如何將io.Reader實體傳遞給Golang中的函式？-有解無憂

我一直在處理一個問題，我必須將一個io.Reader實體作為引數放入由 api 提供的作為端點的函式。我需要做的任務是將本地檔案夾上傳到公司的云存盤。

func (s *server) uploadFileToPutIo(w http.ResponseWriter, r *http.Request) {
    tokenSource := oauth2.StaticTokenSource(&oauth2.Token{AccessToken: token})
    oauthClient := oauth2.NewClient(context.TODO(), tokenSource)
    client := putio.NewClient(oauthClient)

    var testIO io.Reader // ? 

    upload, err := client.Files.Upload(context.TODO(), testIO, "test", 0)
    if err != nil {
        log.Fatal(err)
    }

    fmt.Println(upload.File)
    sendResponse(w, []byte("successful"), http.StatusOK)
}

當我/upload在 POST 方法下向該端點發出請求時。我收到以下錯誤。

2021/12/01 18:28:47 http: panic serving 127.0.0.1:61057: runtime error: invalid memory address or nil pointer dereference
goroutine 8 [running]:
net/http.(*conn).serve.func1(0xc000108d20)
        /usr/local/Cellar/go/1.16.6/libexec/src/net/http/server.go:1804  0x153
panic(0x1390ae0, 0x164fdd0)
        /usr/local/Cellar/go/1.16.6/libexec/src/runtime/panic.go:971  0x499
io.copyBuffer(0x1462700, 0xc000026360, 0x0, 0x0, 0xc000170000, 0x8000, 0x8000, 0x0, 0x0, 0x13d5e01)
        /usr/local/Cellar/go/1.16.6/libexec/src/io/io.go:423  0x10b
io.Copy(...)
        /usr/local/Cellar/go/1.16.6/libexec/src/io/io.go:382
github.com/putdotio/go-putio/putio.(*FilesService).Upload(0xc000010088, 0x1468390, 0xc00001c088, 0x0, 0x0, 0x13ef46f, 0x6, 0x0, 0x170d108, 0x90, ...)
        /Users/barisertas/go/pkg/mod/github.com/putdotio/go-putio/putio@v0.0.0-20200123120452-16d982cac2b8/files.go:235  0x187
main.(*server).uploadFileToPutIo(0xc000010028, 0x1467d60, 0xc00014a2a0, 0xc000154500)
        /Users/barisertas/workspace/mini-project/api/handler.go:79  0xe5
net/http.HandlerFunc.ServeHTTP(0xc000012db0, 0x1467d60, 0xc00014a2a0, 0xc000154500)
        /usr/local/Cellar/go/1.16.6/libexec/src/net/http/server.go:2049  0x44
github.com/gorilla/mux.(*Router).ServeHTTP(0xc000144000, 0x1467d60, 0xc00014a2a0, 0xc000154300)
        /Users/barisertas/go/pkg/mod/github.com/gorilla/mux@v1.8.0/mux.go:210  0xd3
net/http.serverHandler.ServeHTTP(0xc00014a000, 0x1467d60, 0xc00014a2a0, 0xc000154300)
        /usr/local/Cellar/go/1.16.6/libexec/src/net/http/server.go:2867  0xa3
net/http.(*conn).serve(0xc000108d20, 0x1468400, 0xc00005e300)
        /usr/local/Cellar/go/1.16.6/libexec/src/net/http/server.go:1932  0x8cd
created by net/http.(*Server).Serve
        /usr/local/Cellar/go/1.16.6/libexec/src/net/http/server.go:2993  0x39b
2021/12/01 18:28:47 http: panic serving 127.0.0.1:61059: runtime error: invalid memory address or nil pointer dereference
goroutine 11 [running]:
net/http.(*conn).serve.func1(0xc000108dc0)
        /usr/local/Cellar/go/1.16.6/libexec/src/net/http/server.go:1804  0x153
panic(0x1390ae0, 0x164fdd0)
        /usr/local/Cellar/go/1.16.6/libexec/src/runtime/panic.go:971  0x499
io.copyBuffer(0x1462700, 0xc000026400, 0x0, 0x0, 0xc000198000, 0x8000, 0x8000, 0x0, 0x0, 0x13d5e01)
        /usr/local/Cellar/go/1.16.6/libexec/src/io/io.go:423  0x10b
io.Copy(...)
        /usr/local/Cellar/go/1.16.6/libexec/src/io/io.go:382
github.com/putdotio/go-putio/putio.(*FilesService).Upload(0xc0000100c8, 0x1468390, 0xc00001c088, 0x0, 0x0, 0x13ef46f, 0x6, 0x0, 0x170d108, 0x90, ...)
        /Users/barisertas/go/pkg/mod/github.com/putdotio/go-putio/putio@v0.0.0-20200123120452-16d982cac2b8/files.go:235  0x187
main.(*server).uploadFileToPutIo(0xc000010028, 0x1467d60, 0xc00014a380, 0xc000154800)
        /Users/barisertas/workspace/mini-project/api/handler.go:79  0xe5
net/http.HandlerFunc.ServeHTTP(0xc000012db0, 0x1467d60, 0xc00014a380, 0xc000154800)
        /usr/local/Cellar/go/1.16.6/libexec/src/net/http/server.go:2049  0x44
github.com/gorilla/mux.(*Router).ServeHTTP(0xc000144000, 0x1467d60, 0xc00014a380, 0xc000154600)
        /Users/barisertas/go/pkg/mod/github.com/gorilla/mux@v1.8.0/mux.go:210  0xd3
net/http.serverHandler.ServeHTTP(0xc00014a000, 0x1467d60, 0xc00014a380, 0xc000154600)
        /usr/local/Cellar/go/1.16.6/libexec/src/net/http/server.go:2867  0xa3
net/http.(*conn).serve(0xc000108dc0, 0x1468400, 0xc00005e580)
        /usr/local/Cellar/go/1.16.6/libexec/src/net/http/server.go:1932  0x8cd
created by net/http.(*Server).Serve
        /usr/local/Cellar/go/1.16.6/libexec/src/net/http/server.go:2993  0x39b

