github.com/kubiko/snapd@v0.0.0-20201013125620-d4f3094d9ddf/bootloader/assets/assets.go (about)

     1  // -*- Mode: Go; indent-tabs-mode: t -*-
     2  
     3  /*
     4   * Copyright (C) 2020 Canonical Ltd
     5   *
     6   * This program is free software: you can redistribute it and/or modify
     7   * it under the terms of the GNU General Public License version 3 as
     8   * published by the Free Software Foundation.
     9   *
    10   * This program is distributed in the hope that it will be useful,
    11   * but WITHOUT ANY WARRANTY; without even the implied warranty of
    12   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    13   * GNU General Public License for more details.
    14   *
    15   * You should have received a copy of the GNU General Public License
    16   * along with this program.  If not, see <http://www.gnu.org/licenses/>.
    17   *
    18   */
    19  
    20  package assets
    21  
    22  import (
    23  	"fmt"
    24  	"sort"
    25  
    26  	"github.com/snapcore/snapd/osutil"
    27  )
    28  
    29  var registeredAssets = map[string][]byte{}
    30  
    31  // ForEditions wraps a snippet that is used in editions starting with
    32  // FirstEdition.
    33  type ForEditions struct {
    34  	// First edition this snippet is used in
    35  	FirstEdition uint
    36  	// Snippet data
    37  	Snippet []byte
    38  }
    39  
    40  var registeredEditionSnippets = map[string][]ForEditions{}
    41  
    42  // registerInternal registers an internal asset under the given name.
    43  func registerInternal(name string, data []byte) {
    44  	if _, ok := registeredAssets[name]; ok {
    45  		panic(fmt.Sprintf("asset %q is already registered", name))
    46  	}
    47  	registeredAssets[name] = data
    48  }
    49  
    50  // Internal returns the content of an internal asset registered under the given
    51  // name, or nil when none was found.
    52  func Internal(name string) []byte {
    53  	return registeredAssets[name]
    54  }
    55  
    56  type byFirstEdition []ForEditions
    57  
    58  func (b byFirstEdition) Len() int           { return len(b) }
    59  func (b byFirstEdition) Swap(i, j int)      { b[i], b[j] = b[j], b[i] }
    60  func (b byFirstEdition) Less(i, j int) bool { return b[i].FirstEdition < b[j].FirstEdition }
    61  
    62  // registerSnippetForEditions register a set of snippets, each carrying the
    63  // first edition number it applies to, under a given key.
    64  func registerSnippetForEditions(name string, snippets []ForEditions) {
    65  	if _, ok := registeredEditionSnippets[name]; ok {
    66  		panic(fmt.Sprintf("edition snippets %q are already registered", name))
    67  	}
    68  
    69  	if !sort.IsSorted(byFirstEdition(snippets)) {
    70  		panic(fmt.Sprintf("edition snippets %q must be sorted in ascending edition number order", name))
    71  	}
    72  	for i := range snippets {
    73  		if i == 0 {
    74  			continue
    75  		}
    76  		if snippets[i-1].FirstEdition == snippets[i].FirstEdition {
    77  			panic(fmt.Sprintf(`first edition %v repeated in edition snippets %q`,
    78  				snippets[i].FirstEdition, name))
    79  		}
    80  	}
    81  	registeredEditionSnippets[name] = snippets
    82  }
    83  
    84  // SnippetForEdition returns a snippet registered under given name,
    85  // applicable for the provided edition number.
    86  func SnippetForEdition(name string, edition uint) []byte {
    87  	snippets := registeredEditionSnippets[name]
    88  	if snippets == nil {
    89  		return nil
    90  	}
    91  	var current []byte
    92  	// snippets are sorted by ascending edition number when adding
    93  	for _, snip := range snippets {
    94  		if edition >= snip.FirstEdition {
    95  			current = snip.Snippet
    96  		} else {
    97  			break
    98  		}
    99  	}
   100  	return current
   101  }
   102  
   103  // MockInternal mocks the contents of an internal asset for use in testing.
   104  func MockInternal(name string, data []byte) (restore func()) {
   105  	osutil.MustBeTestBinary("mocking can be done only in tests")
   106  
   107  	old, ok := registeredAssets[name]
   108  	registeredAssets[name] = data
   109  	return func() {
   110  		if ok {
   111  			registeredAssets[name] = old
   112  		} else {
   113  			delete(registeredAssets, name)
   114  		}
   115  	}
   116  }
   117  
   118  // MockSnippetsForEdition mocks the contents of per-edition snippets.
   119  func MockSnippetsForEdition(name string, snippets []ForEditions) (restore func()) {
   120  	osutil.MustBeTestBinary("mocking can be done only in tests")
   121  
   122  	old, ok := registeredEditionSnippets[name]
   123  	snippetsCopy := make([]ForEditions, len(snippets))
   124  	copy(snippetsCopy, snippets)
   125  	if ok {
   126  		delete(registeredEditionSnippets, name)
   127  	}
   128  	registerSnippetForEditions(name, snippetsCopy)
   129  
   130  	return func() {
   131  		if ok {
   132  			registeredEditionSnippets[name] = old
   133  		} else {
   134  			delete(registeredAssets, name)
   135  		}
   136  	}
   137  }