使用 http.Request.Context() 而不是 context.Background() 时，文件不会提交到谷歌云存储

PHP小编西瓜在介绍Go语言开发中的一个重要细节时指出，使用Http.Request.Context()代替context.Background()时，上传文件不会被自动提交到谷歌云存储。这个小细节对于开发者来说非常重要，因为它可能会导致文件上传失败或数据丢失。了解并正确使用这个方法可以避免不必要的问题，确保文件的安全上传和存储。

问题内容

我是新手，我编写了一个简单的宠物项目来将加密文件上传到谷歌云存储。 问题： 在我调用 addentry 函数的http处理程序中，当我传递 r.context() 而不是 context.background() 时，文件不会上传到谷歌存储。在谷歌的控制台中，我可以看到收到的字节，而且我根本没有收到任何错误，但文件本身不存在。

处理程序代码：

//imports, structs skipped

func processaddentryrequest(w http.responsewriter, r *http.request) {
    //validation, getting params from Jwt skipped

    reader, err := r.multipartreader()
    if err != nil {
        http.error(w, "multipart/fORM-data expected, not found", http.statusbadrequest)
        log.println("could not init multipartreader from request: %w", err)
        return
    }

    gsservice, err := googlestorageservice.new()
    if err != nil {
        http.error(w, "internal server error", http.statusinternalservererror)
        log.println(err)
        return
    }

    bservice, err := backupservice.new(
        backupservice.withcipher(aes.new()),
        backupservice.withstorageservice(gsservice))

    if err != nil {
        http.error(w, "internal server error", http.statusinternalservererror)
        log.println(err)
        return
    }
    var entry *entryrepo.backupentry
    for {
        part, err := reader.nextpart()
        if err == io.eof {
            break
        }
        if err != nil {
            err = fmt.errorf("error reading: %w", err)
            log.println(err)
            http.error(w, "internal server error", http.statusinternalservererror)
            return
        }

        formname := part.formname()
        if formname == "file" {
            entry, err = bservice.addentry(r.context(), backupid, part.filename(), part.header.get("content-type"), part)
            if err != nil {
                errclose := part.close()
                err = fmt.errorf("failed to add entry for backup %s: %w; error while closing multipart.part: %w", backupid, err, errclose)
                log.println(err)
                http.error(w, "internal server error", http.statusinternalservererror)
                return

            }
        }
        err = part.close()
        if err != nil {
            err = fmt.errorf("failed to close part for backup %s: %w", backupid, err)
            log.println(err)
            http.error(w, "internal server error", http.statusinternalservererror)
            return
        }

    }
    response.entry = *entry
    JSONdata, err := json.marshal(response)
    if err != nil {
        http.error(w, "internal server error", http.statusinternalservererror)
        log.println("failed to marshal json: %w\n", err)
        return
    }
    w.writeheader(http.statusok)
    w.header().set("content-type", "application/json")
    w.write(jsondata)
}

addentry函数代码：

func (backupservice *backupservice) addentry(ctx context.context, backupid string, entryfullname string,
    entrymimetype string, in io.reader) (*ber.backupentry, error) {
    // validation skipped for readability
    entryid := uuid.new()
    outpath := backupid + "/" + entryid.string()

    entrychan := make(chan *ber.backupentry)
    errchan := make(chan error)
    go func() {
        gstorageclient, err := backupservice.storageservice.getclient(ctx)
        if err != nil {
            errchan <- fmt.errorf("could not add entry: %w", err)
        }
        defer gstorageclient.close()

        out := gstorageclient.bucket(config.GCbucketname()).object(outpath).newwriter(ctx)
        defer out.close()

        Mac, size, err := backupservice.cipher.encrypt(ctx, in, out,
            []byte(config.encryptionkey()), []byte(config.hmackey()))
        if err != nil {
            errchan <- fmt.errorf("could not upload encrypted backupentry with id=%s: %w", entryid.string(), err)
        }

