) | |
s := complex128(0) | |
for { | |
z = z - (cmplx.Pow(z,3) - x)/(3 * (z * z)) | |
if cmplx.Abs(s-z) < 1e-17 { | |
break | |
} | |
s = z | |
} | |
return z | |
} | |
func main() { | |
fmt.Println(Cbrt(2)) | |
} | |
/******************************************************************************************************/ | |
/* Exercise: Errors #57 */ | |
package main | |
import ( | |
"fmt" | |
) | |
type ErrNegativeSqrt float64 | |
func (e ErrNegativeSqrt) Error() string { | |
return fmt.Sprintf("cannot Sqrt negativ number: %g", float64(e)) | |
} | |
func Sqrt(f float64) (float64, error) { | |
if f < 0 { | |
return 0, ErrNegativeSqrt(f) | |
} | |
return 0, nil | |
} | |
func main() { | |
fmt.Println(Sqrt(2)) | |
fmt.Println(Sqrt(-2)) | |
} | |
/******************************************************************************************************/ | |
/* Exercise: Images #58 */ | |
package main | |
import ( | |
"image" | |
"tour/pic" | |
"image/color" | |
) | |
type Image struct{ | |
Width, Height int | |
colr uint8 | |
} | |
func (r *Image) Bounds() image.Rectangle { | |
return image.Rect(0, 0, r.Width, r.Height) | |
} | |
func (r *Image) ColorModel() color.Model { | |
return color.RGBAModel | |
} | |
func (r *Image) At(x, y int) color.Color { | |
return color.RGBA{r.colr+uint8(x), r.colr+uint8(y), 255, 255} | |
} | |
func main() { | |
m := Image{100, 100, 128} | |
pic.ShowImage(&m) | |
} | |
/******************************************************************************************************/ | |
/* Exercise: Rot13 Reader #59: 'You cracked the code!' */ | |
package main | |
import ( | |
"io" | |
"os" | |
"strings" | |
) | |
type rot13Reader struct { | |
r io.Reader | |
} | |
func (rot *rot13Reader) Read(p []byte) (n int, err error) { | |
n,err = rot.r.Read(p) | |
for i := 0; i < len(p); i++ { | |
if (p[i] >= 'A' && p[i] < 'N') || (p[i] >='a' && p[i] < 'n') { | |
p[i] += 13 | |
} else if (p[i] > 'M' && p[i] <= 'Z') || (p[i] > 'm' && p[i] <= 'z'){ | |
p[i] -= 13 | |
} | |
} | |
return | |
} | |
func main() { | |
s := strings.NewReader( | |
"Lbh penpxrq gur pbqr!") | |
r := rot13Reader{s} | |
io.Copy(os.Stdout, &r) | |
} | |
/******************************************************************************************************/ | |
/* Exercise: Equivalent Binary Trees #67 */ | |
package main | |
import ( | |
"tour/tree" | |
"fmt" | |
) | |
// Walk walks the tree t sending all values | |
// from the tree to the channel ch. | |
func Walk(t *tree.Tree, ch chan int) { | |
_walk(t, ch) | |
close(ch) | |
} | |
func _walk(t *tree.Tree, ch chan int) { | |
if t != nil { | |
_walk(t.Left, ch) | |
ch <- t.Value | |
_walk(t.Right, ch) | |
} | |
} | |
// Same determines whether the trees | |
// t1 and t2 contain the same values. | |
func Same(t1, t2 *tree.Tree) bool { | |
ch1 := make(chan int) | |
ch2 := make(chan int) | |
go Walk(t1, ch1) | |
go Walk(t2, ch2) | |
for i := range ch1 { | |
if i != <- ch2 { | |
return false | |
} | |
} | |
return true | |
} | |
func main() { | |
//tree.New(2) | |
ch := make(chan int) | |
go Walk(tree.New(1), ch) | |
for v := range ch { | |
fmt.Print(v) | |
} | |
fmt.Println(Same(tree.New(1), tree.New(1))) | |
fmt.Println(Same(tree.New(1), tree.New(2))) | |
} | |
/******************************************************************************************************/ | |
/* Exercise: Web Crawler #69 */ | |
package main | |
import ( | |
"fmt" | |
) | |
type Fetcher interface { | |
