AppFS should normally be mounted on "/opt/appfs".

    /opt/appfs/hostname
    	Fetches: http://hostname/appfs/index
    	Contains CSV file: hash,hashMethod,<certificateInDERFormatInHex>,<PKCS#1v1.5-signature-inDERFormatInHex>
	                   \-------------/
                                  ^- Signed data
    	Fetches: http://hostname/appfs/<hashMethod>/<hash>
    	Contains CSV file: package,version,os,cpuArch,packageManifestHash,isLatest

    /opt/appfs/hostname/package/os-cpuArch/version
    /opt/appfs/hostname/<hashMethod>/
    	Fetches: http://hostname/appfs/<hashMethod>/<packageManifestHash>
    	Contains CSV file:
    		type,time,extraData,name
    		type == directory; extraData = (null)
    		type == symlink; extraData = source
    		type == file; extraData = size,perms,fileHash

    /opt/appfs/hostname/{packageManifestHash,package/os-cpuArch/version}/file
    	Fetches: http://hostname/appfs/<hashMethod>/<fileHash>

Database
--------
    sites(hostname, hashMethod, lastUpdate, ttl)
    packages(hostname, packageManifestHash, package, version, os, cpuArch, isLatest, haveManifest)
    files(packageManifestHash, type, time, source, size, perms, fileHash, file_name, file_directory)

Resources
---------
http://appfs.rkeene.org/

	# User-replaceable function get the home directory of the current user
	proc get_homedir {} {
		return [::appfsd::get_homedir]
	}

	# User-replacable function to update permissions
	proc change_perms {file hash perms {hashMethod "sha1"}} {
		if {[info exists ::appfs::user::add_perms($file)]} {
			append perms $::appfs::user::add_perms($file)
		}

		if {[info exists ::appfs::user::add_perms([list $hashMethod $hash])]} {
			append perms $::appfs::user::add_perms([list $hashMethod $hash])
		} elseif {$hashMethod eq "sha1" && [info exists ::appfs::user::add_perms($hash)]} {
			append perms $::appfs::user::add_perms($hash)
		}

		return $perms
	}

	# User-replacable function to fetch a remote file
	proc download_file {url {outputChannel ""}} {

		return $file
	}


	proc _isHash {value} {
		set value [string tolower $value]





		if {![regexp {^[0-9a-f]*$} $value]} {
			return false
		}

		return true
	}

	proc _verifySignatureAndCertificate {hostname certificate signature hash hashmethod} {
		set certificate [binary format "H*" $certificate]
		set signature   [binary format "H*" $signature]

		set certificate [::pki::x509::parse_cert $certificate]

		array set certificate_arr $certificate
		set certificate_cn [::pki::x509::_dn_to_cn $certificate_arr(subject)]

		if {![::pki::verify $signature "$hash,$hashmethod" $certificate]} {
			return false
		}

		if {[string tolower $certificate_cn] != [string tolower $hostname]} {
			return false
		}

			sqlite3 ::appfs::db [file join $::appfs::cachedir cache.db]

			::appfs::db timeout 30000
		}

		# Create tables
		db eval {CREATE TABLE IF NOT EXISTS sites(hostname PRIMARY KEY, hashMethod, lastUpdate, ttl);}
		db eval {CREATE TABLE IF NOT EXISTS packages(hostname, packageManifestHash, package, version, os, cpuArch, isLatest, haveManifest);}
		db eval {CREATE TABLE IF NOT EXISTS files(packageManifestHash, hashMethod, type, time, source, size, perms, fileHash, file_name, file_directory);}

