discovery.go

     1  // Copyright 2012 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 vcs
     6  
     7  import (
     8  	"encoding/xml"
     9  	"fmt"
    10  	"io"
    11  	"strings"
    12  )
    13  
    14  // charsetReader returns a reader that converts from the given charset to UTF-8.
    15  // Currently it only supports UTF-8 and ASCII. Otherwise, it returns a meaningful
    16  // error which is printed by go get, so the user can find why the package
    17  // wasn't downloaded if the encoding is not supported. Note that, in
    18  // order to reduce potential errors, ASCII is treated as UTF-8 (i.e. characters
    19  // greater than 0x7f are not rejected).
    20  func charsetReader(charset string, input io.Reader) (io.Reader, error) {
    21  	switch strings.ToLower(charset) {
    22  	case "utf-8", "ascii":
    23  		return input, nil
    24  	default:
    25  		return nil, fmt.Errorf("can't decode XML document using charset %q", charset)
    26  	}
    27  }
    28  
    29  // parseMetaGoImports returns meta imports from the HTML in r.
    30  // Parsing ends at the end of the <head> section or the beginning of the <body>.
    31  func parseMetaGoImports(r io.Reader, mod ModuleMode) ([]metaImport, error) {
    32  	d := xml.NewDecoder(r)
    33  	d.CharsetReader = charsetReader
    34  	d.Strict = false
    35  	var imports []metaImport
    36  	for {
    37  		t, err := d.RawToken()
    38  		if err != nil {
    39  			if err != io.EOF && len(imports) == 0 {
    40  				return nil, err
    41  			}
    42  			break
    43  		}
    44  		if e, ok := t.(xml.StartElement); ok && strings.EqualFold(e.Name.Local, "body") {
    45  			break
    46  		}
    47  		if e, ok := t.(xml.EndElement); ok && strings.EqualFold(e.Name.Local, "head") {
    48  			break
    49  		}
    50  		e, ok := t.(xml.StartElement)
    51  		if !ok || !strings.EqualFold(e.Name.Local, "meta") {
    52  			continue
    53  		}
    54  		if attrValue(e.Attr, "name") != "go-import" {
    55  			continue
    56  		}
    57  		if f := strings.Fields(attrValue(e.Attr, "content")); len(f) == 3 {
    58  			imports = append(imports, metaImport{
    59  				Prefix:   f[0],
    60  				VCS:      f[1],
    61  				RepoRoot: f[2],
    62  			})
    63  		}
    64  	}
    65  
    66  	// Extract mod entries if we are paying attention to them.
    67  	var list []metaImport
    68  	var have map[string]bool
    69  	if mod == PreferMod {
    70  		have = make(map[string]bool)
    71  		for _, m := range imports {
    72  			if m.VCS == "mod" {
    73  				have[m.Prefix] = true
    74  				list = append(list, m)
    75  			}
    76  		}
    77  	}
    78  
    79  	// Append non-mod entries, ignoring those superseded by a mod entry.
    80  	for _, m := range imports {
    81  		if m.VCS != "mod" && !have[m.Prefix] {
    82  			list = append(list, m)
    83  		}
    84  	}
    85  	return list, nil
    86  }
    87  
    88  // attrValue returns the attribute value for the case-insensitive key
    89  // `name`, or the empty string if nothing is found.
    90  func attrValue(attrs []xml.Attr, name string) string {
    91  	for _, a := range attrs {
    92  		if strings.EqualFold(a.Name.Local, name) {
    93  			return a.Value
    94  		}
    95  	}
    96  	return ""
    97  }
    98
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