// Fetch returns the body of URL and | |
// a slice of URLs found on that page. | |
Fetch(url string) (body string, urls []string, err error) | |
} | |
var store map[string]bool | |
func Krawl(url string, fetcher Fetcher, Urls chan []string) { | |
body, urls, err := fetcher.Fetch(url) | |
if err != nil { | |
fmt.Println(err) | |
} else { | |
fmt.Printf("found: %s %q\n", url, body) | |
} | |
Urls <- urls | |
} | |
func Crawl(url string, depth int, fetcher Fetcher) { | |
Urls := make(chan []string) | |
go Krawl(url, fetcher, Urls) | |
band := 1 | |
store[url] = true // init for level 0 done | |
for i := 0; i < depth; i++ { | |
for band > 0 { | |
band-- | |
next := <- Urls | |
for _, url := range next { | |
if _, done := store[url] ; !done { | |
store[url] = true | |
band++ | |
go Krawl(url, fetcher, Urls) | |
} | |
} | |
} | |
} | |
return | |
} | |
func main() { | |
store = make(map[string]bool) | |
Crawl("http://golang.org/", 4, fetcher) | |
} | |
// fakeFetcher is Fetcher that returns canned results. | |
type fakeFetcher map[string]*fakeResult | |
type fakeResult struct { | |
body string | |
urls []string | |
} | |
func (f *fakeFetcher) Fetch(url string) (string, []string, error) { | |
if res, ok := (*f)[url]; ok { | |
return res.body, res.urls, nil | |
} | |
return "", nil, fmt.Errorf("not found: %s", url) | |
} | |
// fetcher is a populated fakeFetcher. | |
var fetcher = &fakeFetcher{ | |
"http://golang.org/": &fakeResult{ | |
"The Go Programming Language", | |
[]string{ | |
"http://golang.org/pkg/", | |
"http://golang.org/cmd/", | |
}, | |
}, | |
"http://golang.org/pkg/": &fakeResult{ | |
"Packages", | |
[]string{ | |
"http://golang.org/", | |
"http://golang.org/cmd/", | |
"http://golang.org/pkg/fmt/", | |
"http://golang.org/pkg/os/", | |
}, | |
}, | |
"http://golang.org/pkg/fmt/": &fakeResult{ | |
"Package fmt", | |
[]string{ | |
"http://golang.org/", | |
"http://golang.org/pkg/", | |
}, | |
}, | |
"http://golang.org/pkg/os/": &fakeResult{ | |
"Package os", | |
[]string{ | |
"http://golang.org/", | |
"http://golang.org/pkg/", | |
}, | |
}, | |
} |
At line 61 the code :
ret[i] = make([]uint8, dx)
Can you tell me what is the reasoning behind using dx
as length of slice? It doesnt say the length is dx
but slice is of dx
elements. Kinda confused :/
if we know that trees have 10 nodes, then this variant has a chance of life)):
package main
import (
"golang.org/x/tour/tree"
"fmt"
"sort"
)
// Walk walks the tree t sending all values
// from the tree to the channel ch.
//var cnt1 chan int
func Walk(t *tree.Tree, ch chan int) {
if t != nil {
ch <- t.Value
count:=<-ch
if count == 10 {
close(ch)
return}
Walk(t.Right, ch)
Walk(t.Left, ch)
}
}
// Same determines whether the trees
// t1 and t2 contain the same values.
func Same(t1, t2 *tree.Tree) bool {
ch1 := make(chan int)
go Walk(t1, ch1)
ch2 := make(chan int)
go Walk(t2, ch2)
var n1 [10]int
var n2 [10]int
i1,i2 := 0, 0
for i:=range ch1 {
n1[i1] = i
i1++
ch1<-i1
}
for i:=range ch2 {
n2[i2] = i
i2++
ch2<-i2
}
sort.Ints(n1[:])
sort.Ints(n2[:])
if n1 == n2 {
return true
} else {return false}
}
func main() {
fmt.Println(Same(tree.New(1), tree.New(1)))
fmt.Println(Same(tree.New(1), tree.New(2)))
}
for Crawler, I only used knowledge from previous lessons, such as a SafeCouter (without sync.WaitGroup)
package main
import (
"fmt"
"sync"
"time"
)
type Fetcher interface {
// Fetch returns the body of URL and
// a slice of URLs found on that page.
