1 files changed, 236 insertions, 0 deletions
diff --git a/src/cmd/go/internal/web/api.go b/src/cmd/go/internal/web/api.go
new file mode 100644
index 0000000..9053b16
--- /dev/null
+++ b/src/cmd/go/internal/web/api.go
@@ -0,0 +1,236 @@
+// Copyright 2017 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 web defines minimal helper routines for accessing HTTP/HTTPS
+// resources without requiring external dependencies on the net package.
+//
+// If the cmd_go_bootstrap build tag is present, web avoids the use of the net
+// package and returns errors for all network operations.
+package web
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"io/fs"
+	"net/url"
+	"strings"
+	"unicode"
+	"unicode/utf8"
+)
+
+// SecurityMode specifies whether a function should make network
+// calls using insecure transports (eg, plain text HTTP).
+// The zero value is "secure".
+type SecurityMode int
+
+const (
+	SecureOnly      SecurityMode = iota // Reject plain HTTP; validate HTTPS.
+	DefaultSecurity                     // Allow plain HTTP if explicit; validate HTTPS.
+	Insecure                            // Allow plain HTTP if not explicitly HTTPS; skip HTTPS validation.
+)
+
+// An HTTPError describes an HTTP error response (non-200 result).
+type HTTPError struct {
+	URL        string // redacted
+	Status     string
+	StatusCode int
+	Err        error  // underlying error, if known
+	Detail     string // limited to maxErrorDetailLines and maxErrorDetailBytes
+}
+
+const (
+	maxErrorDetailLines = 8
+	maxErrorDetailBytes = maxErrorDetailLines * 81
+)
+
+func (e *HTTPError) Error() string {
+	if e.Detail != "" {
+		detailSep := " "
+		if strings.ContainsRune(e.Detail, '\n') {
+			detailSep = "\n\t"
+		}
+		return fmt.Sprintf("reading %s: %v\n\tserver response:%s%s", e.URL, e.Status, detailSep, e.Detail)
+	}
+
+	if err := e.Err; err != nil {
+		if pErr, ok := e.Err.(*fs.PathError); ok && strings.HasSuffix(e.URL, pErr.Path) {
+			// Remove the redundant copy of the path.
+			err = pErr.Err
+		}
+		return fmt.Sprintf("reading %s: %v", e.URL, err)
+	}
+
+	return fmt.Sprintf("reading %s: %v", e.URL, e.Status)
+}
+
+func (e *HTTPError) Is(target error) bool {
+	return target == fs.ErrNotExist && (e.StatusCode == 404 || e.StatusCode == 410)
+}
+
+func (e *HTTPError) Unwrap() error {
+	return e.Err
+}
+
+// GetBytes returns the body of the requested resource, or an error if the
+// response status was not http.StatusOK.
+//
+// GetBytes is a convenience wrapper around Get and Response.Err.
+func GetBytes(u *url.URL) ([]byte, error) {
+	resp, err := Get(DefaultSecurity, u)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+	if err := resp.Err(); err != nil {
+		return nil, err
+	}
+	b, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return nil, fmt.Errorf("reading %s: %v", u.Redacted(), err)
+	}
+	return b, nil
+}
+
+type Response struct {
+	URL        string // redacted
+	Status     string
+	StatusCode int
+	Header     map[string][]string
+	Body       io.ReadCloser // Either the original body or &errorDetail.
+
+	fileErr     error
+	errorDetail errorDetailBuffer
+}
+
+// Err returns an *HTTPError corresponding to the response r.
+// If the response r has StatusCode 200 or 0 (unset), Err returns nil.
+// Otherwise, Err may read from r.Body in order to extract relevant error detail.
+func (r *Response) Err() error {
+	if r.StatusCode == 200 || r.StatusCode == 0 {
+		return nil
+	}
+
+	return &HTTPError{
+		URL:        r.URL,
+		Status:     r.Status,
+		StatusCode: r.StatusCode,
+		Err:        r.fileErr,
+		Detail:     r.formatErrorDetail(),
+	}
+}
+
+// formatErrorDetail converts r.errorDetail (a prefix of the output of r.Body)
+// into a short, tab-indented summary.
