Refactor decompression stream creation to remove code duplication

lib/read.js

@@ -147,7 +147,6 @@ function read (req, res, next, parse, debug, options) {
 function contentstream (req, debug, inflate) {
   var encoding = (req.headers['content-encoding'] || 'identity').toLowerCase()
   var length = req.headers['content-length']
-  var stream
 
   debug('content-encoding "%s"', encoding)
 
@@ -158,36 +157,40 @@ function contentstream (req, debug, inflate) {
     })
   }
 
+  if (encoding === 'identity') {
+    req.length = length
+    return req
+  }
+
+  var stream = createDecompressionStream(encoding)
+  req.pipe(stream)
+  return stream
+}
+
+/**
+ * Create a decompression stream for the given encoding.
+ * @param {string} encoding
+ * @param {function} debug
+ * @return {object}
+ * @api private
+ */
+function createDecompressionStream (encoding, debug) {
   switch (encoding) {
     case 'deflate':
-      stream = zlib.createInflate()
       debug('inflate body')
-      req.pipe(stream)
-      break
+      return zlib.createInflate()
     case 'gzip':
-      stream = zlib.createGunzip()
       debug('gunzip body')
-      req.pipe(stream)
-      break
-    case 'identity':
-      stream = req
-      stream.length = length
-      break
+      return zlib.createGunzip()
     case 'br':
-      stream = zlib.createBrotliDecompress()
       debug('brotli decompress body')
-      req.pipe(stream)
-      break
-  }
-
-  if (stream === undefined) {
-    throw createError(415, 'unsupported content encoding "' + encoding + '"', {
-      encoding: encoding,
-      type: 'encoding.unsupported'
-    })
+      return zlib.createBrotliDecompress()
+    default:
+      throw createError(415, 'unsupported content encoding "' + encoding + '"', {
+        encoding: encoding,
+        type: 'encoding.unsupported'
+      })
   }
-
-  return stream
 }
 
 /**