[base64](https://crates.io/crates/base64)
===
[](https://crates.io/crates/base64) [](https://docs.rs/base64)
It's base64. What more could anyone want?
Example
---
```rust
extern crate base64;
use base64::{encode, decode};
fn main() {
let a = b"hello world";
let b = "aGVsbG8gd29ybGQ=";
assert_eq!(encode(a), b);
assert_eq!(a, &decode(b).unwrap()[..]);
}
```
See the [docs](https://docs.rs/base64) for all the details.
Purpose
---
I have a fondness for small dependency footprints, ecosystems where you can pick and choose what functionality you need, and no more. Unix philosophy sort of thing I guess, many tiny utilities interoperating across a common interface. One time making a Twitter bot, I ran into the need to correctly pluralize arbitrary words. I found on npm a module that did nothing but pluralize words. Nothing else, just a couple of functions. I'd like for this to be that "just a couple of functions."
Developing
---
Benchmarks are in `benches/`. Running them requires nightly rust, but `rustup` makes it easy:
```
rustup run nightly cargo bench
```
Decoding is aided by some pre-calculated tables, which are generated by:
```
cargo run --example make_tables > src/tables.rs.tmp && mv src/tables.rs.tmp src/tables.rs
```
Profiling
---
On Linux, you can use [perf](https://perf.wiki.kernel.org/index.php/Main_Page) for profiling. Then compile the benchmarks with `rustup nightly run cargo bench --no-run`.
Run the benchmark binary with `perf` (shown here filtering to one particular benchmark, which will make the results easier to read). `perf` is only available to the root user on most systems as it fiddles with event counters in your CPU, so use `sudo`. We need to run the actual benchmark binary, hence the path into `target`. You can see the actual full path with `rustup run nightly cargo bench -v`; it will print out the commands it runs. If you use the exact path that `bench` outputs, make sure you get the one that's for the benchmarks, not the tests. You may also want to `cargo clean` so you have only one `benchmarks-` binary (they tend to accumulate).
```
sudo perf record target/release/deps/benchmarks-* --bench decode_10mib_reuse
```
Then analyze the results, again with perf:
```
sudo perf annotate -l
```
You'll see a bunch of interleaved rust source and assembly like this. The section with `lib.rs:327` is telling us that 4.02% of samples saw the `movzbl` aka bit shift as the active instruction. However, this percentage is not as exact as it seems due to a phenomenon called *skid*. Basically, a consequence of how fancy modern CPUs are is that this sort of instruction profiling is inherently inaccurate, especially in branch-heavy code.
```
lib.rs:322 0.70 : 10698: mov %rdi,%rax
2.82 : 1069b: shr $0x38,%rax
: if morsel == decode_tables::INVALID_VALUE {
: bad_byte_index = input_index;
: break;
: };
: accum = (morsel as u64) << 58;
lib.rs:327 4.02 : 1069f: movzbl (%r9,%rax,1),%r15d
: // fast loop of 8 bytes at a time
: while input_index < length_of_full_chunks {
: let mut accum: u64;
:
: let input_chunk = BigEndian::read_u64(&input_bytes[input_index..(input_index + 8)]);
: morsel = decode_table[(input_chunk >> 56) as usize];
lib.rs:322 3.68 : 106a4: cmp $0xff,%r15
: if morsel == decode_tables::INVALID_VALUE {
0.00 : 106ab: je 1090e <base64::decode_config_buf::hbf68a45fefa299c1+0x46e>
```
Fuzzing
---
This uses [cargo-fuzz](https://github.com/rust-fuzz/cargo-fuzz). See `fuzz/fuzzers` for the available fuzzing scripts. To run, use an invocation like these:
```
cargo +nightly fuzz run roundtrip
cargo +nightly fuzz run roundtrip_no_pad
cargo +nightly fuzz run roundtrip_mime -- -max_len=10240
cargo +nightly fuzz run roundtrip_random_config -- -max_len=10240
```
License
---
This project is dual-licensed under MIT and Apache 2.0.