        //db operation skipped
        entrychan <- entry
    }()
    select {
    case <-ctx.done():
        dbcleanuperr, storagecleanuperr := backupservice.cleanupentry(entryid.string(), outpath)
        return nil,
            fmt.errorf("could not add entry %s to backup %s: context was cancelled; db cleanup err: %w; gstorage cleanup err: %w",
                entryid.string(), backupid, dbcleanuperr, storagecleanuperr)
    case err := <-errchan:
        dbcleanuperr, storagecleanuperr := backupservice.cleanupentry(entryid.string(), outpath)
        return nil,
            fmt.errorf("could not add entry %s to backup %s: %w; db cleanup err: %w; gstorage cleanup err: %w",
                entryid.string(), backupid, err, dbcleanuperr, storagecleanuperr)
    case entry := <-entrychan:
        return entry, nil
    }
}

我尝试过的：

1. 启用 godebug：http2debug=1 检查调试 http 日志。日志不同，我将它们放在下面。
2. 检查上下文是否在所有级别上都关闭：在http处理程序本身中，在addentry函数中添加encrypt函数。上下文没有关闭，一切似乎都工作正常。
3. 从 r.context() 创建派生上下文，结果与 r.context() 相同
4. 显然，将 context.background() 而不是 r.context() 传递给 addentry 函数，就可以解决问题

当 r.context() 作为参数传递时的调试日志：

ft-api  | 2023/08/02 19:23:46 stdout: 2023/08/02 19:23:46 [2606f10843ab/yuha6i98ak-000004] "post http://0.0.0.0:8080/backup http/1.1" from 172.18.0.1:36052 - 200 570b in 193.850041ms
ft-api  | 2023/08/02 19:23:47 stdout: 2023/08/02 19:23:47 [2606f10843ab/yuha6i98ak-000005] "post http://0.0.0.0:8080/entry http/1.1" from 172.18.0.1:36052 - 200 127b in 171.975584ms
ft-api  | 2023/08/02 19:23:47 stderr: 2023/08/02 19:23:47 h2_bundle.go:9019: http2: transport encoding header ":authority" = "oauth2.googleapis.com"
ft-api  | 2023/08/02 19:23:47 stderr: 2023/08/02 19:23:47 h2_bundle.go:9019: http2: transport encoding header ":method" = "post"
ft-api  | 2023/08/02 19:23:47 stderr: 2023/08/02 19:23:47 h2_bundle.go:9019: http2: transport encoding header ":path" = "/token"
ft-api  | 2023/08/02 19:23:47 stderr: 2023/08/02 19:23:47 h2_bundle.go:9019: http2: transport encoding header ":scheme" = "https"
ft-api  | 2023/08/02 19:23:47 stderr: 2023/08/02 19:23:47 h2_bundle.go:9019: http2: transport encoding header "content-type" = "application/x-www-form-urlencoded"
ft-api  | 2023/08/02 19:23:47 stderr: 2023/08/02 19:23:47 h2_bundle.go:9019: http2: transport encoding header "content-length" = "861"
ft-api  | 2023/08/02 19:23:47 stderr: 2023/08/02 19:23:47 h2_bundle.go:9019: http2: transport encoding header "accept-encoding" = "gzip"
ft-api  | 2023/08/02 19:23:47 stderr: 2023/08/02 19:23:47 h2_bundle.go:9019: http2: transport encoding header "user-agent" = "go-http-client/2.0"
ft-api  | 2023/08/02 19:23:47 stderr: 2023/08/02 19:23:47 h2_bundle.go:9968: http2: transport received headers flags=end_headers stream=3 len=42
ft-api  | 2023/08/02 19:23:47 stderr: 2023/08/02 19:23:47 h2_bundle.go:9968: http2: transport received data flags=padded stream=3 len=974 data="\x1f\x8b\b\x00\x00\x00\x00\x00\x02\xff\x1d\xd4Ɏ\xa3h\x00\x04\xd0\x7f\xf1\xb9ia&\xeb܌]\xb4\xc9*l\x01\x05\x06.\x88%\xd9\xf7d\xcd\xd6\xfc\xfbxs\f).q\x88\xf7\xf7\x12\xa7)&$z\x86\x06\xf7\x97\x7f.g\f\x94\xdf\xe9\uf13DƸ\xe98=\x9a\r\xe33\xe6fѶ\xa3\xcf\xd7Ϫn-\x04\x9b]\x7f\xaf\xfc|\x95\xec!ha\x97^[\xa4\xad\x0f\xe8\xeb\x03:\x051u\xb1\x12~2\x1e\xf5\xbe\xbftν9\x8f\xe7\xedз\xaa\xac\x87\a\xa3\xfd!\x82ȡӝyb\xe3n\xb8\x91\xf8\x91*\xa1\xc5\xe7\x80\xc1|ڗ}p\x99\xd0d\xf7\xf8\xc7\xc7\"\xda\x1d\xabl\x96\xa4\x98\xf1'\xb2g\xef\xb1=\x10o\x7f\x8dc\x96\x8d\xc6\xfe\xfc\xae\xdc?\xb7f\x0f\xc0\xa2k\xb9^\xd5!\xc38\xe2\a\x84\xca1\x83\xfeg6\xbanjpzw\xcf\xfb\xd3jͯn\x8d\xac\xf2[\xbe۰\xfcx\xbfbp\xbd\xdd\x14\xa1--\xbe" (613 bytes omitted)
ft-api  | 2023/08/02 19:23:47 stderr: 2023/08/02 19:23:47 h2_bundle.go:9968: http2: transport received data flags=end_stream|padded stream=3 len=136 data=""
ft-api  | 2023/08/02 19:23:47 stderr: 2023/08/02 19:23:47 h2_bundle.go:9968: http2: transport received ping len=8 ping="\x00\x00\x00\x00\x00\x00\x00\x02"
ft-api  | 2023/08/02 19:23:47 stderr: 2023/08/02 19:23:47 transport.go:3015: http2: transport failed to get client conn for storage.googleapis.com:443: http2: no cached connection was available

