README

The exiftool command handles the arguments then invokes module ExifTool.pm:

$info = $et->ImageInfo(Infile($pipe), \@foundTags);

The ExifTool.pm creates a Random Access File object using the RAF library, also written by exiftool's author:

if ($self->Open(\*EXIFTOOL_FILE, $filename)) {
    # create random access file object
    $raf = new File::RandomAccess(\*EXIFTOOL_FILE);

We could replace the $raf->Function() calls with some new calls to read from HTTP. Unless all the submodules also use RAF, in which case there's a lot of code to change.

Turns out ExifTool.pm 'require's a libary based on the file type, so for a .mov file it opens QuickTime.pm and invokes ProcessMOV:

require "Image/ExifTool/$module.pm";
$func = "Image::ExifTool::${module}::$func";

The media-type-specific module does in fact have calls to $raf->Seek(), Tell(), Read(). All the sublibraries use $raf calls.

After defining all the extraction patterns and functions, it returns to ExifTool.pm to process it:

# process the file
no strict 'refs';
my $result = &$func($self, \%dirInfo);

This library is supposed to mimic File::RandomAccess replacing all its seek(), tell(), read() calls with ones that read from HTTP using byte ranges. We should then be able to do something like:

$raf = httpRandomAccess(URL)
$raf->Seek(0xCAFEBABE, 0)
$raf->Read(42)
$raf->Tell()