ngx unescape uri bug

[David Shee]

I'm Zuwen Shi from China,I find a unescape uri bug in your program.
The source code location is src\core\ngx_string.c->ngx_unescape_uri
If I put a string "%%s%elect",it convert the string to "%slect",and %% to
%,%el to l,actually the right convert is "%%s%elect".
So,I patch the ngx_unescape_uri like below,the red part is which I modified.
Nginx is a really nice project.

void
ngx_unescape_uri(u_char **dst, u_char **src, size_t size, ngx_uint_t type)
{
    u_char  *d, *s, ch, c, decoded;
    enum {
        sw_usual = 0,
        sw_quoted,
        sw_quoted_second
    } state;

    d = *dst;
    s = *src;

    state = 0;
    decoded = 0;

    while (size--) {

        ch = *s++;

        switch (state) {
        case sw_usual:
            if (ch == '?'
                && (type & (NGX_UNESCAPE_URI|NGX_UNESCAPE_REDIRECT)))
            {
                *d++ = ch;
                goto done;
            }

            if (ch == '%'&&size>1) {
                ch=*s;
                c = (u_char) (ch | 0x20);
                if ((ch >= '0' && ch <= '9')||(c >= 'a' && c <= 'f')) {
                ch=*(s+1);
                c = (u_char) (ch | 0x20);
                if ((ch >= '0' && ch <= '9')||(c >= 'a' && c <= 'f')) {
                state = sw_quoted;
                break;
                }
                }
                *d++ = '%';
                break;
            }

            if (ch == '+') {
            *d++ = ' ';
            break;
            }

            *d++ = ch;
            break;

        case sw_quoted:

            if (ch >= '0' && ch <= '9') {
                decoded = (u_char) (ch - '0');
                state = sw_quoted_second;
                break;
            }

            c = (u_char) (ch | 0x20);
            if (c >= 'a' && c <= 'f') {
                decoded = (u_char) (c - 'a' + 10);
                state = sw_quoted_second;
                break;
            }

            /* the invalid quoted character */

            state = sw_usual;

            *d++ = ch;

            break;

        case sw_quoted_second:

            state = sw_usual;

            if (ch >= '0' && ch <= '9') {
                ch = (u_char) ((decoded << 4) + ch - '0');

                if (type & NGX_UNESCAPE_REDIRECT) {
                    if (ch > '%' && ch < 0x7f) {
                        *d++ = ch;
                        break;
                    }

                    *d++ = '%'; *d++ = *(s - 2); *d++ = *(s - 1);

                    break;
                }

                 *d++ = ch;

                break;
            }

            c = (u_char) (ch | 0x20);
            if (c >= 'a' && c <= 'f') {
                ch = (u_char) ((decoded << 4) + c - 'a' + 10);

                if (type & NGX_UNESCAPE_URI) {
                    if (ch == '?') {
                        *d++ = ch;
                        goto done;
                    }

                    *d++ = ch;
                    break;
                }

                if (type & NGX_UNESCAPE_REDIRECT) {
                    if (ch == '?') {
                        *d++ = ch;
                        goto done;
                    }

                    if (ch > '%' && ch < 0x7f) {
                        *d++ = ch;
                        break;
                    }

                    *d++ = '%'; *d++ = *(s - 2); *d++ = *(s - 1);
                    break;
                }

                *d++ = ch;

                break;
            }

            /* the invalid quoted character */

            break;
        }
    }

done:

    *dst = d;
    *src = s;
}

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