Mercurial > cpython-lru_cache-weakref

annotate Python/mysnprintf.c @ 61774:55e2368f72f2 2.6

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Merged revisions 81380 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r81380 | brett.cannon | 2010-05-20 11:37:55 -0700 (Thu, 20 May 2010) | 8 lines Turned out that if you used explicit relative import syntax (e.g. from .os import sep) and it failed, import would still try the implicit relative import semantics of an absolute import (from os import sep). That's not right, so when level is negative, only do explicit relative import semantics. Fixes issue #7902. Thanks to Meador Inge for the patch. ........
author Brett Cannon <bcannon@gmail.com>
date Thu, 20 May 2010 18:41:08 +0000
parents e38335d4df91
children 787b969d37f0
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1 #include "Python.h"
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2 #include <ctype.h>
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3
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4 /* snprintf() wrappers. If the platform has vsnprintf, we use it, else we
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5 emulate it in a half-hearted way. Even if the platform has it, we wrap
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6 it because platforms differ in what vsnprintf does in case the buffer
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7 is too small: C99 behavior is to return the number of characters that
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8 would have been written had the buffer not been too small, and to set
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9 the last byte of the buffer to \0. At least MS _vsnprintf returns a
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10 negative value instead, and fills the entire buffer with non-\0 data.
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11
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12 The wrappers ensure that str[size-1] is always \0 upon return.
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13
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14 PyOS_snprintf and PyOS_vsnprintf never write more than size bytes
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15 (including the trailing '\0') into str.
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16
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17 If the platform doesn't have vsnprintf, and the buffer size needed to
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18 avoid truncation exceeds size by more than 512, Python aborts with a
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19 Py_FatalError.
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20
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21 Return value (rv):
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22
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23 When 0 <= rv < size, the output conversion was unexceptional, and
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24 rv characters were written to str (excluding a trailing \0 byte at
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25 str[rv]).
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26
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27 When rv >= size, output conversion was truncated, and a buffer of
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28 size rv+1 would have been needed to avoid truncation. str[size-1]
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29 is \0 in this case.
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30
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31 When rv < 0, "something bad happened". str[size-1] is \0 in this
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32 case too, but the rest of str is unreliable. It could be that
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33 an error in format codes was detected by libc, or on platforms
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34 with a non-C99 vsnprintf simply that the buffer wasn't big enough
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35 to avoid truncation, or on platforms without any vsnprintf that
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36 PyMem_Malloc couldn't obtain space for a temp buffer.
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37
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38 CAUTION: Unlike C99, str != NULL and size > 0 are required.
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39 */
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40
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41 int
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42 PyOS_snprintf(char *str, size_t size, const char *format, ...)
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43 {
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44 int rc;
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45 va_list va;
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46
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47 va_start(va, format);
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48 rc = PyOS_vsnprintf(str, size, format, va);
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49 va_end(va);
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50 return rc;
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51 }
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52
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53 int
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54 PyOS_vsnprintf(char *str, size_t size, const char *format, va_list va)
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55 {
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56 int len; /* # bytes written, excluding \0 */
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57 #ifdef HAVE_SNPRINTF
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58 #define _PyOS_vsnprintf_EXTRA_SPACE 1
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59 #else
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60 #define _PyOS_vsnprintf_EXTRA_SPACE 512
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61 char *buffer;
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62 #endif
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63 assert(str != NULL);
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64 assert(size > 0);
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65 assert(format != NULL);
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66 /* We take a size_t as input but return an int. Sanity check
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67 * our input so that it won't cause an overflow in the
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68 * vsnprintf return value or the buffer malloc size. */
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69 if (size > INT_MAX - _PyOS_vsnprintf_EXTRA_SPACE) {
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70 len = -666;
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71 goto Done;
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72 }
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73
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74 #ifdef HAVE_SNPRINTF
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75 len = vsnprintf(str, size, format, va);
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76 #else
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77 /* Emulate it. */
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78 buffer = PyMem_MALLOC(size + _PyOS_vsnprintf_EXTRA_SPACE);
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79 if (buffer == NULL) {
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80 len = -666;
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81 goto Done;
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82 }
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83
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84 len = vsprintf(buffer, format, va);
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85 if (len < 0)
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86 /* ignore the error */;
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87
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88 else if ((size_t)len >= size + _PyOS_vsnprintf_EXTRA_SPACE)
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89 Py_FatalError("Buffer overflow in PyOS_snprintf/PyOS_vsnprintf");
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90
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91 else {
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92 const size_t to_copy = (size_t)len < size ?
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93 (size_t)len : size - 1;
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94 assert(to_copy < size);
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95 memcpy(str, buffer, to_copy);
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96 str[to_copy] = '\0';
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97 }
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98 PyMem_FREE(buffer);
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99 #endif
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100 Done:
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101 if (size > 0)
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102 str[size-1] = '\0';
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103 return len;
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104 #undef _PyOS_vsnprintf_EXTRA_SPACE
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105 }