		# Create indexes
		db eval {CREATE INDEX IF NOT EXISTS sites_index ON sites (hostname);}
		db eval {CREATE INDEX IF NOT EXISTS packages_index ON packages (hostname, packageManifestHash, package, version, os, cpuArch);}
		db eval {CREATE INDEX IF NOT EXISTS files_index ON files (packageManifestHash, file_name, file_directory);}
	}

	proc download {hostname hash {method sha1}} {
		set url [::appfs::user::construct_url $hostname $hash $method]
		set file [_cachefile $url $hash $method]

		if {![file exists $file]} {

		set indexhashcert   [lindex $indexhash_data 2]
		set indexhashsig    [lindex $indexhash_data 3]

		if {![_isHash $indexhash]} {
			return -code error "Invalid hash: $indexhash"
		}

		if {![_verifySignatureAndCertificate $hostname $indexhashcert $indexhashsig $indexhash $indexhashmethod]} {
			return -code error "Invalid signature or certificate from $hostname"
		}

		set file [download $hostname $indexhash $indexhashmethod]
		catch {
			set fd [open $file]
		}

		if {![info exists fd]} {
			return -code error "Unable to download or open $file"
		}

			unset -nocomplain pkgInfo
			if {[catch {
				set pkgInfo(package)  [lindex $work 0]
				set pkgInfo(version)  [lindex $work 1]
				set pkgInfo(os)       [_normalizeOS [lindex $work 2]]
				set pkgInfo(cpuArch)  [_normalizeCPU [lindex $work 3]]
				set pkgInfo(hash)     [string tolower [lindex $work 4]]
				set pkgInfo(hash_type) $indexhashmethod
				set pkgInfo(isLatest) [expr {!![lindex $work 5]}]
			}]} {
				continue
			}

			if {![_isHash $pkgInfo(hash)]} {
				continue
			}

			lappend curr_packages $pkgInfo(hash)

			# Do not do any additional work if we already have this package
			set existing_packages [db eval {SELECT package FROM packages WHERE hostname = $hostname AND packageManifestHash = $pkgInfo(hash);}]
			if {[lsearch -exact $existing_packages $pkgInfo(package)] != -1} {
				continue
			}

			if {$pkgInfo(isLatest)} {
				db eval {UPDATE packages SET isLatest = 0 WHERE hostname = $hostname AND package = $pkgInfo(package) AND os = $pkgInfo(os) AND cpuArch = $pkgInfo(cpuArch);}
			}

			db eval {INSERT INTO packages (hostname, packageManifestHash, package, version, os, cpuArch, isLatest, haveManifest) VALUES ($hostname, $pkgInfo(hash), $pkgInfo(package), $pkgInfo(version), $pkgInfo(os), $pkgInfo(cpuArch), $pkgInfo(isLatest), 0);}
		}

		# Look for packages that have been deleted
		set found_packages [db eval {SELECT sha1 FROM packages WHERE hostname = $hostname;}]
		foreach package $found_packages {
			set found_packages_arr($package) 1
		}

		foreach package $curr_packages {
			unset -nocomplain found_packages_arr($package)
		}

		foreach package [array names found_packages_arr] {
			db eval {DELETE FROM packages WHERE hostname = $hostname AND packageManifestHash = $package;}
		}

		db eval {INSERT OR REPLACE INTO sites (hostname, hashMethod, lastUpdate, ttl) VALUES ($hostname, $indexhashmethod, $now, $::appfs::ttl);}

		appfsd::get_path_info_cache_flush

		return COMPLETE
	}

	proc getpkgmanifest {hostname packageManifestHash} {
		set haveManifest [db onecolumn {SELECT haveManifest FROM packages WHERE packageManifestHash = $packageManifestHash LIMIT 1;}]
		set siteHashMethod [db onecolumn {SELECT hashMethod FROM sites WHERE hostname = $hostname LIMIT 1;}

		if {$haveManifest == "1"} {
			return COMPLETE
		}

		if {![_isHash $packageManifestHash]} {
			return FAIL
		}

		set file [download $hostname $packageManifestHash $siteHashMethod]

		catch {
			set fd [open $file]
		}

		if {![info exists fd]} {
			return -code error "Unable to download or open $file"