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      1 /*
      2  * Copyright 2017 Google Inc. All rights reserved.
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *     http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 #ifndef FLATBUFFERS_REGISTRY_H_
     18 #define FLATBUFFERS_REGISTRY_H_
     19 
     20 #include "flatbuffers/idl.h"
     21 
     22 namespace flatbuffers {
     23 
     24 // Convenience class to easily parse or generate text for arbitrary FlatBuffers.
     25 // Simply pre-populate it with all schema filenames that may be in use, and
     26 // This class will look them up using the file_identifier declared in the
     27 // schema.
     28 class Registry {
     29  public:
     30   // Call this for all schemas that may be in use. The identifier has
     31   // a function in the generated code, e.g. MonsterIdentifier().
     32   void Register(const char *file_identifier, const char *schema_path) {
     33     Schema schema;
     34     schema.path_ = schema_path;
     35     schemas_[file_identifier] = schema;
     36   }
     37 
     38   // Generate text from an arbitrary FlatBuffer by looking up its
     39   // file_identifier in the registry.
     40   bool FlatBufferToText(const uint8_t *flatbuf, size_t len, std::string *dest) {
     41     // Get the identifier out of the buffer.
     42     // If the buffer is truncated, exit.
     43     if (len < sizeof(uoffset_t) + FlatBufferBuilder::kFileIdentifierLength) {
     44       lasterror_ = "buffer truncated";
     45       return false;
     46     }
     47     std::string ident(
     48         reinterpret_cast<const char *>(flatbuf) + sizeof(uoffset_t),
     49         FlatBufferBuilder::kFileIdentifierLength);
     50     // Load and parse the schema.
     51     Parser parser;
     52     if (!LoadSchema(ident, &parser)) return false;
     53     // Now we're ready to generate text.
     54     if (!GenerateText(parser, flatbuf, dest)) {
     55       lasterror_ = "unable to generate text for FlatBuffer binary";
     56       return false;
     57     }
     58     return true;
     59   }
     60 
     61   // Converts a binary buffer to text using one of the schemas in the registry,
     62   // use the file_identifier to indicate which.
     63   // If DetachedBuffer::data() is null then parsing failed.
     64   DetachedBuffer TextToFlatBuffer(const char *text,
     65                                   const char *file_identifier) {
     66     // Load and parse the schema.
     67     Parser parser;
     68     if (!LoadSchema(file_identifier, &parser)) return DetachedBuffer();
     69     // Parse the text.
     70     if (!parser.Parse(text)) {
     71       lasterror_ = parser.error_;
     72       return DetachedBuffer();
     73     }
     74     // We have a valid FlatBuffer. Detach it from the builder and return.
     75     return parser.builder_.Release();
     76   }
     77 
     78   // Modify any parsing / output options used by the other functions.
     79   void SetOptions(const IDLOptions &opts) { opts_ = opts; }
     80 
     81   // If schemas used contain include statements, call this function for every
     82   // directory the parser should search them for.
     83   void AddIncludeDirectory(const char *path) { include_paths_.push_back(path); }
     84 
     85   // Returns a human readable error if any of the above functions fail.
     86   const std::string &GetLastError() { return lasterror_; }
     87 
     88  private:
     89   bool LoadSchema(const std::string &ident, Parser *parser) {
     90     // Find the schema, if not, exit.
     91     auto it = schemas_.find(ident);
     92     if (it == schemas_.end()) {
     93       // Don't attach the identifier, since it may not be human readable.
     94       lasterror_ = "identifier for this buffer not in the registry";
     95       return false;
     96     }
     97     auto &schema = it->second;
     98     // Load the schema from disk. If not, exit.
     99     std::string schematext;
    100     if (!LoadFile(schema.path_.c_str(), false, &schematext)) {
    101       lasterror_ = "could not load schema: " + schema.path_;
    102       return false;
    103     }
    104     // Parse schema.
    105     parser->opts = opts_;
    106     if (!parser->Parse(schematext.c_str(), vector_data(include_paths_),
    107                        schema.path_.c_str())) {
    108       lasterror_ = parser->error_;
    109       return false;
    110     }
    111     return true;
    112   }
    113 
    114   struct Schema {
    115     std::string path_;
    116     // TODO(wvo) optionally cache schema file or parsed schema here.
    117   };
    118 
    119   std::string lasterror_;
    120   IDLOptions opts_;
    121   std::vector<const char *> include_paths_;
    122   std::map<std::string, Schema> schemas_;
    123 };
    124 
    125 }  // namespace flatbuffers
    126 
    127 #endif  // FLATBUFFERS_REGISTRY_H_
    128