From 24443fa33ad20a178536e7d3c21c3b2bcf1167a9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jo=C3=A3o=20Valverde?= <j@v6e.pt>
Date: Sun, 10 Apr 2022 18:19:45 +0100
Subject: [PATCH] tshark: Add underline to dfilter errors

$ tshark -Y 'frame.number == 123foobar and ip' -r /dev/null
tshark: "123foobar" is not a valid number.
    frame.number == 123foobar and ip
                    ^~~~~~~~~
---
 epan/dfilter/dfilter.h |  3 +++
 tshark.c               | 13 ++++++++++---
 wsutil/str_util.c      | 20 ++++++++++++++++++++
 wsutil/str_util.h      |  3 +++
 4 files changed, 36 insertions(+), 3 deletions(-)

diff --git a/epan/dfilter/dfilter.h b/epan/dfilter/dfilter.h
index 7cbb4b1539..031ed667ff 100644
--- a/epan/dfilter/dfilter.h
+++ b/epan/dfilter/dfilter.h
@@ -67,6 +67,9 @@ dfilter_compile_real(const gchar *text, dfilter_t **dfp,
 #define dfilter_compile(text, dfp, err_msg) \
 	dfilter_compile_real(text, dfp, err_msg, NULL, __func__, FALSE, TRUE)
 
+#define dfilter_compile2(text, dfp, err_msg, loc_ptr) \
+	dfilter_compile_real(text, dfp, err_msg, loc_ptr, __func__, FALSE, TRUE)
+
 /* Frees all memory used by dfilter, and frees
  * the dfilter itself. */
 WS_DLL_PUBLIC
diff --git a/tshark.c b/tshark.c
index d39ffcd33f..012c6ded3d 100644
--- a/tshark.c
+++ b/tshark.c
@@ -722,7 +722,7 @@ must_do_dissection(dfilter_t *rfcode, dfilter_t *dfcode,
 int
 main(int argc, char *argv[])
 {
-    char                *err_msg;
+    char                *err_msg, *err_msg_cont;
     static const struct report_message_routines tshark_report_routines = {
         failure_message,
         failure_message,
@@ -777,6 +777,7 @@ main(int argc, char *argv[])
     gchar               *volatile dfilter = NULL;
     dfilter_t           *rfcode = NULL;
     dfilter_t           *dfcode = NULL;
+    dfilter_loc_t       df_loc;
     e_prefs             *prefs_p;
     gchar               *output_only = NULL;
     gchar               *volatile pdu_export_arg = NULL;
@@ -2013,9 +2014,12 @@ main(int argc, char *argv[])
 
     if (rfilter != NULL) {
         ws_debug("Compiling read filter: '%s'", rfilter);
-        if (!dfilter_compile(rfilter, &rfcode, &err_msg)) {
+        if (!dfilter_compile2(rfilter, &rfcode, &err_msg, &df_loc)) {
             cmdarg_err("%s", err_msg);
+            err_msg_cont = ws_strdup_error_offset(NULL, df_loc.col_start, df_loc.col_len);
+            cmdarg_err_cont("    %s\n    %s\n", rfilter, err_msg_cont);
             g_free(err_msg);
+            g_free(err_msg_cont);
             epan_cleanup();
             extcap_cleanup();
 
@@ -2040,9 +2044,12 @@ main(int argc, char *argv[])
 
     if (dfilter != NULL) {
         ws_debug("Compiling display filter: '%s'", dfilter);
-        if (!dfilter_compile(dfilter, &dfcode, &err_msg)) {
+        if (!dfilter_compile2(dfilter, &dfcode, &err_msg, &df_loc)) {
             cmdarg_err("%s", err_msg);
+            err_msg_cont = ws_strdup_error_offset(NULL, df_loc.col_start, df_loc.col_len);
+            cmdarg_err_cont("    %s\n    %s\n", dfilter, err_msg_cont);
             g_free(err_msg);
+            g_free(err_msg_cont);
             epan_cleanup();
             extcap_cleanup();
 
diff --git a/wsutil/str_util.c b/wsutil/str_util.c
index 099e331295..71ac049fe0 100644
--- a/wsutil/str_util.c
+++ b/wsutil/str_util.c
@@ -548,6 +548,26 @@ ws_strerrorname_r(int errnum, char *buf, size_t buf_size)
     return buf;
 }
 
+char *
+ws_strdup_error_offset(wmem_allocator_t *allocator, int offset, size_t len)
+{
+    if (offset < 0)
+        return NULL;
+
+    wmem_strbuf_t *buf = wmem_strbuf_sized_new(allocator, offset + len, 0);
+
+    for (int i = 0; i < offset; i++) {
+        wmem_strbuf_append_c(buf, ' ');
+    }
+    wmem_strbuf_append_c(buf, '^');
+
+    for (size_t l = len; l > 1; l--) {
+        wmem_strbuf_append_c(buf, '~');
+    }
+
+    return wmem_strbuf_finalize(buf);
+}
+
 /*
  * Editor modelines  -  https://www.wireshark.org/tools/modelines.html
  *
diff --git a/wsutil/str_util.h b/wsutil/str_util.h
index be6ce12485..d3278f8369 100644
--- a/wsutil/str_util.h
+++ b/wsutil/str_util.h
@@ -218,6 +218,9 @@ gchar printable_char_or_period(gchar c);
 WS_DLL_PUBLIC WS_RETNONNULL
 const char *ws_strerrorname_r(int errnum, char *buf, size_t buf_size);
 
+WS_DLL_PUBLIC
+char *ws_strdup_error_offset(wmem_allocator_t *allocator, int offset, size_t len);
+
 /* To pass one of two strings, singular or plural */
 #define plurality(d,s,p) ((d) == 1 ? (s) : (p))