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      1 //===--- llvm/Support/DataStream.cpp - Lazy streamed data -----------------===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 //
     10 // This file implements DataStreamer, which fetches bytes of Data from
     11 // a stream source. It provides support for streaming (lazy reading) of
     12 // bitcode. An example implementation of streaming from a file or stdin
     13 // is included.
     14 //
     15 //===----------------------------------------------------------------------===//
     16 
     17 #include "llvm/Support/DataStream.h"
     18 #include "llvm/ADT/Statistic.h"
     19 #include "llvm/ADT/STLExtras.h"
     20 #include "llvm/Support/FileSystem.h"
     21 #include "llvm/Support/Program.h"
     22 #include <string>
     23 #include <system_error>
     24 #if !defined(_MSC_VER) && !defined(__MINGW32__)
     25 #include <unistd.h>
     26 #else
     27 #include <io.h>
     28 #endif
     29 using namespace llvm;
     30 
     31 #define DEBUG_TYPE "Data-stream"
     32 
     33 // Interface goals:
     34 // * StreamingMemoryObject doesn't care about complexities like using
     35 //   threads/async callbacks to actually overlap download+compile
     36 // * Don't want to duplicate Data in memory
     37 // * Don't need to know total Data len in advance
     38 // Non-goals:
     39 // StreamingMemoryObject already has random access so this interface only does
     40 // in-order streaming (no arbitrary seeking, else we'd have to buffer all the
     41 // Data here in addition to MemoryObject).  This also means that if we want
     42 // to be able to to free Data, BitstreamBytes/BitcodeReader will implement it
     43 
     44 STATISTIC(NumStreamFetches, "Number of calls to Data stream fetch");
     45 
     46 namespace llvm {
     47 DataStreamer::~DataStreamer() {}
     48 }
     49 
     50 namespace {
     51 
     52 // Very simple stream backed by a file. Mostly useful for stdin and debugging;
     53 // actual file access is probably still best done with mmap.
     54 class DataFileStreamer : public DataStreamer {
     55  int Fd;
     56 public:
     57   DataFileStreamer() : Fd(0) {}
     58   ~DataFileStreamer() override { close(Fd); }
     59   size_t GetBytes(unsigned char *buf, size_t len) override {
     60     NumStreamFetches++;
     61     return read(Fd, buf, len);
     62   }
     63 
     64   std::error_code OpenFile(const std::string &Filename) {
     65     if (Filename == "-") {
     66       Fd = 0;
     67       sys::ChangeStdinToBinary();
     68       return std::error_code();
     69     }
     70 
     71     return sys::fs::openFileForRead(Filename, Fd);
     72   }
     73 };
     74 
     75 }
     76 
     77 std::unique_ptr<DataStreamer>
     78 llvm::getDataFileStreamer(const std::string &Filename, std::string *StrError) {
     79   std::unique_ptr<DataFileStreamer> s = make_unique<DataFileStreamer>();
     80   if (std::error_code e = s->OpenFile(Filename)) {
     81     *StrError = std::string("Could not open ") + Filename + ": " +
     82         e.message() + "\n";
     83     return nullptr;
     84   }
     85   return std::move(s);
     86 }
     87