net/http: FileServer is sending 304 even if it is running in a different directory

[averms]

Go version

go version go1.24.3 linux/amd64

Output of go env in your module/workspace:

AR='ar'
CC='cc'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='c++'
GCCGO='gccgo'
GO111MODULE=''
GOAMD64='v1'
GOARCH='amd64'
GOAUTH='netrc'
GOBIN=''
GOCACHE='/var/home/anon/.cache/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/var/home/anon/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build3141057410=/tmp/go-build -gno-record-gcc-switches'
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMOD='/dev/null'
GOMODCACHE='/var/home/anon/.local/share/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/var/home/anon/.local/share/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/var/home/linuxbrew/.linuxbrew/Cellar/go/1.24.3/libexec'
GOSUMDB='sum.golang.org'
GOTELEMETRY='off'
GOTELEMETRYDIR='/var/home/anon/.config/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/var/home/linuxbrew/.linuxbrew/Cellar/go/1.24.3/libexec/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.24.3'
GOWORK=''
PKG_CONFIG='pkg-config'

What did you do?

This is just #42051. Re-reported because I think it was incorrectly closed.

The program is still:

package main

import (
	"flag"
	"fmt"
	"log"
	"net/http"
	"os"
	"strconv"
)

func main() {
	port := flag.Int("p", 8000, "port number")
	dir := flag.String("d", ".", "directory path")
	flag.Parse()

	fi, err := os.Stat(*dir)
	if err != nil {
		log.Fatal(err)
	}
	if !fi.IsDir() {
		log.Fatal(fmt.Errorf("%s isn't a directory\n", *dir))
	}

	addr := ":" + strconv.Itoa(*port)
	handler := http.FileServer(http.Dir(*dir))

	fmt.Printf("serving %s on http://localhost:%d\n", *dir, *port)
	log.Fatal(http.ListenAndServe(addr, handler))
}

1. Run the program in directory A.
2. Navigate to localhost:8000 in Chrome or Firefox.
3. A directory listing for directory A is shown.
4. Now terminate the program and reopen it in directory B
5. Refresh the page in Chrome or Firefox.
6. The directory listing for directory A is still shown.

I believe this has something to do with the interaction between the Last-Modified response and If-Modified-Since request headers.

I have tested this on Firefox and Chrome on both Linux and macOS.

What did you see happen?

The content of the directory where the server was previously running and status code 304

What did you expect to see?

The current directory listing

[gabyhelp]

Related Issues

• net/http: Server is sending 304 even if it is running in a different directory #42051 (closed)
• net/http: Last-Modified header did not correctly check the time #66807 (closed)
• net/http: http.FileServer goes into infinite redirect loop when root is a file #63769 (closed)
• net/http: FileServer returns 304 Not Modified on modified index pages #3414 (closed)
• net/http: FileServer no longer serves content for POST #59375 (closed)
• net/http: 301 instead of 404 for unmatched requests #65624 (closed)
• net/http: http.FileServer returns 500 when a null byte is passed in the URL #72091 (closed)
• net/http: FileServer responds with 500 status when syscall.ENOTDIR is returned from fs.Open #18984 (closed)

Related Code Changes

• net/http: fix infinite 301 redirects of http.FileServe

Related Discussions

• http.fileserver not refreshing properly

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[seankhliao]

FileServer uses the directory's modtime as the Last-Modified date.
Given the current behaviour is mostly reasonable (use unique URIs for unique resources), I don't think much will change unless #60940 is implemented.