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Add CBufferedFile

tags/v0.15.1
Pieter Wuille 8 years ago
parent
commit
b5d5f44c95
1 changed files with 144 additions and 0 deletions
  1. 144
    0
      src/serialize.h

+ 144
- 0
src/serialize.h View File

@@ -1225,4 +1225,148 @@ public:
}
};

/** Wrapper around a FILE* that implements a ring buffer to
* deserialize from. It guarantees the ability to rewind
* a given number of bytes. */
class CBufferedFile
{
private:
FILE *src; // source file
uint64 nSrcPos; // how many bytes have been read from source
uint64 nReadPos; // how many bytes have been read from this
uint64 nReadLimit; // up to which position we're allowed to read
uint64 nRewind; // how many bytes we guarantee to rewind
std::vector<char> vchBuf; // the buffer

short state;
short exceptmask;

protected:
void setstate(short bits, const char *psz) {
state |= bits;
if (state & exceptmask)
throw std::ios_base::failure(psz);
}

// read data from the source to fill the buffer
bool Fill() {
unsigned int pos = nSrcPos % vchBuf.size();
unsigned int readNow = vchBuf.size() - pos;
unsigned int nAvail = vchBuf.size() - (nSrcPos - nReadPos) - nRewind;
if (nAvail < readNow)
readNow = nAvail;
if (readNow == 0)
return false;
size_t read = fread((void*)&vchBuf[pos], 1, readNow, src);
if (read == 0) {
setstate(std::ios_base::failbit, feof(src) ? "CBufferedFile::Fill : end of file" : "CBufferedFile::Fill : fread failed");
return false;
} else {
nSrcPos += read;
return true;
}
}

public:
int nType;
int nVersion;

CBufferedFile(FILE *fileIn, uint64 nBufSize, uint64 nRewindIn, int nTypeIn, int nVersionIn) :
src(fileIn), nSrcPos(0), nReadPos(0), nReadLimit((uint64)(-1)), nRewind(nRewindIn), vchBuf(nBufSize, 0),
state(0), exceptmask(std::ios_base::badbit | std::ios_base::failbit), nType(nTypeIn), nVersion(nVersionIn) {
}

// check whether no error occurred
bool good() const {
return state == 0;
}

// check whether we're at the end of the source file
bool eof() const {
return nReadPos == nSrcPos && feof(src);
}

// read a number of bytes
CBufferedFile& read(char *pch, size_t nSize) {
if (nSize + nReadPos > nReadLimit)
throw std::ios_base::failure("Read attempted past buffer limit");
if (nSize + nRewind > vchBuf.size())
throw std::ios_base::failure("Read larger than buffer size");
while (nSize > 0) {
if (nReadPos == nSrcPos)
Fill();
unsigned int pos = nReadPos % vchBuf.size();
size_t nNow = nSize;
if (nNow + pos > vchBuf.size())
nNow = vchBuf.size() - pos;
if (nNow + nReadPos > nSrcPos)
nNow = nSrcPos - nReadPos;
memcpy(pch, &vchBuf[pos], nNow);
nReadPos += nNow;
pch += nNow;
nSize -= nNow;
}
return (*this);
}

// return the current reading position
uint64 GetPos() {
return nReadPos;
}

// rewind to a given reading position
bool SetPos(uint64 nPos) {
nReadPos = nPos;
if (nReadPos + nRewind < nSrcPos) {
nReadPos = nSrcPos - nRewind;
return false;
} else if (nReadPos > nSrcPos) {
nReadPos = nSrcPos;
return false;
} else {
return true;
}
}

bool Seek(uint64 nPos) {
long nLongPos = nPos;
if (nPos != (uint64)nLongPos)
return false;
if (fseek(src, nLongPos, SEEK_SET))
return false;
nLongPos = ftell(src);
nSrcPos = nLongPos;
nReadPos = nLongPos;
state = 0;
return true;
}

// prevent reading beyond a certain position
// no argument removes the limit
bool SetLimit(uint64 nPos = (uint64)(-1)) {
if (nPos < nReadPos)
return false;
nReadLimit = nPos;
return true;
}

template<typename T>
CBufferedFile& operator>>(T& obj) {
// Unserialize from this stream
::Unserialize(*this, obj, nType, nVersion);
return (*this);
}

// search for a given byte in the stream, and remain positioned on it
void FindByte(char ch) {
while (true) {
if (nReadPos == nSrcPos)
Fill();
if (vchBuf[nReadPos % vchBuf.size()] == ch)
break;
nReadPos++;
}
}
};

#endif

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