Make link checker also read from stdin

bin/build/checks/links.pl

@@ -25,13 +25,14 @@ use Fcntl qw(SEEK_SET);
 
 $\ = "\n"; # set output record separator
 
-my ($file) = @ARGV;
-die "Usage: $0 FILE\n" if not $file;
-open my $fh, '<', $file or die "Can't open $file: $!";
+my $filePath = shift;
+die "Usage: $0 FILEPATH [FILE]\n" if not $filePath;
+
+# Read stdin or file to in-memory array
+my @lines = <>;
 
 my $domainMatch = qr/(localhost|eth2book.info|upgrading-ethereum.info)/;
 my $newPagePath = qr/^(#{1,3} ).* <!-- ([^*]+)\*? -->$/;
-my $filePath = $file =~ s|[^/]+$||r;
 my $pagePath;
 my $inCode;
 
@@ -43,7 +44,7 @@ my %fns;
 
 # First pass: build lists of anchors and footnotes
 $inCode = 0;
-while(<$fh>) {
+foreach (@lines) {
 
     $inCode = 1 - $inCode if /^```/;
     next if $inCode;
@@ -75,11 +76,8 @@ while(<$fh>) {
 
 $inCode and die "Error: unbalanced code block markers!";
 
-# Reset position to start of file
-seek $fh, $. = 0, SEEK_SET;
-
 # Second pass: check anchors and footnotes exist
-while(<$fh>) {
+foreach (@lines) {
 
     /^```/ and $inCode = 1 - $inCode;
     next if $inCode;
@@ -99,7 +97,7 @@ while(<$fh>) {
 
         if ($isImg) {
             unless(-e $filePath . $link) {
-                print "Nonexistent image file: $link line $.";
+                print "Image file $link not found in $filePath: line $.";
             }
         } else {
             if ($link =~ /^\/\.\./) {

bin/build/checks/lint_source_md.js

@@ -68,7 +68,7 @@ export default async function (file) {
     },
   };
 
-  const result = await lint(options);
-
-  return result[file].length > 0 ? result.toString() : '';
+  return lint(options).then((result) =>
+    result[file].length ? result.toString() : '',
+  );
 }

bin/build/prebuild.js

@@ -27,6 +27,7 @@ const whitespaceChecker = 'bin/build/checks/whitespace.pl';
 const latexChecker = 'bin/build/checks/latex.pl';
 
 const sourceMarkdown = 'src/book.md';
+const imagePath = 'src/';
 const ourSpellings = 'src/spellings.en.pws';
 
 async function execAsync(cmd) {
@@ -42,7 +43,7 @@ const checks = [
   {
     name: 'internal links',
     enabled: doInternalLinks,
-    checker: () => execAsync(`${linkChecker} ${sourceMarkdown}`),
+    checker: () => execAsync(`${linkChecker} ${imagePath} ${sourceMarkdown}`),
   },
   {
     name: 'HTML',