/* The contents of this file are subject to the license and copyright terms
* detailed in the license directory at the root of the source tree (also
* available online at http://fedora-commons.org/license/).
*/
package fedora.server.storage.lowlevel.akubra;
import java.io.UnsupportedEncodingException;
import java.net.URI;
import java.net.URLDecoder;
import java.net.URLEncoder;
import org.akubraproject.map.IdMapper;
import fedora.server.utilities.MD5Utility;
/**
* Provides a hash-based <code>file:</code> mapping for any URI.
* <p>
* The path component of each internal URI is derived from an MD5 hash of
* the external URI. The filename component is a reversible encoding of the
* external URI that is safe to use as a filename on modern filesystems.
* <p>
* <h2>Hash Path Patterns</h2>
* The pattern given at construction time determines how the path component
* of each internal URI will be composed. Within the pattern, the # character
* is a stand-in for a hexadecimal [0-f] digit from the MD5 hash of the
* external id.
* <p>
* Patterns:
* <ul>
* <li> must consist only of # and / characters.</li>
* <li> must contain between 1 and 32 # characters.</li>
* <li> must not begin or end with the / character.</li>
* <li> must not contain consecutive / characters.</li>
* </ul>
* <p>
* Example patterns:
* <ul>
* <li> Good: #</li>
* <li> Good: ##/#</li>
* <li> Good: ##/##/##</li>
* <li> Bad: a</li>
* <li> Bad: ##/</li>
* <li> Bad: ##//##</li>
* </ul>
* <p>
* <h2>Filesystem-Safe Encoding</h2>
* The last part of the internal URI is a "filesystem-safe" encoding of the
* external URI. All characters will be UTF-8 percent-encoded ("URI escaped")
* except for the following: <code>a-z A-Z 0-9 = ( ) [ ] -</code>
* In addition, <code>.</code> (period) will be escaped as <code>%2E</code> when
* it occurs as the last character of the URI.
* <p>
* <h2>Example Mappings</h2>
* With pattern <em>#/#</em>:
* <ul>
* <li> <code>urn:example1</code> becomes <code>file:0/8/urn%3Aexample1</code></li>
* <li> <code>http://tinyurl.com/cxzzf</code> becomes <code>file:6/2/http%3A%2F%2Ftinyurl.com%2Fcxzzf</code></li>
* </ul>
* With pattern <em>##/##</em>:
* <ul>
* <li> <code>urn:example1</code> becomes <code>file:08/86/urn%3Aexample1</code></li>
* <li> <code>http://tinyurl.com/cxzzf</code> becomes <code>file:62/ca/http%3A%2F%2Ftinyurl.com%2Fcxzzf</code></li>
* </ul>
*
* @author Chris Wilper
*/
public class HashPathIdMapper
implements IdMapper {
private static final String internalScheme = "file";
private final String pattern;
/**
* Creates an instance that will use the given pattern.
*
* @param pathPattern the pattern to use, possibly <code>null</code> or "".
* @throws IllegalArgumentException if the pattern is invalid.
*/
public HashPathIdMapper(String pattern) {
this.pattern = validatePattern(pattern);
}
//@Override
public URI getExternalId(URI internalId) throws NullPointerException {
String fullPath = internalId.toString().substring(
internalScheme.length() + 1);
int i = fullPath.lastIndexOf('/');
String encodedURI;
if (i == -1)
encodedURI = fullPath;
else
encodedURI = fullPath.substring(i + 1);
return URI.create(decode(encodedURI));
}
//@Override
public URI getInternalId(URI externalId) throws NullPointerException {
if (externalId == null) {
throw new NullPointerException();
}
String uri = externalId.toString();
return URI.create(internalScheme + ":" + getPath(uri) + encode(uri));
}
//@Override
public String getInternalPrefix(String externalPrefix)
throws NullPointerException {
if (externalPrefix == null) {
throw new NullPointerException();
}
// we can only do this if pattern is ""
if (pattern.length() == 0) {
return internalScheme + ":" + encode(externalPrefix);
} else {
return null;
}
}
// gets the path based on the hash of the uri, or "" if the pattern is empty
private String getPath(String uri) {
if (pattern.length() == 0) {
return "";
}
StringBuilder builder = new StringBuilder();
String hash = getHash(uri);
int hashPos = 0;
for (int i = 0; i < pattern.length(); i++) {
char c = pattern.charAt(i);
if (c == '#') {
builder.append(hash.charAt(hashPos++));
} else {
builder.append(c);
}
}
builder.append('/');
return builder.toString();
}
// computes the md5 and returns a 32-char lowercase hex string
private static String getHash(String uri) {
return MD5Utility.getBase16Hash(uri);
}
private static String encode(String uri) {
// encode char-by-char because we only want to borrow
// URLEncoder.encode's behavior for some characters
StringBuilder out = new StringBuilder();
for (int i = 0; i < uri.length(); i++) {
char c = uri.charAt(i);
if (c >= 'a' && c <= 'z') {
out.append(c);
} else if (c >= '0' && c <= '9') {
out.append(c);
} else if (c >= 'A' && c <= 'Z') {
out.append(c);
} else if (c == '-' || c == '=' || c == '(' || c == ')'
|| c == '[' || c == ']' || c == ';') {
out.append(c);
} else if (c == ':') {
out.append("%3A");
} else if (c == ' ') {
out.append("%20");
} else if (c == '+') {
out.append("%2B");
} else if (c == '_') {
out.append("%5F");
} else if (c == '*') {
out.append("%2A");
} else if (c == '.') {
if (i == uri.length() - 1) {
out.append("%2E");
} else {
out.append(".");
}
} else {
try {
out.append(URLEncoder.encode("" + c, "UTF-8"));
} catch (UnsupportedEncodingException wontHappen) {
throw new RuntimeException(wontHappen);
}
}
}
return out.toString();
}
private static String decode(String encodedURI) {
if (encodedURI.endsWith("%2E")) {
encodedURI = encodedURI.substring(0, encodedURI.length() - 3) + ".";
}
try {
return URLDecoder.decode(encodedURI, "UTF-8");
} catch (UnsupportedEncodingException wontHappen) {
throw new RuntimeException(wontHappen);
}
}
private static String validatePattern(String pattern) {
if (pattern == null) {
return "";
}
int count = 0;
boolean prevWasSlash = false;
for (int i = 0; i < pattern.length(); i++) {
char c = pattern.charAt(i);
if (c == '#') {
count++;
prevWasSlash = false;
} else if (c == '/') {
if (i == 0 || i == pattern.length() - 1) {
throw new IllegalArgumentException("Pattern must not begin"
+ " or end with '/'");
} else if (prevWasSlash) {
throw new IllegalArgumentException("Pattern must not"
+ " contain consecutive '/' characters");
} else {
prevWasSlash = true;
}
} else {
throw new IllegalArgumentException("Illegal character in"
+ " pattern: " + c);
}
}
if (count > 32) {
throw new IllegalArgumentException("Pattern must not contain more"
+ " than 32 '#' characters");
}
return pattern;
}
}