nfq: consistent nfq_snprintf_xml() return value with snprintf()

With this patch, nfq_snprintf_xml() returns the number of characters
printed. If the output was truncated, then the return value is the
number of characters that would have been written if enough space
had been available. This makes nfq_snprintf_xml() consistent with
the behaviour of snprintf().

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/src/libnetfilter_queue.c b/src/libnetfilter_queue.c
index bb2771a..7da16be 100644 (file)
--- a/src/libnetfilter_queue.c
+++ b/src/libnetfilter_queue.c
@@ -1012,24 +1012,27 @@ int nfq_get_payload(struct nfq_data *nfad, unsigned char **data)
        return -1;
 }
 
-#define SNPRINTF_FAILURE(size, len, offset)                    \
+#define SNPRINTF_FAILURE(ret, rem, offset, len)                        \
 do {                                                           \
-       if (size < 0 || (unsigned int) size >= len)             \
-               return size;                                    \
-       offset += size;                                         \
-       len -= size;                                            \
+       if (ret < 0)                                            \
+               return ret;                                     \
+       len += ret;                                             \
+       if (ret > rem)                                          \
+               ret = rem;                                      \
+       offset += ret;                                          \
+       rem -= ret;                                             \
 } while (0)
 
-int nfq_snprintf_xml(char *buf, size_t len, struct nfq_data *tb, int flags)
+int nfq_snprintf_xml(char *buf, size_t rem, struct nfq_data *tb, int flags)
 {
        struct nfqnl_msg_packet_hdr *ph;
        struct nfqnl_msg_packet_hw *hwph;
        u_int32_t mark, ifi;
-       int size, offset = 0, ret;
+       int size, offset = 0, len = 0, ret;
        unsigned char *data;
 
-       size = snprintf(buf + offset, len, "<pkt>");
-       SNPRINTF_FAILURE(size, len, offset);
+       size = snprintf(buf + offset, rem, "<pkt>");
+       SNPRINTF_FAILURE(size, rem, offset, len);
 
        if (flags & NFQ_XML_TIME) {
                time_t t;
@@ -1039,128 +1042,128 @@ int nfq_snprintf_xml(char *buf, size_t len, struct nfq_data *tb, int flags)
                if (localtime_r(&t, &tm) == NULL)
                        return -1;
 
-               size = snprintf(buf + offset, len, "<when>");
-               SNPRINTF_FAILURE(size, len, offset);
+               size = snprintf(buf + offset, rem, "<when>");
+               SNPRINTF_FAILURE(size, rem, offset, len);
 
-               size = snprintf(buf + offset, len,
+               size = snprintf(buf + offset, rem,
                                "<hour>%d</hour>", tm.tm_hour);
-               SNPRINTF_FAILURE(size, len, offset);
+               SNPRINTF_FAILURE(size, rem, offset, len);
 
                size = snprintf(buf + offset,
-                               len, "<min>%02d</min>", tm.tm_min);
-               SNPRINTF_FAILURE(size, len, offset);
+                               rem, "<min>%02d</min>", tm.tm_min);
+               SNPRINTF_FAILURE(size, rem, offset, len);
 
                size = snprintf(buf + offset,
-                               len, "<sec>%02d</sec>", tm.tm_sec);
-               SNPRINTF_FAILURE(size, len, offset);
+                               rem, "<sec>%02d</sec>", tm.tm_sec);
+               SNPRINTF_FAILURE(size, rem, offset, len);
 
-               size = snprintf(buf + offset, len, "<wday>%d</wday>",
+               size = snprintf(buf + offset, rem, "<wday>%d</wday>",
                                tm.tm_wday + 1);
-               SNPRINTF_FAILURE(size, len, offset);
+               SNPRINTF_FAILURE(size, rem, offset, len);
 
-               size = snprintf(buf + offset, len, "<day>%d</day>", tm.tm_mday);
-               SNPRINTF_FAILURE(size, len, offset);
+               size = snprintf(buf + offset, rem, "<day>%d</day>", tm.tm_mday);
+               SNPRINTF_FAILURE(size, rem, offset, len);
 
-               size = snprintf(buf + offset, len, "<month>%d</month>",
+               size = snprintf(buf + offset, rem, "<month>%d</month>",
                                tm.tm_mon + 1);
-               SNPRINTF_FAILURE(size, len, offset);
+               SNPRINTF_FAILURE(size, rem, offset, len);
 
-               size = snprintf(buf + offset, len, "<year>%d</year>",
+               size = snprintf(buf + offset, rem, "<year>%d</year>",
                                1900 + tm.tm_year);
-               SNPRINTF_FAILURE(size, len, offset);
+               SNPRINTF_FAILURE(size, rem, offset, len);
 
-               size = snprintf(buf + offset, len, "</when>");
-               SNPRINTF_FAILURE(size, len, offset);
+               size = snprintf(buf + offset, rem, "</when>");
+               SNPRINTF_FAILURE(size, rem, offset, len);
        }
 
        ph = nfq_get_msg_packet_hdr(tb);
        if (ph) {
-               size = snprintf(buf + offset, len,
+               size = snprintf(buf + offset, rem,
                                "<hook>%u</hook><id>%u</id>",
                                ph->hook, ntohl(ph->packet_id));
-               SNPRINTF_FAILURE(size, len, offset);
+               SNPRINTF_FAILURE(size, rem, offset, len);
 
                hwph = nfq_get_packet_hw(tb);
                if (hwph && (flags & NFQ_XML_HW)) {
                        int i, hlen = ntohs(hwph->hw_addrlen);
 
