英文:
what is the differences between r.Static() and context.File() to get the picture in gin?
问题
我正在基于Gin Web框架开发一个Go程序。
我想从本地文件系统中提供图片。
func main() {
r := gin.Default()
r.Static("/page2", "resources/pictures")
r.GET("/test", func(context *gin.Context) {
name := context.Query("name")
context.JSON(http.StatusOK, gin.H{
"name": name,
})
})
r.GET("/page", func(context *gin.Context) {
name := context.Query("picname")
context.File("resources/pictures/" + name + ".jpg")
context.JSON(http.StatusOK, "That is "+name)
})
r.Run(":9090")
}
我发现当我使用/page2来获取图片（URL为http://localhost:9090/page2/xiamei.jpg）时，一切正常。
但是当我使用/page来获取图片（URL为http://localhost:9090/page/xiamei.jpg）时，出现了错误。
http: wrote more than the declared Content-Length
这是什么内部原因，这两种访问方法之间的差异的根本原因是什么？
英文:
I'm developing a Go program based on Gin web framework.
I want to serve pictures from the local file system.
func main() {
r := gin.Default()
r.Static("/page2", "resources/pictures")
r.GET("/test", func(context *gin.Context) {
name := context.Query("name")
context.JSON(http.StatusOK, gin.H{
"name": name,
})
})
r.GET("/page", func(context *gin.Context) {
name := context.Query("picname")
context.File("resources/pictures/" + name + ".jpg")
context.JSON(http.StatusOK, "That is "+name)
})
r.Run(":9090")
}
I find it strange that when I use /page2 to get the pictures (url http://localhost:9090/page2/xiamei.jpg), it works fine.
But when I use /page to get the pictures (url http://localhost:9090/page/xiamei.jpg) an error happens.
> http: wrote more than the declared Content-Length
What is the internal reason, and what is the root cause of the difference between these two access methods?
答案1
得分: 0
在/page处理程序中，你同时调用了Context.File和Context.JSON。
第一次调用Context.File已经将文件写入响应并设置了Content-Length头。
通过再次使用更多的有效负载调用Context.JSON，你增加了实际内容的长度，但没有更新Content-Length头；这导致了你看到的错误。
r.Static没有这个问题，因为它只提供一个文件，并且不会添加超过应有的有效负载。
在Gin处理程序中，你应该只调用一个渲染器函数。如果你正在提供一个文件，你可以完全删除最后一个c.JSON。
英文:
In the /page handler, you call both Context.File, and Context.JSON.
The first call to Context.File already writes the file to the response and sets Content-Length header.
By calling Context.JSON again with more payload, you are increasing the actual length of the content without updating the Content-Length header; this results in the error you see.
r.Static doesn't have this issue because it serves one file and doesn't add more payload than it should.
In a Gin handler you should call only one renderer function. If you are serving a file, you can remove the last c.JSON altogether.
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