从存储桶将多个文件传递给 exec.Command 调用

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我正在尝试构建一个用 go 编写的云函数，它将使用 google cloud functions 基础架构中可用的 imagemagick 库来将多个图像合成和操作为最终的输出图像。

问题的根源是我想使用的 imagemagick 函数可用，但它需要多个不同的输入才能工作。我的输入是存储桶中的对象。

os/exec cmd 结构允许您通过使用“extrafiles”数组来执行此操作，并且我知道如何向我的 imagemagick 命令提供这些额外文件。

但是，“extrafiles”数组只想存储 os.file 的实例，而 gcp 存储客户端在您打开文件时会为您提供一个“reader”实例。

backgroundBlob := storageClient.Bucket(inputBucket).Object(background)
        backgroundImg, err := backgroundBlob.NewReader(ctx)
        if err != nil {
                return "", fmt.Errorf("backgroundImg: %v", err)
        }

        foregroundBlob := storageClient.Bucket(inputBucket).Object(foreground)
        foregroundImg, err := foregroundBlob.NewReader(ctx)
        if err != nil {
                return "", fmt.Errorf("foregroundImg: %v", err)
        }

        outputBlob := storageClient.Bucket(outputBucket).Object(output)
        outputImg := outputBlob.NewWriter(ctx)
        defer outputImg.Close()

        // Set up some additional file handles since we're dealing with more inputs than STDIN Can cope with
        cmd := exec.Command("convert", "fd:3", "fd:4", "-composite", "fd:5")
        cmd.ExtraFiles = append(cmd.ExtraFiles,backgroundImg)
        cmd.ExtraFiles = append(cmd.ExtraFiles,foregroundImg)
        cmd.ExtraFiles = append(cmd.ExtraFiles,outputImg)

        if err := cmd.Run(); err != nil {
                return "", fmt.Errorf("cmd.Run: %v", err)
        }

        log.Printf("Blurred image has been uploaded to %s", outputBlob.ObjectName())

        return outputBlob.ObjectName(), nil
}```

So, from where I am at the moment, I need to do one of the following two things:
1. Figure out how to get Google's storage API to treat/use objects in their storage buckets as "os.File"s
OR
2. Figure out how to execute my "convert" command using multiple Readers as input, rather than leveraging the ExtraFiles array.

If anybody out there has any ideas on how to achieve either of the above, or has alternate ways of solving this problem, I would be very grateful to hear them!

解决方案

对于将来遇到这个问题的任何人 - 我找到了一个解决方法。我对它并不满意，但它很实用。

本质上，我能够获取存储读取器的内容，然后在 cloud functions 上下文中创建我自己的 os.file 对象。然后，将该 os.file 传递给 exec.cmd 调用。这绝对不理想，但代码如下：

func Overlay(ctx context.Context, inputBucket, outputBucket, background string, foreground string, output string) (string, error) {
        // Retrieve the Background Image from the storage API
        backgroundBlob := storageClient.Bucket(inputBucket).Object(background)
        backgroundImg, err := backgroundBlob.NewReader(ctx)
        if err != nil {
                return "", fmt.Errorf("backgroundImg: %v", err)
        }        
        // Read the contents of the file into a variable
        backgroundSlurp, err := ioutil.ReadAll(backgroundImg)
        if err != nil {
                return "", fmt.Errorf("readFile: unable to read data from bucket %q, file %q: %v", inputBucket, background, err)
        }
        // Write the contents of Background Image to an os.File instance
        err = ioutil.WriteFile(fmt.Sprintf("/tmp/%s",background), backgroundSlurp, 0644)
        if err != nil {
                return "", fmt.Errorf("backgroundImg: %v", err)
        }
        // Open the os.File instance to pass it on to os.exec later
        backgroundFile, err := os.Open(fmt.Sprintf("/tmp/%s",background))
        if err != nil {
                return "", fmt.Errorf("backgroundFile: %v", err)
        }

        foregroundBlob := storageClient.Bucket(inputBucket).Object(foreground)
        foregroundImg, err := foregroundBlob.NewReader(ctx)
        if err != nil {
                return "", fmt.Errorf("foregroundImg: %v", err)
        }
        // Read the contents of the file into a variable
        foreroundSlurp, err := ioutil.ReadAll(foregroundImg)
        if err != nil {
                return "", fmt.Errorf("readFile: unable to read data from bucket %q, file %q: %v", inputBucket, foreground, err)
        }
        // Write the contents of Foreground Image to an os.File instance
        err = ioutil.WriteFile(fmt.Sprintf("/tmp/%s",foreground), foreroundSlurp, 0644)
        if err != nil {
                return "", fmt.Errorf("foregroundImg: %v", err)
        }
        // Open the os.File instance to pass it on to os.exec later
        foregroundFile, err := os.Open(fmt.Sprintf("/tmp/%s",foreground))
        if err != nil {
                return "", fmt.Errorf("foregroundFile: %v", err)
        }

        outputBlob := storageClient.Bucket(outputBucket).Object(output)
        outputImg := outputBlob.NewWriter(ctx)
        defer outputImg.Close()

        // Set up some additional file handles since we're delaqing with more inputs than STDIN Can cope with
        cmd := exec.Command("convert", "fd:3", "fd:4", "-composite", "-")
        cmd.Stdout = outputImg
        cmd.ExtraFiles = append(cmd.ExtraFiles,backgroundFile)
        cmd.ExtraFiles = append(cmd.ExtraFiles,foregroundFile)

        if err := cmd.Run(); err != nil {
                return "", fmt.Errorf("cmd.Run: %v", err)
        }

        log.Printf("Blurred image has been uploaded to %s", outputBlob.ObjectName())

        return outputBlob.ObjectName(), nil
}

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