- 客户端没有执行操作的权限
- 客户端没有访问资源的权限
- 客户端要访问的项目不存在
- 等等 ...

遇到这些情况时，通常要返回 **4XX**（400 至 499）**HTTP 状态码**。

**4XX** 状态码与表示请求成功的 **2XX**（200 至 299） HTTP 状态码类似。

只不过，**4XX** 状态码表示客户端发生的错误。

大家都知道**「404 Not Found」**错误，还有调侃这个错误的笑话吧？

## 使用 `HTTPException`

向客户端返回 HTTP 错误响应，可以使用 `HTTPException`。

### 导入 `HTTPException`

{* ../../docs_src/handling_errors/tutorial001.py hl[1] *}

### 触发 `HTTPException`

// Copyright 2016 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package tar

import (
	"bytes"
	"fmt"
	"strconv"
	"strings"
	"time"
)

// hasNUL reports whether the NUL character exists within s.
func hasNUL(s string) bool {
	return strings.Contains(s, "\x00")
}

// isASCII reports whether the input is an ASCII C-style string.

                            + upgrade.minVersion);
                }
            } else {
                context.warning("Property " + propertyName + " not found in POM properties");
            }
        } else {
            context.warning("No properties section found in POM for property " + propertyName);
        }

        return false;
    }

    /**

   *
   * <p><b>Java 21+ users:</b> Use {@code Math.clamp} instead.
   *
   * @param value the {@code double} value to constrain
   * @param min the lower bound (inclusive) of the range to constrain {@code value} to
   * @param max the upper bound (inclusive) of the range to constrain {@code value} to
   * @throws IllegalArgumentException if {@code min > max}
   * @since 21.0
   */

./mc rm sitea/delissue/hello --insecure

count=$(./mc ls --versions sitea/delissue --insecure | wc -l)

if [ ${count} -ne 3 ]; then
	echo "BUG: expected number of versions to be '3' found ${count}"
	echo "===== DEBUG ====="
	./mc ls --versions sitea/delissue
fi

./mc mb sitea/testbucket

./mc version enable sitea/testbucket

./mc put --quiet README.md sitea/testbucket/file

        fun selectVersionsFrom(minimumSupported: String, allVersions: List<String>): List<String> {
            require(minimumSupported in allVersions) {
                "Minimum supported '$minimumSupported' was not found in available versions: $allVersions"
            }
            val versionsByMinor = allVersions
                .groupBy { it.take(3) } // e.g. 1.9
                .toSortedMap()
            val latests = buildList {

    /*
     * uncheckedCastNullableTToT is safe as long as the callers are careful to pass a "real" T
     * whenever they pass `true` for the matching `has*Bound` parameter.
     */
    if (hasLowerBound) {
      int unused =
          comparator.compare(
              uncheckedCastNullableTToT(lowerEndpoint), uncheckedCastNullableTToT(lowerEndpoint));
    }

   * Range#contains contained} by the range.
   *
   * @throws IllegalArgumentException if neither range nor the domain has a lower bound, or if
   *     neither has an upper bound
   * @since 13.0
   */
  public static <C extends Comparable> ContiguousSet<C> create(
      Range<C> range, DiscreteDomain<C> domain) {
    checkNotNull(range);
    checkNotNull(domain);

				}
			}
		default:
			bts, err = msgp.Skip(bts)
			if err != nil {
				err = msgp.WrapError(err)
				return
			}
		}
	}
	o = bts
	return
}

// Msgsize returns an upper bound estimate of the number of bytes occupied by the serialized message
func (z *nsScannerOptions) Msgsize() (s int) {
	s = 1 + 3 + msgp.StringPrefixSize + len(z.DiskID) + 2 + msgp.IntSize + 2
	if z.Cache == nil {

			dcinfo.FSType = di.FSType
			if root {
				return dcinfo, errDriveIsRoot
			}

			diskID, err := s.GetDiskID()
			// Healing is 'true' when
			// - if we found an unformatted disk (no 'format.json')
			// - if we found healing tracker 'healing.bin'
			dcinfo.Healing = errors.Is(err, errUnformattedDisk)
			if !dcinfo.Healing {
				if hi := s.Healing(); hi != nil && !hi.Finished {
					dcinfo.Healing = true