journal: implement message catalog

The message catalog can be used to attach short help texts to log lines,
keyed by their MESSAGE_ID= fields. This is useful to help the
administrator understand the context and cause of a message, find
possible solutions and find further related documentation.

Since this is keyed off MESSAGE_ID= this will only work for native
journal messages.

The message catalog supports i18n, and is useful to augment english
language system messages with explanations in the local language.

This commit only includes short explanatory messages for a few example
message IDs, we'll add more complete documentation for the relevant
systemd messages later on.

1 files changed, 60 insertions, 0 deletions

diff --git a/src/journal/sd-journal.c b/src/journal/sd-journal.c
index a346691e21..c86f1eaab1 100644
--- a/src/journal/sd-journal.c
+++ b/src/journal/sd-journal.c
@@ -38,11 +38,15 @@
 #include "compress.h"
 #include "journal-internal.h"
 #include "missing.h"
+#include "catalog.h"
+#include "replace-var.h"
 
 #define JOURNAL_FILES_MAX 1024
 
 #define JOURNAL_FILES_RECHECK_USEC (2 * USEC_PER_SEC)
 
+#define REPLACE_VAR_MAX 256
+
 static void detach_location(sd_journal *j) {
         Iterator i;
         JournalFile *f;
@@ -2389,3 +2393,59 @@ _public_ int sd_journal_reliable_fd(sd_journal *j) {
 
         return !j->on_network;
 }
+
+static char *lookup_field(const char *field, void *userdata) {
+        sd_journal *j = userdata;
+        const void *data;
+        size_t size, d;
+        int r;
+
+        assert(field);
+        assert(j);
+
+        r = sd_journal_get_data(j, field, &data, &size);
+        if (r < 0 ||
+            size > REPLACE_VAR_MAX)
+                return strdup(field);
+
+        d = strlen(field) + 1;
+
+        return strndup((const char*) data + d, size - d);
+}
+
+_public_ int sd_journal_get_catalog(sd_journal *j, char **ret) {
+        const void *data;
+        size_t size;
+        sd_id128_t id;
+        _cleanup_free_ char *text = NULL, *cid = NULL;
+        char *t;
+        int r;
+
+        if (!j)
+                return -EINVAL;
+        if (!ret)
+                return -EINVAL;
+
+        r = sd_journal_get_data(j, "MESSAGE_ID", &data, &size);
+        if (r < 0)
+                return r;
+
+        cid = strndup((const char*) data + 11, size - 11);
+        if (!cid)
+                return -ENOMEM;
+
+        r = sd_id128_from_string(cid, &id);
+        if (r < 0)
+                return r;
+
+        r = catalog_get(id, &text);
+        if (r < 0)
+                return r;
+
+        t = replace_var(text, lookup_field, j);
+        if (!t)
+                return -ENOMEM;
+
+        *ret = t;
+        return 0;
+}