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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/Support/FileSystem.h"
     20 #include "llvm/Support/Program.h"
     21 #include <cerrno>
     22 #include <cstdio>
     23 #include <string>
     24 #include <system_error>
     25 #if !defined(_MSC_VER) && !defined(__MINGW32__)
     26 #include <unistd.h>
     27 #else
     28 #include <io.h>
     29 #endif
     30 using namespace llvm;
     31 
     32 #define DEBUG_TYPE "Data-stream"
     33 
     34 // Interface goals:
     35 // * StreamableMemoryObject doesn't care about complexities like using
     36 //   threads/async callbacks to actually overlap download+compile
     37 // * Don't want to duplicate Data in memory
     38 // * Don't need to know total Data len in advance
     39 // Non-goals:
     40 // StreamableMemoryObject already has random access so this interface only does
     41 // in-order streaming (no arbitrary seeking, else we'd have to buffer all the
     42 // Data here in addition to MemoryObject).  This also means that if we want
     43 // to be able to to free Data, BitstreamBytes/BitcodeReader will implement it
     44 
     45 STATISTIC(NumStreamFetches, "Number of calls to Data stream fetch");
     46 
     47 namespace llvm {
     48 DataStreamer::~DataStreamer() {}
     49 }
     50 
     51 namespace {
     52 
     53 // Very simple stream backed by a file. Mostly useful for stdin and debugging;
     54 // actual file access is probably still best done with mmap.
     55 class DataFileStreamer : public DataStreamer {
     56  int Fd;
     57 public:
     58   DataFileStreamer() : Fd(0) {}
     59   virtual ~DataFileStreamer() {
     60     close(Fd);
     61   }
     62   size_t GetBytes(unsigned char *buf, size_t len) override {
     63     NumStreamFetches++;
     64     return read(Fd, buf, len);
     65   }
     66 
     67   std::error_code OpenFile(const std::string &Filename) {
     68     if (Filename == "-") {
     69       Fd = 0;
     70       sys::ChangeStdinToBinary();
     71       return std::error_code();
     72     }
     73 
     74     return sys::fs::openFileForRead(Filename, Fd);
     75   }
     76 };
     77 
     78 }
     79 
     80 namespace llvm {
     81 DataStreamer *getDataFileStreamer(const std::string &Filename,
     82                                   std::string *StrError) {
     83   DataFileStreamer *s = new DataFileStreamer();
     84   if (std::error_code e = s->OpenFile(Filename)) {
     85     *StrError = std::string("Could not open ") + Filename + ": " +
     86         e.message() + "\n";
     87     return nullptr;
     88   }
     89   return s;
     90 }
     91 
     92 }
     93