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1 // Copyright 2016 The Chromium Authors. All rights reserved. | |
2 // Use of this source code is governed by a BSD-style license that can be | |
3 // found in the LICENSE file. | |
4 | |
5 #include "chromeos/printing/ppd_cache.h" | |
6 | |
7 #include <vector> | |
8 | |
9 #include "base/files/file_util.h" | |
10 #include "base/memory/ptr_util.h" | |
11 #include "base/strings/string_number_conversions.h" | |
12 #include "base/strings/string_util.h" | |
13 #include "crypto/sha2.h" | |
14 #include "net/base/io_buffer.h" | |
15 #include "net/filter/filter.h" | |
16 #include "net/filter/gzip_header.h" | |
17 | |
18 using base::FilePath; | |
19 using std::string; | |
20 | |
21 namespace chromeos { | |
22 namespace printing { | |
23 namespace { | |
24 | |
25 // Return true if it looks like contents is already gzipped, false otherwise. | |
26 bool IsGZipped(const string& contents) { | |
27 const char* ignored; | |
28 net::GZipHeader header; | |
29 return header.ReadMore(contents.data(), contents.size(), &ignored) == | |
30 net::GZipHeader::COMPLETE_HEADER; | |
31 } | |
32 | |
33 class PpdCacheImpl : public PpdCache { | |
34 public: | |
35 explicit PpdCacheImpl(const FilePath& cache_base_dir) | |
36 : cache_base_dir_(cache_base_dir) {} | |
37 ~PpdCacheImpl() override {} | |
38 | |
39 // Public API functions. | |
40 base::Optional<FilePath> Find( | |
41 const Printer::PpdReference& reference) const override { | |
42 base::Optional<FilePath> ret; | |
43 | |
44 // We can't know here if we have a gzipped or un-gzipped version, so just | |
45 // look for both. | |
46 FilePath contents_path_base = GetCachePathBase(reference); | |
47 for (const string& extension : {".ppd", ".ppd.gz"}) { | |
48 FilePath contents_path = contents_path_base.AddExtension(extension); | |
49 if (base::PathExists(contents_path)) { | |
50 ret = contents_path; | |
51 break; | |
52 } | |
53 } | |
54 return ret; | |
55 } | |
56 | |
57 base::Optional<FilePath> Store(const Printer::PpdReference& reference, | |
58 const string& ppd_contents) override { | |
59 base::Optional<FilePath> ret; | |
60 FilePath contents_path = GetCachePathBase(reference).AddExtension(".ppd"); | |
61 if (IsGZipped(ppd_contents)) { | |
62 contents_path = contents_path.AddExtension(".gz"); | |
63 } | |
64 if (base::WriteFile(contents_path, ppd_contents.data(), | |
65 ppd_contents.size()) == | |
66 static_cast<int>(ppd_contents.size())) { | |
67 ret = contents_path; | |
68 } else { | |
69 LOG(ERROR) << "Failed to write " << contents_path.LossyDisplayName(); | |
70 // Try to clean up the file, as it may have partial contents. Note | |
skau
2016/10/21 16:12:56
spaces before Try
Carlson
2016/10/24 17:32:33
Done.
| |
71 // that DeleteFile(nonexistant file) should return true, so failure here | |
72 // means something is exceptionally hosed. | |
73 if (!base::DeleteFile(contents_path, false)) { | |
74 LOG(ERROR) << "Failed to cleanup partially-written file " | |
75 << contents_path.LossyDisplayName(); | |
76 return ret; | |
77 } | |
78 } | |
79 return ret; | |
80 } | |
81 | |
82 private: | |
83 // Get the file path at which we expect to find a PPD if it's cached. | |
84 // | |
85 // This is, ultimately, just a hash function. It's extremely infrequently | |
86 // used (called once when trying to look up information on a printer or store | |
87 // a PPD), and should be stable, as changing the function will make previously | |
88 // cached entries unfindable, causing resolve logic to be reinvoked | |
89 // unnecessarily. | |
90 // | |
91 // There's also a faint possibility that a bad actor might try to do something | |
92 // nefarious by intentionally causing a cache collision that makes the wrong | |
93 // PPD be used for a printer. There's no obvious attack vector, but | |
94 // there's also no real cost to being paranoid here, so we use SHA-256 as the | |
95 // underlying hash function, and inject fixed field prefixes to prevent | |
96 // field-substitution spoofing. This also buys us hash function stability at | |
97 // the same time. | |
98 // | |
99 // Also, care should be taken to preserve the existing hash values if new | |
100 // fields are added to PpdReference -- that is, if a new field F is added | |
101 // to PpdReference, a PpdReference with a default F value should hash to | |
102 // the same thing as a PpdReference that predates the addition of F to the | |
103 // structure. | |
104 // | |
105 // Note this function expects that the caller will append ".ppd", or ".ppd.gz" | |
106 // to the output as needed. | |
107 FilePath GetCachePathBase(const Printer::PpdReference& ref) const { | |
108 std::vector<string> pieces; | |
109 if (!ref.user_supplied_ppd_url.empty()) { | |
110 pieces.push_back("user_supplied_ppd_url:"); | |
111 pieces.push_back(ref.user_supplied_ppd_url); | |
112 } else if (!ref.effective_manufacturer.empty() && | |
113 !ref.effective_model.empty()) { | |
114 pieces.push_back("manufacturer:"); | |
115 pieces.push_back(ref.effective_manufacturer); | |
116 pieces.push_back("model:"); | |
117 pieces.push_back(ref.effective_model); | |
118 } else { | |
119 NOTREACHED() << "PpdCache hashing empty PpdReference, this probably " | |
120 << "means something is wrong"; | |
skau
2016/10/21 16:12:56
nit: noting that something is wrong is implied by
Carlson
2016/10/24 17:32:33
Decreased comedy level.
| |
121 } | |
122 // The separator here is not needed, but makes debug output more readable. | |
123 string full_key = base::JoinString(pieces, "|"); | |
124 string hashed_key = crypto::SHA256HashString(full_key); | |
125 string ascii_hash = base::HexEncode(hashed_key.data(), hashed_key.size()); | |
126 VLOG(3) << "PPD Cache key is " << full_key << " which hashes to " | |
127 << ascii_hash; | |
128 | |
129 return cache_base_dir_.Append(ascii_hash); | |
130 } | |
131 | |
132 const FilePath cache_base_dir_; | |
133 | |
134 DISALLOW_COPY_AND_ASSIGN(PpdCacheImpl); | |
135 }; | |
136 | |
137 } // namespace | |
138 | |
139 // static | |
140 std::unique_ptr<PpdCache> PpdCache::Create(const FilePath& cache_base_dir) { | |
141 return base::MakeUnique<PpdCacheImpl>(cache_base_dir); | |
142 } | |
143 | |
144 } // namespace printing | |
145 } // namespace chromeos | |
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