在 Python 应用程序中,我有一个包含一些数据的字节数组。我的python代码由一些外部 native 库(DLL/so/dylib)调用(使用ctypes及其 callback functions )。回调函数之一包括指向在该外部库中分配的非托管缓冲区的指针。
我需要将字节数组的一部分复制到此非托管缓冲区中,或将非托管缓冲区的内容复制到特定位置的字节数组中。
简单来说,我有
def copy_from_python_callback(c_void_p_parameter : c_void_p, offset : int, size : int):
managed_buf = bytearray(some_size) # suppose we have data in this buffer already
unmanaged_buf = c_void_p_parameter
# what do I need to do here?
# src_buf = pointer_to_specific_byte_in_managed_buf
memmove(unmanaged_buf, src_buf, size)
def copy_to_python_callback(c_void_p_parameter : c_void_p, offset : int, size : int):
managed_buf = bytearray(some_size) #some_size is assumed to be larger than offset + size
unmanaged_buf = c_void_p_parameter
# what do I need to do here?
# dst_buf = pointer_to_specific_byte_in_managed_buf
memmove(dst_buf, unmanaged_buf, size)
在其他语言中,答案很简单 - 我要么调用专用方法(例如在 .NET Framework 的 Marshal 类中),要么获取指向字节数组中特定字节的指针(在 C++ 或 Pascal 等 native 语言中) )并完成。不幸的是,我不知道如何在没有中间 bytes() 或类似缓冲区的情况下在 Python 中执行这些操作。
我有一些使用中间 bytes() 实例的方法,但是仅仅因为无法获取指针而复制数据对我来说似乎很奇怪。
如果可能的话,我正在寻找与版本无关的解决方案,但也可以使用仅包含 python3 的解决方案。先感谢您。
最佳答案
列出 [Python.Docs]: ctypes - A foreign function library for Python 。
您正在寻找的东西是可能的。数组(CType)派上用场。
下面是一个“小”示例。出于演示目的,缓冲区仅包含“人类友好的”char。
dll00.c:
#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#if defined(_WIN32)
# define DLL00_EXPORT_API __declspec(dllexport)
#else
# define DLL00_EXPORT_API
#endif
#define C_TAG "From C - "
typedef int (*ReadFunc)(void *ptr, uint32_t offset, uint32_t size);
typedef int (*WriteFunc)(void *ptr, uint32_t offset, uint32_t size);
#if defined(__cplusplus)
extern "C" {
#endif
DLL00_EXPORT_API int testBufferCallbacks(uint32_t bufSize,
ReadFunc read, uint32_t readOffset, uint32_t readSize,
WriteFunc write, uint32_t writeOffset, uint32_t writeSize);
#if defined(__cplusplus)
}
#endif
void prinBuffer(const uint8_t *buf, uint32_t size) {
printf("%sBuffer (size %d) 0x%016llX\n Contents: ", C_TAG, size, (uint64_t)buf);
for (uint32_t i = 0; i < size; i++) {
printf("%c", ((uint8_t*)buf)[i]);
}
printf("\n");
}
int testBufferCallbacks(uint32_t bufSize,
ReadFunc read, uint32_t readOffset, uint32_t readSize,
WriteFunc write, uint32_t writeOffset, uint32_t writeSize) {
const uint8_t charOffset = 0x41;
void *buf = malloc(bufSize);
uint8_t *cBuf = (uint8_t*)buf;
for (uint32_t i = 0; i < bufSize; i++) {
cBuf[i] = (uint8_t)((i + charOffset) % 0x100);
}
prinBuffer(cBuf, bufSize);
if ((read != NULL) && (readSize > 0)) {
printf("\n%sCalling read(0x%016llX, %u, %u)...\n", C_TAG, (uint64_t)buf, readOffset, readSize);
read(buf, readOffset, readSize);
}
if ((write != NULL) && (writeSize > 0)) {
printf("\n%sCalling write(0x%016llX, %u, %u)...\n", C_TAG, (uint64_t)buf, writeOffset, writeSize);
write(buf, writeOffset, writeSize);
prinBuffer(cBuf, bufSize);
}
if ((read != NULL) && (readSize > 0)) {
printf("\n%sCalling read(0x%016llX, %u, %u)...\n", C_TAG, (uint64_t)buf, readOffset, readSize);
read(buf, readOffset, readSize);
}
prinBuffer(cBuf, bufSize);
free(buf);
printf("\n%sDone.\n", C_TAG);
return 0;
}
code00.py:
#!/usr/bin/env python3
import sys
import ctypes as ct
DLL_NAME = "./dll00.dll"
ReadFunc = ct.CFUNCTYPE(ct.c_int, ct.c_void_p, ct.c_uint32, ct.c_uint32)
WriteFunc = ct.CFUNCTYPE(ct.c_int, ct.c_void_p, ct.c_uint32, ct.c_uint32)
def create_bytearray(size, offset_char=0x61):
contents = "".join(chr(i) for i in range(offset_char, offset_char + size))
return bytearray(contents.encode())
def read_c_buf(buf : ct.c_void_p, offset : ct.c_uint32, size : ct.c_uint32):