Fetch(url string) (body string, urls []string, err error)
}
type SafeHashset struct {
mux sync.Mutex
h map[string]bool
}
func (counter *SafeCounter) Inc(inc int) {
counter.mux.Lock()
defer counter.mux.Unlock()
counter.c = counter.c + inc
}
type SafeCounter struct {
mux sync.Mutex
c int
}
func (counter *SafeCounter) Value() int {
counter.mux.Lock()
defer counter.mux.Unlock()
return counter.c
}
func (hashset *SafeHashset) Add(url string) bool {
hashset.mux.Lock()
defer hashset.mux.Unlock()
if _, ok := hashset.h[url]; !ok {
hashset.h[url] = true
return true
} else {
return false
}
}
//var ch chan struct{} = make(chan struct {})
// Crawl uses fetcher to recursively crawl
// pages starting with url, to a maximum of depth.
var hashset = SafeHashset{h: make(map[string]bool)}
var count =SafeCounter{}
func Crawl(url string, depth int, fetcher Fetcher) {
defer count.Inc(-1)
// TODO: Fetch URLs in parallel.
// TODO: Don't fetch the same URL twice.
// This implementation doesn't do either:
if depth <= 0 {
return
}
if hashset.Add(url) {
body, urls, err := fetcher.Fetch(url)
if err != nil {
fmt.Println(err)
return
}
fmt.Printf("found: %s %q\n", url, body)
for _, u := range urls {
count.Inc(1)
go Crawl(u, depth-1, fetcher)
//defer <-ch
}
}
return
}
func main() {
count.Inc(1)
Crawl("http://golang.org/", 4, fetcher)
for {
if count.Value() == 0 {
break
}
time.Sleep(time.Second)
}
}
// fakeFetcher is Fetcher that returns canned results.
type fakeFetcher map[string]*fakeResult
type fakeResult struct {
body string
urls []string
}
func (f fakeFetcher) Fetch(url string) (string, []string, error) {
if res, ok := f[url]; ok {
return res.body, res.urls, nil
}
return "", nil, fmt.Errorf("not found: %s", url)
}
// fetcher is a populated fakeFetcher.
var fetcher = fakeFetcher{
"http://golang.org/": &fakeResult{
"The Go Programming Language",
[]string{
"http://golang.org/pkg/",
"http://golang.org/cmd/",
},
},
"http://golang.org/pkg/": &fakeResult{
"Packages",
[]string{
"http://golang.org/",
"http://golang.org/cmd/",
"http://golang.org/pkg/fmt/",
"http://golang.org/pkg/os/",
},
},
"http://golang.org/pkg/fmt/": &fakeResult{
"Package fmt",
[]string{
"http://golang.org/",
"http://golang.org/pkg/",
},
},
"http://golang.org/pkg/os/": &fakeResult{
"Package os",
[]string{
"http://golang.org/",
"http://golang.org/pkg/",
},
},
}
my binary tree #67 solution
package main
import (
"golang.org/x/tour/tree"
"fmt"
)
// Walk walks the tree t sending all values
// from the tree to the channel ch.
func Walk(t *tree.Tree, ch chan int, layer int) {
if t == nil {
return
}
Walk(t.Left, ch, layer + 1)
ch <- t.Value
Walk(t.Right, ch, layer + 1)
if layer == 0 {
close(ch)
}
}
// Same determines whether the trees
// t1 and t2 contain the same values.
