builder.h

/* builder.h */

/*    Copyright 2009 10gen Inc.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */

#pragma once

#include <cfloat>
#include <sstream>
#include <stdio.h>
#include <string>

#include <boost/static_assert.hpp>

#include "mongo/base/data_view.h"
#include "mongo/base/string_data.h"
#include "mongo/bson/inline_decls.h"
#include "mongo/util/assert_util.h"

namespace mongo {

/* Note the limit here is rather arbitrary and is simply a standard. generally the code works
   with any object that fits in ram.

   Also note that the server has some basic checks to enforce this limit but those checks are not
   exhaustive for example need to check for size too big after
     update $push (append) operation
     various db.eval() type operations
*/
const int BSONObjMaxUserSize = 16 * 1024 * 1024;

/*
   Sometimes we need objects slightly larger - an object in the replication local.oplog
   is slightly larger than a user object for example.
*/
const int BSONObjMaxInternalSize = BSONObjMaxUserSize + (16 * 1024);

const int BufferMaxSize = 64 * 1024 * 1024;

template <typename Allocator>
class StringBuilderImpl;

class TrivialAllocator {
public:
    void* Malloc(size_t sz) {
        return malloc(sz);
    }
    void* Realloc(void* p, size_t sz) {
        return realloc(p, sz);
    }
    void Free(void* p) {
        free(p);
    }
};

class StackAllocator {
public:
    enum { SZ = 512 };
    void* Malloc(size_t sz) {
        if (sz <= SZ)
            return buf;
        return malloc(sz);
    }
    void* Realloc(void* p, size_t sz) {
        if (p == buf) {
            if (sz <= SZ)
                return buf;
            void* d = malloc(sz);
            if (d == 0)
                msgasserted(15912, "out of memory StackAllocator::Realloc");
            memcpy(d, p, SZ);
            return d;
        }
        return realloc(p, sz);
    }
    void Free(void* p) {
        if (p != buf)
            free(p);
    }

private:
    char buf[SZ];
};

template <class Allocator>
class _BufBuilder {
    // non-copyable, non-assignable
    _BufBuilder(const _BufBuilder&);
    _BufBuilder& operator=(const _BufBuilder&);
    Allocator al;

public:
    _BufBuilder(int initsize = 512) : size(initsize) {
        if (size > 0) {
            data = (char*)al.Malloc(size);
            if (data == 0)
                msgasserted(10000, "out of memory BufBuilder");
        } else {
            data = 0;
        }
        l = 0;
        reservedBytes = 0;
    }
    ~_BufBuilder() {
        kill();
    }

    void kill() {
        if (data) {
            al.Free(data);
            data = 0;
        }
    }

    void reset() {
        l = 0;
        reservedBytes = 0;
    }
    void reset(int maxSize) {
        l = 0;
        reservedBytes = 0;
        if (maxSize && size > maxSize) {
            al.Free(data);
            data = (char*)al.Malloc(maxSize);
            if (data == 0)
                msgasserted(15913, "out of memory BufBuilder::reset");
            size = maxSize;
        }
    }

    char* skip(int n) {
        return grow(n);
    }

    /* note this may be deallocated (realloced) if you keep writing. */
    char* buf() {
        return data;
    }
    const char* buf() const {
        return data;
    }

    /* assume ownership of the buffer - you must then free() it */
    void decouple() {
        data = 0;
    }

    void appendUChar(unsigned char j) {
        BOOST_STATIC_ASSERT(CHAR_BIT == 8);
        appendNumImpl(j);
    }
    void appendChar(char j) {
        appendNumImpl(j);
    }
    void appendNum(char j) {
        appendNumImpl(j);
    }
    void appendNum(short j) {
        BOOST_STATIC_ASSERT(sizeof(short) == 2);
        appendNumImpl(j);
    }
    void appendNum(int j) {
        BOOST_STATIC_ASSERT(sizeof(int) == 4);
        appendNumImpl(j);
    }
    void appendNum(unsigned j) {
        appendNumImpl(j);
    }

// Bool does not have a well defined encoding.
#if __cplusplus >= 201103L
    void appendNum(bool j) = delete;
#else
    void appendNum(bool j) {
        invariant(false);
    }
#endif

    void appendNum(double j) {
        BOOST_STATIC_ASSERT(sizeof(double) == 8);
        appendNumImpl(j);
    }
    void appendNum(long long j) {
        BOOST_STATIC_ASSERT(sizeof(long long) == 8);
        appendNumImpl(j);
    }
    void appendNum(unsigned long long j) {
        appendNumImpl(j);
    }

    void appendBuf(const void* src, size_t len) {
        memcpy(grow((int)len), src, len);
    }

    template <class T>
    void appendStruct(const T& s) {
        appendBuf(&s, sizeof(T));
    }

    void appendStr(const StringData& str, bool includeEndingNull = true) {
        const int len = str.size() + (includeEndingNull ? 1 : 0);
        str.copyTo(grow(len), includeEndingNull);
    }

    int len() const {
        return l;
    }
    void setlen(int newLen) {
        l = newLen;
    }
    int getSize() const {
        return size;
    }

    /* returns the pre-grow write position */
    inline char* grow(int by) {
        int oldlen = l;
        int newLen = l + by;
        int minSize = newLen + reservedBytes;
        if (minSize > size) {
            grow_reallocate(minSize);
        }
        l = newLen;
        return data + oldlen;
    }

    void reserveBytes(int bytes) {
        int minSize = l + reservedBytes + bytes;
        if (minSize > size)
            grow_reallocate(minSize);

