make Response#to_s non-destructive, and keep the body around

for most cases, this didn't make sense, i.e. response bodies were so
    small, and the user is fine with keeping it all in mem, whereas
    clearing the string is more confusing. And it breaks pattern
    matching when matching body multiple times.

lib/httpx/response.rb

@@ -134,18 +134,28 @@ module HTTPX
       end
 
       def to_s
-        rewind
-        if @buffer
+        case @buffer
+        when StringIO
+          begin
+            @buffer.string.force_encoding(@encoding)
+          rescue ArgumentError
+            @buffer.string
+          end
+        when Tempfile, File
+          rewind
           content = @buffer.read
           begin
-            return content.force_encoding(@encoding)
+            content.force_encoding(@encoding)
           rescue ArgumentError # ex: unknown encoding name - utf
-            return content
+            content
+          ensure
+            close
           end
+        when nil
+          "".b
+        else
+          @buffer
         end
-        "".b
-      ensure
-        close
       end
       alias_method :to_str, :to_s
 

test/response_test.rb

@@ -43,6 +43,7 @@ class ResponseTest < Minitest::Test
 
   def test_response_body_to_s
     body1 = Response::Body.new(Response.new(request, 200, "2.0", {}), Options.new(body_threshold_size: 1024))
+    assert body1 == "", "body should be empty"
     assert body1.empty?, "body must be empty after initialization"
     body1.write("foo")
     assert body1 == "foo", "body must be updated"
@@ -62,6 +63,11 @@ class ResponseTest < Minitest::Test
     body4.write(text)
     req_text = body4.to_s
     assert text == req_text, "request body must be in original encoding (#{req_text})"
+
+    payload = "a" * 2048
+    body5 = Response::Body.new(Response.new(request, 200, "2.0", {}), Options.new(body_threshold_size: 1024))
+    body5.write(payload)
+    assert body5 == "a" * 2048, "body messed up with file"
   end
 
   def test_response_body_copy_to_memory