fix: omit body field from SDK client request/response logs when not logging bodies (#20729)

In SDK request logs, when we don't enable LogBodies, before this change it looks in the logs like we are sending empty bodies.

```
2025-11-08 01:03:54.710 [debu]  sdk request  method=POST  url=https://coder.example/api/v2/workspaceagents/aws-instance-identity  body=""
2025-11-08 01:03:54.765 [debu]  sdk response  method=POST  url=https://coder.example/api/v2/workspaceagents/aws-instance-identity  status=400  body=""  trace_id=""  span_id=""
```

This changes our request and response logging so we omit the `body` field when not logging bodies, rather than show a misleading empty string.

codersdk/client.go

@@ -251,16 +251,17 @@ func (c *Client) RequestWithoutSessionToken(ctx context.Context, method, path st
 	}
 
 	// Copy the request body so we can log it.
-	var reqBody []byte
+	var reqLogFields []any
 	c.mu.RLock()
 	logBodies := c.logBodies
 	c.mu.RUnlock()
 	if r != nil && logBodies {
-		reqBody, err = io.ReadAll(r)
+		reqBody, err := io.ReadAll(r)
 		if err != nil {
 			return nil, xerrors.Errorf("read request body: %w", err)
 		}
 		r = bytes.NewReader(reqBody)
+		reqLogFields = append(reqLogFields, slog.F("body", string(reqBody)))
 	}
 
 	req, err := http.NewRequestWithContext(ctx, method, serverURL.String(), r)
@@ -291,7 +292,7 @@ func (c *Client) RequestWithoutSessionToken(ctx context.Context, method, path st
 		slog.F("url", req.URL.String()),
 	)
 	tracing.RunWithoutSpan(ctx, func(ctx context.Context) {
-		c.Logger().Debug(ctx, "sdk request", slog.F("body", string(reqBody)))
+		c.Logger().Debug(ctx, "sdk request", reqLogFields...)
 	})
 
 	resp, err := c.HTTPClient.Do(req)
@@ -324,11 +325,11 @@ func (c *Client) RequestWithoutSessionToken(ctx context.Context, method, path st
 	span.SetStatus(httpconv.ClientStatus(resp.StatusCode))
 
 	// Copy the response body so we can log it if it's a loggable mime type.
-	var respBody []byte
+	var respLogFields []any
 	if resp.Body != nil && logBodies {
 		mimeType := parseMimeType(resp.Header.Get("Content-Type"))
 		if _, ok := loggableMimeTypes[mimeType]; ok {
-			respBody, err = io.ReadAll(resp.Body)
+			respBody, err := io.ReadAll(resp.Body)
 			if err != nil {
 				return nil, xerrors.Errorf("copy response body for logs: %w", err)
 			}
@@ -337,16 +338,18 @@ func (c *Client) RequestWithoutSessionToken(ctx context.Context, method, path st
 				return nil, xerrors.Errorf("close response body: %w", err)
 			}
 			resp.Body = io.NopCloser(bytes.NewReader(respBody))
+			respLogFields = append(respLogFields, slog.F("body", string(respBody)))
 		}
 	}
 
 	// See above for why this is not logged to the span.
 	tracing.RunWithoutSpan(ctx, func(ctx context.Context) {
 		c.Logger().Debug(ctx, "sdk response",
-			slog.F("status", resp.StatusCode),
-			slog.F("body", string(respBody)),
-			slog.F("trace_id", resp.Header.Get("X-Trace-Id")),
-			slog.F("span_id", resp.Header.Get("X-Span-Id")),
+			append(respLogFields,
+				slog.F("status", resp.StatusCode),
+				slog.F("trace_id", resp.Header.Get("X-Trace-Id")),
+				slog.F("span_id", resp.Header.Get("X-Span-Id")),
+			)...,
 		)
 	})
 

codersdk/client_internal_test.go

@@ -162,6 +162,45 @@ func Test_Client(t *testing.T) {
 	require.Contains(t, logStr, strings.ReplaceAll(resBody, `"`, `\"`))
 }
 
+func Test_Client_LogBodiesFalse(t *testing.T) {
+	t.Parallel()
+
+	const method = http.MethodPost
+	const path = "/ok"
+	const reqBody = `{"msg": "request body"}`
+	const resBody = `{"status": "ok"}`
+
+	s := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", jsonCT)
+		w.WriteHeader(http.StatusOK)
+		_, _ = io.WriteString(w, resBody)
+	}))
+
+	u, err := url.Parse(s.URL)
+	require.NoError(t, err)
+	client := New(u)
+
+	logBuf := bytes.NewBuffer(nil)
+	client.SetLogger(slog.Make(sloghuman.Sink(logBuf)).Leveled(slog.LevelDebug))
+	client.SetLogBodies(false)
+
+	ctx, cancel := context.WithTimeout(context.Background(), testutil.WaitLong)
+	defer cancel()
+
+	resp, err := client.Request(ctx, method, path, []byte(reqBody))
+	require.NoError(t, err)
+	defer resp.Body.Close()
+
+	body, err := io.ReadAll(resp.Body)
+	require.NoError(t, err)
+	require.Equal(t, resBody, string(body))
+
+	logStr := logBuf.String()
+	require.Contains(t, logStr, "sdk request")
+	require.Contains(t, logStr, "sdk response")
+	require.NotContains(t, logStr, "body")
+}
+
 func Test_readBodyAsError(t *testing.T) {
 	t.Parallel()