当 context.background() 作为参数传递时的调试日志（我从日志中删除了 jwt 令牌值，但它在那里）

ft-api  | 2023/08/02 19:24:51 stdout: 2023/08/02 19:24:51 [2606f10843ab/ukd5p0sXox-000001] "POST http://0.0.0.0:8080/backup HTTP/1.1" from 172.18.0.1:38934 - 200 570B in 465.2635ms
ft-api  | 2023/08/02 19:24:52 stdout: 2023/08/02 19:24:52 [2606f10843ab/ukd5p0sXox-000002] "POST http://0.0.0.0:8080/entry HTTP/1.1" from 172.18.0.1:38934 - 200 127B in 172.084834ms
ft-api  | 2023/08/02 19:24:52 stderr: 2023/08/02 19:24:52 h2_bundle.go:9968: http2: Transport failed to get client conn for oauth2.googleapis.com:443: http2: no cached connection was available
ft-api  | 2023/08/02 19:24:52 stderr: 2023/08/02 19:24:52 h2_bundle.go:9968: http2: Transport creating client conn 0x40003cc780 to 142.250.186.74:443
ft-api  | 2023/08/02 19:24:52 stderr: 2023/08/02 19:24:52 h2_bundle.go:9019: http2: Transport encoding header ":authority" = "oauth2.googleapis.com"
ft-api  | 2023/08/02 19:24:52 stderr: 2023/08/02 19:24:52 h2_bundle.go:9019: http2: Transport encoding header ":method" = "POST"
ft-api  | 2023/08/02 19:24:52 stderr: 2023/08/02 19:24:52 h2_bundle.go:9019: http2: Transport encoding header ":path" = "/token"
ft-api  | 2023/08/02 19:24:52 stderr: 2023/08/02 19:24:52 h2_bundle.go:9019: http2: Transport encoding header ":scheme" = "https"
ft-api  | 2023/08/02 19:24:52 stderr: 2023/08/02 19:24:52 h2_bundle.go:9019: http2: Transport encoding header "content-type" = "application/x-www-form-urlencoded"
ft-api  | 2023/08/02 19:24:52 stderr: 2023/08/02 19:24:52 h2_bundle.go:9019: http2: Transport encoding header "content-length" = "861"
ft-api  | 2023/08/02 19:24:52 stderr: 2023/08/02 19:24:52 h2_bundle.go:9019: http2: Transport encoding header "accept-encoding" = "gzip"
ft-api  | 2023/08/02 19:24:52 stderr: 2023/08/02 19:24:52 h2_bundle.go:9019: http2: Transport encoding header "user-agent" = "Go-http-client/2.0"
ft-api  | 2023/08/02 19:24:52 stderr: 2023/08/02 19:24:52 h2_bundle.go:9968: http2: Transport received SETTINGS len=18, settings: MAX_CONCURRENT_STREAMS=100, INITIAL_WINDOW_SIZE=1048576, MAX_HEADER_LIST_SIZE=65536
ft-api  | 2023/08/02 19:24:52 stderr: 2023/08/02 19:24:52 h2_bundle.go:9968: http2: Transport received WINDOW_UPDATE len=4 (conn) incr=983041
ft-api  | 2023/08/02 19:24:52 stderr: 2023/08/02 19:24:52 h2_bundle.go:9968: http2: Transport received SETTINGS flags=ACK len=0
ft-api  | 2023/08/02 19:24:52 stderr: 2023/08/02 19:24:52 h2_bundle.go:9968: http2: Transport received HEADERS flags=END_HEADERS stream=1 len=220
