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