-                       size = snprintf(buf + offset, len, "<hw><proto>0x%04x"
+                       size = snprintf(buf + offset, rem, "<hw><proto>0x%04x"
                                                           "</proto>",
                                        ntohs(ph->hw_protocol));
-                       SNPRINTF_FAILURE(size, len, offset);
+                       SNPRINTF_FAILURE(size, rem, offset, len);
 
-                       size = snprintf(buf + offset, len, "<src>");
-                       SNPRINTF_FAILURE(size, len, offset);
+                       size = snprintf(buf + offset, rem, "<src>");
+                       SNPRINTF_FAILURE(size, rem, offset, len);
 
                        for (i=0; i<hlen-1; i++) {
-                               size = snprintf(buf + offset, len, "%02x:",
+                               size = snprintf(buf + offset, rem, "%02x:",
                                                ntohs(ph->hw_protocol));
-                               SNPRINTF_FAILURE(size, len, offset);
+                               SNPRINTF_FAILURE(size, rem, offset, len);
                        }
 
-                       size = snprintf(buf + offset, len, "</src></hw>");
-                       SNPRINTF_FAILURE(size, len, offset);
+                       size = snprintf(buf + offset, rem, "</src></hw>");
+                       SNPRINTF_FAILURE(size, rem, offset, len);
                } else if (flags & NFQ_XML_HW) {
-                       size = snprintf(buf + offset, len, "<hw><proto>0x%04x"
+                       size = snprintf(buf + offset, rem, "<hw><proto>0x%04x"
                                                    "</proto></hw>",
                                 ntohs(ph->hw_protocol));
-                       SNPRINTF_FAILURE(size, len, offset);
+                       SNPRINTF_FAILURE(size, rem, offset, len);
                }
        }
 
        mark = nfq_get_nfmark(tb);
        if (mark && (flags & NFQ_XML_MARK)) {
-               size = snprintf(buf + offset, len, "<mark>%u</mark>", mark);
-               SNPRINTF_FAILURE(size, len, offset);
+               size = snprintf(buf + offset, rem, "<mark>%u</mark>", mark);
+               SNPRINTF_FAILURE(size, rem, offset, len);
        }
 
        ifi = nfq_get_indev(tb);
        if (ifi && (flags & NFQ_XML_DEV)) {
-               size = snprintf(buf + offset, len, "<indev>%u</indev>", ifi);
-               SNPRINTF_FAILURE(size, len, offset);
+               size = snprintf(buf + offset, rem, "<indev>%u</indev>", ifi);
+               SNPRINTF_FAILURE(size, rem, offset, len);
        }
 
        ifi = nfq_get_outdev(tb);
        if (ifi && (flags & NFQ_XML_DEV)) {
-               size = snprintf(buf + offset, len, "<outdev>%u</outdev>", ifi);
-               SNPRINTF_FAILURE(size, len, offset);
+               size = snprintf(buf + offset, rem, "<outdev>%u</outdev>", ifi);
+               SNPRINTF_FAILURE(size, rem, offset, len);
        }
 
        ifi = nfq_get_physindev(tb);
        if (ifi && (flags & NFQ_XML_PHYSDEV)) {
-               size = snprintf(buf + offset, len,
+               size = snprintf(buf + offset, rem,
                                "<physindev>%u</physindev>", ifi);
-               SNPRINTF_FAILURE(size, len, offset);
+               SNPRINTF_FAILURE(size, rem, offset, len);
        }
 
        ifi = nfq_get_physoutdev(tb);
        if (ifi && (flags & NFQ_XML_PHYSDEV)) {
-               size = snprintf(buf + offset, len,
+               size = snprintf(buf + offset, rem,
                                "<physoutdev>%u</physoutdev>", ifi);
-               SNPRINTF_FAILURE(size, len, offset);
+               SNPRINTF_FAILURE(size, rem, offset, len);
        }
 
        ret = nfq_get_payload(tb, &data);
        if (ret >= 0 && (flags & NFQ_XML_PAYLOAD)) {
                int i;
 
-               size = snprintf(buf + offset, len, "<payload>");
-               SNPRINTF_FAILURE(size, len, offset);
+               size = snprintf(buf + offset, rem, "<payload>");
+               SNPRINTF_FAILURE(size, rem, offset, len);
 
                for (i=0; i<ret; i++) {
-                       size = snprintf(buf + offset, len, "%02x",
+                       size = snprintf(buf + offset, rem, "%02x",
                                        data[i] & 0xff);
-                       SNPRINTF_FAILURE(size, len, offset);
+                       SNPRINTF_FAILURE(size, rem, offset, len);
                }
 
-               size = snprintf(buf + offset, len, "</payload>");
-               SNPRINTF_FAILURE(size, len, offset);
+               size = snprintf(buf + offset, rem, "</payload>");
+               SNPRINTF_FAILURE(size, rem, offset, len);
        }
 
-       size = snprintf(buf + offset, len, "</pkt>");
-       SNPRINTF_FAILURE(size, len, offset);
+       size = snprintf(buf + offset, rem, "</pkt>");
+       SNPRINTF_FAILURE(size, rem, offset, len);
 
-       return size;
+       return len;
 }
 
 /**