fix: parse Instant correctly from epoch offset even when exponential notation is used (#679)

Author: ianbotsf

.changes/7448bdc7-3a4b-4338-8342-3bfa364ecc7c.json

@@ -0,0 +1,8 @@
+{
+    "id": "7448bdc7-3a4b-4338-8342-3bfa364ecc7c",
+    "type": "bugfix",
+    "description": "Parse timestamps correctly when they are written in exponential notation (e.g., `1.924390954E9`)",
+    "issues": [
+        "awslabs/aws-sdk-kotlin#665"
+    ]
+}

runtime/runtime-core/common/src/aws/smithy/kotlin/runtime/time/Parsers.kt

@@ -154,15 +154,49 @@ internal fun parseIso8601(input: String): ParsedDatetime {
     return ParsedDatetime(date.year, date.month, date.day, ts.hour, ts.min, ts.sec, ts.ns, ts.offsetSec)
 }
 
+private val exponentialNotationNumber = """(-)?(\d+(.(\d+))?)E(-?\d+)""".toRegex(RegexOption.IGNORE_CASE)
+
+private fun expandExponent(input: String): String =
+    exponentialNotationNumber.matchEntire(input)?.let { match ->
+        val (baseSign, base, _, _, exp) = match.destructured
+        buildString {
+            append(baseSign)
+            val (mantissa, oldDecimalPos) = base.removeChar('.')
+            val shift = exp.toIntOrNull() ?: throw ParseException(input, "Failed to read exponent", 0)
+            val newDecimalPos = oldDecimalPos + shift
+            val (int, frac) = mantissa.splitAt(newDecimalPos)
+            append(int)
+            append('.')
+            append(frac)
+        }
+    } ?: input
+
+private fun String.splitAt(position: Int, padChar: Char = '0'): Pair<String, String> = when {
+    position <= 0 -> padChar.toString() to padStart(length - position, padChar)
+    position >= length -> padEnd(position, padChar) to padChar.toString()
+    else -> substring(0, position) to substring(position)
+}
+
+private fun String.removeChar(char: Char): Pair<String, Int> = when {
+    contains(char) -> {
+        val pos = indexOf(char)
+        val removed = substring(0, pos) + substring(pos + 1)
+        removed to pos
+    }
+    else -> this to length
+}
+
 /**
  * Parse an epoch timestamp (with or without fractional seconds) into an instant
  */
 internal fun parseEpoch(input: String): Instant {
-    val (pos0, secs) = takeMNDigitsLong(1, 19)(input, 0)
-    return if (pos0 == input.length) {
+    val expandedInput = expandExponent(input)
+
+    val (pos0, secs) = takeMNDigitsLong(1, 19)(expandedInput, 0)
+    return if (pos0 == expandedInput.length) {
         Instant.fromEpochSeconds(secs, 0)
     } else {
-        val (_, ns) = preceded(char('.'), fraction(1, 9, 9))(input, pos0)
+        val (_, ns) = preceded(char('.'), fraction(1, 9, 9))(expandedInput, pos0)
         Instant.fromEpochSeconds(secs, ns)
     }
 }

runtime/runtime-core/common/test/aws/smithy/kotlin/runtime/time/ParseEpochTest.kt

@@ -18,7 +18,15 @@ class ParseEpochTest {
             Triple("1604588357.1", 1604588357L, 100_000_000),
             Triple("1604588357.0345", 1604588357L, 34_500_000),
             Triple("1604588357.000001", 1604588357L, 1000),
-            Triple("1604588357.000000001", 1604588357L, 1)
+            Triple("1604588357.000000001", 1604588357L, 1),
+            Triple("1.604588357E9", 1604588357L, 0),
+            Triple("1.604588357e9", 1604588357L, 0),
+            Triple("1604.588357E6", 1604588357L, 0),
+            Triple("1604588357000E-3", 1604588357L, 0),
+            Triple("0.001604588357E12", 1604588357L, 0),
+            Triple("1.6045883570345E9", 1604588357L, 34_500_000),
+            Triple("1.604588357000001E9", 1604588357L, 1000),
+            Triple("1.604588357000000001E9", 1604588357L, 1),
         )
 
         for ((idx, test) in tests.withIndex()) {

runtime/serde/serde-json/common/test/aws/smithy/kotlin/runtime/serde/json/JsonDeserializerTest.kt

@@ -21,6 +21,8 @@ class JsonDeserializerTest {
             "\"-Infinity\"" to Double.NEGATIVE_INFINITY,
             "\"Infinity\"" to Double.POSITIVE_INFINITY,
             "\"NaN\"" to Double.NaN,
+            "1.5e5" to 150000.0,
+            "1.5e-5" to 0.000015,
         )
 
         for ((input, expected) in tests) {
@@ -44,6 +46,8 @@ class JsonDeserializerTest {
             "\"-Infinity\"" to Float.NEGATIVE_INFINITY,
             "\"Infinity\"" to Float.POSITIVE_INFINITY,
             "\"NaN\"" to Float.NaN,
+            "1.5e5" to 150000f,
+            "1.5e-5" to 0.000015f,
         )
 
         for ((input, expected) in tests) {