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refactor: handle err with fprintln io compose ifaces

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This commit is contained in:
Inanc Gumus
2019-11-08 11:38:56 +03:00
parent 88d16d86d5
commit b0a835818b
2 changed files with 10 additions and 15 deletions
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4
interfaces/16-io-compose/.gitignore vendored
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@ -1,2 +1,4 @@
rosie.unknown rosie.unknown
rosie.png rosie.png
_other.go
toc

21
interfaces/16-io-compose/main.go
View File

@ -13,7 +13,6 @@ import (
"errors" "errors"
"fmt" "fmt"
"io" "io"
"log"
"net/http" "net/http"
"os" "os"
) )
@ -21,25 +20,23 @@ import (
func main() { func main() {
resp, err := http.Get("https://inancgumus.github.com/x/rosie.unknown") resp, err := http.Get("https://inancgumus.github.com/x/rosie.unknown")
if err != nil { if err != nil {
log.Fatal(err) fmt.Fprintln(os.Stderr, err)
return
} }
defer resp.Body.Close() defer resp.Body.Close()
// creates a file (or truncates if the file exists) // creates a file (or truncates if the file exists)
file, err := os.Create("rosie.png") file, err := os.Create("rosie.png")
if err != nil { if err != nil {
log.Fatal(err) fmt.Fprintln(os.Stderr, err)
return
} }
defer file.Close() defer file.Close()
n, err := transfer(resp.Body, file) n, err := transfer(resp.Body, file)
// check whether the error was due to the PNG signature.
if errors.Is(err, errNotPNG) {
log.Fatalln("Please provide a PNG image:", err)
}
if err != nil { if err != nil {
log.Fatal(err) fmt.Fprintln(os.Stderr, err)
return
} }
fmt.Printf("%d bytes transferred.\n", n) fmt.Printf("%d bytes transferred.\n", n)
@ -48,10 +45,6 @@ func main() {
// resp.Body.Close() // resp.Body.Close()
} }
// create an error at the package-level.
// so the other funcs in the package can check.
var errNotPNG = errors.New("not a png image")
// transfer streams data from a reader to a writer. // transfer streams data from a reader to a writer.
// if the reader doesn't contain a PNG signature, transfer returns errNotPNG. // if the reader doesn't contain a PNG signature, transfer returns errNotPNG.
// otherwise, it transfers the data to the writer. // otherwise, it transfers the data to the writer.
@ -74,7 +67,7 @@ func transfer(r io.Reader, w io.Writer) (n int64, err error) {
// check the png signature. // check the png signature.
if !bytes.HasPrefix(memory.Bytes(), []byte(pngSign)) { if !bytes.HasPrefix(memory.Bytes(), []byte(pngSign)) {
return n, errNotPNG return n, errors.New("not png")
} }
// stitch the PNG signature (memory) and the response body reader together. // stitch the PNG signature (memory) and the response body reader together.