diff options
Diffstat (limited to 'include/osmocom/core/utils.h')
| -rw-r--r-- | include/osmocom/core/utils.h | 85 |
1 files changed, 85 insertions, 0 deletions
diff --git a/include/osmocom/core/utils.h b/include/osmocom/core/utils.h index fe360b33..16159d3d 100644 --- a/include/osmocom/core/utils.h +++ b/include/osmocom/core/utils.h @@ -145,4 +145,89 @@ uint32_t osmo_isqrt32(uint32_t x); const char osmo_luhn(const char* in, int in_len); +/*! State for OSMO_STRBUF_APPEND() and OSMO_STRBUF_PRINTF(). See there for examples. */ +struct osmo_strbuf { + /*! Point to the start of a string buffer. */ + char *buf; + /*! Total sizeof() the buffer buf points at. */ + size_t len; + /*! Current writing position in buf (end of the string written so far). */ + char *pos; + /*! After all OSMO_STRBUF_APPEND operations, reflects the total number of characters that would be written had + * buf been large enough. Like snprintf()'s return value, this does not include the terminating nul character. + * Hence, to allocate an adequately sized buffer, add 1 to this number. */ + size_t chars_needed; +}; + +/*! Append a string to a buffer, as printed by an snprintf()-like function and with similar bounds checking. + * Make sure to never write past the end of the buffer, and collect the total size that would be needed. + * + * // an example function implementation to append: write N spaces. + * int print_spaces(char *dst, size_t dst_len, int n) + * { + * int i; + * if (n < 0) + * return -EINVAL; + * for (i = 0; i < n && i < dst_len; i++) + * dst[i] = ' '; + * if (dst_len) + * dst[OSMO_MIN(dst_len - 1, n)] = '\0'; + * // return the n that we would have liked to write if space were available: + * return n; + * } + * + * // append above spaces as well as an snprintf() + * void strbuf_example() + * { + * char buf[23]; + * struct osmo_strbuf sb = { .buf = buf, .len = sizeof(buf) }; + * + * OSMO_STRBUF_APPEND(sb, print_spaces, 5); + * OSMO_STRBUF_APPEND(sb, snprintf, "The answer is %d but what is the question?", 42); + * OSMO_STRBUF_APPEND(sb, print_spaces, 423423); + * + * printf("%s\n", buf); + * printf("would have needed %zu bytes\n", sb.chars_needed); + * } + * + * \param[inout] STRBUF A struct osmo_strbuf instance. + * \param[in] func A function with a signature of int func(char *dst, size_t dst_len [, args]) with semantics like + * snprintf(). + * \param[in] args Arguments passed to func, if any. + */ +#define OSMO_STRBUF_APPEND(STRBUF, func, args...) do { \ + if (!(STRBUF).pos) \ + (STRBUF).pos = (STRBUF).buf; \ + size_t remain = (STRBUF).buf ? (STRBUF).len - ((STRBUF).pos - (STRBUF).buf) : 0; \ + int l = func((STRBUF).pos, remain, ##args); \ + if (l < 0 || l > remain) \ + (STRBUF).pos = (STRBUF).buf + (STRBUF).len; \ + else \ + (STRBUF).pos += l; \ + if (l > 0) \ + (STRBUF).chars_needed += l; \ + } while(0) + +/*! Shortcut for OSMO_STRBUF_APPEND() invocation using snprintf(). + * + * int strbuf_example2(char *buf, size_t buflen) + * { + * int i; + * struct osmo_strbuf sb = { .buf = buf, .len = buflen }; + * + * OSMO_STRBUF_PRINTF(sb, "T minus"); + * for (i = 10; i; i--) + * OSMO_STRBUF_PRINTF(sb, " %d", i); + * OSMO_STRBUF_PRINTF(sb, " ... Lift off!"); + * + * return sb.chars_needed; + * } + * + * \param[inout] STRBUF A struct osmo_strbuf instance. + * \param[in] fmt Format string passed to snprintf. + * \param[in] args Additional arguments passed to snprintf, if any. + */ +#define OSMO_STRBUF_PRINTF(STRBUF, fmt, args...) \ + OSMO_STRBUF_APPEND(STRBUF, snprintf, fmt, ##args) + /*! @} */ |