Missing header Content-Length in output of head handler #781
Description
Issue Summary
I created a simple HEAD handler using the Humago adapter that should return two headers: Content-Length and Last-Modified. However, when I make a HEAD request, only the Last-Modified header appears, while Content-Length is missing.
Code Example
Below is the complete code to reproduce the issue:
package main
import (
"context"
"fmt"
"github.com/danielgtaylor/huma/v2/adapters/humago"
"log"
"net/http"
"os"
"time"
"github.com/danielgtaylor/huma/v2"
)
func main() {
// Create a new API instance with a title and version.
mux := http.NewServeMux()
api := humago.New(mux, huma.DefaultConfig("Siben", "1.0.0"))
// Register a HEAD endpoint at /files.
huma.Head(api, "/files/{path...}", headHandler)
// Start the server on port 8080.
log.Fatal(http.ListenAndServe(":8080", mux))
}
// HeadInput represents the input for the HEAD request.
type HeadInput struct {
Path string `path:"path"`
}
// HeadOutput represents the headers returned by the HEAD request.
type HeadOutput struct {
ContentLength int64 `header:"Content-Length"`
LastModified string `header:"Last-Modified"`
}
func headHandler(ctx context.Context, in *HeadInput) (*HeadOutput, error) {
// Open the file and retrieve file information.
file, err := os.Open(in.Path)
if err != nil {
return nil, fmt.Errorf("failed to open file: %w", err)
}
stat, err := file.Stat()
if err != nil {
return nil, fmt.Errorf("failed to get file stat: %w", err)
}
return &HeadOutput{
ContentLength: stat.Size(),
LastModified: stat.ModTime().Format(time.RFC3339),
}, nil
}Observed Behavior
When making a HEAD request (using curl -I), the response only includes the Last-Modified header:
└──╼ $ curl -I localhost:8080/files/custom-gcl
HTTP/1.1 204 No Content
Last-Modified: 2025-03-29T09:26:21+01:00
Date: Sat, 29 Mar 2025 12:32:22 GMTWorkaround
If I modify the model to use custom header names (e.g., prefixing with Custom-), both headers are returned as expected:
type HeadOutput struct {
ContentLength int64 `header:"Custom-Content-Length"`
LastModified string `header:"Custom-Last-Modified"`
}With this change, the response becomes:
└──╼ $ curl -I localhost:8080/files/custom-gcl
HTTP/1.1 204 No Content
Custom-Content-Length: 45213664
Custom-Last-Modified: 2025-03-29T09:26:21+01:00
Date: Sat, 29 Mar 2025 12:32:57 GMTRequest for Assistance
I have searched the code but have not found the cause of this behavior. Could someone help me understand why the Content-Length header is omitted unless a custom prefix is used? Once clarified, I'll raise a PR with the proposed fix.