func Same(t1, t2 *tree.Tree) bool {
ch1 := make(chan int, 10)
ch2 := make(chan int, 10)
go Walk(t1, ch1, 0)
go Walk(t2, ch2, 0)
for {
n1, ok1 := <- ch1
n2, ok2 := <- ch2
if n1 != n2 || ok1 != ok2 {
return false
} else if ok1 == ok2 && ok1 == false {
return true
}
}
}
func main() {
fmt.Println(Same(tree.New(1), tree.New(2)));
fmt.Println(Same(tree.New(1), tree.New(1)));
}
IP Address Solution:
package tour
import "fmt"
type IPAddr [4]byte
func (ipAddr IPAddr) String() string {
return fmt.Sprintf("%d.%d.%d.%d", ipAddr[0], ipAddr[1], ipAddr[2], ipAddr[3])
}
func IPAddress() {
hosts := map[string]IPAddr{
"loopback": {127, 0, 0, 1},
"googleDNS": {8, 8, 8, 8},
}
for name, ip := range hosts {
fmt.Printf("%v: %v\n", name, ip)
}
}
Reader Solution:
package tour
import (
"fmt"
)
type MyReader struct{}
func (r MyReader) Read(b []byte) (int, error) {
bufferLength := len(b)
if bufferLength <= 0 {
return 0, fmt.Errorf("buffer length must be greater than 0")
}
buffer := make([]byte, bufferLength)
for k := range buffer {
buffer[k] = uint8('A')
}
n := copy(b, buffer)
return n, nil
}
rot13Reader Solution:
❓ this solution saves an extra loop by returning io.EOF
as early as possible.
package tour
import (
"io"
"os"
"strings"
)
type rot13Reader struct {
r io.Reader
}
func (r rot13Reader) Read(b []byte) (int, error) {
n, err := r.r.Read(b)
// short circuit: EOF
if err == io.EOF {
return 0, io.EOF
}
for k, v := range b {
b[k] = rot13(v)
}
return n, err
}
func Rot13ReaderMain() {
s := strings.NewReader("Lbh penpxrq gur pbqr!")
r := rot13Reader{s}
io.Copy(os.Stdout, &r)
}
func rot13(b byte) byte {
if b >= 'A' && b <= 'Z' {
b = 'A' + (b-'A'+13)%26
} else if b >= 'a' && b <= 'z' {
b = 'a' + (b-'a'+13)%26
}
return b
}
Images exercise solution:
package tour
import (
"image"
"image/color"
)
type Image struct {
Width int
Height int
}
func (i Image) ColorModel() color.Model {
return color.RGBAModel
}
func (i Image) Bounds() image.Rectangle {
return image.Rect(0, 0, i.Width, i.Height)
}
func (i Image) At(x, y int) color.Color {
r := uint8(x + y)
g := uint8(x ^ y)
b := uint8(x * y)
//fmt.Println("R:", r, "G:", g, "B:", b)
return color.RGBA{r, g, b, 255}
}
This is my solution to the Exercise "Stringers":
package main
import "fmt"
type IPAddr [4]byte
// TODO: Add a "String() string" method to IPAddr.
// What I did was I returned the call to Sprintf (in the fmt package) and formatted each of the four byte values in the array
// of bytes, separated with dots:
func (ip IPAddr) String() string{
// The 'Sprintf' function formats according to a format specifier and returns the resulting string.
// In other words: you first return the resulting string of the function 'Sprintf' and then
// this method (String()) returns the previously returned string by 'Sprintf':
return fmt.Sprintf("%v.%v.%v.%v",ip[0],ip[1],ip[2],ip[3])
}
func main() {
hosts := map[string]IPAddr{
"loopback": {127, 0, 0, 1},
"googleDNS": {8, 8, 8, 8},
}
for nombre, ip := range hosts {
fmt.Printf("%v: %v\n", nombre, ip)
}
}
I hope it helps!
Excuse me:
In the rot13Reader exercise, how is Read(p []byte) called? I'm a bit confused, since I don't see it being invoked in main()...
package main
import (
"io"
"os"
"strings"
)
type rot13Reader struct {
r io.Reader
}
func (rot *rot13Reader) Read(p []byte) (n int, err error) {
n,err = rot.r.Read(p)
for i := 0; i < len(p); i++ {
if (p[i] >= 'A' && p[i] < 'N') || (p[i] >='a' && p[i] < 'n') {
p[i] += 13
} else if (p[i] > 'M' && p[i] <= 'Z') || (p[i] > 'm' && p[i] <= 'z'){
p[i] -= 13
}
}
return
}
func main() {
s := strings.NewReader(
"Lbh penpxrq gur pbqr!")
