Rewrite as a recursive descent parser

This simplifies some of our validation, and opens the door to let users of the module run their own DNS check through a general-purpose API.

lib/constants.js

@@ -0,0 +1,90 @@
+'use strict';
+
+exports.categories = {
+    valid: 1,
+    dnsWarn: 7,
+    rfc5321: 15,
+    cfws: 31,
+    deprecated: 63,
+    rfc5322: 127,
+    error: 255
+};
+
+exports.diagnoses = {
+
+    // Address is valid
+
+    valid: 0,
+
+    // Address is valid for SMTP but has unusual elements
+
+    rfc5321TLD: 9,
+    rfc5321TLDNumeric: 10,
+    rfc5321QuotedString: 11,
+    rfc5321AddressLiteral: 12,
+
+    // Address is valid for message, but must be modified for envelope
+
+    cfwsComment: 17,
+    cfwsFWS: 18,
+
+    // Address contains non-ASCII when the allowUnicode option is false
+    // Has to be > internals.defaultThreshold so that it's rejected
+    // without an explicit errorLevel:
+    undesiredNonAscii: 25,
+
+    // Address contains deprecated elements, but may still be valid in some contexts
+
+    deprecatedLocalPart: 33,
+    deprecatedFWS: 34,
+    deprecatedQTEXT: 35,
+    deprecatedQP: 36,
+    deprecatedComment: 37,
+    deprecatedCTEXT: 38,
+    deprecatedIPv6: 39,
+    deprecatedCFWSNearAt: 49,
+
+    // Address is only valid according to broad definition in RFC 5322, but is otherwise invalid
+
+    rfc5322Domain: 65,
+    rfc5322TooLong: 66,
+    rfc5322LocalTooLong: 67,
+    rfc5322DomainTooLong: 68,
+    rfc5322LabelTooLong: 69,
+    rfc5322DomainLiteral: 70,
+    rfc5322DomainLiteralOBSDText: 71,
+    rfc5322IPv6GroupCount: 72,
+    rfc5322IPv62x2xColon: 73,
+    rfc5322IPv6BadCharacter: 74,
+    rfc5322IPv6MaxGroups: 75,
+    rfc5322IPv6ColonStart: 76,
+    rfc5322IPv6ColonEnd: 77,
+
+    // Address is invalid for any purpose
+
+    errExpectingDTEXT: 129,
+    errNoLocalPart: 130,
+    errNoDomain: 131,
+    errConsecutiveDots: 132,
+    errATEXTAfterCFWS: 133,
+    errATEXTAfterQS: 134,
+    errATEXTAfterDomainLiteral: 135,
+    errExpectingQPair: 136,
+    errExpectingATEXT: 137,
+    errExpectingQTEXT: 138,
+    errExpectingCTEXT: 139,
+    errBackslashEnd: 140,
+    errDotStart: 141,
+    errDotEnd: 142,
+    errDomainHyphenStart: 143,
+    errDomainHyphenEnd: 144,
+    errUnclosedQuotedString: 145,
+    errUnclosedComment: 146,
+    errUnclosedDomainLiteral: 147,
+    errFWSCRLFx2: 148,
+    errFWSCRLFEnd: 149,
+    errCRNoLF: 150,
+    errUnknownTLD: 160,
+    errDomainTooShort: 161,
+    errDotAfterDomainLiteral: 162
+};

lib/diagnoses.js

@@ -0,0 +1,86 @@
+'use strict';
+
+// Load modules
+
+const Constants = require('./constants');
+
+/**
+ * Diagnosis stores a diagnosis-index pair.
+ */
+class Diagnosis {
+    /**
+     * @param {number} type The diagnostic code.
+     * @param {number} index The index of the diagnosis.
+     */
+    constructor(type, index) {
+
+        this.type = type;
+        this.index = index;
+    }
+}
+
+
+/**
+ * Diagnoses tracks a set of diagnostic codes for a string, along with their
+ * positions in the string.
+ */
+class Diagnoses {
+    constructor() {
+
+        this._diagnoses = [];
+        this._legacyDiagnosis = null;
+        this._worstDiagnosis = null;
+    }
+
+    /**
+     * Report the given diagnosis at the given index.
+     *
+     * @param {number} type The diagnosis to report.
+     * @param {number} index The
+     */
+    diagnose(type, index) {
+
+        const diagnosis = new Diagnosis(type, index);
+
+        if (this._worstDiagnosis === null || type > this._worstDiagnosis.type) {
+            this._worstDiagnosis = diagnosis;
+        }
+
+        this._diagnoses.push(diagnosis);
+    }
+
+    /**
+     * Check whether the given diagnosis has been reported.
+     *
+     * @param {number} queryType The diagnosis to query.
+     * @return {boolean} Whether the diagnosis has been reported.
+     */
+    hasDiagnosis(queryType) {
+
+        return this._diagnoses.some(({ type }) => type === queryType);
+    }
+
+    /**
+     * Get the worst diagnosis encountered.
+     *
+     * @return {number} The worst diagnosis.
+     */
+    getWorstDiagnosis() {
+
+        return this._worstDiagnosis;
+    }
+
+    /**
+     * For compatibility with existing versions of isemail, this function gets
+     * the first fatal diagnosis, or the worst non-fatal diagnosis.
+     *
+     * @return {number} The backwards-compatible diagnosis.
+     */
+    getLegacyDiagnosis() {
+
+        return this._diagnoses.find(({ type }) => type >= Constants.categories.rfc5322) || this._worstDiagnosis;
+    }
+}
+
+
+module.exports = Diagnoses;