Adding upstream version 124.0.1.upstream/124.0.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 170 insertions, 0 deletions

diff --git a/toolkit/components/utils/Sampling.sys.mjs b/toolkit/components/utils/Sampling.sys.mjs
new file mode 100644
index 0000000000..770e5bf6a5
--- /dev/null
+++ b/toolkit/components/utils/Sampling.sys.mjs
@@ -0,0 +1,170 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+const hashBits = 48;
+const hashLength = hashBits / 4; // each hexadecimal digit represents 4 bits
+const hashMultiplier = Math.pow(2, hashBits) - 1;
+
+export var Sampling = {
+  /**
+   * Map from the range [0, 1] to [0, 2^48].
+   * @param  {number} frac A float from 0.0 to 1.0.
+   * @return {string} A 48 bit number represented in hex, padded to 12 characters.
+   */
+  fractionToKey(frac) {
+    if (frac < 0 || frac > 1) {
+      throw new Error(`frac must be between 0 and 1 inclusive (got ${frac})`);
+    }
+
+    return Math.floor(frac * hashMultiplier)
+      .toString(16)
+      .padStart(hashLength, "0");
+  },
+
+  /**
+   * @param {ArrayBuffer} buffer Data to convert
+   * @returns {String}    `buffer`'s content, converted to a hexadecimal string.
+   */
+  bufferToHex(buffer) {
+    const hexCodes = [];
+    const view = new DataView(buffer);
+    for (let i = 0; i < view.byteLength; i += 4) {
+      // Using getUint32 reduces the number of iterations needed (we process 4 bytes each time)
+      const value = view.getUint32(i);
+      // toString(16) will give the hex representation of the number without padding
+      hexCodes.push(value.toString(16).padStart(8, "0"));
+    }
+
+    // Join all the hex strings into one
+    return hexCodes.join("");
+  },
+
+  /**
+   * Check if an input hash is contained in a bucket range.
+   *
+   * isHashInBucket(fractionToKey(0.5), 3, 6, 10) -> returns true
+   *
+   *              minBucket
+   *              |     hash
+   *              v     v
+   *    [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
+   *                       ^
+   *                       maxBucket
+   *
+   * @param inputHash {String}
+   * @param minBucket {int} The lower boundary, inclusive, of the range to check.
+   * @param maxBucket {int} The upper boundary, exclusive, of the range to check.
+   * @param bucketCount {int} The total number of buckets. Should be greater than
+   *                          or equal to maxBucket.
+   */
+  isHashInBucket(inputHash, minBucket, maxBucket, bucketCount) {
+    const minHash = Sampling.fractionToKey(minBucket / bucketCount);
+    const maxHash = Sampling.fractionToKey(maxBucket / bucketCount);
+    return minHash <= inputHash && inputHash < maxHash;
+  },
+
+  /**
+   * @promise A hash of `data`, truncated to the 12 most significant characters.
+   */
+  async truncatedHash(data) {
+    const hasher = crypto.subtle;
+    const input = new TextEncoder().encode(JSON.stringify(data));
+    const hash = await hasher.digest("SHA-256", input);
+    // truncate hash to 12 characters (2^48), because the full hash is larger
+    // than JS can meaningfully represent as a number.
+    return Sampling.bufferToHex(hash).slice(0, 12);
+  },
+
+  /**
+   * Sample by splitting the input into two buckets, one with a size (rate) and
+   * another with a size (1.0 - rate), and then check if the input's hash falls
+   * into the first bucket.
+   *
+   * @param    {object}  input Input to hash to determine the sample.
+   * @param    {Number}  rate  Number between 0.0 and 1.0 to sample at. A value of
+   *                           0.25 returns true 25% of the time.
+   * @promises {boolean} True if the input is in the sample.
+   */
+  async stableSample(input, rate) {
+    const inputHash = await Sampling.truncatedHash(input);
+    const samplePoint = Sampling.fractionToKey(rate);
+
+    return inputHash < samplePoint;
+  },
+
+  /**
+   * Sample by splitting the input space into a series of buckets, and checking
+   * if the given input is in a range of buckets.
+   *
+   * The range to check is defined by a start point and length, and can wrap
+   * around the input space. For example, if there are 100 buckets, and we ask to
+   * check 50 buckets starting from bucket 70, then buckets 70-99 and 0-19 will
+   * be checked.
+   *
+   * @param {object}     input Input to hash to determine the matching bucket.
+   * @param {integer}    start Index of the bucket to start checking.
+   * @param {integer}    count Number of buckets to check.
+   * @param {integer}    total Total number of buckets to group inputs into.
+   * @promises {boolean} True if the given input is within the range of buckets
+   *                     we're checking. */
+  async bucketSample(input, start, count, total) {
+    const inputHash = await Sampling.truncatedHash(input);
+    const wrappedStart = start % total;
+    const end = wrappedStart + count;
+
+    // If the range we're testing wraps, we have to check two ranges: from start
+    // to max, and from min to end.
+    if (end > total) {
+      return (
+        Sampling.isHashInBucket(inputHash, 0, end % total, total) ||
+        Sampling.isHashInBucket(inputHash, wrappedStart, total, total)
+      );
+    }
+
+    return Sampling.isHashInBucket(inputHash, wrappedStart, end, total);
+  },
+
+  /**
+   * Sample over a list of ratios such that, over the input space, each ratio
+   * has a number of matches in correct proportion to the other ratios.
+   *
+   * For example, given the ratios:
+   *
+   * [1, 2, 3, 4]
+   *
+   * 10% of all inputs will return 0, 20% of all inputs will return 1, 30% will
+   * return 2, and 40% will return 3. You can determine the percent of inputs
+   * that will return an index by dividing the ratio by the sum of all ratios
+   * passed in. In the case above, 4 / (1 + 2 + 3 + 4) == 0.4, or 40% of the
+   * inputs.
+   *
+   * @param {object} input
+   * @param {Array<integer>} ratios
+   * @promises {integer}
+   *   Index of the ratio that matched the input
+   * @rejects {Error}
+   *   If the list of ratios doesn't have at least one element
+   */
+  async ratioSample(input, ratios) {
+    if (ratios.length < 1) {
+      throw new Error(
+        `ratios must be at least 1 element long (got length: ${ratios.length})`
+      );
+    }
+
+    const inputHash = await Sampling.truncatedHash(input);
+    const ratioTotal = ratios.reduce((acc, ratio) => acc + ratio);
+
+    let samplePoint = 0;
+    for (let k = 0; k < ratios.length - 1; k++) {
+      samplePoint += ratios[k];
+      if (inputHash <= Sampling.fractionToKey(samplePoint / ratioTotal)) {
+        return k;
+      }
+    }
+
+    // No need to check the last bucket if the others didn't match.
+    return ratios.length - 1;
+  },
+};