+func (r *Response) formatErrorDetail() string {
+	if r.Body != &r.errorDetail {
+		return "" // Error detail collection not enabled.
+	}
+
+	// Ensure that r.errorDetail has been populated.
+	_, _ = io.Copy(io.Discard, r.Body)
+
+	s := r.errorDetail.buf.String()
+	if !utf8.ValidString(s) {
+		return "" // Don't try to recover non-UTF-8 error messages.
+	}
+	for _, r := range s {
+		if !unicode.IsGraphic(r) && !unicode.IsSpace(r) {
+			return "" // Don't let the server do any funny business with the user's terminal.
+		}
+	}
+
+	var detail strings.Builder
+	for i, line := range strings.Split(s, "\n") {
+		if strings.TrimSpace(line) == "" {
+			break // Stop at the first blank line.
+		}
+		if i > 0 {
+			detail.WriteString("\n\t")
+		}
+		if i >= maxErrorDetailLines {
+			detail.WriteString("[Truncated: too many lines.]")
+			break
+		}
+		if detail.Len()+len(line) > maxErrorDetailBytes {
+			detail.WriteString("[Truncated: too long.]")
+			break
+		}
+		detail.WriteString(line)
+	}
+
+	return detail.String()
+}
+
+// Get returns the body of the HTTP or HTTPS resource specified at the given URL.
+//
+// If the URL does not include an explicit scheme, Get first tries "https".
+// If the server does not respond under that scheme and the security mode is
+// Insecure, Get then tries "http".
+// The URL included in the response indicates which scheme was actually used,
+// and it is a redacted URL suitable for use in error messages.
+//
+// For the "https" scheme only, credentials are attached using the
+// cmd/go/internal/auth package. If the URL itself includes a username and
+// password, it will not be attempted under the "http" scheme unless the
+// security mode is Insecure.
+//
+// Get returns a non-nil error only if the request did not receive a response
+// under any applicable scheme. (A non-2xx response does not cause an error.)
+func Get(security SecurityMode, u *url.URL) (*Response, error) {
+	return get(security, u)
+}
+
+// OpenBrowser attempts to open the requested URL in a web browser.
+func OpenBrowser(url string) (opened bool) {
+	return openBrowser(url)
+}
+
+// Join returns the result of adding the slash-separated
+// path elements to the end of u's path.
+func Join(u *url.URL, path string) *url.URL {
+	j := *u
+	if path == "" {
+		return &j
+	}
+	j.Path = strings.TrimSuffix(u.Path, "/") + "/" + strings.TrimPrefix(path, "/")
+	j.RawPath = strings.TrimSuffix(u.RawPath, "/") + "/" + strings.TrimPrefix(path, "/")
+	return &j
+}
+
+// An errorDetailBuffer is an io.ReadCloser that copies up to
+// maxErrorDetailLines into a buffer for later inspection.
+type errorDetailBuffer struct {
+	r        io.ReadCloser
+	buf      strings.Builder
+	bufLines int
+}
+
+func (b *errorDetailBuffer) Close() error {
+	return b.r.Close()
+}
+
+func (b *errorDetailBuffer) Read(p []byte) (n int, err error) {
+	n, err = b.r.Read(p)
+
+	// Copy the first maxErrorDetailLines+1 lines into b.buf,
+	// discarding any further lines.
+	//
+	// Note that the read may begin or end in the middle of a UTF-8 character,
+	// so don't try to do anything fancy with characters that encode to larger
+	// than one byte.
+	if b.bufLines <= maxErrorDetailLines {
+		for _, line := range bytes.SplitAfterN(p[:n], []byte("\n"), maxErrorDetailLines-b.bufLines) {
+			b.buf.Write(line)
+			if len(line) > 0 && line[len(line)-1] == '\n' {
+				b.bufLines++
+				if b.bufLines > maxErrorDetailLines {
+					break
+				}
+			}
+		}
+	}
+
+	return n, err
+}