1 files changed, 448 insertions, 0 deletions
diff --git a/src/cmd/go/internal/modfetch/proxy.go b/src/cmd/go/internal/modfetch/proxy.go
new file mode 100644
index 0000000..d237468
--- /dev/null
+++ b/src/cmd/go/internal/modfetch/proxy.go
@@ -0,0 +1,448 @@
+// Copyright 2018 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.
+
+package modfetch
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"io/fs"
+	"net/url"
+	"path"
+	pathpkg "path"
+	"path/filepath"
+	"strings"
+	"sync"
+	"time"
+
+	"cmd/go/internal/base"
+	"cmd/go/internal/cfg"
+	"cmd/go/internal/modfetch/codehost"
+	"cmd/go/internal/web"
+
+	"golang.org/x/mod/module"
+	"golang.org/x/mod/semver"
+)
+
+var HelpGoproxy = &base.Command{
+	UsageLine: "goproxy",
+	Short:     "module proxy protocol",
+	Long: `
+A Go module proxy is any web server that can respond to GET requests for
+URLs of a specified form. The requests have no query parameters, so even
+a site serving from a fixed file system (including a file:/// URL)
+can be a module proxy.
+
+For details on the GOPROXY protocol, see
+https://golang.org/ref/mod#goproxy-protocol.
+`,
+}
+
+var proxyOnce struct {
+	sync.Once
+	list []proxySpec
+	err  error
+}
+
+type proxySpec struct {
+	// url is the proxy URL or one of "off", "direct", "noproxy".
+	url string
+
+	// fallBackOnError is true if a request should be attempted on the next proxy
+	// in the list after any error from this proxy. If fallBackOnError is false,
+	// the request will only be attempted on the next proxy if the error is
+	// equivalent to os.ErrNotFound, which is true for 404 and 410 responses.
+	fallBackOnError bool
+}
+
+func proxyList() ([]proxySpec, error) {
+	proxyOnce.Do(func() {
+		if cfg.GONOPROXY != "" && cfg.GOPROXY != "direct" {
+			proxyOnce.list = append(proxyOnce.list, proxySpec{url: "noproxy"})
+		}
+
+		goproxy := cfg.GOPROXY
+		for goproxy != "" {
+			var url string
+			fallBackOnError := false
+			if i := strings.IndexAny(goproxy, ",|"); i >= 0 {
+				url = goproxy[:i]
+				fallBackOnError = goproxy[i] == '|'
+				goproxy = goproxy[i+1:]
+			} else {
+				url = goproxy
+				goproxy = ""
+			}
+
+			url = strings.TrimSpace(url)
+			if url == "" {
+				continue
+			}
+			if url == "off" {
+				// "off" always fails hard, so can stop walking list.
+				proxyOnce.list = append(proxyOnce.list, proxySpec{url: "off"})
+				break
+			}
+			if url == "direct" {
+				proxyOnce.list = append(proxyOnce.list, proxySpec{url: "direct"})
+				// For now, "direct" is the end of the line. We may decide to add some
+				// sort of fallback behavior for them in the future, so ignore
+				// subsequent entries for forward-compatibility.
+				break
+			}
+
+			// Single-word tokens are reserved for built-in behaviors, and anything
+			// containing the string ":/" or matching an absolute file path must be a
+			// complete URL. For all other paths, implicitly add "https://".
+			if strings.ContainsAny(url, ".:/") && !strings.Contains(url, ":/") && !filepath.IsAbs(url) && !path.IsAbs(url) {
+				url = "https://" + url
+			}
+
+			// Check that newProxyRepo accepts the URL.
+			// It won't do anything with the path.
+			if _, err := newProxyRepo(url, "golang.org/x/text"); err != nil {
+				proxyOnce.err = err
+				return
+			}
+
+			proxyOnce.list = append(proxyOnce.list, proxySpec{
+				url:             url,
+				fallBackOnError: fallBackOnError,
+			})
+		}
+
+		if len(proxyOnce.list) == 0 ||
+			len(proxyOnce.list) == 1 && proxyOnce.list[0].url == "noproxy" {
+			// There were no proxies, other than the implicit "noproxy" added when
+			// GONOPROXY is set. This can happen if GOPROXY is a non-empty string
+			// like "," or " ".
