1 files changed, 97 insertions, 0 deletions
diff --git a/src/cmd/go/internal/vcs/discovery.go b/src/cmd/go/internal/vcs/discovery.go
new file mode 100644
index 0000000000..327b44cb9a
--- /dev/null
+++ b/src/cmd/go/internal/vcs/discovery.go
@@ -0,0 +1,97 @@
+// Copyright 2012 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 vcs
+
+import (
+	"encoding/xml"
+	"fmt"
+	"io"
+	"strings"
+)
+
+// charsetReader returns a reader that converts from the given charset to UTF-8.
+// Currently it only supports UTF-8 and ASCII. Otherwise, it returns a meaningful
+// error which is printed by go get, so the user can find why the package
+// wasn't downloaded if the encoding is not supported. Note that, in
+// order to reduce potential errors, ASCII is treated as UTF-8 (i.e. characters
+// greater than 0x7f are not rejected).
+func charsetReader(charset string, input io.Reader) (io.Reader, error) {
+	switch strings.ToLower(charset) {
+	case "utf-8", "ascii":
+		return input, nil
+	default:
+		return nil, fmt.Errorf("can't decode XML document using charset %q", charset)
+	}
+}
+
+// parseMetaGoImports returns meta imports from the HTML in r.
+// Parsing ends at the end of the <head> section or the beginning of the <body>.
+func parseMetaGoImports(r io.Reader, mod ModuleMode) ([]metaImport, error) {
+	d := xml.NewDecoder(r)
+	d.CharsetReader = charsetReader
+	d.Strict = false
+	var imports []metaImport
+	for {
+		t, err := d.RawToken()
+		if err != nil {
+			if err != io.EOF && len(imports) == 0 {
+				return nil, err
+			}
+			break
+		}
+		if e, ok := t.(xml.StartElement); ok && strings.EqualFold(e.Name.Local, "body") {
+			break
+		}
+		if e, ok := t.(xml.EndElement); ok && strings.EqualFold(e.Name.Local, "head") {
+			break
+		}
+		e, ok := t.(xml.StartElement)
+		if !ok || !strings.EqualFold(e.Name.Local, "meta") {
+			continue
+		}
+		if attrValue(e.Attr, "name") != "go-import" {
+			continue
+		}
+		if f := strings.Fields(attrValue(e.Attr, "content")); len(f) == 3 {
+			imports = append(imports, metaImport{
+				Prefix:   f[0],
+				VCS:      f[1],
+				RepoRoot: f[2],
+			})
+		}
+	}
+
+	// Extract mod entries if we are paying attention to them.
+	var list []metaImport
+	var have map[string]bool
+	if mod == PreferMod {
+		have = make(map[string]bool)
+		for _, m := range imports {
+			if m.VCS == "mod" {
+				have[m.Prefix] = true
+				list = append(list, m)
+			}
+		}
+	}
+
+	// Append non-mod entries, ignoring those superseded by a mod entry.
+	for _, m := range imports {
+		if m.VCS != "mod" && !have[m.Prefix] {
+			list = append(list, m)
+		}
+	}
+	return list, nil
+}
+
+// attrValue returns the attribute value for the case-insensitive key
+// `name', or the empty string if nothing is found.
+func attrValue(attrs []xml.Attr, name string) string {
+	for _, a := range attrs {
+		if strings.EqualFold(a.Name.Local, name) {
+			return a.Value
+		}
+	}
+	return ""
+}