r := rot13Reader{s}
io.Copy(os.Stdout, &r)
}
MIT Phd crawl solution
package main
import (
"fmt"
"sync"
)
type Cache struct {
m sync.Mutex
v map[string]uint
}
func (s *Cache) Exist(key string) bool {
s.m.Lock()
defer s.m.Unlock()
if _, ok := s.v[key]; ok {
s.v[key]++
return true
} else {
s.v[key] = 1
return false
}
}
func (s *Cache) String() string {
s.m.Lock()
defer s.m.Unlock()
var sb string
for k, v := range s.v {
sb += fmt.Sprintf("key: %s => value: %q", k, v)
}
return fmt.Sprintln(sb)
}
type Fetcher interface {
Fetch(url string) (body string, urls []string, err error)
}
//
// Serial crawler
//
func SerialCrawl(url string, depth int, fetcher Fetcher, cache *Cache) {
if cache.Exist(url) {
return
}
//fmt.Printf("cached values %q\n", cache)
fmt.Println("depth ", depth)
if depth <= 0 {
return
}
body, urls, err := fetcher.Fetch(url)
if err != nil {
fmt.Println(err)
return
}
fmt.Printf("Found: %s %q\n", url, body)
//fmt.Printf("fetch children %q\n", urls)
for _, u := range urls {
//fmt.Printf("recursive crawl url %s\n", u)
SerialCrawl(u, depth-1, fetcher, cache)
}
}
//
// Concurrent crawler with shared state and Mutex
//
func ConcurrentMutex(url string, depth int, fetcher Fetcher, cache *Cache) {
if cache.Exist(url) {
return
}
//fmt.Printf("cached values %q\n", cache)
if depth <= 0 {
return
}
body, urls, err := fetcher.Fetch(url)
if err != nil {
fmt.Println(err)
return
}
fmt.Printf("Found: %s %q\n", url, body)
//fmt.Printf("fetch children %q\n", urls)
var done sync.WaitGroup
for _, u := range urls {
done.Add(1)
//fmt.Printf("recursive crawl url %s\n", u)
u2 := u
go func() {
defer done.Done()
ConcurrentMutex(u2, depth-1, fetcher, cache)
}()
//go func(u string) {
// defer done.Done()
// ConcurrentMutex(u, depth -1,fetcher, cache)
//}(u)
}
done.Wait()
}
//
// Concurrent crawler with channels
//
func worker(url string, depth uint, ch chan []string, fetcher Fetcher, cache *Cache) {
//fmt.Printf("working on url %s depth %d\n", url, depth)
body, urls, err := fetcher.Fetch(url)
if err != nil {
ch <- []string{}
} else {
fmt.Printf("Found: %s %q\n", url, body)
ch <- urls
}
}
func master(url string, ch chan []string, depth uint, fetcher Fetcher, cache *Cache) {
n := 1
copyDepth := depth
for urls := range ch {
// fmt.Printf("dep :%s\n", fmt.Sprintf("%q", copyDepth))
if copyDepth == 0 {
break
}
for _, url := range urls {
if !cache.Exist(url) {
n += 1
go worker(url, depth, ch, fetcher, cache)
}
}
depth--
n -= 1
if n == 0 {
break
}
}
}
func ConcurrentChan(url string, depth uint, fetcher Fetcher, cache *Cache) {
ch := make(chan []string)
go func() {
ch <- []string{url}
}()
master(url, ch, depth, fetcher, cache)
}
func main() {
cache := Cache{v: make(map[string]uint)}
SerialCrawl("https://golang.org/", 4, fetcher, &cache)
ConcurrentMutex("https://golang.org/", 4, fetcher, &cache)
ConcurrentChan("https://golang.org/", 4, fetcher, &cache)
fmt.Printf("\nCached urls %q\n", cache.v)
}
type fakeFetcher map[string]*fakeResult // to avoid copy value
type fakeResult struct {
body string
urls []string
}
func (f fakeFetcher) Fetch(url string) (string, []string, error) {
if res, ok := f[url]; ok {
return res.body, res.urls, nil
}
return "", nil, fmt.Errorf("not found: %s", url)
}
var fetcher = fakeFetcher{
"https://golang.org/": &fakeResult{
"The Go Programming Language",
[]string{
"https://golang.org/pkg/",
"https://golang.org/cmd/",
},
},
"https://golang.org/pkg/": &fakeResult{
"Packages",
[]string{
"https://golang.org/",
"https://golang.org/cmd/",
"https://golang.org/pkg/fmt/",
"https://golang.org/pkg/os/",
},
},
"https://golang.org/pkg/fmt/": &fakeResult{
"Package fmt",
[]string{
"https://golang.org/",
"https://golang.org/pkg/",
},
},
"https://golang.org/pkg/os/": &fakeResult{
"Package os",
[]string{
"https://golang.org/",
"https://golang.org/pkg/",
},
},
}
My relatively simple solution for crawl w/o global variables and channels and with mutex and WaitGroup:
package main
import (
"fmt"
"sync"
)
type UrlCache struct {
urls map[string]bool
mu sync.Mutex
}
func (uc *UrlCache) Add(url string) {
uc.mu.Lock()
uc.urls[url] = true
uc.mu.Unlock()
}
func (uc *UrlCache) Get(url string) bool {
uc.mu.Lock()
defer uc.mu.Unlock()
return uc.urls[url]
}
type Fetcher interface {
// Fetch returns the body of URL and
// a slice of URLs found on that page.
