wiretap: candump: Don't generate a temporary PCAP file

It's preferable to parse text files and generate packets on demand,
rather than generate a temporary PCAP file and dump all available
packets into it.

Parsing on the fly has a benefit of handling damaged files up to the
point of damage, while the approach with a temporary file doesn't
allow either to report that the original file is damaged or perform
conversion in the first place.

This version works faster than the previous one.

Command:
time ./run/tshark -r ./candump-2019-07-01_111120.log.gz > /dev/null

The test file is attached to the bug 15889

The current version:
real    0m0,597s
user    0m0,533s
sys     0m0,118s

The previous version:
real    0m2,176s
user    0m1,966s
sys     0m0,100s

Bug: 15889
Change-Id: I862ce47752531c2e9d9459f5d865c1fc08f32fea
Reviewed-on: https://code.wireshark.org/review/34007
Petri-Dish: Anders Broman <a.broman58@gmail.com>
Tested-by: Petri Dish Buildbot
Reviewed-by: Anders Broman <a.broman58@gmail.com>

1 files changed, 14 insertions, 8 deletions

diff --git a/wiretap/candump_scanner.l b/wiretap/candump_scanner.l
index 98b98ee791..b74f14cc17 100644
--- a/wiretap/candump_scanner.l
+++ b/wiretap/candump_scanner.l
@@ -48,22 +48,28 @@
 #define YY_NO_UNISTD_H
 #endif
 
-static int candump_yyinput(void *buf, unsigned int max_size,
-                           candump_state_t *state)
+static int candump_yyinput(void *buf, candump_state_t *state)
 {
-    int result = file_read(buf, max_size, state->fh);
+    int c = file_getc(state->fh);
 
-    if (result == EOF)
+    if (c == EOF)
     {
         state->err = file_error(state->fh, &state->err_info);
-        result     = YY_NULL;
+        return YY_NULL;
     }
 
-    return result;
+    *(char *)buf = c;
+
+    return 1;
 }
 
 #define YY_INPUT(buf, result, max_size) \
-    do { (result) = candump_yyinput((buf), (max_size), yyextra); } while (0)
+    do { (result) = candump_yyinput((buf), yyextra); } while (0)
+
+/* Count bytes read. This is required in order to rewind the file
+ * to the beginning of the next packet, since flex reads more bytes
+ * before executing the action that does yyterminate(). */
+#define YY_USER_ACTION do { yyextra->file_bytes_read += yyleng; } while (0);
 
 /*
  * Sleazy hack to suppress compiler warnings in yy_fatal_error().
@@ -87,7 +93,7 @@ HEX [0-9A-Fa-f]
 %%
 
 [ \t]                   { return TOKEN_SPACE; };
-[\r\n]                  { return TOKEN_ENDL; }
+[\r\n][ \t\r\n]*        { yyterminate(); }
 
 \({INT}+\.{INT}+\)      {
                             yyextra->token.v0 = strtoul(yytext + 1, NULL, 10);