Objects json: write incrementally and in numeric order

The following script was used to adjust test data:

----------
#!/usr/bin/env python3
import json
import sys
import re

def json_dumps(data):
    return json.dumps(data, ensure_ascii=False,
                      indent=2, separators=(',', ': '))

for filename in sys.argv[1:]:
    with open(filename, 'r') as f:
        data = json.loads(f.read())
    if 'objects' not in data:
        continue
    trailer = None
    to_sort = []
    for k, v in data['objects'].items():
        if k == 'trailer':
            trailer = v
        else:
            m = re.match(r'^(\d+) \d+ R', k)
            if m:
                to_sort.append([int(m.group(1)), k, v])
    newobjects = {x[1]: x[2] for x in sorted(to_sort)}
    if trailer is not None:
        newobjects['trailer'] = trailer
    data['objects'] = newobjects
print(json_dumps(data))
----------

1 files changed, 9 insertions, 2 deletions

diff --git a/libqpdf/JSON.cc b/libqpdf/JSON.cc
index 31675a42..1c49f9ee 100644
--- a/libqpdf/JSON.cc
+++ b/libqpdf/JSON.cc
@@ -78,6 +78,14 @@ JSON::writeArrayClose(Pipeline* p, bool first, size_t depth)
 }
 
 void
+JSON::writeDictionaryKey(
+    Pipeline* p, bool& first, std::string const& key, size_t depth)
+{
+    writeNext(p, first, depth);
+    *p << "\"" << key << "\": ";
+}
+
+void
 JSON::writeDictionaryItem(
     Pipeline* p,
     bool& first,
@@ -85,8 +93,7 @@ JSON::writeDictionaryItem(
     JSON const& value,
     size_t depth)
 {
-    writeNext(p, first, depth);
-    *p << "\"" << key << "\": ";
+    writeDictionaryKey(p, first, key, depth);
     value.write(p, 1 + depth);
 }