Don't reserve capacity for NIOPCAPRingBuffer (#209)

Motivation:

The NIOPCAPRingBuffer can limit the number of fragment or the total
number of bytes in its buffer or both. When configuring the buffer to
limit only the maximum number of bytes it sets the maximum number of
fragments allowed to `.max`. On `init` the buffer has enough capacity
reserved to store tha maximum number of fragments.

This would be a large and potentially totally unnecessary allocation.
That is, if it didn't crash at runtime. It crashes at runtime as
`CircularBuffer` converts the requested capacity to a `UInt32` which
traps if you pass it an `Int.max`.

Modifications:

- Don't reserve capacity on init
- Adjust the test which tests the byte limit to not set a capacity as
  well

Result:

- `NIOPCAPRingBuffer(maximumBytes:)` doesn't crash

Sources/NIOExtras/PCAPRingBuffer.swift

@@ -35,7 +35,8 @@ public class NIOPCAPRingBuffer {
         self.maximumFragments = maximumFragments
         self.maximumBytes = maximumBytes
         self.pcapCurrentBytes = 0
-        self.pcapFragments = CircularBuffer(initialCapacity: maximumFragments)
+        // Don't default to `maximumFragments` as it will be `.max` on some paths.
+        self.pcapFragments = CircularBuffer()
     }
 
     /// Initialise the buffer, setting constraints
@@ -88,7 +89,7 @@ public class NIOPCAPRingBuffer {
     }
 
     /// Emit the captured data to a consuming function; then clear the captured data.
-    /// - Returns: A ciruclar buffer of captured fragments.
+    /// - Returns: A circular buffer of captured fragments.
     public func emitPCAP() -> CircularBuffer<ByteBuffer> {
         let toReturn = self.pcapFragments // Copy before clearing.
         self.pcapFragments.removeAll(keepingCapacity: true)

Tests/NIOExtrasTests/PCAPRingBufferTest.swift

@@ -66,7 +66,7 @@ class PCAPRingBufferTest: XCTestCase {
     
     func testByteLimit() {
         let expectedData = 150 + 25 + 75 + 120
-        let ringBuffer = NIOPCAPRingBuffer(maximumFragments: 1000, maximumBytes: expectedData + 10)
+        let ringBuffer = NIOPCAPRingBuffer(maximumBytes: expectedData + 10)
         for fragment in dataForTests() {
             ringBuffer.addFragment(fragment)
         }