英文:
Golang: Why does the compress/gzip Read function not read file contents?
问题
我创建了一个文本文件，然后用gzip进行了压缩。然后我运行了下面的go程序来读取该压缩文件的内容。
package main
import (
"compress/gzip"
"fmt"
"os"
)
func main() {
handle, err := os.Open("zipfile.gz")
if err != nil {
fmt.Println("[ERROR] 文件打开错误:", err)
}
defer handle.Close()
zipReader, err := gzip.NewReader(handle)
if err != nil {
fmt.Println("[ERROR] 新建gzip读取器错误:", err)
}
defer zipReader.Close()
var fileContents []byte
bytesRead, err := zipReader.Read(fileContents)
if err != nil {
fmt.Println("[ERROR] 读取gzip文件错误:", err)
}
fmt.Println("[INFO] 从文件中读取的字节数:", bytesRead)
fmt.Printf("[INFO] 未压缩内容: '%s'\n", fileContents)
}
我得到的响应如下：
$ go run zipRead.go
[INFO] 从文件中读取的字节数: 0
[INFO] 未压缩内容: ''
为什么我没有从文件中获取到任何内容？
我在OS X和Ubuntu上创建了zip文件，并在两个操作系统上构建了相同的go程序，但结果相同。
英文:
I made a text file, that I then compressed with gzip. I then run the following go program to read the contents of that compressed file.
package main
import (
"compress/gzip"
"fmt"
"os"
)
func main() {
handle, err := os.Open("zipfile.gz")
if err != nil {
fmt.Println("[ERROR] File Open:", err)
}
defer handle.Close()
zipReader, err := gzip.NewReader(handle)
if err != nil {
fmt.Println("[ERROR] New gzip reader:", err)
}
defer zipReader.Close()
var fileContents []byte
bytesRead, err := zipReader.Read(fileContents)
if err != nil {
fmt.Println("[ERROR] Reading gzip file:", err)
}
fmt.Println("[INFO] Number of bytes read from the file:", bytesRead)
fmt.Printf("[INFO] Uncompressed contents: '%s'\n", fileContents)
}
The response that I get is the following:
$ go run zipRead.go
[INFO] Number of bytes read from the file: 0
[INFO] Uncompressed contents: ''
Why am I not getting any contents from the file?
I have created zip files on both OS X and Ubuntu. I have build this go program on both OS X and Ubuntu with the same result.
答案1
得分: 4
io.Reader.Read 只会读取最多 len(b) 字节。由于你的 fileContents 是空的，它的长度为 0。为其分配一些空间以便读取：
fileContents := make([]byte, 1024) // 每次读取 1 KiB。
bytesRead, err := zipReader.Read(fileContents)
if err != nil {
fmt.Println("[ERROR] 读取 gzip 文件：", err)
}
fileContents = fileContents[:bytesRead]
如果你想读取整个文件，你需要多次使用 Read，或者使用 ioutil.ReadAll（对于大文件可能不太好）。
英文:
io.Reader.Read will only read up to len(b) bytes. Since your fileContents is nil, its length is 0. Allocate some space for it to read into:
fileContents := make([]byte, 1024) // Read by 1 KiB.
bytesRead, err := zipReader.Read(fileContents)
if err != nil {
fmt.Println("[ERROR] Reading gzip file:", err)
}
fileContents = fileContents[:bytesRead]
If you want to read the whole file, you'll have to either use Read several times, or use things like ioutil.ReadAll (which may be bad for big files).
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