[ci skip] wip refactoring siteId

index.js

@@ -35,7 +35,7 @@ module.exports = {
         VersioningConstants: require('./lib/versioning/constants.js')
             .VersioningConstants,
         Version: require('./lib/versioning/Version.js').Version,
-        VersionID: require('./lib/versioning/VersionID.js'),
+        VersionID: require('./lib/versioning/VersionID.js').instance,
     },
     network: {
         http: {

lib/versioning/VersionID.js

@@ -40,21 +40,6 @@ function padRight(value, template) {
     return `${value}${template}`.slice(0, template.length);
 }
 
-// site identifier, like PARIS, TOKYO; will be trimmed if exceeding max length
-const SITE_ID = padRight(process.env.SITE_ID, TEMPLATE_SITE);
-
-// constants for max epoch and max sequential number in the same epoch
-const MAX_TS = Math.pow(10, LENGTH_TS) - 1; // good until 16 Nov 5138
-const MAX_SEQ = Math.pow(10, LENGTH_SEQ) - 1; // good for 1 billion ops
-
-// the earliest versionId, used for versions before versioning
-const VID_INF = (padLeft(MAX_TS, TEMPLATE_TS) +
-                 padLeft(MAX_SEQ, TEMPLATE_SEQ) + SITE_ID);
-
-// internal state of the module
-let lastTimestamp = 0; // epoch of the last versionId
-let lastSeq = 0; // sequential number of the last versionId
-
 /**
  * This function ACTIVELY (wastes CPU cycles and) waits for an amount of time
  * before returning to the caller. This should not be used frequently.
@@ -72,75 +57,124 @@ function wait(span) {
     }
 }
 
-/**
- * This function returns a "versionId" string indicating the current time as a
- * combination of the current time in millisecond, the position of the request
- * in that millisecond, and the identifier of the local site (which could be
- * datacenter, region, or server depending on the notion of geographics). This
- * function is stateful which means it keeps some values in the memory and the
- * next call depends on the previous call.
- *
- * @param {string} info - the additional info to ensure uniqueness if desired
- * @return {string} - the formated versionId string
- */
-function generateVersionId(info) {
-    // Need to wait for the millisecond slot got "flushed". We wait for
-    // only a single millisecond when the module is restarted, which is
-    // necessary for the correctness of the system. This is therefore cheap.
-    if (lastTimestamp === 0) {
-        wait(1000000);
+// constants for max epoch and max sequential number in the same epoch
+const MAX_TS = Math.pow(10, LENGTH_TS) - 1; // good until 16 Nov 5138
+const MAX_SEQ = Math.pow(10, LENGTH_SEQ) - 1; // good for 1 billion ops
+
+// default site name in CRR context for single/bucketfile/membackend deployments
+const SITE = 'PARIS';
+
+class VersionID {
+
+    /**
+     * Instantiate VersionID; the result should be initalized before use.
+     */
+    constructor() {
+        // some configurable variables
+        this.SITE_ID = padRight(SITE_ID, TEMPLATE_SITE); // site identifier
+        this.VID_INF = padLeft(MAX_TS, TEMPLATE_TS) +
+            padLeft(MAX_SEQ, TEMPLATE_SEQ) + this.SITE_ID; // earliest versionId
+        // internal state of the module
+        this.lastTimestamp = 0; // epoch of the last versionId
+        this.lastSeq = 0; // sequential number of the last versionId
     }
-    // get the present epoch (in millisecond)
-    const ts = Date.now();
-    // A bit more rationale: why do we use a sequence number instead of using
-    // process.hrtime which gives us time in nanoseconds? The idea is that at
-    // any time resolution, some concurrent requests may have the same time due
-    // to the way the OS is queueing requests or getting clock cycles. Our
-    // approach however will give the time based on the position of a request
-    // in the queue for the same millisecond which is supposed to be unique.
 
-    // increase the position if this request is in the same epoch
-    lastSeq = (lastTimestamp === ts) ? lastSeq + 1 : 0;
-    lastTimestamp = ts;
+    /**
+     * Initialize the VersionID instance.
+     *
+     * @param {object} params - input parameters for initalization
+     * @param {string} params.siteId - region identifier in CRR context
+     * @return {VersionID} - this instance
+     */
+    init(params) {
+        assert(params && params.siteId, 'input parameters is required');
+        // formated site identifier, like PARIS, TOKYO, SF000
+        this.SITE_ID = padRight(params.siteId, TEMPLATE_SITE);
+        // the earliest versionId, used for versions before versioning
+        this.VID_INF = padLeft(MAX_TS, TEMPLATE_TS) +
+            padLeft(MAX_SEQ, TEMPLATE_SEQ) + this.SITE_ID;
+        return this;
+    }
 
