Add unaltered lowercase headers to golang http request

Question

I am trying to set all-lowercase headers in a golang program and CanonicalMIMEHeaderKey is uppercasing the first letter. The API I am consuming only takes this particular header in all-lowercase at the moment. It's not an option to change that at this point in time. Is there a way to override that?

http://golang.org/pkg/net/textproto/#CanonicalMIMEHeaderKey

So for example, the header I want to add is:

req.Header.Add("myheader", "myheadervalue")

But it comes out as:

req.Header.Add("Myheader", "myheadervalue")

Can anyone help please?

Thanks

Apparently the OP got an answer that solved their problem, but there are cases where httputil simply won't allow you to control the case (ReverseProxy). The rationale that I have seen is that HTTP/2 requires lowercase -- therefore, they needn't bother letting you control this in HTTP/1 either. — Brent Bradburn
– Brent Bradburn, Commented Nov 24, 2019 at 16:36

nemo · Accepted Answer · 2014-07-25 00:04:26Z

12

I do not see a way to circumvent this but if you really have to use lower-case header names, then you can work around this by creating your own http.Header with lower-case keys. Example (on play):

import "fmt"
import "strings"
import "net/http"

// ...

req, _ := http.NewRequest("GET", "http://foo", nil) 
req.Header.Add("myheader", "myheadervalue")

lowerCaseHeader := make(http.Header)

for key, value := range req.Header {
    lowerCaseHeader[strings.ToLower(key)] = value
}

req.Header = lowerCaseHeader

answered Jul 25, 2014 at 0:04

nemo

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rclod · Accepted Answer · 2016-03-17 21:15:36Z

I ran into a similar problem and solved it a slightly different way that I thought might be helpful for others coming to this post in the future...

Since http.Header is just a map[string][]string under the hood, you can create an http.Header then assign it to the request's header. Because this does not use the Add nor the Set method, this will preserve casing.

Like so:

import "net/http"

// ...

headers := http.Header{
            "my-lowercase-header": []string{"myvalue1"},
            "Accept": []string{"text/plain", "text/html"},
        }

client := &http.Client{}

req, err := http.NewRequest("GET", "http://www.example.com", nil)
if err != nil {
    panic(err)
}

req.Header = headers

resp, err := client.Do(req)

diño · Accepted Answer · 2020-05-20 04:45:43Z

4

There is another easy way to do it.

req.Header["myheader"] = []string{"myheadervalue"}

edited May 20, 2020 at 4:45

diño

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answered Dec 10, 2018 at 23:56

Sreenidhi Sreesha

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