這是我嘗試使用的函式的檔案：

// Upload reads from given io.Reader and uploads the file contents to Put.io
// servers under directory given by parent. If parent is negative, user's
// preferred folder is used.
//
// If the uploaded file is a torrent file, Put.io will interpret it as a
// transfer and Transfer field will be present to represent the status of the
// tranfer. Likewise, if the uploaded file is a regular file, Transfer field
// would be nil and the uploaded file will be represented by the File field.
//
// This method reads the file contents into the memory, so it should be used for
// <150MB files.
func (f *FilesService) Upload(ctx context.Context, r io.Reader, filename string, parent int64) (Upload, error) {
    if filename == "" {
        return Upload{}, fmt.Errorf("filename cannot be empty")
    }

    var buf bytes.Buffer
    mw := multipart.NewWriter(&buf)

    // negative parent means use user's preferred download folder.
    if parent >= 0 {
        err := mw.WriteField("parent_id", itoa(parent))
        if err != nil {
            return Upload{}, err
        }
    }

    formfile, err := mw.CreateFormFile("file", filename)
    if err != nil {
        return Upload{}, err
    }

    _, err = io.Copy(formfile, r)
    if err != nil {
        return Upload{}, err
    }

    err = mw.Close()
    if err != nil {
        return Upload{}, err
    }

    req, err := f.client.NewRequest(ctx, "POST", "/v2/files/upload", &buf)
    if err != nil {
        return Upload{}, err
    }
    req.Header.Set("Content-Type", mw.FormDataContentType())

    var response struct {
        Upload
    }
    _, err = f.client.Do(req, &response)
    if err != nil {
        return Upload{}, err
    }
    return response.Upload, nil
}

我對將io.Reader實體放入函式感到困惑。io.Reader在這種情況下，如何正確放置該功能。創建后只是一個實體，如下所示： var testIO io.Reader還是應該做一些額外的操作？

uj5u.com熱心網友回復：

runtime error: invalid memory address or nil pointer dereference

你肯定知道，這是因為你已經宣告了 anio.Reader但你還沒有設定它的值，所以它仍然等于介面的默認值，即nil.

    var testIO io.Reader // ?

傳遞io.Readerto 的目的Upload是提供要上傳的資料。通過傳遞io.Reader，任意資料源可以提供任意數量的位元組，不受記憶體可用性的限制（不像[]byte，它需要在上傳之前將所有資料保存在記憶體中）。 io.Reader通常用于為這種“流式”操作提供資料。

Upload reads from given io.Reader and uploads the file contents

那io.Reader應該是要上傳的資料的來源。

io.Reader可能是來自os.Open().

但它可以是任何滿足條件的東西io.Reader——例如，它也可以是bytes.Buffer.

它甚至可能是更深奧的東西，比如GetObject對來自 AWS 的流行 S3 服務的API 呼叫的結果，它也回傳io.ReadCloser滿足io.Reader.

io.Reader是 Go 介面如何允許獨立庫相互連接的一個很好的例子。你使用的 SDK 并不關心io.Reader它傳遞了什么；滿足該值就足夠了，這是io.Reader在編譯時強制執行的要求。您可以將任何滿足的東西傳遞給它io.Reader，并且介面型別保證Upload()能夠正確處理它。

Upload需要一個io.Reader. 如果您想傳遞諸如*os.Filefromos.Open或io.ReadCloserfrom 之類的東西，例如 S3 GetObject，那會起作用，因為io.ReadCloser滿足io.Reader. 但是，由于不Upload接受，您可以確信它只會呼叫該介面中定義的函式。在被呼叫后，您必須自己進行任何關閉操作。io.Readerio.ReadCloserUpload

確保花時間了解如何io.Reader使此函式的輸入保持開放式，同時還要具體說明它所期望的介面。這是 Go 中最重要的概念之一。

uj5u.com熱心網友回復：

這個：

var testIO io.Reader

相當于：

testIO := io.Reader(nil)

所以這就是為什么您對空指標參考感到恐慌的原因：

2021/12/01 18:28:47 http: panic serving 127.0.0.1:61059: runtime error: invalid memory address or nil pointer dereference
goroutine 11 [running]:

一個io.Reader是一個介面，它允許一個通過一般值，只要它們實作的介面（即，實作的Read方法）。

由于您正在上傳檔案，因此您的位元組流應該來自作業系統檔案。os.File實作了正確的Read方法 - 所以是兼容的io.Reader。

所以嘗試：

f, err := os.Open(uploadFilePath)
if err != nil { /* ... */ }

upload, err := client.Files.Upload(context.TODO(), f, "test", 0)

uj5u.com熱心網友回復：

當您定義一個變數時，它的初始值是該zero value型別的。io.Reader是一個介面，它的零值是nil。因此 nil pointer dereference error. 只需io.Reader在將其傳遞給 Upload 之前對其進行初始化：

file, err := os.Open("path/to/file")
// if err != nil { ... }

upload, err := client.Files.Upload(context.TODO(), file, "test", 0)

轉載請註明出處，本文鏈接：https://www.uj5u.com/caozuo/371074.html

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