-    // In the default cases, we reverse the chronological order of the
-    // timestamps so that all versions of an object can be retrieved in the
-    // reversed chronological order---newest versions first. This is because of
-    // the limitation of leveldb for listing keys in the reverse order.
-    return padLeft(MAX_TS - lastTimestamp, TEMPLATE_TS) +
-           padLeft(MAX_SEQ - lastSeq, TEMPLATE_SEQ) + SITE_ID + info;
-}
-
-/**
- * Encode a versionId to obscure internal information contained
- * in a version ID.
- *
- * @param {string} str - the versionId to encode
- * @return {string} - the encoded versionId
- */
-function encode(str) {
-    return Buffer.from(str, 'utf8').toString('hex');
-}
-
-/**
- * Decode a versionId. May return an error if the input string is
- * invalid hex string or results in an invalid value.
- *
- * @param {string} str - the encoded versionId to decode
- * @return {(string|Error)} - the decoded versionId or an error
- */
-function decode(str) {
-    try {
-        const result = Buffer.from(str, 'hex').toString('utf8');
-        if (result === '') {
-            return new Error('invalid decoded value');
+    /**
+     * This function returns a "versionId" string indicating the current time as a
+     * combination of the current time in millisecond, the position of the request
+     * in that millisecond, and the identifier of the local site (which could be
+     * datacenter, region, or server depending on the notion of geographics). This
+     * function is stateful which means it keeps some values in the memory and the
+     * next call depends on the previous call.
+     *
+     * @param {string} info - the additional info to ensure uniqueness if desired
+     * @return {string} - the formated versionId string
+     */
+    generateVersionId(info) {
+        // Need to wait for the millisecond slot got "flushed". We wait for
+        // only a single millisecond when the module is restarted, which is
+        // necessary for the correctness of the system. This is therefore cheap.
+        if (this.lastTimestamp === 0) {
+            wait(1000000);
+        }
+        // get the present epoch (in millisecond)
+        const ts = Date.now();
+        // A bit more rationale: why do we use a sequence number instead of using
+        // process.hrtime which gives us time in nanoseconds? The idea is that at
+        // any time resolution, some concurrent requests may have the same time due
+        // to the way the OS is queueing requests or getting clock cycles. Our
+        // approach however will give the time based on the position of a request
+        // in the queue for the same millisecond which is supposed to be unique.
+
+        // increase the position if this request is in the same epoch
+        this.lastSeq = (this.lastTimestamp === ts) ? this.lastSeq + 1 : 0;
+        this.lastTimestamp = ts;
+
+        // In the default cases, we reverse the chronological order of the
+        // timestamps so that all versions of an object can be retrieved in the
+        // reversed chronological order---newest versions first. This is because of
+        // the limitation of leveldb for listing keys in the reverse order.
+        return padLeft(MAX_TS - this.lastTimestamp, TEMPLATE_TS) +
+            padLeft(MAX_SEQ - this.lastSeq, TEMPLATE_SEQ) + this.SITE_ID + info;
+    }
+
+    /**
+     * Get the predefined-earliest versionId of this site.
+     *
+     * @return {string} - the predefined-earliest versionId
+     */
+    getINF() {
+        return this.VID_INF;
+    }
+
+    /**
+     * Encode a versionId to obscure internal information contained
+     * in a version ID.
+     *
+     * @param {string} str - the versionId to encode
+     * @return {string} - the encoded versionId
+     */
+    static encode(str) {
+        return Buffer.from(str, 'utf8').toString('hex');
+    }
+
+    /**
+     * Decode a versionId. May return an error if the input string is
+     * invalid hex string or results in an invalid value.
+     *
+     * @param {string} str - the encoded versionId to decode
+     * @return {(string|Error)} - the decoded versionId or an error
+     */
+    static decode(str) {
+        try {
+            const result = Buffer.from(str, 'hex').toString('utf8');
+            if (result === '') {
+                return new Error('invalid decoded value');
+            }
+            return result;
+        } catch (err) {
+            // Buffer.from() may throw TypeError if invalid input, e.g. non-string
+            // or string with inappropriate charlength
+            return err;
         }
-        return result;
-    } catch (err) {
-        // Buffer.from() may throw TypeError if invalid input, e.g. non-string
-        // or string with inappropriate charlength
-        return err;
     }
 }
 
-module.exports = { generateVersionId, VID_INF, encode, decode };
+module.exports = { instance: new VersionID() };