Add hl7 fingerprinting function.

Signed-off-by: Christopher Schultz <chris@christopherschultz.net>

Author: ChristopherSchultz

Code Templates/Fingerprint HL7 Message Fields/README.md

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+# Fingerprint HL7 Message Fields
+Takes a simple fingerprint of an HL7 message, including some fields and optionally ignoring others.
+
+### Examples
+Fingerprint some fields:
+
+```javascript
+var msg = /* XML object */
+var fields = [ 'PID.2', 'PID.3', 'OBX' ];
+var ignores = [ 'MSH', 'EVN' ];
+
+var fingerprint = fingerprint(msg, fields, ignores);
+```

Code Templates/Fingerprint HL7 Message Fields/fingerprint.js

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+/**
+ * Takes a fingerprint of a message.
+ *
+ * @param {XML} msg An XML object representing HL7.
+ * @param {String[]} fields An array of field names to hash (e.g. 'PID', 'SCH.5', or 'MSH.5.1')
+ * @param {String[]} ignores (optional) An array of fields to *completely* ignore (e.g. 'MSH', 'PID.5')
+ *        NOTE: You can't (currently) ignore a field inside of one of the 'fields' you have already requested
+ * @param {String} hfunc (optional) The name of the hashing function to use. Valid values are 'hashcode' (which uses a simple Arrays.hashCode call) or any of the function supported by your JVM's MessageDigest class (e.g. MD5, SHA-1, SHA-256, etc.). The default is 'hashcode'.
+ *
+ * @return {String} A string fingerprint of the requested fields.
+ *
+ * @throws If no requested fields could be found in the message.
+ */
+function fingerprint(msg, fields, ignores, hfunc) {
+  if(!hfunc) {
+  	hfunc = 'hashcode';
+  }
+
+  var captures = capture(msg, fields, ignores);
+
+  if(0 < captures.length) {
+    // Convert to a Java array of Java strings
+    var len = captures.length;
+    var javaStrings = java.lang.reflect.Array.newInstance(new java.lang.String().getClass(), len);
+    for(i=0; i<len; ++i) {
+      javaStrings[i] = captures[i].toString();
+    }
+
+    // Return a js string
+    if(hfunc == 'hashcode') {
+      return '' + java.lang.Integer.toHexString(java.util.Arrays.hashCode(javaStrings));
+    } else {
+      var md = java.security.MessageDigest.getInstance(hfunc);
+      for(i=0; i<len; ++i) {
+        md.update(javaStrings[i].getBytes('UTF-8'));
+      }
+      return toHex(md.digest());
+    }
+  } else {
+    throw 'Captured no data from message; cannot take fingerprint';
+  }
+}
+
+/**
+ * Convert a byte array to a string if hex digits.
+ *
+ * For example, toHex([ 0xca, 0xfe ]) would return "cafe".
+ *
+ * @param {byte[]} bytes A byte array
+ *
+ * @return {String} A js string representation of the bytes in simple hex encoding.
+ */
+function toHex(bytes) {
+  var hexString = "";
+  for (var i = 0; i < bytes.length; i++) {
+    var byteValue = bytes[i] & 0xFF; 
+    var hex = byteValue.toString(16);
+    if (hex.length === 1) {
+      // Ped if necessary
+      hex = "0" + hex;
+    }
+    hexString += hex;
+  }
+  return hexString;
+}
+
+/**
+ * Captures field (etc.) values from an HL7 message.
+ *
+ * @param {XML} msg An XML object representing HL7.
+ * @param {String[]} fields An array of field names whose values should be captured (e.g. 'PID', 'SCH.5', or 'MSH.5.1')
+ * @param {String[]} ignores (optional) An array of fields to *completely* ignore (e.g. 'MSH', 'PID.5')
+ *        NOTE: You can't (currently) ignore a field inside of one of the 'fields' you have already requested
+ *
+ * @returns {String[]} An array of captured field values (without any indication of which fields they came from)
+ */
+function capture(msg, fields, ignores) {
+  // Clone the incoming 'fields' array; We may mutate it
+  var fieldNames = fields.map(s => ''+s); // Convert all strings to js strings, just in case
+
+  var captures = [];
+
+  for each (seg in msg.children()) {
+    scan_node(seg, fields, captures, ignores);
+    if(0 == fields.length) {
+      return captures;
+    }
+  }
+
+  return captures;
+}
+
+/**
+ * Scans a node and its children for data to capture.
+ *
+ * @param {XML} msg An XML object representing HL7.
+ * @param {String[]} fields An array of field names whose values should be captured (e.g. 'PID', 'SCH.5', or 'MSH.5.1')
+ * @param {String[]} captures An array to append captured values to
+ * @param {String[]} ignores (optional) An array of fields to *completely* ignore (e.g. 'MSH', 'PID.5')
+ *        NOTE: You can't (currently) ignore a field inside of one of the 'fields' you have already requested
+ *
+ * @returns Nothing
+ */
+function scan_node(node, fields, captures, ignores) {
+  var nodeName = node.localName(); // nodeName is a js string
+
+  if(fields.includes(nodeName)) {
+    collect_node(node, captures);
+  } else if(ignores && ignores.includes(nodeName)) {
+    // Ignore this whole node and all its children
+  } else {
+    if(0 < node.children().length()) {
+      for each (child in node.children()) {
+        if('element' == child.nodeKind()) { // Only scan actual elements
+          scan_node(child, fields, captures, ignores);
+
+          if(0 == fields.length) {
+            // No more fields to find; we are done
+            return;
+          }
+        }
+      }
+    }
+  }
+}
+
+/**
+ * Captures all field values for the current node and its children.
+ *
+ * @param {XML} msg An XML object representing HL7.
+ * @param {String[]} captures An array to append captured values to
+ *
+ * @returns Nothing
+ */
+function collect_node(node, captures) {
+  if('element' == node.nodeKind() && 0 < node.children().length()) {
+    for each (child in node.children()) {
+      if('element' == node.nodeKind()) { // Only process actual elements
+        collect_node(child, captures);
+      }
+    }
+  } else {
+    var value = node.toString(); // value is a js string
+    if(0 < value.length) {
+      captures.push(value);
+    }
+  }
+}
+