From e44b5004840c80610a732e014ae8672277f16ee2 Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart@poettering.net>
Date: Thu, 11 Jun 2020 13:16:53 +0200
Subject: [PATCH] journalctl: make libqrencode a weak dependency

This way journalctl can make use of libqrencode if it's there, but will
quietly not use it if it isn't.

This means libqrencode remains a build-time dep, but not a strict
runtime dependency.

I figure we should do something similar for a bunch of other "leaf"
libraries we only use few symbols of. Specifically the following are
probably good candidates:

* pcre2
* libpwquality
* p11kit
* elfutils

and possibly:

* libcryptsetup (only in some parts. i.e. building systemd-cryptsetup
  without it makes no sense. However building the dissect option with
  libcryptsetup as optional dep does make sense)
* possibly the compression libraries (at least the ones we never use for
  compression, but only as alternative ones for decompression)

Already covered like this is:

* libxkcommon
---
 meson.build                  |  2 +-
 src/journal/journal-qrcode.c | 22 ++++++++++++++++++++--
 2 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/meson.build b/meson.build
index 8f1d1b5897..3a86967938 100644
--- a/meson.build
+++ b/meson.build
@@ -1780,7 +1780,7 @@ public_programs += executable(
         include_directories : includes,
         link_with : [libshared],
         dependencies : [threads,
-                        libqrencode,
+                        libdl,
                         libxz,
                         liblz4,
                         libpcre2,
diff --git a/src/journal/journal-qrcode.c b/src/journal/journal-qrcode.c
index 706d33c38a..dddbd7b381 100644
--- a/src/journal/journal-qrcode.c
+++ b/src/journal/journal-qrcode.c
@@ -7,6 +7,7 @@
 #include <stdlib.h>
 
 #include "alloc-util.h"
+#include "dlfcn-util.h"
 #include "fd-util.h"
 #include "fileio.h"
 #include "journal-qrcode.h"
@@ -40,6 +41,9 @@ int print_qr_code(
                 const char *hn,
                 sd_id128_t machine) {
 
+        QRcode* (*sym_QRcode_encodeString)(const char *string, int version, QRecLevel level, QRencodeMode hint, int casesensitive);
+        void (*sym_QRcode_free)(QRcode *qrcode);
+        _cleanup_(dlclosep) void *dl = NULL;
         _cleanup_free_ char *url = NULL;
         _cleanup_fclose_ FILE *f = NULL;
         size_t url_size = 0, i;
@@ -55,6 +59,20 @@ int print_qr_code(
         if (!is_locale_utf8() || !colors_enabled())
                 return -EOPNOTSUPP;
 
+        dl = dlopen("libqrencode.so.4", RTLD_LAZY);
+        if (!dl)
+                return log_debug_errno(SYNTHETIC_ERRNO(EOPNOTSUPP),
+                                       "QRCODE support is not installed: %s", dlerror());
+
+        r = dlsym_many_and_warn(
+                        dl,
+                        LOG_DEBUG,
+                        &sym_QRcode_encodeString, "QRcode_encodeString",
+                        &sym_QRcode_free, "QRcode_free",
+                        NULL);
+        if (r < 0)
+                return r;
+
         f = open_memstream_unlocked(&url, &url_size);
         if (!f)
                 return -ENOMEM;
@@ -81,7 +99,7 @@ int print_qr_code(
 
         f = safe_fclose(f);
 
-        qr = QRcode_encodeString(url, 0, QR_ECLEVEL_L, QR_MODE_8, 1);
+        qr = sym_QRcode_encodeString(url, 0, QR_ECLEVEL_L, QR_MODE_8, 1);
         if (!qr)
                 return -ENOMEM;
 
@@ -123,6 +141,6 @@ int print_qr_code(
 
         print_border(output, qr->width);
 
-        QRcode_free(qr);
+        sym_QRcode_free(qr);
         return 0;
 }