From 4d5d1bba731f7dabc4511abce305584d769dfe60 Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart@poettering.net>
Date: Thu, 30 Apr 2020 14:52:25 +0200
Subject: [PATCH] journalctl: optionally, show a different field than MESSAGE
 in -o cat mode

Fixes: #15621
---
 src/shared/logs-show.c | 98 ++++++++++++++++++++++++++----------------
 1 file changed, 62 insertions(+), 36 deletions(-)

diff --git a/src/shared/logs-show.c b/src/shared/logs-show.c
index 6f8de02781..6737cda1d2 100644
--- a/src/shared/logs-show.c
+++ b/src/shared/logs-show.c
@@ -1016,6 +1016,57 @@ finish:
         return r;
 }
 
+static int output_cat_field(
+                FILE *f,
+                sd_journal *j,
+                OutputFlags flags,
+                const char *field,
+                const size_t highlight[2]) {
+
+        const char *highlight_on, *highlight_off;
+        const void *data;
+        size_t l, fl;
+        int r;
+
+        if (FLAGS_SET(flags, OUTPUT_COLOR)) {
+                highlight_on = ANSI_HIGHLIGHT_RED;
+                highlight_off = ANSI_NORMAL;
+        } else
+                highlight_on = highlight_off = "";
+
+        r = sd_journal_get_data(j, field, &data, &l);
+        if (r == -EBADMSG) {
+                log_debug_errno(r, "Skipping message we can't read: %m");
+                return 0;
+        }
+        if (r == -ENOENT) /* An entry without the requested field */
+                return 0;
+        if (r < 0)
+                return log_error_errno(r, "Failed to get data: %m");
+
+        fl = strlen(field);
+        assert(l >= fl + 1);
+        assert(((char*) data)[fl] == '=');
+
+        data = (const uint8_t*) data + fl + 1;
+        l -= fl + 1;
+
+        if (highlight && FLAGS_SET(flags, OUTPUT_COLOR)) {
+                assert(highlight[0] <= highlight[1]);
+                assert(highlight[1] <= l);
+
+                fwrite((const char*) data, 1, highlight[0], f);
+                fwrite(highlight_on, 1, strlen(highlight_on), f);
+                fwrite((const char*) data + highlight[0], 1, highlight[1] - highlight[0], f);
+                fwrite(highlight_off, 1, strlen(highlight_off), f);
+                fwrite((const char*) data + highlight[1], 1, l - highlight[1], f);
+        } else
+                fwrite((const char*) data, 1, l, f);
+
+        fputc('\n', f);
+        return 0;
+}
+
 static int output_cat(
                 FILE *f,
                 sd_journal *j,
@@ -1025,49 +1076,24 @@ static int output_cat(
                 Set *output_fields,
                 const size_t highlight[2]) {
 
-        const void *data;
-        size_t l;
+        const char *field;
+        Iterator iterator;
         int r;
-        const char *highlight_on = "", *highlight_off = "";
 
         assert(j);
         assert(f);
 
-        if (flags & OUTPUT_COLOR) {
-                highlight_on = ANSI_HIGHLIGHT_RED;
-                highlight_off = ANSI_NORMAL;
+        (void) sd_journal_set_data_threshold(j, 0);
+
+        if (set_isempty(output_fields))
+                return output_cat_field(f, j, flags, "MESSAGE", highlight);
+
+        SET_FOREACH(field, output_fields, iterator) {
+                r = output_cat_field(f, j, flags, field, streq(field, "MESSAGE") ? highlight : NULL);
+                if (r < 0)
+                        return r;
         }
 
-        sd_journal_set_data_threshold(j, 0);
-
-        r = sd_journal_get_data(j, "MESSAGE", &data, &l);
-        if (r == -EBADMSG) {
-                log_debug_errno(r, "Skipping message we can't read: %m");
-                return 0;
-        }
-        if (r < 0) {
-                /* An entry without MESSAGE=? */
-                if (r == -ENOENT)
-                        return 0;
-
-                return log_error_errno(r, "Failed to get data: %m");
-        }
-
-        assert(l >= 8);
-
-        if (highlight && (flags & OUTPUT_COLOR)) {
-                assert(highlight[0] <= highlight[1]);
-                assert(highlight[1] <= l - 8);
-
-                fwrite((const char*) data + 8, 1, highlight[0], f);
-                fwrite(highlight_on, 1, strlen(highlight_on), f);
-                fwrite((const char*) data + 8 + highlight[0], 1, highlight[1] - highlight[0], f);
-                fwrite(highlight_off, 1, strlen(highlight_off), f);
-                fwrite((const char*) data + 8 + highlight[1], 1, l - 8 - highlight[1], f);
-        } else
-                fwrite((const char*) data + 8, 1, l - 8, f);
-        fputc('\n', f);
-
         return 0;
 }