print("C buf: 0x{0:016X}".format(buf))
ba = create_bytearray(0x1A)
print("Python initial buffer: {0:}".format(ba))
UCharArr = ct.c_uint8 * size
uchar_arr = UCharArr.from_buffer(ba, offset) # Shared memory
ct.memmove(uchar_arr, buf, size)
print("Python final buffer: {0:}\n".format(ba))
return 0
def write_c_buf(buf : ct.c_void_p, offset : ct.c_uint32, size : ct.c_uint32):
print("C buf: 0x{0:016X}".format(buf))
ba = create_bytearray(size + offset, offset_char=0x30 - offset)
print("Python buffer: {0:}\n".format(ba))
UCharArr = ct.c_uint8 * size
uchar_arr = UCharArr.from_buffer(ba, offset) # Shared memory
ct.memmove(buf, uchar_arr, size)
return 0
def main(*argv):
dll00 = ct.CDLL(DLL_NAME)
testBufferCallbacks = dll00.testBufferCallbacks
testBufferCallbacks.argtypes = (ct.c_uint32, ReadFunc, ct.c_uint32, ct.c_uint32, WriteFunc, ct.c_uint32, ct.c_uint32)
testBufferCallbacks.restype = ct.c_int
read_callback = ReadFunc(read_c_buf)
buf_size = 0x1A
read_offset = 10
read_size = 16
write_callback = WriteFunc(write_c_buf)
write_offset = 5
write_size = 10
res = testBufferCallbacks(buf_size, read_callback, read_offset, read_size, write_callback, write_offset, write_size)
print("\n{0:s} returned: {1:d}".format(testBufferCallbacks.__name__, res))
if __name__ == "__main__":
print("Python {:s} {:03d}bit on {:s}\n".format(" ".join(elem.strip() for elem in sys.version.split("\n")),
64 if sys.maxsize > 0x100000000 else 32, sys.platform))
rc = main(*sys.argv[1:])
print("\nDone.")
sys.exit(rc)
输出:
[cfati@CFATI-5510-0:e:\Work\Dev\StackOverflow\q059255471]> sopr.bat ### Set shorter prompt to better fit when pasted in StackOverflow (or other) pages ### [prompt]> "c:\Install\x86\Microsoft\Visual Studio Community\2017\VC\Auxiliary\Build\vcvarsall.bat" x64 ********************************************************************** ** Visual Studio 2017 Developer Command Prompt v15.9.17 ** Copyright (c) 2017 Microsoft Corporation ********************************************************************** [vcvarsall.bat] Environment initialized for: 'x64' [prompt]> dir /b code00.py code01.py dll00.c [prompt]> cl /nologo /MD /DDLL dll00.c /link /NOLOGO /DLL /OUT:dll00.dll dll00.c Creating library dll00.lib and object dll00.exp [prompt]> dir /b code00.py code01.py dll00.c dll00.dll dll00.exp dll00.lib dll00.obj [prompt]> "e:\Work\Dev\VEnvs\py_064_03.07.03_test0\Scripts\python.exe" code00.py Python 3.7.3 (v3.7.3:ef4ec6ed12, Mar 25 2019, 22:22:05) [MSC v.1916 64 bit (AMD64)] 064bit on win32 From C - Buffer (size 26) 0x0000016BFE546EB0 Contents: ABCDEFGHIJKLMNOPQRSTUVWXYZ From C - Calling read(0x0000016BFE546EB0, 10, 16)... C buf: 0x0000016BFE546EB0 Python initial buffer: bytearray(b'abcdefghijklmnopqrstuvwxyz') Python final buffer: bytearray(b'abcdefghijABCDEFGHIJKLMNOP') From C - Calling write(0x0000016BFE546EB0, 5, 10)... C buf: 0x0000016BFE546EB0 Python buffer: bytearray(b'+,-./0123456789') From C - Buffer (size 26) 0x0000016BFE546EB0 Contents: 0123456789KLMNOPQRSTUVWXYZ From C - Calling read(0x0000016BFE546EB0, 10, 16)... C buf: 0x0000016BFE546EB0 Python initial buffer: bytearray(b'abcdefghijklmnopqrstuvwxyz') Python final buffer: bytearray(b'abcdefghij0123456789KLMNOP') From C - Buffer (size 26) 0x0000016BFE546EB0 Contents: 0123456789KLMNOPQRSTUVWXYZ From C - Done. testBufferCallbacks returned: 0 Done.
不用说,超出(C)缓冲区的边界,会产生U未定义的B行为(并且我的代码不执行此类检查)。
关于python - 如何将 bytearray 的一部分复制到 c_void_p 引用的内存,反之亦然?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/59255471/