        // This must happen *after* any attempt to grow.
        reservedBytes += bytes;
    }

    void claimReservedBytes(int bytes) {
        invariant(reservedBytes >= bytes);
        reservedBytes -= bytes;
    }

private:
    template <typename T>
    void appendNumImpl(T t) {
        // NOTE: For now, we assume that all things written
        // by a BufBuilder are intended for external use: either written to disk
        // or to the wire. Since all of our encoding formats are little endian,
        // we bake that assumption in here. This decision should be revisited soon.
        DataView(grow(sizeof(t))).writeLE(t);
    }


    /* "slow" portion of 'grow()'  */
    void NOINLINE_DECL grow_reallocate(int minSize) {
        int a = 64;
        while (a < minSize)
            a = a * 2;

        if (a > BufferMaxSize) {
            std::stringstream ss;
            ss << "BufBuilder attempted to grow() to " << a << " bytes, past the 64MB limit.";
            msgasserted(13548, ss.str().c_str());
        }
        data = (char*)al.Realloc(data, a);
        if (data == NULL)
            msgasserted(16070, "out of memory BufBuilder::grow_reallocate");
        size = a;
    }

    char* data;
    int l;
    int size;
    int reservedBytes;  // eagerly grow_reallocate to keep this many bytes of spare room.

    friend class StringBuilderImpl<Allocator>;
};

typedef _BufBuilder<TrivialAllocator> BufBuilder;

class StackBufBuilder : public _BufBuilder<StackAllocator> {
public:
    StackBufBuilder() : _BufBuilder<StackAllocator>(StackAllocator::SZ) {}
    void decouple();  // not allowed. not implemented.
};

#if defined(_WIN32)
#pragma push_macro("snprintf")
#define snprintf _snprintf
#endif

template <typename Allocator>
class StringBuilderImpl {
public:
    // Sizes are determined based on the number of characters in 64-bit + the trailing '\0'
    static const size_t MONGO_DBL_SIZE = 3 + DBL_MANT_DIG - DBL_MIN_EXP + 1;
    static const size_t MONGO_S32_SIZE = 12;
    static const size_t MONGO_U32_SIZE = 11;
    static const size_t MONGO_S64_SIZE = 23;
    static const size_t MONGO_U64_SIZE = 22;
    static const size_t MONGO_S16_SIZE = 7;
    static const size_t MONGO_PTR_SIZE = 19;  // Accounts for the 0x prefix

    StringBuilderImpl() {}

    StringBuilderImpl& operator<<(double x) {
        return SBNUM(x, MONGO_DBL_SIZE, "%g");
    }
    StringBuilderImpl& operator<<(int x) {
        return SBNUM(x, MONGO_S32_SIZE, "%d");
    }
    StringBuilderImpl& operator<<(unsigned x) {
        return SBNUM(x, MONGO_U32_SIZE, "%u");
    }
    StringBuilderImpl& operator<<(long x) {
        return SBNUM(x, MONGO_S64_SIZE, "%ld");
    }
    StringBuilderImpl& operator<<(unsigned long x) {
        return SBNUM(x, MONGO_U64_SIZE, "%lu");
    }
    StringBuilderImpl& operator<<(long long x) {
        return SBNUM(x, MONGO_S64_SIZE, "%lld");
    }
    StringBuilderImpl& operator<<(unsigned long long x) {
        return SBNUM(x, MONGO_U64_SIZE, "%llu");
    }
    StringBuilderImpl& operator<<(short x) {
        return SBNUM(x, MONGO_S16_SIZE, "%hd");
    }
    StringBuilderImpl& operator<<(const void* x) {
        if (sizeof(x) == 8) {
            return SBNUM(x, MONGO_PTR_SIZE, "0x%llX");
        } else {
            return SBNUM(x, MONGO_PTR_SIZE, "0x%lX");
        }
    }
    StringBuilderImpl& operator<<(char c) {
        _buf.grow(1)[0] = c;
        return *this;
    }
    StringBuilderImpl& operator<<(const char* str) {
        return *this << StringData(str);
    }
    StringBuilderImpl& operator<<(const StringData& str) {
        append(str);
        return *this;
    }

    void appendDoubleNice(double x) {
        const int prev = _buf.l;
        const int maxSize = 32;
        char* start = _buf.grow(maxSize);
        int z = snprintf(start, maxSize, "%.16g", x);
        verify(z >= 0);
        verify(z < maxSize);
        _buf.l = prev + z;
        if (strchr(start, '.') == 0 && strchr(start, 'E') == 0 && strchr(start, 'N') == 0) {
            write(".0", 2);
        }
    }

    void write(const char* buf, int len) {
        memcpy(_buf.grow(len), buf, len);
    }

    void append(const StringData& str) {
        str.copyTo(_buf.grow(str.size()), false);
    }

    void reset(int maxSize = 0) {
        _buf.reset(maxSize);
    }

    std::string str() const {
        return std::string(_buf.data, _buf.l);
    }

    int len() const {
        return _buf.l;
    }

private:
    _BufBuilder<Allocator> _buf;

    // non-copyable, non-assignable
    StringBuilderImpl(const StringBuilderImpl&);
    StringBuilderImpl& operator=(const StringBuilderImpl&);

    template <typename T>
    StringBuilderImpl& SBNUM(T val, int maxSize, const char* macro) {
        int prev = _buf.l;
        int z = snprintf(_buf.grow(maxSize), maxSize, macro, (val));
        verify(z >= 0);
        verify(z < maxSize);
        _buf.l = prev + z;
        return *this;
    }
};

typedef StringBuilderImpl<TrivialAllocator> StringBuilder;
typedef StringBuilderImpl<StackAllocator> StackStringBuilder;

#if defined(_WIN32)
#undef snprintf
#pragma pop_macro("snprintf")
#endif
}  // namespace mongo