+			proxyOnce.err = fmt.Errorf("GOPROXY list is not the empty string, but contains no entries")
+		}
+	})
+
+	return proxyOnce.list, proxyOnce.err
+}
+
+// TryProxies iterates f over each configured proxy (including "noproxy" and
+// "direct" if applicable) until f returns no error or until f returns an
+// error that is not equivalent to fs.ErrNotExist on a proxy configured
+// not to fall back on errors.
+//
+// TryProxies then returns that final error.
+//
+// If GOPROXY is set to "off", TryProxies invokes f once with the argument
+// "off".
+func TryProxies(f func(proxy string) error) error {
+	proxies, err := proxyList()
+	if err != nil {
+		return err
+	}
+	if len(proxies) == 0 {
+		panic("GOPROXY list is empty")
+	}
+
+	// We try to report the most helpful error to the user. "direct" and "noproxy"
+	// errors are best, followed by proxy errors other than ErrNotExist, followed
+	// by ErrNotExist.
+	//
+	// Note that errProxyOff, errNoproxy, and errUseProxy are equivalent to
+	// ErrNotExist. errUseProxy should only be returned if "noproxy" is the only
+	// proxy. errNoproxy should never be returned, since there should always be a
+	// more useful error from "noproxy" first.
+	const (
+		notExistRank = iota
+		proxyRank
+		directRank
+	)
+	var bestErr error
+	bestErrRank := notExistRank
+	for _, proxy := range proxies {
+		err := f(proxy.url)
+		if err == nil {
+			return nil
+		}
+		isNotExistErr := errors.Is(err, fs.ErrNotExist)
+
+		if proxy.url == "direct" || (proxy.url == "noproxy" && err != errUseProxy) {
+			bestErr = err
+			bestErrRank = directRank
+		} else if bestErrRank <= proxyRank && !isNotExistErr {
+			bestErr = err
+			bestErrRank = proxyRank
+		} else if bestErrRank == notExistRank {
+			bestErr = err
+		}
+
+		if !proxy.fallBackOnError && !isNotExistErr {
+			break
+		}
+	}
+	return bestErr
+}
+
+type proxyRepo struct {
+	url         *url.URL
+	path        string
+	redactedURL string
+
+	listLatestOnce sync.Once
+	listLatest     *RevInfo
+	listLatestErr  error
+}
+
+func newProxyRepo(baseURL, path string) (Repo, error) {
+	base, err := url.Parse(baseURL)
+	if err != nil {
+		return nil, err
+	}
+	switch base.Scheme {
+	case "http", "https":
+		// ok
+	case "file":
+		if *base != (url.URL{Scheme: base.Scheme, Path: base.Path, RawPath: base.RawPath}) {
+			return nil, fmt.Errorf("invalid file:// proxy URL with non-path elements: %s", base.Redacted())
+		}
+	case "":
+		return nil, fmt.Errorf("invalid proxy URL missing scheme: %s", base.Redacted())
+	default:
+		return nil, fmt.Errorf("invalid proxy URL scheme (must be https, http, file): %s", base.Redacted())
+	}
+
+	enc, err := module.EscapePath(path)
+	if err != nil {
+		return nil, err
+	}
+	redactedURL := base.Redacted()
+	base.Path = strings.TrimSuffix(base.Path, "/") + "/" + enc
+	base.RawPath = strings.TrimSuffix(base.RawPath, "/") + "/" + pathEscape(enc)
+	return &proxyRepo{base, path, redactedURL, sync.Once{}, nil, nil}, nil
+}
+
+func (p *proxyRepo) ModulePath() string {
+	return p.path
+}
+
+var errProxyReuse = fmt.Errorf("proxy does not support CheckReuse")
+
+func (p *proxyRepo) CheckReuse(old *codehost.Origin) error {
+	return errProxyReuse
+}
+
+// versionError returns err wrapped in a ModuleError for p.path.
