libjob: add convenience idf58() function

Problem: The F58 representation of a Flux jobid is now the de facto
default representation of a jobid, but converting the flux_jobid_t
representation to this format for logging and other purposes is a bit
awkward. This makes it less likely for in-tree users to represent a
job in this format, and when they do, this requires a local buffer,
a call to flux_job_id_encode(3), etc.

Add a very simple, header-only conversion function to libjob for
this purpose

 const char *idf58 (flux_jobid_t id);

This function uses a thread-local buffer to avoid requiring callers
to allocate their own on the stack. This makes it much easier (and
thus much more likely) to log jobids in F58, since this function can
just be placed around the jobid, instead of requiring a local buffer
and previous function call the encode the id.

Author: grondo

src/common/libjob/Makefile.am

@@ -39,7 +39,8 @@ libjob_la_SOURCES = \
 	jj.c \
 	jj.h \
 	unwrap.c \
-	unwrap.h
+	unwrap.h \
+	idf58.h
 
 TESTS = \
 	test_job.t \

src/common/libjob/idf58.h

@@ -0,0 +1,35 @@
+/************************************************************\
+ * Copyright 2023 Lawrence Livermore National Security, LLC
+ * (c.f. AUTHORS, NOTICE.LLNS, COPYING)
+ *
+ * This file is part of the Flux resource manager framework.
+ * For details, see https://github.com/flux-framework.
+ *
+ * SPDX-License-Identifier: LGPL-3.0
+\************************************************************/
+
+#ifndef _IDF58_H
+#define _IDF58_H
+
+#include <flux/core.h>
+
+/*  Convenience function to convert a flux_jobid_t to F58 encoding
+ *  If the encode fails (unlikely), then the decimal encoding is returned.
+ */
+static inline const char *idf58 (flux_jobid_t id)
+{
+    static __thread char buf[21];
+    if (flux_job_id_encode (id, "f58", buf, sizeof (buf)) < 0) {
+        /* 64bit integer is guaranteed to fit in 21 bytes
+         * floor(log(2^64-1)/log(1)) + 1 = 20
+         */
+        (void) sprintf (buf, "%ju", (uintmax_t) id);
+    }
+    return buf;
+}
+
+#endif /* !_IDF58_H */
+
+/*
+ * vi:tabstop=4 shiftwidth=4 expandtab
+ */