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@kjk kjk/test_gob.go
Created Dec 18, 2013

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Shows that one cannot append data to a gob file - the decoder will error out with 'extra data in buffer` when trying to decode data written by append.
package main
import (
"encoding/gob"
"fmt"
"io"
"log"
"math/rand"
"os"
)
type Struct1 struct {
IntVal int
StringVal string
}
func PathExists(path string) bool {
_, err := os.Stat(path)
if err == nil {
return true
}
if os.IsNotExist(err) {
return false
}
return false
}
func readData(filePath string) {
if !PathExists(filePath) {
return
}
file, err := os.Open(filePath)
defer file.Close()
if err != nil {
log.Fatalf("os.Open('%s') failed with '%s'\n", filePath, err.Error())
}
dec := gob.NewDecoder(file)
var val Struct1
for {
err = dec.Decode(&val)
if err != nil {
if err == io.EOF {
return
}
log.Fatalf("dec.Decode() failed with '%s'\n", err.Error())
}
fmt.Printf("Read: %#v\n", val)
}
}
func addData(filePath string) {
file, err := os.OpenFile(filePath, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
if err != nil {
log.Fatalf("os.OpenFile('%s') failed with '%s'\n", filePath, err.Error())
}
defer file.Close()
enc := gob.NewEncoder(file)
for i := 0; i < 1; i++ {
n := int(rand.Intn(65536))
v := Struct1{
IntVal: n,
StringVal: fmt.Sprintf("%d", n),
}
err = enc.Encode(v)
if err != nil {
log.Fatalf("enc.Encode() failed with '%s'\n", err.Error())
}
fmt.Printf("Wrote: %#v\n", v)
}
}
func main() {
filePath := "test.gob"
readData(filePath)
addData(filePath)
readData(filePath)
addData(filePath)
readData(filePath)
}
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