+func (p *proxyRepo) versionError(version string, err error) error {
+	if version != "" && version != module.CanonicalVersion(version) {
+		return &module.ModuleError{
+			Path: p.path,
+			Err: &module.InvalidVersionError{
+				Version: version,
+				Pseudo:  module.IsPseudoVersion(version),
+				Err:     err,
+			},
+		}
+	}
+
+	return &module.ModuleError{
+		Path:    p.path,
+		Version: version,
+		Err:     err,
+	}
+}
+
+func (p *proxyRepo) getBytes(path string) ([]byte, error) {
+	body, err := p.getBody(path)
+	if err != nil {
+		return nil, err
+	}
+	defer body.Close()
+
+	b, err := io.ReadAll(body)
+	if err != nil {
+		// net/http doesn't add context to Body errors, so add it here.
+		// (See https://go.dev/issue/52727.)
+		return b, &url.Error{Op: "read", URL: pathpkg.Join(p.redactedURL, path), Err: err}
+	}
+	return b, nil
+}
+
+func (p *proxyRepo) getBody(path string) (r io.ReadCloser, err error) {
+	fullPath := pathpkg.Join(p.url.Path, path)
+
+	target := *p.url
+	target.Path = fullPath
+	target.RawPath = pathpkg.Join(target.RawPath, pathEscape(path))
+
+	resp, err := web.Get(web.DefaultSecurity, &target)
+	if err != nil {
+		return nil, err
+	}
+	if err := resp.Err(); err != nil {
+		resp.Body.Close()
+		return nil, err
+	}
+	return resp.Body, nil
+}
+
+func (p *proxyRepo) Versions(prefix string) (*Versions, error) {
+	data, err := p.getBytes("@v/list")
+	if err != nil {
+		p.listLatestOnce.Do(func() {
+			p.listLatest, p.listLatestErr = nil, p.versionError("", err)
+		})
+		return nil, p.versionError("", err)
+	}
+	var list []string
+	allLine := strings.Split(string(data), "\n")
+	for _, line := range allLine {
+		f := strings.Fields(line)
+		if len(f) >= 1 && semver.IsValid(f[0]) && strings.HasPrefix(f[0], prefix) && !module.IsPseudoVersion(f[0]) {
+			list = append(list, f[0])
+		}
+	}
+	p.listLatestOnce.Do(func() {
+		p.listLatest, p.listLatestErr = p.latestFromList(allLine)
+	})
+	semver.Sort(list)
+	return &Versions{List: list}, nil
+}
+
+func (p *proxyRepo) latest() (*RevInfo, error) {
+	p.listLatestOnce.Do(func() {
+		data, err := p.getBytes("@v/list")
+		if err != nil {
+			p.listLatestErr = p.versionError("", err)
+			return
+		}
+		list := strings.Split(string(data), "\n")
+		p.listLatest, p.listLatestErr = p.latestFromList(list)
+	})
+	return p.listLatest, p.listLatestErr
+}
+
+func (p *proxyRepo) latestFromList(allLine []string) (*RevInfo, error) {
+	var (
+		bestTime    time.Time
+		bestVersion string
+	)
+	for _, line := range allLine {
+		f := strings.Fields(line)
+		if len(f) >= 1 && semver.IsValid(f[0]) {
+			// If the proxy includes timestamps, prefer the timestamp it reports.
+			// Otherwise, derive the timestamp from the pseudo-version.
+			var (
+				ft time.Time
+			)
+			if len(f) >= 2 {
+				ft, _ = time.Parse(time.RFC3339, f[1])
+			} else if module.IsPseudoVersion(f[0]) {
+				ft, _ = module.PseudoVersionTime(f[0])
+			} else {
+				// Repo.Latest promises that this method is only called where there are
+				// no tagged versions. Ignore any tagged versions that were added in the
+				// meantime.
