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/*
_BlocksOutputBuffer is used to maintain an output buffer
that has unpredictable size. Suitable for compression/decompression
API (bz2/lzma/zlib) that has stream->next_out and stream->avail_out:
stream->next_out: point to the next output position.
stream->avail_out: the number of available bytes left in the buffer.
It maintains a list of bytes object, so there is no overhead of resizing
the buffer.
Usage:
1, Initialize the struct instance like this:
_BlocksOutputBuffer buffer = {.list = NULL};
Set .list to NULL for _BlocksOutputBuffer_OnError()
2, Initialize the buffer use one of these functions:
_BlocksOutputBuffer_InitAndGrow()
_BlocksOutputBuffer_InitWithSize()
3, If (avail_out == 0), grow the buffer:
_BlocksOutputBuffer_Grow()
4, Get the current outputted data size:
_BlocksOutputBuffer_GetDataSize()
5, Finish the buffer, and return a bytes object:
_BlocksOutputBuffer_Finish()
6, Clean up the buffer when an error occurred:
_BlocksOutputBuffer_OnError()
*/
#ifndef Py_INTERNAL_BLOCKS_OUTPUT_BUFFER_H
#define Py_INTERNAL_BLOCKS_OUTPUT_BUFFER_H
#ifdef __cplusplus
extern "C" {
#endif
#include "Python.h"
typedef struct {
// List of bytes objects
PyObject *list;
// Number of whole allocated size
Py_ssize_t allocated;
// Max length of the buffer, negative number means unlimited length.
Py_ssize_t max_length;
} _BlocksOutputBuffer;
static const char unable_allocate_msg[] = "Unable to allocate output buffer.";
/* In 32-bit build, the max block size should <= INT32_MAX. */
#define OUTPUT_BUFFER_MAX_BLOCK_SIZE (256*1024*1024)
/* Block size sequence */
#define KB (1024)
#define MB (1024*1024)
static const Py_ssize_t BUFFER_BLOCK_SIZE[] =
{ 32*KB, 64*KB, 256*KB, 1*MB, 4*MB, 8*MB, 16*MB, 16*MB,
32*MB, 32*MB, 32*MB, 32*MB, 64*MB, 64*MB, 128*MB, 128*MB,
OUTPUT_BUFFER_MAX_BLOCK_SIZE };
#undef KB
#undef MB
/* According to the block sizes defined by BUFFER_BLOCK_SIZE, the whole
allocated size growth step is:
1 32 KB +32 KB
2 96 KB +64 KB
3 352 KB +256 KB
4 1.34 MB +1 MB
5 5.34 MB +4 MB
6 13.34 MB +8 MB
7 29.34 MB +16 MB
8 45.34 MB +16 MB
9 77.34 MB +32 MB
10 109.34 MB +32 MB
11 141.34 MB +32 MB
12 173.34 MB +32 MB
13 237.34 MB +64 MB
14 301.34 MB +64 MB
15 429.34 MB +128 MB
16 557.34 MB +128 MB
17 813.34 MB +256 MB
18 1069.34 MB +256 MB
19 1325.34 MB +256 MB
20 1581.34 MB +256 MB
21 1837.34 MB +256 MB
22 2093.34 MB +256 MB
...
*/
/* Initialize the buffer, and grow the buffer.
max_length: Max length of the buffer, -1 for unlimited length.
On success, return allocated size (>=0)
On failure, return -1
*/
static inline Py_ssize_t
_BlocksOutputBuffer_InitAndGrow(_BlocksOutputBuffer *buffer,
const Py_ssize_t max_length,
void **next_out)
{
PyObject *b;
Py_ssize_t block_size;
// ensure .list was set to NULL
assert(buffer->list == NULL);
// get block size
if (0 <= max_length && max_length < BUFFER_BLOCK_SIZE[0]) {
block_size = max_length;
} else {
block_size = BUFFER_BLOCK_SIZE[0];
}
// the first block
b = PyBytes_FromStringAndSize(NULL, block_size);
if (b == NULL) {
return -1;
}
// create the list
buffer->list = PyList_New(1);
if (buffer->list == NULL) {
Py_DECREF(b);
return -1;
}
PyList_SET_ITEM(buffer->list, 0, b);
// set variables
buffer->allocated = block_size;
buffer->max_length = max_length;
*next_out = PyBytes_AS_STRING(b);
return block_size;
}
/* Initialize the buffer, with an initial size.
Check block size limit in the outer wrapper function. For example, some libs
accept UINT32_MAX as the maximum block size, then init_size should <= it.
