Add first attempt at JID class

src/main/java/eu/siacs/conversations/xmpp/jid/Jid.java

@@ -0,0 +1,151 @@
+package eu.siacs.conversations.xmpp.jid;
+
+import java.net.IDN;
+
+import gnu.inet.encoding.Stringprep;
+import gnu.inet.encoding.StringprepException;
+
+/**
+ * The `Jid' class provides an immutable representation of a JID.
+ */
+public final class Jid {
+
+    public final static class InvalidJidException extends Exception { }
+
+    private final String localpart;
+    private final String domainpart;
+    private final String resourcepart;
+
+    // It's much more efficient to store the ful JID as well as the parts instead of figuring them
+    // all out every time (since some characters are displayed but aren't used for comparisons).
+    private final String displayjid;
+
+    public String getLocalpart() {
+        return IDN.toUnicode(localpart);
+    }
+
+    public String getDomainpart() {
+        return IDN.toUnicode(domainpart);
+    }
+
+    public String getResourcepart() {
+        return IDN.toUnicode(resourcepart);
+    }
+
+    // Special private constructor that doesn't do any checking...
+    private Jid(final String localpart, final String domainpart) {
+        this.localpart = localpart;
+        this.domainpart = domainpart;
+        this.resourcepart = "";
+        if (localpart.isEmpty()) {
+            this.displayjid = domainpart;
+        } else {
+            this.displayjid = localpart + "@" + domainpart;
+        }
+    }
+
+    // Note: If introducing a mutable instance variable for some reason, make the constructor
+    // private and add a factory method to ensure thread safety and hash-cach-ability (tm).
+    public Jid(final String jid) throws InvalidJidException {
+
+        // Hackish Android way to count the number of chars in a string... should work everywhere.
+        final int atCount = jid.length() - jid.replace("@", "").length();
+        final int slashCount = jid.length() - jid.replace("/", "").length();
+
+        // Throw an error if there's anything obvious wrong with the JID...
+        if (atCount > 1 || slashCount > 1 ||
+                jid.length() == 0 || jid.length() > 3071 ||
+                jid.startsWith("@") || jid.endsWith("@") ||
+                jid.startsWith("/") || jid.endsWith("/")) {
+            throw new InvalidJidException();
+        }
+
+        String finaljid;
+
+        final int domainpartStart;
+        if (atCount == 1) {
+            final int atLoc = jid.indexOf("@");
+            final String lp = jid.substring(0, atLoc);
+            try {
+                localpart = Stringprep.nodeprep(lp);
+            } catch (final StringprepException e) {
+                throw new InvalidJidException();
+            }
+            if (localpart.isEmpty() || localpart.length() > 1023) {
+                throw new InvalidJidException();
+            }
+            domainpartStart = atLoc;
+            finaljid = lp + "@";
+        } else {
+            localpart = "";
+            finaljid = "";
+            domainpartStart = 0;
+        }
+
+        final String dp;
+        if (slashCount == 1) {
+            final int slashLoc = jid.indexOf("/");
+            final String rp = jid.substring(slashLoc + 1, jid.length());
+            try {
+                resourcepart = Stringprep.resourceprep(rp);
+            } catch (final StringprepException e) {
+                throw new InvalidJidException();
+            }
+            if (resourcepart.isEmpty() || resourcepart.length() > 1023) {
+                throw new InvalidJidException();
+            }
+            dp = jid.substring(domainpartStart, slashLoc);
+            finaljid = finaljid + dp + "/" + rp;
+        } else {
+            resourcepart = "";
+            dp = jid.substring(domainpartStart, jid.length());
+            finaljid = finaljid + dp;
+        }
+
+        // Remove trailling "." before storing the domain part.
+        if (dp.endsWith(".")) {
+            domainpart = IDN.toASCII(dp.substring(0, dp.length() - 1), IDN.USE_STD3_ASCII_RULES);
+        } else {
+            domainpart = IDN.toASCII(dp, IDN.USE_STD3_ASCII_RULES);
+        }
+
+        // TODO: Find a proper domain validation library; validate individual parts, separators, etc.
+        if (domainpart.isEmpty() || domainpart.length() > 1023) {
+            throw new InvalidJidException();
+        }
+
+        this.displayjid = finaljid;
+    }
+
+    public Jid getBareJid() {
+        return displayjid.contains("/") ? new Jid(localpart, domainpart) : this;
+    }
+
+    @Override
+    public String toString() {
+        return displayjid;
+    }
+
+    @Override
+    public boolean equals(final Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+
+        final Jid jid = (Jid) o;
+
+        // Since we're immutable, the JVM will cache hashcodes, making this very fast.
+        // I'm assuming Dalvik does the same sorts of optimizations...
+        // Since the hashcode does not include the displayJID it can be used for IDN comparison as
+        // well.
+        return jid.hashCode() == this.hashCode();
+
+    }
+
+    @Override
+    public int hashCode() {
+        int result = localpart.hashCode();
+        result = 31 * result + domainpart.hashCode();
+        result = 31 * result + resourcepart.hashCode();
+        return result;
+    }
+}