[feature] add varint encoding/decoding

Signed-off-by: yenda <eric@status.im>

src/status_im/utils/varint.cljs

@@ -0,0 +1,54 @@
+(ns ^{:doc "Implementation of varint based on https://github.com/chrisdickinson/varint"}
+ status-im.utils.varint
+  (:require [status-im.utils.ethereum.abi-spec :as abi-spec]
+            [status-im.js-dependencies :as dependencies]))
+
+(def utils dependencies/web3-utils)
+
+(def most-significant-bit 0x80)
+(def biggest-int-per-byte 0x7F)
+(def biggest-int 2147483648) ;; 2^31
+
+(defn encode [num]
+  (loop [num num
+         out []]
+    (if (>= num 128)
+      (recur (if (>= num biggest-int)
+               (/ num 128)
+               (bit-shift-right num 7))
+             (conj out (bit-or (bit-and num 0xFF)
+                               most-significant-bit)))
+      (conj out (bit-or num 0)))))
+
+(defn encode-hex [num]
+  (reduce (fn [hex current-bit]
+            (str hex
+                 (.leftPad utils
+                           (abi-spec/number-to-hex current-bit)
+                           2)))
+          ""
+          (encode num)))
+
+(defn add-b-to-res
+  [res b shift]
+  (+ res (if (< shift 28)
+           (bit-shift-left (bit-and b biggest-int-per-byte)
+                           shift)
+           (* (bit-and b biggest-int-per-byte)
+              shift shift))))
+
+(defn decode [buf]
+  (loop [res 0
+         shift 0
+         [b & rest-buf] buf]
+    (if (>= b most-significant-bit)
+      (recur (add-b-to-res res b shift)
+             (+ shift 7)
+             rest-buf)
+      (add-b-to-res res b shift))))
+
+(defn decode-hex [hex]
+  (->> hex
+       (partition 2)
+       (mapv #(abi-spec/hex-to-number (apply str %)))
+       decode))

test/cljs/status_im/test/utils/varint.cljs

@@ -0,0 +1,28 @@
+(ns status-im.test.utils.varint
+  (:require [cljs.test :refer-macros [deftest is testing]]
+            [status-im.utils.varint :as varint]))
+
+(deftest encode
+  (is (= (varint/encode-hex 0x0)
+         "0"))
+  (is (= (varint/encode-hex 0x70)
+         "70"))
+  (is (= (varint/encode-hex 0xe3)
+         "e301")))
+
+(deftest decode
+  (is (= (varint/decode-hex "0")
+         0x0))
+  (is (= (varint/decode-hex "70")
+         0x70))
+  (is (= (varint/decode-hex "e301")
+         0xe301)))
+
+(defn test-roundtrip [n]
+  (= (varint/decode-hex (varint/encode-hex n))
+     n))
+
+(deftest roundtrip
+  (is (test-roundtrip 0))
+  (is (test-roundtrip 23948))
+  (is (test-roundtrip 2684453)))