git.go

     1  // Copyright 2017 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package vcweb
     6  
     7  import (
     8  	"log"
     9  	"net/http"
    10  	"net/http/cgi"
    11  	"os/exec"
    12  	"runtime"
    13  	"slices"
    14  	"sync"
    15  )
    16  
    17  type gitHandler struct {
    18  	once       sync.Once
    19  	gitPath    string
    20  	gitPathErr error
    21  }
    22  
    23  func (h *gitHandler) Available() bool {
    24  	if runtime.GOOS == "plan9" {
    25  		// The Git command is usually not the real Git on Plan 9.
    26  		// See https://golang.org/issues/29640.
    27  		return false
    28  	}
    29  	h.once.Do(func() {
    30  		h.gitPath, h.gitPathErr = exec.LookPath("git")
    31  	})
    32  	return h.gitPathErr == nil
    33  }
    34  
    35  func (h *gitHandler) Handler(dir string, env []string, logger *log.Logger) (http.Handler, error) {
    36  	if !h.Available() {
    37  		return nil, ServerNotInstalledError{name: "git"}
    38  	}
    39  
    40  	baseEnv := append(slices.Clip(env),
    41  		"GIT_PROJECT_ROOT="+dir,
    42  		"GIT_HTTP_EXPORT_ALL=1",
    43  	)
    44  
    45  	handler := http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
    46  		// The Git client sends the requested Git protocol version as a
    47  		// "Git-Protocol" HTTP request header, which the CGI host then converts
    48  		// to an environment variable (HTTP_GIT_PROTOCOL).
    49  		//
    50  		// However, versions of Git older that 2.34.0 don't recognize the
    51  		// HTTP_GIT_PROTOCOL variable, and instead need that value to be set in the
    52  		// GIT_PROTOCOL variable. We do so here so that vcweb can work reliably
    53  		// with older Git releases. (As of the time of writing, the Go project's
    54  		// builders were on Git version 2.30.2.)
    55  		env := slices.Clip(baseEnv)
    56  		if p := req.Header.Get("Git-Protocol"); p != "" {
    57  			env = append(env, "GIT_PROTOCOL="+p)
    58  		}
    59  
    60  		h := &cgi.Handler{
    61  			Path:   h.gitPath,
    62  			Logger: logger,
    63  			Args:   []string{"http-backend"},
    64  			Dir:    dir,
    65  			Env:    env,
    66  		}
    67  		h.ServeHTTP(w, req)
    68  	})
    69  
    70  	return handler, nil
    71  }
    72
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