如何在Gleam中为HTTP Header格式化日期？

你需要的Date响应头格式为：

Date: <星期缩写>, <日> <月份缩写> <年> <时>:<分>:<秒> GMT
示例：Date: Wed, 21 Oct 2015 07:28:00 GMT

你的当前实现代码如下：

import gleam/http/elli
import gleam/http/response.{type Response}
import gleam/http/request.{type Request}
import gleam/bytes_builder.{type BytesBuilder}
import birl

// Define a HTTP service
//
pub fn my_service(_request: Request(t)) -> Response(BytesBuilder) {
  let body = bytes_builder.from_string("Hello, world!")

  response.new(200)
  |> response.prepend_header("content-type", "text/plain")
  |> response.prepend_header("server", "gleam")
  |> response.prepend_header("date", birl.to_iso8601(birl.now()))
  |> response.set_body(body)
}

pub fn main() {
  elli.become(my_service, on_port: 8080)
}

问题分析 #

birl.to_iso8601生成的是ISO8601格式的时间字符串（例如2024-05-20T12:34:56Z），不符合HTTP标准要求的Date头格式，需要手动实现时间格式化逻辑。

修改后的代码 #

import gleam/http/elli
import gleam/http/response.{type Response}
import gleam/http/request.{type Request}
import gleam/bytes_builder.{type BytesBuilder}
import birl
import gleam/int
import gleam/string
import gleam/list

// 月份缩写列表，对应1-12月
const MONTHS = [
  "Jan", "Feb", "Mar", "Apr", "May", "Jun",
  "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
]

// 星期缩写列表，对应周日到周六
const WEEKDAYS = [
  "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
]

// 将时间格式化为HTTP标准的Date格式
fn format_http_date(time: birl.Time) -> String {
  let utc_dt = birl.to_utc_datetime(time)
  // 获取星期缩写，默认取周三避免索引越界
  let weekday = list.at(WEEKDAYS, utc_dt.weekday) |> string.unwrap("Wed")
  // 日期补零为两位
  let day = int.to_string(utc_dt.day) |> string.pad_left(2, '0')
  // 月份从0开始索引，取对应缩写
  let month = list.at(MONTHS, utc_dt.month - 1) |> string.unwrap("Oct")
  let year = int.to_string(utc_dt.year)
  // 时分秒均补零为两位
  let hour = int.to_string(utc_dt.hour) |> string.pad_left(2, '0')
  let minute = int.to_string(utc_dt.minute) |> string.pad_left(2, '0')
  let second = int.to_string(utc_dt.second) |> string.pad_left(2, '0')

  // 拼接成最终的Date头字符串
  string.concat([
    weekday, ", ", day, " ", month, " ", year, " ",
    hour, ":", minute, ":", second, " GMT"
  ])
}

// HTTP服务实现
pub fn my_service(_request: Request(t)) -> Response(BytesBuilder) {
  let body = bytes_builder.from_string("Hello, world!")
  let current_http_date = format_http_date(birl.now())

  response.new(200)
  |> response.prepend_header("content-type", "text/plain")
  |> response.prepend_header("server", "gleam")
  |> response.prepend_header("date", current_http_date)
  |> response.set_body(body)
}

pub fn main() {
  elli.become(my_service, on_port: 8080)
}

说明 #

1. 定义了MONTHS和WEEKDAYS常量，对应HTTP日期要求的月份和星期缩写
2. format_http_date函数将当前时间转换为UTC datetime，提取各时间组件并补零，最终拼接成符合标准的格式
3. 在服务函数中调用该函数生成Date头的值，替换原有的ISO8601格式化逻辑

内容的提问来源于stack exchange，提问作者Andy Fleming