1 files changed, 222 insertions, 0 deletions
diff --git a/src/net/http/cgi/child.go b/src/net/http/cgi/child.go
new file mode 100644
index 0000000..e29fe20
--- /dev/null
+++ b/src/net/http/cgi/child.go
@@ -0,0 +1,222 @@
+// 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()
+}