Add load_file().

Build.PL

@@ -14,6 +14,7 @@ Module::Build->new(
     },
     requires => {
         'Carp'   => 0,
+        'JSON'   => 0,
         'perl'   => 5.010,
         'SemVer' => '0.2.0',
     },

lib/PGXN/Meta/Validator.pm

@@ -4,6 +4,8 @@ use 5.010;
 use strict;
 use warnings;
 use SemVer;
+use JSON;
+use Carp qw(croak);
 our $VERSION = v0.10.0;
 
 =head1 Name
@@ -160,7 +162,7 @@ The constructor must be passed a metadata structure.
 =cut
 
 sub new {
-  my ($class,$data) = @_;
+  my ($class, $data) = @_;
 
   # create an attributes hash
   my $self = {
@@ -173,6 +175,30 @@ sub new {
   return bless $self, $class;
 }
 
+=head3 C<load_file>
+
+  my $meta = PGXN::Meta::Validator->load_file('META.json');
+
+Reads in the specified JSON file and passes the resulting data structure to
+C<new()>, returning the resulting PGXN::Meta::Validator object. An exception
+will be thrown if the file does not exist or if its contents are not valid
+JSON.
+
+=cut
+
+sub load_file {
+    my ($class, $file) = @_;
+
+    croak "load_file() requires a valid, readable filename"
+        unless -r $file;
+
+    $class->new(JSON->new->decode(do {
+        local $/;
+        open my $fh, '<:raw', $file or croak "Cannot open $file: $!\n";
+        <$fh>;
+    }));
+}
+
 =head2 Instance Methods
 
 =head3 C<is_valid>

t/META.json

@@ -0,0 +1,54 @@
+{
+   "name": "pgTAP",
+   "abstract": "Unit testing for PostgreSQL",
+   "description": "pgTAP is a suite of database functions that make it easy to write TAP-emitting unit tests in psql scripts or xUnit-style test functions.",
+   "version": "0.26.0",
+   "maintainer": [
+      "David E. Wheeler <david@kineticode.com>",
+      "pgTAP List <pgtap-users@pgfoundry.org>"
+   ],
+   "license": {
+      "PostgreSQL": "http://www.postgresql.org/about/licence"
+   },
+   "prereqs": {
+      "runtime": {
+         "requires": {
+            "plpgsql": 0,
+            "PostgreSQL": "8.0.0"
+         },
+         "recommends": {
+            "PostgreSQL": "8.4.0"
+         }
+      }
+   },
+   "provides": {
+     "pgtap": {
+       "abstract": "Unit testing for PostgreSQL",
+       "file": "pgtap.sql",
+       "version": "0.26.0"
+     }
+   },
+   "resources": {
+      "homepage": "http://pgtap.org/",
+      "bugtracker": {
+         "web": "https://github.com/theory/pgtap/issues"
+      },
+      "repository": {
+        "url":  "https://github.com/theory/pgtap.git",
+        "web":  "https://github.com/theory/pgtap",
+        "type": "git"
+      }
+   },
+   "generated_by": "David E. Wheeler",
+   "meta-spec": {
+      "version": "1.0.0",
+      "url": "http://pgxn.org/meta/spec.txt"
+   },
+   "tags": [
+      "testing",
+      "unit testing",
+      "tap",
+      "tddd",
+      "test driven database development"
+   ]
+}

t/base.t

@@ -0,0 +1,33 @@
+use strict;
+use warnings;
+use Test::More tests => 7;
+use File::Spec;
+
+BEGIN {
+    use_ok 'PGXN::Meta::Validator' or die;
+}
+
+my $file = File::Spec->catfile(qw(t META.json));
+
+ok my $pmv = PGXN::Meta::Validator->new(JSON->new->decode(do {
+    local $/;
+    open my $fh, '<:raw', $file or die "Cannot open $file: $!\n";
+    <$fh>;
+})), 'Construct from data structure';
+ok $pmv->is_valid, 'Structure should be valid';
+
+ok $pmv = PGXN::Meta::Validator->load_file($file), 'Load from file';
+ok $pmv->is_valid, 'File should be valid';
+
+local $@;
+eval {
+    PGXN::Meta::Validator->load_file('nonexistent');
+};
+like $@, qr{^load_file\(\) requires a valid, readable filename},
+    'Should catch exception for nonexistent file';
+
+eval {
+    PGXN::Meta::Validator->load_file('Changes');
+};
+like $@, qr{^malformed JSON string},
+    'Should catch exception for invalid JSON';