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// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// This file implements CGI from the perspective of a child
// process.
package cgi
import (
"bufio"
"crypto/tls"
"errors"
"fmt"
"io"
"net"
"net/http"
"net/url"
"os"
"strconv"
"strings"
)
// Request returns the HTTP request as represented in the current
// environment. This assumes the current program is being run
// by a web server in a CGI environment.
// The returned Request's Body is populated, if applicable.
func Request() (*http.Request, error) {
r, err := RequestFromMap(envMap(os.Environ()))
if err != nil {
return nil, err
}
if r.ContentLength > 0 {
r.Body = io.NopCloser(io.LimitReader(os.Stdin, r.ContentLength))
}
return r, nil
}
func envMap(env []string) map[string]string {
m := make(map[string]string)
for _, kv := range env {
if k, v, ok := strings.Cut(kv, "="); ok {
m[k] = v
}
}
return m
}
// RequestFromMap creates an http.Request from CGI variables.
// The returned Request's Body field is not populated.
func RequestFromMap(params map[string]string) (*http.Request, error) {
r := new(http.Request)
r.Method = params["REQUEST_METHOD"]
if r.Method == "" {
return nil, errors.New("cgi: no REQUEST_METHOD in environment")
}
r.Proto = params["SERVER_PROTOCOL"]
var ok bool
r.ProtoMajor, r.ProtoMinor, ok = http.ParseHTTPVersion(r.Proto)
if !ok {
return nil, errors.New("cgi: invalid SERVER_PROTOCOL version")
}
r.Close = true
r.Trailer = http.Header{}
r.Header = http.Header{}
r.Host = params["HTTP_HOST"]
if lenstr := params["CONTENT_LENGTH"]; lenstr != "" {
clen, err := strconv.ParseInt(lenstr, 10, 64)
if err != nil {
return nil, errors.New("cgi: bad CONTENT_LENGTH in environment: " + lenstr)
}
r.ContentLength = clen
}
if ct := params["CONTENT_TYPE"]; ct != "" {
r.Header.Set("Content-Type", ct)
}
// Copy "HTTP_FOO_BAR" variables to "Foo-Bar" Headers
for k, v := range params {
if k == "HTTP_HOST" {
continue
}
if after, found := strings.CutPrefix(k, "HTTP_"); found {
r.Header.Add(strings.ReplaceAll(after, "_", "-"), v)
}
}
uriStr := params["REQUEST_URI"]
if uriStr == "" {
// Fallback to SCRIPT_NAME, PATH_INFO and QUERY_STRING.
uriStr = params["SCRIPT_NAME"] + params["PATH_INFO"]
s := params["QUERY_STRING"]
if s != "" {
uriStr += "?" + s
}
}
// There's apparently a de-facto standard for this.
// https://web.archive.org/web/20170105004655/http://docstore.mik.ua/orelly/linux/cgi/ch03_02.htm#ch03-35636
if s := params["HTTPS"]; s == "on" || s == "ON" || s == "1" {
r.TLS = &tls.ConnectionState{HandshakeComplete: true}
}
if r.Host != "" {
// Hostname is provided, so we can reasonably construct a URL.
rawurl := r.Host + uriStr
if r.TLS == nil {
rawurl = "http://" + rawurl
} else {
rawurl = "https://" + rawurl
}
url, err := url.Parse(rawurl)
if err != nil {
return nil, errors.New("cgi: failed to parse host and REQUEST_URI into a URL: " + rawurl)
}
r.URL = url
}
// Fallback logic if we don't have a Host header or the URL
// failed to parse
if r.URL == nil {
url, err := url.Parse(uriStr)
if err != nil {
return nil, errors.New("cgi: failed to parse REQUEST_URI into a URL: " + uriStr)
}
r.URL = url
}
// Request.RemoteAddr has its port set by Go's standard http
// server, so we do here too.
remotePort, _ := strconv.Atoi(params["REMOTE_PORT"]) // zero if unset or invalid
r.RemoteAddr = net.JoinHostPort(params["REMOTE_ADDR"], strconv.Itoa(remotePort))
return r, nil
}
// Serve executes the provided Handler on the currently active CGI
// request, if any. If there's no current CGI environment
// an error is returned. The provided handler may be nil to use
// http.DefaultServeMux.
func Serve(handler http.Handler) error {
req, err := Request()
if err != nil {
return err
}
if req.Body == nil {
req.Body = http.NoBody
}
if handler == nil {
handler = http.DefaultServeMux
}
rw := &response{
req: req,
header: make(http.Header),
bufw: bufio.NewWriter(os.Stdout),
}
handler.ServeHTTP(rw, req)
rw.Write(nil) // make sure a response is sent
if err = rw.bufw.Flush(); err != nil {
return err
}
return nil
}
type response struct {
req *http.Request
header http.Header
code int
wroteHeader bool
wroteCGIHeader bool
bufw *bufio.Writer
}
func (r *response) Flush() {
r.bufw.Flush()
}
func (r *response) Header() http.Header {
return r.header
}
func (r *response) Write(p []byte) (n int, err error) {
if !r.wroteHeader {
r.WriteHeader(http.StatusOK)
}
if !r.wroteCGIHeader {
r.writeCGIHeader(p)
}
return r.bufw.Write(p)
}
func (r *response) WriteHeader(code int) {
if r.wroteHeader {
// Note: explicitly using Stderr, as Stdout is our HTTP output.
fmt.Fprintf(os.Stderr, "CGI attempted to write header twice on request for %s", r.req.URL)
return
}
r.wroteHeader = true
r.code = code
}
// writeCGIHeader finalizes the header sent to the client and writes it to the output.
// p is not written by writeHeader, but is the first chunk of the body
// that will be written. It is sniffed for a Content-Type if none is
// set explicitly.
func (r *response) writeCGIHeader(p []byte) {
if r.wroteCGIHeader {
return
}
r.wroteCGIHeader = true
fmt.Fprintf(r.bufw, "Status: %d %s\r\n", r.code, http.StatusText(r.code))
if _, hasType := r.header["Content-Type"]; !hasType {
r.header.Set("Content-Type", http.DetectContentType(p))
}
r.header.Write(r.bufw)
r.bufw.WriteString("\r\n")
r.bufw.Flush()
}
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