core/Lucy/Store/InStream.cfh

/* Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.
 */

parcel Lucy;

/** Read index files.
 *
 * InStream objects are the primary interface for reading from index files.
 * They are high-level (relatively speaking), media-agnostic wrappers
 * around low-level, media-specific FileHandle objects.
 *
 * InStreams provide a number of routines for safely decoding common constructs
 * such as big-endian or compressed integers; for the most part, these
 * routines throw exceptions rather than require manual checking of return
 * values for error conditions.
 *
 * Multiple InStream objects often share the same underlying FileHandle; this
 * practice is safe because InStreams do not modify or rely upon the file
 * position or other state within the FileHandle.
 */
class Lucy::Store::InStream inherits Lucy::Object::Obj {

    int64_t     offset;
    int64_t     len;
    char       *buf;
    char       *limit;
    CharBuf    *filename;
    FileHandle *file_handle;
    FileWindow *window;

    inert incremented nullable InStream*
    open(Obj *file);

    /** Return a new InStream, or set Err_error and return NULL on failure.
     *
     * @param file A FileHandle, a file path, or a RAMFile.
     */
    inert nullable InStream*
    do_open(InStream *self, Obj *file);

    /** Clone the instream, but specify a new offset, length, and possibly
     * filename.  Initial file position will be set to the top of the file
     * (taking <code>offset</code> into account).
     *
     * @param filename An alias filename.  If NULL, the filename of the
     * underlying FileHandle will be used.
     * @param offset Top of the file as seen by the new InStream, in bytes
     * from the top of the file as seen by the underlying FileHandle.
     * @param len Length of the file as seen by the new InStream.
     */
    incremented InStream*
    Reopen(InStream *self, const CharBuf *filename = NULL, int64_t offset,
           int64_t len);

    /** Clone the InStream.  Clones share the same underlying FileHandle and
     * start at the current file position, but are able to seek and read
     * independently.
     */
    public incremented InStream*
    Clone(InStream *self);

    /** Decrement the number of streams using the underlying FileHandle.  When
     * the number drops to zero, possibly release system resources.
     */
    void
    Close(InStream *self);

    public void
    Destroy(InStream *self);

    /** Seek to <code>target</code>.
     */
    final void
    Seek(InStream *self, int64_t target);

    /** Return the current file position.
     */
    final int64_t
    Tell(InStream *self);

    /** Return the length of the "file" in bytes.
     */
    final int64_t
    Length(InStream *self);

    /** Fill the InStream's buffer, letting the FileHandle decide how many bytes
     * of data to fill it with.
     */
    void
    Refill(InStream *self);

    /** Pour an exact number of bytes into the InStream's buffer.
     */
    void
    Fill(InStream *self, int64_t amount);

    /** Get the InStream's buffer.  Check to see whether <code>request</code>
     * bytes are already in the buffer.  If not, fill the buffer with either
     * <code>request</code> bytes or the number of bytes remaining before EOF,
     * whichever is smaller.
     *
     * @param request Advisory byte size request.
     * @return Pointer to the InStream's internal buffer.
     */
    final char*
    Buf(InStream *self, size_t request);

    /** Set the buf to a new value, checking for overrun.  The idiom is for
     * the caller to call Buf(), use no more bytes than requested, then use
     * Advance_Buf() to update the InStream object.
     */
    final void
    Advance_Buf(InStream *self, char *buf);

    /** Read <code>len</code> bytes from the InStream into <code>buf</code>.
     */
    final void
    Read_Bytes(InStream *self, char *buf, size_t len);

    /** Read a signed 8-bit integer.
     */
    final int8_t
    Read_I8(InStream *self);

    /** Read an unsigned 8-bit integer.
     */
    final uint8_t
    Read_U8(InStream *self);

    /** Read a signed 32-bit integer.
     */
    final int32_t
    Read_I32(InStream *self);

    /** Read an unsigned 32-bit integer.
     */
    final uint32_t
    Read_U32(InStream *self);

    /** Read a signed 64-bit integer.
     */
    final int64_t
    Read_I64(InStream *self);

    /** Read an unsigned 64-bit integer.
     */
    final uint64_t
    Read_U64(InStream *self);

    /** Read an IEEE 764 32-bit floating point number.
     */
    final float
    Read_F32(InStream *self);

    /** Read an IEEE 764 64-bit floating point number.
     */
    final double
    Read_F64(InStream *self);

    /** Read in a compressed 32-bit unsigned integer.
     */
    uint32_t
    Read_C32(InStream *self);

    /** Read a 64-bit integer, using the same encoding as a C32 but occupying
     * as many as 10 bytes.
     */
    final uint64_t
    Read_C64(InStream *self);

    /** Read the bytes for a C32/C64 into <code>buf</code>.  Return the number
     * of bytes read.  The caller must ensure that sufficient space exists in
     * <code>buf</code> (worst case is 10 bytes).
     */
    final int
    Read_Raw_C64(InStream *self, char *buf);

    /** Accessor for filename member.
     */
    CharBuf*
    Get_Filename(InStream *self);
}