MINOR: log: always consider "+M" option in lf_text_len()

Historically, when lf_text_len() or lf_text() were called with a NULL
string and "+M" option was set, "-" would be printed.

However, if the input string was simply an empty one with len > 0, then
nothing would be printed. This can happen if lf_text() is called with
an empty string because in this case len is set to size (indeed, for
performance reasons we don't pre-compute the length, we stop as soon
as we encounter a NULL-byte)

In practise, a lot of call places making use of lf_text() or lf_text_len()
try their best to avoid calling lf_text() with an empty string, and
instead explicitly call lf_text_len() with NULL as parameter to consider
the "+M" option.

But this is not enough, as shown in GH #2797, there could still be places
where lf_text() is called with an empty string. In such case, instead of
ignoring the "+M" option, let's check after _lf_text_len() if the returned
pointer differs from the original one. If both are equal, then it means
that nothing was printed (ie: result of empty string): in that case we
check the "+M" option to print "-" when possible.

While this commit seems harmless, it's probably better to avoid
backporting it since it could break existing applications relying on the
historical behavior.

diff --git a/src/log.c b/src/log.c
index ac94f5fbc74a89b15b998ba74d881cc87a7f34aa..441e692850507d558cc59165955f9d96e2c17a1e 100644 (file)
--- a/src/log.c
+++ b/src/log.c
@@ -2461,21 +2461,23 @@ static inline char *_lf_quotetext_len(char *dst, const char *src,
  */
 static char *lf_text_len(char *dst, const char *src, size_t len, size_t size, struct lf_buildctx *ctx)
 {
+       char *ret;
+
        if ((ctx->options & (LOG_OPT_QUOTE | LOG_OPT_ENCODE_JSON)))
                return _lf_quotetext_len(dst, src, len, size, ctx);
-       else if ((ctx->options & LOG_OPT_ENCODE_CBOR) ||
-                (src && len))
-               return _lf_text_len(dst, src, len, size, ctx);
 
-       if (size < 2)
-               return NULL;
+       ret = _lf_text_len(dst, src, len, size, ctx);
+       if (dst != ret ||
+           (ctx->options & LOG_OPT_ENCODE_CBOR) ||
+           !(ctx->options & LOG_OPT_MANDATORY))
+               return ret;
 
-       if ((ctx->options & LOG_OPT_MANDATORY))
-               return _lf_text_len(dst, "-", 1, size, ctx);
+       /* empty output and "+M" option is set, try to print '-' */
 
-       *dst = '\0';
+       if (size < 2)
+               return NULL;
 
-       return dst;
+       return _lf_text_len(dst, "-", 1, size, ctx);
 }
 
 /*