ft-api  | 2023/08/02 19:24:52 stderr: 2023/08/02 19:24:52 h2_bundle.go:9968: http2: Transport received DATA flags=PADDED stream=1 len=1030 data="\x1f\x8b\b\x00\x00\x00\x00\x00\x02\xff\x1d\xd4Ir\xa3:\x00\x00лx\xddt1\x83z\x179&\x86\x84`#3n(!F3\v̠\xae\x7f\xf7\x9f\xea;\xbcz\x7fO\x98\x90|\x9e\x93eh\xf2\xfe\xf4\xe7t`\x11\xfc&\xbfS\xfe\r\xe7M'|\x9d\x83\x1b'\x06\xdf\x1f\xa2\xfa\xcd]78\xf5\xc4,\xedf\x8f\x18r\xb9+\xf8\x1aņl\xaf\x0f<\\#\x14\xa3\xeb\xce8O\xfb\xec\xa8p\xef#|}&\xeeM\x1e\xc5E\x94\x91-<Е\xbd\xea\x88X\xc8y\xbf<\x94\xfeHL5\xb8\x19&\x1e{?\xe3\x1a\xa3\xb2y\xf3\xd2T:ȿ\x1dX9K[4ԟ\x98a\x0e9\xfe \xea\xe1h\x910\xac\x9a\xf7h\xaf\xba\xa2\xd1\xeak\x1b\xc2\xcb\xea\xe4\x03\x9c\xaf\xfa\xed\xbd\x05\x89\x1f\xbf)\x1d5\xfc\xfevT\xf8\x9d\x9c\x81*4\xe9\xad|P̍(\xdb\xe8l=d\xe3\xc3c\xf5\xf2q\xdd\x05\xf4\xf6\x95\xc7\x10Ŗ\xbe\xa6\xf6\xf9Q|w" (611 bytes omitted)
ft-api  | 2023/08/02 19:24:52 stderr: 2023/08/02 19:24:52 h2_bundle.go:9968: http2: Transport received DATA flags=END_STREAM|PADDED stream=1 len=208 data=""
ft-api  | 2023/08/02 19:24:52 stderr: 2023/08/02 19:24:52 h2_bundle.go:9968: http2: Transport received PING len=8 ping="\x00\x00\x00\x00\x00\x00\x00\x00"
ft-api  | 2023/08/02 19:24:52 stderr: 2023/08/02 19:24:52 transport.go:3015: http2: Transport failed to get client conn for storage.googleapis.com:443: http2: no cached connection was available
ft-api  | 2023/08/02 19:24:52 stderr: 2023/08/02 19:24:52 transport.go:3015: http2: Transport creating client conn 0x400029e000 to 216.58.212.144:443
ft-api  | 2023/08/02 19:24:52 stderr: 2023/08/02 19:24:52 transport.go:2076: http2: Transport encoding header ":authority" = "storage.googleapis.com"
ft-api  | 2023/08/02 19:24:52 stderr: 2023/08/02 19:24:52 transport.go:2076: http2: Transport encoding header ":method" = "POST"
ft-api  | 2023/08/02 19:24:52 stderr: 2023/08/02 19:24:52 transport.go:2076: http2: Transport encoding header ":path" = "/upload/storage/v1/b/bucketname/o?alt=json&name=a934c415-07bd-4686-8ad0-90ff5ef68c7e%2F6e6b9563-c9d9-484e-a24f-cd2f8bd1fcd8&prettyPrint=false&projection=full&uploadType=multipart"
ft-api  | 2023/08/02 19:24:52 stderr: 2023/08/02 19:24:52 transport.go:2076: http2: Transport encoding header ":scheme" = "https"
ft-api  | 2023/08/02 19:24:52 stderr: 2023/08/02 19:24:52 transport.go:2076: http2: Transport encoding header "content-type" = "multipart/related; boundary=976d8006696028fea8c40fc53fe0a817a80f334ae41925d1e08c3bb3c917"
