Alpine is tiny. The alpine:3.14 Docker image is only 5.6MB uncompressed on amd64.
Alpine achieves this partly thanks to busybox, which Docker image busybox is only 1.24MB.
Alpine comes with wget implemented in its Busybox multi-call binary.
You can try it with:
docker run -it --rm busybox wget
But why isn’t curl implemented as well, or instead of wget?? 🤔
wget vs curl
The following table shows some key differences between the two, comparing the two installs on Alpine by using
docker run -it --rm alpine:3.14
apk add wget
apk add curl
wget | curl | |
|---|---|---|
| Binary size | 445KB | 230KB |
| Size with dependencies | 2MB | 2MB |
| Dependencies | libunistring, libidn2 | brotli-libs, nghttp2-libs, libcurl |
| License | GPL v3 | MIT |
| Recursive downloading | yes | no |
| HTTP(S) | GET, POST and CONNECT requests only | yes |
| FTP(S) | yes | yes |
| GOPHER(S) | no | yes |
| HTTP(S) | no | yes |
| SCP | no | yes |
| SFTP | no | yes |
| TFTP | no | yes |
| TELNET | no | yes |
| DICT | no | yes |
| LDAP(S) | no | yes |
| MQTT | no | yes |
| FILE | no | yes |
| POP3(S) | no | yes |
| IMAP(S) | no | yes |
| SMB(S) | no | yes |
| SMTP(S) | no | yes |
| RTMP | no | yes |
| RTSP | no | yes |
| SOCKS | no | yes |
All developers know of curl and love it.
Given the limited abilities of wget, not many developers know about it.
Why not curl?
Size
From a first look, the binary size and dependencies size of the wget and curl Alpine packages are about 2MB.
So that does not look to be a size issue.
Now, busybox implements the code for wget so it’s all bundled in a single static binary.
BusyBox combines tiny versions of many common UNIX utilities into a single small executable. (source)
The size of busybox being about 1MB, it clearly shows it’s a trimmed down version of wget, especially since busybox can do plenty of other things too.
You can also see that:
docker run -it --rm alpine:3.14 wget --help
and
docker run -it --rm alpine:3.14 apk add wget && wget --help
result in quite different help messages, where the second one is a lot more complete.
This is because busybox implements the bare minimum to have wget working, it’s not the complete wget you get with the Alpine package manager.
The utilities in BusyBox generally have fewer options than their full-featured GNU cousins; however, the options that are included provide the expected functionality and behave very much like their GNU counterparts. (source)
Supporting all the features of curl would result in a much larger multi-call binary. Probably only 1MB extra, but this would still be a 100% increase in size!
Complexity to implement
curl has so many features it is harder to implement and maintain it as part of the busybox multi-call binary.
Security
There may also be a security aspect to it, since curl offers so many protocols and features, it is a harder piece to keep secured than wget.
EDIT (2021-07-02): It turns out that, as @tianon very well says it:
I mean, yes, but also very much no: #80 (TLS validation is Broken-By-Design)
🤯🤯🤯🤯🤯
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