英文:
Why is my go handler not producing valid FormData?
问题
我正在尝试让一个使用Go编写的服务器对“mime/multipart”表单进行响应，但是遇到了问题。使用下面的代码，我得到了Uncaught (in promise) TypeError: Could not parse content as FormData.的错误。
我的Go代码如下：
package mainimport ("log""mime/multipart""net/http")func handler(resp http.ResponseWriter, req *http.Request) {req.ParseMultipartForm(2097152)mw := multipart.NewWriter(resp)mw.WriteField("name", req.FormValue("user_name"))mw.WriteField("email", req.FormValue("user_email"))mw.WriteField("message", req.FormValue("user_message"))resp.Header().Set("Content-Type", mw.FormDataContentType())mw.Close()}func main() {http.HandleFunc("/", handler)log.Fatal(http.ListenAndServe(":8080", nil))}
我的浏览器代码如下：
<!DOCTYPE html><html><head><meta charset="utf-8" /><title>Your first HTML form</title><link rel="stylesheet" href="form.css"></head><body><form name="theForm" method="post"><ul><li><label for="name">Name:</label><input type="text" id="name" name="user_name"></li><li><label for="mail">E-mail:</label><input type="email" id="mail" name="user_email"></li><li><label for="msg">Message:</label><textarea id="msg" name="user_message"></textarea></li><li class="button"><button type="submit">Send your message</button></li></ul></form><pre id="response"></pre><script>const form = document.forms["theForm"];form.addEventListener( 'submit', function ( event ) {event.preventDefault();const fd = new FormData(form);fetch('/form-handler', {method: 'POST',body: fd}).then(response => response.formData()).then(data => document.getElementById("response").innerText = JSON.stringify(data));});</script></body></html>
如果我将JavaScript代码更改为.then(response => response.text)，我会得到看起来正确的响应，所以不确定是否缺少了结尾的CRLF或其他原因。
英文:
I'm tinkering around trying to get a server written in go to respond to a "mime/multipart" form with a "mime/multipart" form.
With the code below, I'm getting Uncaught (in promise) TypeError: Could not parse content as FormData.
My go looks like this:
package mainimport ("log""mime/multipart""net/http")func handler(resp http.ResponseWriter, req *http.Request) {req.ParseMultipartForm(2097152)mw := multipart.NewWriter(resp)mw.WriteField("name", req.FormValue("user_name"))mw.WriteField("email", req.FormValue("user_email"))mw.WriteField("message", req.FormValue("user_message"))resp.Header().Set("Content-Type", mw.FormDataContentType())mw.Close()}func main() {http.HandleFunc("/", handler)log.Fatal(http.ListenAndServe(":8080", nil))}
My browser code looks like this:
<!DOCTYPE html><html><head><meta charset="utf-8" /><title>Your first HTML form</title><link rel="stylesheet" href="form.css"></head><body><form name="theForm" method="post"><ul><li><label for="name">Name:</label><input type="text" id="name" name="user_name"></li><li><label for="mail">E-mail:</label><input type="email" id="mail" name="user_email"></li><li><label for="msg">Message:</label><textarea id="msg" name="user_message"></textarea></li><li class="button"><button type="submit">Send your message</button></li></ul></form><pre id="response"></pre><script>const form = document.forms["theForm"];form.addEventListener( 'submit', function ( event ) {event.preventDefault();const fd = new FormData(form);fetch('/form-handler', {method: 'POST',body: fd}).then(response => response.formData()).then(data => document.getElementById("response").innerText = JSON.stringify(data));});</script></body></html>
If I change the JavaScript to .then(response => response.text), I get what looks like the right response, so not sure if there's a missing CRLF at the end or what?
答案1
得分: 3
你需要将resp.Header().Set("Content-Type", mw.FormDataContentType())移到第一个写操作之前。像这样：
func handler(resp http.ResponseWriter, req *http.Request) {req.ParseMultipartForm(2097152)mw := multipart.NewWriter(resp)resp.Header().Set("Content-Type", mw.FormDataContentType())mw.WriteField("name", req.FormValue("user_name"))mw.WriteField("email", req.FormValue("user_email"))mw.WriteField("message", req.FormValue("user_message"))mw.Close()}
在对ResponseWriter进行第一次写操作后，无法修改HTTP头。如果在那时没有设置Content-Type，它将默认为Content-Type: text/plain; charset=utf-8，而浏览器无法解析该类型，因为它需要在Content-Type头中提供边界信息。
英文:
You have to move resp.Header().Set("Content-Type", mw.FormDataContentType()) to above the first write. Like so:
func handler(resp http.ResponseWriter, req *http.Request) {req.ParseMultipartForm(2097152)mw := multipart.NewWriter(resp)resp.Header().Set("Content-Type", mw.FormDataContentType())mw.WriteField("name", req.FormValue("user_name"))mw.WriteField("email", req.FormValue("user_email"))mw.WriteField("message", req.FormValue("user_message"))mw.Close()}
HTTP headers can't be modified after the first write to the ResponseWriter. If no Content-Type is set at that point it defaults to Content-Type: text/plain; charset=utf-8 which the browser can't parse since it needs the boundary which is given in the Content-Type header
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