On success, return allocated size (>=0)
On failure, return -1
*/
static inline Py_ssize_t
_BlocksOutputBuffer_InitWithSize(_BlocksOutputBuffer *buffer,
const Py_ssize_t init_size,
void **next_out)
{
PyObject *b;
// ensure .list was set to NULL
assert(buffer->list == NULL);
// the first block
b = PyBytes_FromStringAndSize(NULL, init_size);
if (b == NULL) {
PyErr_SetString(PyExc_MemoryError, unable_allocate_msg);
return -1;
}
// create the list
buffer->list = PyList_New(1);
if (buffer->list == NULL) {
Py_DECREF(b);
return -1;
}
PyList_SET_ITEM(buffer->list, 0, b);
// set variables
buffer->allocated = init_size;
buffer->max_length = -1;
*next_out = PyBytes_AS_STRING(b);
return init_size;
}
/* Grow the buffer. The avail_out must be 0, please check it before calling.
On success, return allocated size (>=0)
On failure, return -1
*/
static inline Py_ssize_t
_BlocksOutputBuffer_Grow(_BlocksOutputBuffer *buffer,
void **next_out,
const Py_ssize_t avail_out)
{
PyObject *b;
const Py_ssize_t list_len = Py_SIZE(buffer->list);
Py_ssize_t block_size;
// ensure no gaps in the data
if (avail_out != 0) {
PyErr_SetString(PyExc_SystemError,
"avail_out is non-zero in _BlocksOutputBuffer_Grow().");
return -1;
}
// get block size
if (list_len < (Py_ssize_t) Py_ARRAY_LENGTH(BUFFER_BLOCK_SIZE)) {
block_size = BUFFER_BLOCK_SIZE[list_len];
} else {
block_size = BUFFER_BLOCK_SIZE[Py_ARRAY_LENGTH(BUFFER_BLOCK_SIZE) - 1];
}
// check max_length
if (buffer->max_length >= 0) {
// if (rest == 0), should not grow the buffer.
Py_ssize_t rest = buffer->max_length - buffer->allocated;
assert(rest > 0);
// block_size of the last block
if (block_size > rest) {
block_size = rest;
}
}
// check buffer->allocated overflow
if (block_size > PY_SSIZE_T_MAX - buffer->allocated) {
PyErr_SetString(PyExc_MemoryError, unable_allocate_msg);
return -1;
}
// create the block
b = PyBytes_FromStringAndSize(NULL, block_size);
if (b == NULL) {
PyErr_SetString(PyExc_MemoryError, unable_allocate_msg);
return -1;
}
if (PyList_Append(buffer->list, b) < 0) {
Py_DECREF(b);
return -1;
}
Py_DECREF(b);
// set variables
buffer->allocated += block_size;
*next_out = PyBytes_AS_STRING(b);
return block_size;
}
/* Return the current outputted data size. */
static inline Py_ssize_t
_BlocksOutputBuffer_GetDataSize(_BlocksOutputBuffer *buffer,
const Py_ssize_t avail_out)
{
return buffer->allocated - avail_out;
}
/* Finish the buffer.
Return a bytes object on success
Return NULL on failure
*/
static inline PyObject *
_BlocksOutputBuffer_Finish(_BlocksOutputBuffer *buffer,
const Py_ssize_t avail_out)
{
PyObject *result, *block;
const Py_ssize_t list_len = Py_SIZE(buffer->list);
// fast path for single block
if ((list_len == 1 && avail_out == 0) ||
(list_len == 2 && Py_SIZE(PyList_GET_ITEM(buffer->list, 1)) == avail_out))
{
block = PyList_GET_ITEM(buffer->list, 0);
Py_INCREF(block);
Py_CLEAR(buffer->list);
return block;
}
// final bytes object
result = PyBytes_FromStringAndSize(NULL, buffer->allocated - avail_out);
if (result == NULL) {
PyErr_SetString(PyExc_MemoryError, unable_allocate_msg);
return NULL;
}
// memory copy
if (list_len > 0) {
char *posi = PyBytes_AS_STRING(result);
// blocks except the last one
Py_ssize_t i = 0;
for (; i < list_len-1; i++) {
block = PyList_GET_ITEM(buffer->list, i);
memcpy(posi, PyBytes_AS_STRING(block), Py_SIZE(block));
posi += Py_SIZE(block);
}
// the last block
block = PyList_GET_ITEM(buffer->list, i);
memcpy(posi, PyBytes_AS_STRING(block), Py_SIZE(block) - avail_out);
} else {
assert(Py_SIZE(result) == 0);
}
Py_CLEAR(buffer->list);
return result;
}
/* Clean up the buffer when an error occurred. */
static inline void
_BlocksOutputBuffer_OnError(_BlocksOutputBuffer *buffer)
{
Py_CLEAR(buffer->list);
}
#ifdef __cplusplus
}
#endif
#endif /* Py_INTERNAL_BLOCKS_OUTPUT_BUFFER_H */
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