Merge pull request apple#1064 from tbkka/tbkka/avoidFoundationStringFormat

Reduce foundation usage

Author: tbkka

Sources/SwiftProtobuf/Google_Protobuf_Duration+Extensions.swift

@@ -99,16 +99,8 @@ private func formatDuration(seconds: Int64, nanos: Int32) -> String? {
   guard seconds >= minDurationSeconds && seconds <= maxDurationSeconds else {
     return nil
   }
-
-  if nanos == 0 {
-    return String(format: "%llds", seconds)
-  } else if nanos % 1000000 == 0 {
-    return String(format: "%lld.%03ds", seconds, abs(nanos) / 1000000)
-  } else if nanos % 1000 == 0 {
-    return String(format: "%lld.%06ds", seconds, abs(nanos) / 1000)
-  } else {
-    return String(format: "%lld.%09ds", seconds, abs(nanos))
-  }
+  let nanosString = nanosToString(nanos: nanos) // Includes leading '.' if needed
+  return "\(seconds)\(nanosString)s"
 }
 
 extension Google_Protobuf_Duration {

Sources/SwiftProtobuf/Google_Protobuf_Timestamp+Extensions.swift

@@ -191,19 +191,11 @@ private func formatTimestamp(seconds: Int64, nanos: Int32) -> String? {
   let (hh, mm, ss) = timeOfDayFromSecondsSince1970(seconds: seconds)
   let (YY, MM, DD) = gregorianDateFromSecondsSince1970(seconds: seconds)
 
-  if nanos == 0 {
-    return String(format: "%04d-%02d-%02dT%02d:%02d:%02dZ",
-                  YY, MM, DD, hh, mm, ss)
-  } else if nanos % 1000000 == 0 {
-    return String(format: "%04d-%02d-%02dT%02d:%02d:%02d.%03dZ",
-                  YY, MM, DD, hh, mm, ss, nanos / 1000000)
-  } else if nanos % 1000 == 0 {
-    return String(format: "%04d-%02d-%02dT%02d:%02d:%02d.%06dZ",
-                  YY, MM, DD, hh, mm, ss, nanos / 1000)
-  } else {
-    return String(format: "%04d-%02d-%02dT%02d:%02d:%02d.%09dZ",
-                  YY, MM, DD, hh, mm, ss, nanos)
-  }
+  let dateString = "\(fourDigit(YY))-\(twoDigit(MM))-\(twoDigit(DD))"
+  let timeString = "\(twoDigit(hh)):\(twoDigit(mm)):\(twoDigit(ss))"
+  let nanosString = nanosToString(nanos: nanos) // Includes leading '.' if needed
+
+  return "\(dateString)T\(timeString)\(nanosString)Z"
 }
 
 extension Google_Protobuf_Timestamp {

Sources/SwiftProtobuf/StringUtils.swift

@@ -20,6 +20,42 @@
 
 import Foundation
 
+/*
+  Note: Once our minimum support version is at least Swift 5.3, we
+  should probably recast the following to use
+  String(unsafeUninitializedCapacity:)
+*/
+
+// Note: We're trying to avoid Foundation's String(format:) since that's not
+// universally available.
+
+fileprivate func formatZeroPaddedInt(_ value: Int32, digits: Int) -> String {
+  precondition(value >= 0)
+  let s = String(value)
+  if s.count >= digits {
+    return s
+  } else {
+    let pad = String(repeating: "0", count: digits - s.count)
+    return pad + s
+  }
+}
+
+internal func twoDigit(_ value: Int32) -> String {
+  return formatZeroPaddedInt(value, digits: 2)
+}
+internal func threeDigit(_ value: Int32) -> String {
+  return formatZeroPaddedInt(value, digits: 3)
+}
+internal func fourDigit(_ value: Int32) -> String {
+  return formatZeroPaddedInt(value, digits: 4)
+}
+internal func sixDigit(_ value: Int32) -> String {
+  return formatZeroPaddedInt(value, digits: 6)
+}
+internal func nineDigit(_ value: Int32) -> String {
+  return formatZeroPaddedInt(value, digits: 9)
+}
+
 // Wrapper that takes a buffer and start/end offsets
 internal func utf8ToString(
   bytes: UnsafeRawBufferPointer,

Sources/SwiftProtobuf/TimeUtils.swift

@@ -51,3 +51,15 @@ internal func gregorianDateFromSecondsSince1970(seconds: Int64) -> (YY: Int32, M
 
     return (YY: Int32(YY), MM: Int32(MM), DD: Int32(DD))
 }
+
+internal func nanosToString(nanos: Int32) -> String {
+  if nanos == 0 {
+    return ""
+  } else if nanos % 1000000 == 0 {
+    return ".\(threeDigit(abs(nanos) / 1000000))"
+  } else if nanos % 1000 == 0 {
+    return ".\(sixDigit(abs(nanos) / 1000))"
+  } else {
+    return ".\(nineDigit(abs(nanos)))"
+  }
+}