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# htpdate
A tool to synchronize system time from web servers, for linux, windows and macos. [Download](https://github.com/bobwen-dev/htpdate/releases)
**htpdate** is a tool to synchronize system time from web servers, supporting Windows, Linux, BSD, and macOS. It provides time calibration with 0.5-second accuracy and can be used as a backup measure or in cases where NTP (Network Time Protocol) is not available.
`htpdate` provides time calibration with `0.5` second accuracy.
## Features
## But, why not use ntp?
- **High Accuracy**: Provides time calibration with 0.5-second accuracy.
- **Cross-Platform**: Supports Windows, Linux, BSD, and macOS.
- **Flexible**: Can be used as a backup measure or in environments where NTP is not available.
- **Easy to Use**: Simple command-line interface with various options for customization.
- Websites are everywhere in the world, ntp servers are scarce that the access is centralized.
- `htpdate` can be used as a backup measure.
- There are always cases where the device cannot use ntp.
## Why htpdate?
## Examples
- **Ubiquity of Web Servers**: Websites are everywhere, making them a more accessible source for time synchronization compared to NTP servers.
- **Backup Measure**: htpdate can serve as a backup when NTP is not available.
- **Versatility**: Useful in scenarios where devices cannot use NTP.
Synchronize time from multiple URLs
## Installation
```text
C:\> htpdate -s www.pool.ntp.org www.openssl.org nodejs.org
HEAD https://www.pool.ntp.org
#1: +367325 ms
#2: +366966 ms
#3: +367462 ms
#4: +366960 ms
HEAD https://www.openssl.org
#1: +367258 ms
#2: +366983 ms
#3: +367487 ms
#4: +366986 ms
HEAD https://nodejs.org
#1: +367647 ms
#2: +367278 ms
#3: +367670 ms
#4: +367516 ms
Median: 367301.5 ms
Adjust time...
>
$ time 13:22:42.28 && date 11-04-21
>
$ exit
Done
```
### Prerequisites
Note: Windows users need to be aware of the date format in their region. Default format(from [dayjs](https://day.js.org/docs/en/display/format)) is `MM-DD-YY`, users in non-U.S. regions may need to customize it with the `-C` parameter, eg:
- **gcc**: Ensure you have the GNU Compiler Collection (gcc) installed.
- **libcurl-dev**: Ensure you have the libcurl development package installed.
`htpdate -s -C "[time ]HH:mm:ss.SS[ && date ]YY-MM-DD" github.com`.
### Build
Query from multiple URLs
To build htpdate, use the following command:
```text
$ htpdate -c 5 -v www.pool.ntp.org www.openssl.org
HEAD https://www.pool.ntp.org
#1: -419 ms DNS: 95 TCP: 27 TSL: 43 Send: 3 Recv: 38
#2: +403 ms DNS: 0 TCP: 0 TSL: 0 Send: 1 Recv: 26
#3: -94 ms DNS: 0 TCP: 0 TSL: 0 Send: 1 Recv: 24
#4: +372 ms DNS: 0 TCP: 0 TSL: 0 Send: 1 Recv: 46
#5: -97 ms DNS: 0 TCP: 0 TSL: 0 Send: 1 Recv: 24
HEAD https://www.openssl.org
#1: +251 ms DNS: 38 TCP: 27 TSL: 67 Send: 1 Recv: 33
#2: -107 ms DNS: 0 TCP: 0 TSL: 0 Send: 1 Recv: 28
#3: +396 ms DNS: 0 TCP: 0 TSL: 0 Send: 1 Recv: 25
#4: -113 ms DNS: 0 TCP: 0 TSL: 0 Send: 1 Recv: 30
#5: +385 ms DNS: 0 TCP: 0 TSL: 0 Send: 0 Recv: 31
Median: 78.5 ms
```
Change default protocol to 'http'
```bash
htpdate -s -p http www.pool.ntp.org
```
Mix http and https URLs
```bash
htpdate -s http://www.pool.ntp.org https://www.openssl.org
```
Access through a http proxy
```bash
export http_proxy=http://127.0.0.1:8118
htpdate -s www.pool.ntp.org
```sh
gcc -o htpdate htpdate.c -lcurl
```
## Usage
`htpdate [options...] URLs...`
```sh
htpdate [options...] URLs...
```
### Options
```text
-c, --count The number of requests for each URL
Default: 4
- `-c, --count`: The number of requests for each URL. Default: 4.
- `-C, --command`: Command to adjust system time, in [https://day.js.org/](https://day.js.org/) format.
- Default (Linux/Mac): `'[date -s ]YYYY[-]MM[-]DDTHH[:]mm[:]ss[.]SSS'`
- Default (Windows): `'[time ]HH[:]mm[:]ss[.]SS[ && date ]MM[-]DD[-]YY'`
- `-h, --help`: Display this help text. Default: false.
- `--http2`: Try to choose either HTTP/1.1 or HTTP/2 depending on the ALPN protocol. Default: false.
