PHP 原始碼探祕 – 為什麼 trim 會導致亂碼

周夢康發表於2019-02-16
PHP原始碼

我的部落格 https://mengkang.net/1039.html

執行以下程式碼：

$tag = "網際網路產品、";
$text = rtrim($tag, "、");
print_r($text);

我們可能以為會得到的結果是網際網路產品，實際結果是網際網路產�。為什麼會這樣呢？

科普

PHP 裡使用mb_字首的都是多位元組函式 http://php.net/manual/zh/ref….

比如

$str = "abcd";
print_r(strlen($str)."
"); // 4
print_r(mb_strlen($str)."
"); // 4

$str = "周夢康";
print_r(strlen($str)."
"); // 9
print_r(mb_strlen($str)."
"); // 3

mb_系列函式是以“多個位元組組成的一個字元”為顆粒度來操作的，不帶mb_則是按實際的位元組數來操作的。

原理

trim 函式文件

string trim ( string $str [, string $character_mask = " 	

 x0B" ] )

該函式不是多位元組函式，也就是說，漢字這樣的多位元組字元，會拿其頭或尾的單位元組來和後面的$character_mask對應的char陣列進行匹配，如果在後面的陣列中，則刪掉，繼續匹配。比如：

echo ltrim("bcdf","abc"); // df

如下面的 demo 中的函式string_print_char所示：
、由0xe3 0x80 0x81三位元組組成，
品由0xe5 0x93 0x81三位元組組成。
所以在執行rtrim的時候，通過位元組比對，會將0x81去掉，導致了最後出現了亂碼。

原始碼探究

檢視 PHP7 的原始碼，然後提煉出下面的小 demo ，方便大家一起學習，其實PHP原始碼的學習並不難，每天進步一點點。

//
//  main.c
//  trim
//
//  Created by 周夢康 on 2017/10/18.
//  Copyright © 2017年 周夢康. All rights reserved.
//

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void string_print_char(char *str);
void php_charmask(unsigned char *input, size_t len, char *mask);
char *ltrim(char *str,char *character_mask);
char *rtrim(char *str,char *character_mask);


int main(int argc, char const *argv[])
{
    printf("%s
",ltrim("bcdf","abc"));
    
    string_print_char("品"); // e5    93    81
    string_print_char("、"); // e3    80    81
    
    printf("%s
",rtrim("網際網路產品、","、"));
    
    
    return 0;
}

char *ltrim(char *str,char *character_mask)
{
    char *res;
    char mask[256];
    register size_t i;
    int trimmed = 0;
    
    size_t len = strlen(str);
    
    php_charmask((unsigned char*)character_mask, strlen(character_mask), mask);
    
    for (i = 0; i < len; i++) {
        if (mask[(unsigned char)str[i]]) {
            trimmed++;
        } else {
            break;
        }
    }
    
    len -= trimmed;
    str += trimmed;
    
    res = (char *) malloc(sizeof(char) * (len+1));
    memcpy(res,str,len);
    
    return res;
}

char *rtrim(char *str,char *character_mask)
{
    char *res;
    char mask[256];
    register size_t i;
    
    size_t len = strlen(str);
    
    php_charmask((unsigned char*)character_mask, strlen(character_mask), mask);
    
    if (len > 0) {
        i = len - 1;
        do {
            if (mask[(unsigned char)str[i]]) {
                len--;
            } else {
                break;
            }
        } while (i-- != 0);
    }
    
    res = (char *) malloc(sizeof(char) * (len+1));
    memcpy(res,str,len);
    
    return res;
}

void string_print_char(char *str)
{
    unsigned long l = strlen(str);
    
    for (int i=0; i < l; i++) {
        printf("%02hhx	",str[i]);
    }
    
    printf("
");
}

void php_charmask(unsigned char *input, size_t len, char *mask)
{
    unsigned char *end;
    unsigned char c;
    
    memset(mask, 0, 256);
    
    for (end = input+len; input < end; input++) {
        c = *input;
        mask[c]= 1;
    }
}

如果覺得 demo 還不夠清晰的，複製下來，自己執行一次吧~
C 語言基礎較差的同學也不用擔心，我準備後面專門寫一個PHP小白學習 C 語言的系列入門短文哈。

解決方案

那麼我們就依葫蘆畫瓢，用 php 本身的多位元組函式來實現下吧：

function mb_rtrim($string, $trim, $encoding)
{

    $mask = [];
    $trimLength = mb_strlen($trim, $encoding);
    for ($i = 0; $i < $trimLength; $i++) {
        $item = mb_substr($trim, $i, 1, $encoding);
        $mask[] = $item;
    }

    $len = mb_strlen($string, $encoding);
    if ($len > 0) {
        $i = $len - 1;
        do {
            $item = mb_substr($string, $i, 1, $encoding);
            if (in_array($item, $mask)) {
                $len--;
            } else {
                break;
            }
        } while ($i-- != 0);
    }

    return mb_substr($string, 0, $len, $encoding);
}

mb_internal_encoding("UTF-8");
$tag = "網際網路產品、";
$encoding = mb_internal_encoding();
print_r(mb_rtrim($tag, "、",$encoding));

