json_writer: new routines to create JSON data

Add "struct json_writer" and a series of jw_ routines to compose JSON
data into a string buffer.  The resulting string may then be printed by
commands wanting to support a JSON-like output format.

The json_writer is limited to correctly formatting structured data for
output.  It does not attempt to build an object model of the JSON data.

We say "JSON-like" because we do not enforce the Unicode (usually UTF-8)
requirement on string fields.  Internally, Git does not necessarily have
Unicode/UTF-8 data for most fields, so it is currently unclear the best
way to enforce that requirement.  For example, on Linux pathnames can
contain arbitrary 8-bit character data, so a command like "status" would
not know how to encode the reported pathnames.  We may want to revisit
this (or double encode such strings) in the future.

Helped-by: Eric Sunshine <sunshine@sunshineco.com>
Helped-by: René Scharfe <l.s.r@web.de>
Helped-by: Wink Saville <wink@saville.com>
Helped-by: Ramsay Jones <ramsay@ramsayjones.plus.com>
Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 52 insertions, 0 deletions

diff --git a/t/t0019/parse_json.perl b/t/t0019/parse_json.perl
new file mode 100644
index 0000000000..ca4e5bfa78
--- /dev/null
+++ b/t/t0019/parse_json.perl
@@ -0,0 +1,52 @@
+#!/usr/bin/perl
+use strict;
+use warnings;
+use JSON;
+
+sub dump_array {
+    my ($label_in, $ary_ref) = @_;
+    my @ary = @$ary_ref;
+
+    for ( my $i = 0; $i <= $#{ $ary_ref }; $i++ )
+    {
+	my $label = "$label_in\[$i\]";
+	dump_item($label, $ary[$i]);
+    }
+}
+
+sub dump_hash {
+    my ($label_in, $obj_ref) = @_;
+    my %obj = %$obj_ref;
+
+    foreach my $k (sort keys %obj) {
+	my $label = (length($label_in) > 0) ? "$label_in.$k" : "$k";
+	my $value = $obj{$k};
+
+	dump_item($label, $value);
+    }
+}
+
+sub dump_item {
+    my ($label_in, $value) = @_;
+    if (ref($value) eq 'ARRAY') {
+	print "$label_in array\n";
+	dump_array($label_in, $value);
+    } elsif (ref($value) eq 'HASH') {
+	print "$label_in hash\n";
+	dump_hash($label_in, $value);
+    } elsif (defined $value) {
+	print "$label_in $value\n";
+    } else {
+	print "$label_in null\n";
+    }
+}
+
+my $row = 0;
+while (<>) {
+    my $data = decode_json( $_ );
+    my $label = "row[$row]";
+
+    dump_hash($label, $data);
+    $row++;
+}
+