feat(api): improve codegen outputs (#41)

* Use `[]byte` for generated request bodies when the source schema has `format: byte`
* Gzip-compress request bodies when `Content-Encoding: gzip` is set
* Require that all models returned as error conditions in our API implement the `error` interface
* Move the implementation for `api.HealthCheck` out of `ping.go` and into `api/error.go`


Co-authored-by: William Baker <55118525+wbaker85@users.noreply.github.com>

internal/api/client_internal_test.go

@@ -0,0 +1,52 @@
+package api
+
+import (
+	"bytes"
+	"compress/gzip"
+	"context"
+	"io"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestNoGzipRequest(t *testing.T) {
+	client := APIClient{cfg: NewConfiguration()}
+	body := []byte("This should not get gzipped")
+	req, err := client.prepareRequest(
+		context.Background(),
+		"/foo", "POST", body,
+		map[string]string{},
+		nil, nil, "", "", nil,
+	)
+	require.NoError(t, err)
+	defer req.Body.Close()
+
+	out := bytes.Buffer{}
+	_, err = io.Copy(&out, req.Body)
+	require.NoError(t, err)
+
+	require.Equal(t, string(body), out.String())
+}
+
+func TestGzipRequest(t *testing.T) {
+	client := APIClient{cfg: NewConfiguration()}
+	body := []byte("This should get gzipped")
+	req, err := client.prepareRequest(
+		context.Background(),
+		"/foo", "POST", body,
+		map[string]string{"Content-Encoding": "gzip"},
+		nil, nil, "", "", nil,
+	)
+	require.NoError(t, err)
+	defer req.Body.Close()
+
+	out := bytes.Buffer{}
+	gzr, err := gzip.NewReader(req.Body)
+	require.NoError(t, err)
+	defer gzr.Close()
+	_, err = io.Copy(&out, gzr)
+	require.NoError(t, err)
+
+	require.Equal(t, string(body), out.String())
+}