+				continue
+			}
+			if bestTime.Before(ft) {
+				bestTime = ft
+				bestVersion = f[0]
+			}
+		}
+	}
+	if bestVersion == "" {
+		return nil, p.versionError("", codehost.ErrNoCommits)
+	}
+
+	// Call Stat to get all the other fields, including Origin information.
+	return p.Stat(bestVersion)
+}
+
+func (p *proxyRepo) Stat(rev string) (*RevInfo, error) {
+	encRev, err := module.EscapeVersion(rev)
+	if err != nil {
+		return nil, p.versionError(rev, err)
+	}
+	data, err := p.getBytes("@v/" + encRev + ".info")
+	if err != nil {
+		return nil, p.versionError(rev, err)
+	}
+	info := new(RevInfo)
+	if err := json.Unmarshal(data, info); err != nil {
+		return nil, p.versionError(rev, fmt.Errorf("invalid response from proxy %q: %w", p.redactedURL, err))
+	}
+	if info.Version != rev && rev == module.CanonicalVersion(rev) && module.Check(p.path, rev) == nil {
+		// If we request a correct, appropriate version for the module path, the
+		// proxy must return either exactly that version or an error — not some
+		// arbitrary other version.
+		return nil, p.versionError(rev, fmt.Errorf("proxy returned info for version %s instead of requested version", info.Version))
+	}
+	return info, nil
+}
+
+func (p *proxyRepo) Latest() (*RevInfo, error) {
+	data, err := p.getBytes("@latest")
+	if err != nil {
+		if !errors.Is(err, fs.ErrNotExist) {
+			return nil, p.versionError("", err)
+		}
+		return p.latest()
+	}
+	info := new(RevInfo)
+	if err := json.Unmarshal(data, info); err != nil {
+		return nil, p.versionError("", fmt.Errorf("invalid response from proxy %q: %w", p.redactedURL, err))
+	}
+	return info, nil
+}
+
+func (p *proxyRepo) GoMod(version string) ([]byte, error) {
+	if version != module.CanonicalVersion(version) {
+		return nil, p.versionError(version, fmt.Errorf("internal error: version passed to GoMod is not canonical"))
+	}
+
+	encVer, err := module.EscapeVersion(version)
+	if err != nil {
+		return nil, p.versionError(version, err)
+	}
+	data, err := p.getBytes("@v/" + encVer + ".mod")
+	if err != nil {
+		return nil, p.versionError(version, err)
+	}
+	return data, nil
+}
+
+func (p *proxyRepo) Zip(dst io.Writer, version string) error {
+	if version != module.CanonicalVersion(version) {
+		return p.versionError(version, fmt.Errorf("internal error: version passed to Zip is not canonical"))
+	}
+
+	encVer, err := module.EscapeVersion(version)
+	if err != nil {
+		return p.versionError(version, err)
+	}
+	path := "@v/" + encVer + ".zip"
+	body, err := p.getBody(path)
+	if err != nil {
+		return p.versionError(version, err)
+	}
+	defer body.Close()
+
+	lr := &io.LimitedReader{R: body, N: codehost.MaxZipFile + 1}
+	if _, err := io.Copy(dst, lr); err != nil {
+		// net/http doesn't add context to Body errors, so add it here.
+		// (See https://go.dev/issue/52727.)
+		err = &url.Error{Op: "read", URL: pathpkg.Join(p.redactedURL, path), Err: err}
+		return p.versionError(version, err)
+	}
+	if lr.N <= 0 {
+		return p.versionError(version, fmt.Errorf("downloaded zip file too large"))
+	}
+	return nil
+}
+
+// pathEscape escapes s so it can be used in a path.
+// That is, it escapes things like ? and # (which really shouldn't appear anyway).
+// It does not escape / to %2F: our REST API is designed so that / can be left as is.
+func pathEscape(s string) string {
+	return strings.ReplaceAll(url.PathEscape(s), "%2F", "/")
+}