英文:
image.Decode results in "unknown format" when source is multipart.File
问题
我有一个multipart.File，用户将其上传到我的服务器，然后我使用aws-sdk-go将该文件上传到S3，但我还想创建该图像的缩略图。
在我的测试中，以下代码在file是本地文件的os.Open(...的返回值时运行良好，但当我将相同的变量发送给s3，它会进入err块，因为s3要求一个io.Reader。
import (
"image"
"image/jpeg"
)
func UploadToS3(file multipart.File, /*snip*/) {
_, uploadErr := uploader.Upload(&s3manager.UploadInput{
Bucket: aws.String(bucket),
Key: aws.String(key),
Body: file,
ContentType: aws.String(mimeType),
ACL: aws.String("public-read"),
})
reader, err := CreateThumbnail(file)
}
func CreateThumbnail(imageFile io.Reader) (io.Reader, error) {
decodedImage, _, err := image.Decode(imageFile)
if err != nil {
fmt.Println("Error decoding", err, decodedImage) // "unknown format"
return nil, err
}
/*snip*/
}
我看到的大多数答案都涉及添加import _ "image/jpeg"，但已经导入了它（以及png和gif）。
我对Golang还比较陌生，所以不太清楚我做错了什么。我也尝试了image.Decode(bufio.NewReader(imageFile))，但结果是相同的err。
英文:
I have a multipart.File that a user uploads to my server, and then I take that file and upload it to s3 using aws-sdk-go, but I also want to create a thumbnail of that image.
The code below works fine in my tests when I file is the return value of an os.Open(... of a local file, but it hit's the err block when I send CreateThumbnail the same variable I sent to s3, which asks for an io.Reader
import (
"image"
"image/jpeg"
)
func UploadToS3(file multipart.File, /*snip*/) {
_, uploadErr := uploader.Upload(&s3manager.UploadInput{
Bucket: aws.String(bucket),
Key: aws.String(key),
Body: file,
ContentType: aws.String(mimeType),
ACL: aws.String("public-read"),
})
reader, err := CreateThumbnail(file)
}
func CreateThumbnail(imageFile io.Reader) (io.Reader, error) {
decodedImage, _, err := image.Decode(imageFile)
if err != nil {
fmt.Println("Error decoding", err, decodedImage) // "unknown format"
return nil, err
}
/*snip*/
Most of the answers I see for the problem involve adding import _ "image/jpeg", but that's already imported (as well as png and gif).
I'm fairly new to Golang, so I'm a bit lost as to what I'm doing wrong. I tried image.Decode(bufio.NewReader(imageFile)) as well, but that results in the same err.
答案1
得分: 8
uploader.Upload调用会读取文件直到文件末尾。在调用CreateThumbnail之前，请将文件的指针定位回文件开头：
func UploadToS3(file multipart.File, /*snip*/) {
_, uploadErr := uploader.Upload(&s3manager.UploadInput{
Bucket: aws.String(bucket),
Key: aws.String(key),
Body: file,
ContentType: aws.String(mimeType),
ACL: aws.String("public-read"),
})
// 将文件指针定位回文件开头以供CreateThumbnail使用
if _, err := file.Seek(0, 0); err != nil {
// 处理错误
}
reader, err := CreateThumbnail(file)
}
英文:
The call uploader.Upload reads to the end of the file. Seek back to the beginning of the file before calling CreateThumbnail:
func UploadToS3(file multipart.File, /*snip*/) {
_, uploadErr := uploader.Upload(&s3manager.UploadInput{
Bucket: aws.String(bucket),
Key: aws.String(key),
Body: file,
ContentType: aws.String(mimeType),
ACL: aws.String("public-read"),
})
// Seek back to beginning of file for CreateThumbnail
if _, err := file.Seek(0, 0); err != nil {
// handle error
}
reader, err := CreateThumbnail(file)
}
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