Fetch(url string) (body string, urls []string, err error)
}
// Crawl uses fetcher to recursively crawl
// pages starting with url, to a maximum of depth.
func Crawl(url string, depth int, fetcher Fetcher) {
var wg sync.WaitGroup
cache := UrlCache{urls: make(map[string]bool)}
wg.Add(1)
go crawl(url, depth, fetcher, &cache, &wg)
wg.Wait()
}
func crawl(url string, depth int, fetcher Fetcher, cache *UrlCache, wg *sync.WaitGroup) {
defer wg.Done()
if depth <= 0 || cache.Get(url) {
return
}
cache.Add(url)
body, urls, err := fetcher.Fetch(url)
if err != nil {
fmt.Println(err)
return
}
fmt.Printf("found: %s %q\n", url, body)
for _, u := range urls {
wg.Add(1)
go crawl(u, depth-1, fetcher, cache, wg)
}
}
func main() {
Crawl("https://golang.org/", 4, fetcher)
}
// fakeFetcher is Fetcher that returns canned results.
type fakeFetcher map[string]*fakeResult
type fakeResult struct {
body string
urls []string
}
func (f fakeFetcher) Fetch(url string) (string, []string, error) {
if res, ok := f[url]; ok {
return res.body, res.urls, nil
}
return "", nil, fmt.Errorf("not found: %s", url)
}
// fetcher is a populated fakeFetcher.
var fetcher = fakeFetcher{
"https://golang.org/": &fakeResult{
"The Go Programming Language",
[]string{
"https://golang.org/pkg/",
"https://golang.org/cmd/",
},
},
"https://golang.org/pkg/": &fakeResult{
"Packages",
[]string{
"https://golang.org/",
"https://golang.org/cmd/",
"https://golang.org/pkg/fmt/",
"https://golang.org/pkg/os/",
},
},
"https://golang.org/pkg/fmt/": &fakeResult{
"Package fmt",
[]string{
"https://golang.org/",
"https://golang.org/pkg/",
},
},
"https://golang.org/pkg/os/": &fakeResult{
"Package os",
[]string{
"https://golang.org/",
"https://golang.org/pkg/",
},
},
}
Reader Solution:
package tour import ( "fmt" ) type MyReader struct{} func (r MyReader) Read(b []byte) (int, error) { bufferLength := len(b) if bufferLength <= 0 { return 0, fmt.Errorf("buffer length must be greater than 0") } buffer := make([]byte, bufferLength) for k := range buffer { buffer[k] = uint8('A') } n := copy(b, buffer) return n, nil }
Is there a reason why you just don't set the 'A' directly in b? Why creating an internal slice and then copying to b? Just curious...
Here is my solution to the crawler. It uses a mutex within the url cache and a wait group in order to terminate once all go routines have finished. I'm not sure whether this is idiomatic or not (especially with the
UrlCache
, andCrawler
structs/methods), if anyone has any feedback I would appreciate it.