- `-i, --interval`: The minimum milliseconds between requests. Default: 500.
- `-k, --insecure`: Allow insecure server connections when using HTTPS. Default: false.
- `-m, --method`: HTTP method. Default: 'HEAD'.
- `-p, --protocol`: Use this protocol when no protocol is specified in the URL. Default: 'https'.
- `-r, --retry`: Number of retries. Default: 0.
- `-R, --redirect`: If redirect responses should be followed. Default: false.
- `-s, --set`: Adjust system time if necessary. Default: false.
- `-t, --threshold`: At least how many milliseconds are considered to adjust system time. Default: 1500.
- `-T, --timeout`: Total timeout value, milliseconds. Default: 6000.
- `-u, --user-agent`: Browser user agent name.
- `-V, --version`: Display the version of htpdate and exit. Default: false.
- `-v, --verbose`: Make the operation more talkative. Default: false.
-C, --command Command to adjust system time, in https://day.js.org/ format
Default(Linux/Mac): '[date -s ]YYYY[-]MM[-]DDTHH[:]mm[:]ss[.]SSS'
Default(Windows): '[time ]HH[:]mm[:]ss[.]SS[ && date ]MM[-]DD[-]YY'
## Time Synchronization Principle
-h, --help This help text
Default: false
According to the definition of RFC 7230/2822/2616, websites include a `Date` field in the response header, like this:
--http2 Try to choose either HTTP/1.1 or HTTP/2 depending on the ALPN protocol
Default: false
-i, --interval The minimum milliseconds between requests
Default: 500
-k, --insecure Allow insecure server connections when using https
Default: false
-m, --method HTTP method
Default: 'HEAD'
-p, --protocol Use this protocol when no protocol is specified in the URL
Default: 'https'
-r, --retry
Default: 0
-R, --redirect If redirect responses should be followed
Default: false
-s, --set Adjust system time if necessary
Default: false
-t, --threshold At least how many milliseconds are considered to adjust system time
Default: 1500
-T, --timeout
Default: 6000
-u, --user-agent
Type: string
-V, --version display the version of htpdate and exit
Default: false
-v, --verbose Make the operation more talkative
Default: false
```
## Install Precompiled package
Download the precompiled binary package from [Releases page](https://github.com/bobwen-dev/htpdate/releases), uncompress it, and run it independently as an executable.
## Compile
```bash
git clone https://github.com/bobwen-dev/htpdate
cd htpdate
npm install
npm run build
```
## The principle
According to the definition of [rfc7230](https://datatracker.ietf.org/doc/html/rfc7230)/[2822](https://datatracker.ietf.org/doc/html/rfc2822)/[2616](https://tools.ietf.org/html/rfc2616), website places a `Date` field in the response header, like this:
```text
HTTP/2 200
Content-Type: text/html; charset=utf-8
Date: Wed, 03 Nov 2021 11:46:19 GMT
...
```
This field `Date: Wed, 03 Nov 2021 11:46:19 GMT` is the moment the website was processing the request, which is between the time we sent the request and the time we received the response. Simply assuming that the period to send request and receive is equal, we can calculate that the difference between local time and website time:
This `Date` field represents the moment the website processed the request, which is between the time we sent the request and the time we received the response. By assuming that the time to send the request and receive the response is equal, we can calculate the difference between local time and website time:
```text
duration = received_at - sent_at
delta = server_time - received_at - duration / 2
```
1. **Duration Calculation**:
```
duration = received_at - sent_at
```
There is one more thing: the precision of the field. Imagine we get a value end with `:23 GMT`, which could be `23.000` seconds, or `23.999` seconds. So we give `+0.5s` as a compensation.
2. **Time Difference Calculation**:
```
delta = server_time - received_at - duration / 2
```
3. **Precision Compensation**:
Since the precision of the `Date` field can vary (e.g., `:23 GMT` could be `23.000` seconds or `23.999` seconds), we add a compensation of +0.5 seconds.
## Platform-Specific Handling
### Windows
On Windows, htpdate uses the `reg` command to query the short date format from the registry and constructs the appropriate date and time adjustment commands.
### Linux/MacOS
On Linux and macOS, htpdate uses the `date` command to adjust the system time.
## License
© 2021 Bob Wen
This project is licensed under the AGPL-3.0 License. See the [LICENSE](LICENSE) file for details.
Licensed under the [GNU Affero General Public License v3.0](https://www.gnu.org/licenses/agpl-3.0.en.html) or later.
## Contributing
Contributions are welcome! Please open an issue or submit a pull request.
## Acknowledgments
- Thanks to the original CoffeeScript version for the inspiration.
- Special thanks to the contributors and users of htpdate.
## Contact
For any questions or feedback, please open an issue on GitHub.
---
**htpdate** is a powerful tool for time synchronization, offering a reliable alternative to NTP. Try it out and ensure your system time is always accurate!