ft-api  | 2023/08/02 19:24:52 stderr: 2023/08/02 19:24:52 transport.go:2076: http2: Transport encoding header "x-cloud-trace-context" = "cb5a9d07f5007be3d8dfe277e1fb6beb/9294889295348469653;o=0"
ft-api  | 2023/08/02 19:24:52 stderr: 2023/08/02 19:24:52 transport.go:2076: http2: Transport encoding header "authorization" = "Bearer <>"
ft-api  | 2023/08/02 19:24:52 stderr: 2023/08/02 19:24:52 transport.go:2076: http2: Transport encoding header "x-goog-api-client" = "gl-go/1.20.6 gccl/1.30.1"
ft-api  | 2023/08/02 19:24:52 stderr: 2023/08/02 19:24:52 transport.go:2076: http2: Transport encoding header "user-agent" = "gcloud-golang-storage/1.30.1"
ft-api  | 2023/08/02 19:24:52 stderr: 2023/08/02 19:24:52 transport.go:2076: http2: Transport encoding header "accept-encoding" = "gzip"
ft-api  | 2023/08/02 19:24:52 stderr: 2023/08/02 19:24:52 transport.go:3015: http2: Transport received SETTINGS len=18, settings: MAX_CONCURRENT_STREAMS=100, INITIAL_WINDOW_SIZE=1048576, MAX_HEADER_LIST_SIZE=65536
ft-api  | 2023/08/02 19:24:52 stderr: 2023/08/02 19:24:52 transport.go:3015: http2: Transport received WINDOW_UPDATE len=4 (conn) incr=983041
ft-api  | 2023/08/02 19:24:52 stderr: 2023/08/02 19:24:52 transport.go:3015: http2: Transport received SETTINGS flags=ACK len=0
ft-api  | 2023/08/02 19:24:52 stderr: 2023/08/02 19:24:52 transport.go:3015: http2: Transport received HEADERS flags=END_HEADERS stream=1 len=314
ft-api  | 2023/08/02 19:24:52 stderr: 2023/08/02 19:24:52 transport.go:3015: http2: Transport received DATA stream=1 len=944 data="{\"kind\":\"storage#object\",\"id\":\"bucketname/a934c415-07bd-4686-8ad0-90ff5ef68c7e/6e6b9563-c9d9-484e-a24f-cd2f8bd1fcd8/1691004292747760\",\"selflink\":\"https://www.googleapis.com/storage/v1/b/bucketname/o/a934c415-07bd-4686-8ad0-90ff5ef68c7e%2F6e6b9563" (688 bytes omitted)
ft-api  | 2023/08/02 19:24:52 stderr: 2023/08/02 19:24:52 transport.go:3015: http2: Transport received DATA flags=END_STREAM stream=1 len=0 data=""
ft-api  | 2023/08/02 19:24:52 stderr: 2023/08/02 19:24:52 transport.go:3015: http2: Transport received PING len=8 ping="\x00\x00\x00\x00\x00\x00\x00\x00"

解决方法

通过在 gstorage 对象编写器上显式调用 Close() 方法而不是推迟它来解决该问题。我仍然不完全确定此行为的原因（我知道除非编写器关闭，否则文件不会提交到 gstorage，但不涉及上下文取消，因此它应该已关闭）。

编辑：在我看来，问题可能出在 go 执行 goroutine 内部声明的延迟函数的顺序上。如果有人对此有解释，我们将非常欢迎。

以上就是使用 http.Request.Context() 而不是 context.Background() 时，文件不会提交到谷歌云存储的详细内容，更多请关注编程网其它相关文章！