當然你也可以使用正則來做。通過上面的函式學習，單位元組函式和多位元組函式，你學會了嗎？

PHP7 相關原始碼

PHP_FUNCTION(trim)
{
    php_do_trim(INTERNAL_FUNCTION_PARAM_PASSTHRU, 3);
}
PHP_FUNCTION(rtrim)
{
    php_do_trim(INTERNAL_FUNCTION_PARAM_PASSTHRU, 2);
}
PHP_FUNCTION(ltrim)
{
    php_do_trim(INTERNAL_FUNCTION_PARAM_PASSTHRU, 1);
}
static void php_do_trim(INTERNAL_FUNCTION_PARAMETERS, int mode)
{
    zend_string *str;
    zend_string *what = NULL;

    ZEND_PARSE_PARAMETERS_START(1, 2)
        Z_PARAM_STR(str)
        Z_PARAM_OPTIONAL
        Z_PARAM_STR(what)
    ZEND_PARSE_PARAMETERS_END();

    ZVAL_STR(return_value, php_trim(str, (what ? ZSTR_VAL(what) : NULL), (what ? ZSTR_LEN(what) : 0), mode));
}
PHPAPI zend_string *php_trim(zend_string *str, char *what, size_t what_len, int mode)
{
    const char *c = ZSTR_VAL(str);
    size_t len = ZSTR_LEN(str);
    register size_t i;
    size_t trimmed = 0;
    char mask[256];

    if (what) {
        if (what_len == 1) {
            char p = *what;
            if (mode & 1) {
                for (i = 0; i < len; i++) {
                    if (c[i] == p) {
                        trimmed++;
                    } else {
                        break;
                    }
                }
                len -= trimmed;
                c += trimmed;
            }
            if (mode & 2) {
                if (len > 0) {
                    i = len - 1;
                    do {
                        if (c[i] == p) {
                            len--;
                        } else {
                            break;
                        }
                    } while (i-- != 0);
                }
            }
        } else {
            php_charmask((unsigned char*)what, what_len, mask);

            if (mode & 1) {
                for (i = 0; i < len; i++) {
                    if (mask[(unsigned char)c[i]]) {
                        trimmed++;
                    } else {
                        break;
                    }
                }
                len -= trimmed;
                c += trimmed;
            }
            if (mode & 2) {
                if (len > 0) {
                    i = len - 1;
                    do {
                        if (mask[(unsigned char)c[i]]) {
                            len--;
                        } else {
                            break;
                        }
                    } while (i-- != 0);
                }
            }
        }
    } else {
        if (mode & 1) {
            for (i = 0; i < len; i++) {
                if ((unsigned char)c[i] <= ` ` &&
                    (c[i] == ` ` || c[i] == `
` || c[i] == `
` || c[i] == `	` || c[i] == `v` || c[i] == ` `)) {
                    trimmed++;
                } else {
                    break;
                }
            }
            len -= trimmed;
            c += trimmed;
        }
        if (mode & 2) {
            if (len > 0) {
                i = len - 1;
                do {
                    if ((unsigned char)c[i] <= ` ` &&
                        (c[i] == ` ` || c[i] == `
` || c[i] == `
` || c[i] == `	` || c[i] == `v` || c[i] == ` `)) {
                        len--;
                    } else {
                        break;
                    }
                } while (i-- != 0);
            }
        }
    }

    if (ZSTR_LEN(str) == len) {
        return zend_string_copy(str);
    } else {
        return zend_string_init(c, len, 0);
    }
}
/* {{{ php_charmask
 * Fills a 256-byte bytemask with input. You can specify a range like `a..z`,
 * it needs to be incrementing.
 * Returns: FAILURE/SUCCESS whether the input was correct (i.e. no range errors)
 */
static inline int php_charmask(unsigned char *input, size_t len, char *mask)
{
    unsigned char *end;
    unsigned char c;
    int result = SUCCESS;

    memset(mask, 0, 256);
    for (end = input+len; input < end; input++) {
        c=*input;
        if ((input+3 < end) && input[1] == `.` && input[2] == `.`
                && input[3] >= c) {
            memset(mask+c, 1, input[3] - c + 1);
            input+=3;
        } else if ((input+1 < end) && input[0] == `.` && input[1] == `.`) {
            /* Error, try to be as helpful as possible:
               (a range ending/starting with `.` won`t be captured here) */
            if (end-len >= input) { /* there was no `left` char */
                php_error_docref(NULL, E_WARNING, "Invalid `..`-range, no character to the left of `..`");
                result = FAILURE;
                continue;
            }
            if (input+2 >= end) { /* there is no `right` char */
                php_error_docref(NULL, E_WARNING, "Invalid `..`-range, no character to the right of `..`");
                result = FAILURE;
                continue;
            }
            if (input[-1] > input[2]) { /* wrong order */
                php_error_docref(NULL, E_WARNING, "Invalid `..`-range, `..`-range needs to be incrementing");
                result = FAILURE;
                continue;
            }
            /* FIXME: better error (a..b..c is the only left possibility?) */
            php_error_docref(NULL, E_WARNING, "Invalid `..`-range");
            result = FAILURE;
            continue;
        } else {
            mask[c]=1;
        }
    }
    return result;
}
/* }}} */

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