Getting Started

If you're looking to write your own Wuffs code outside of its standard library, e.g. you want to safely decode your own custom file format, see the Wuffs the Language document and the /hello-wuffs-c example instead of this document.

If you‘re looking to just use the Wuffs standard library, e.g. you want to safely decode some gzip’ed data in your C program, see the Wuffs the Library document and the other examples instead of this document.

If you‘re looking to modify the Wuffs language, it’s probably best to ask the mailing list.

If you're looking to modify the Wuffs standard library, keep reading.

First, install the Go toolchain in order to build the Wuffs tools. To run the test suite, you might also have to install C compilers like clang and gcc, as well as C libraries (and their .h files) like libjpeg and libpng, as some tests compare that Wuffs produces exactly the same output as these other libraries.

Run git clone to get the latest Wuffs code, cd into its directory and run go install -v ./cmd/wuffs* to install the Wuffs tools. The Wuffs tools that you'll most often use are wuffsfmt (analogous to clang-format, gofmt or rustfmt) and wuffs (roughly analogous to make, go or cargo).

You should now be able to run wuffs test. If you only have the gcc C compiler installed, but not clang, then you can run wuffs test -ccompilers=gcc instead. If all goes well, you should see some output containing the word “PASS” multiple times.

Remember to re-run go install etc whenever you‘ve modified the Wuffs *tools’* source code (i.e. *.go files) or after a manually issued git pull. If you‘re only modifying the Wuffs *standard library’s* source code (i.e. *.wuffs files), re-running go install etc is unnecessary.

If you're modifying just one particular codec in the standard library, such as the std/png/*.wuffs files, then you can exclude unrelated tests by running wuffs test std/png.

Poking Around

Feel free to edit the std/lzw/decode_lzw.wuffs file, which implements the GIF LZW decoder. After editing, run wuffs gen std/gif or wuffs test std/gif to re-generate the C edition of the Wuffs standard library's GIF codec, and optionally run its tests.

Try deleting an assert statement and re-running wuffs gen. The result should be syntactically valid, but a compile error, as some bounds checks can no longer be proven.

Find the var bits : base.u32 line, which declares the bits variable, implicitly initialized to zero. Try adding bits -= 1 on a new line of code after all of the var lines. Again, wuffs gen should fail, as the computation can underflow.

Similarly, changing the 4095 in var prev_code : base.u32[..= 4095] either higher or lower should fail.

Try adding assert false at various places, which should obviously fail, but should also cause wuffs gen to print what facts the compiler knows at that point. This can be useful when debugging why Wuffs can't prove something you think it should be able to.

Running the Tests

If you've changed any of the tools (i.e. changed any .go code), re-run go install -v and go test

If you‘ve changed any of the libraries (i.e. changed any .wuffs code), run wuffs test or, ideally, wuffs test -mimic to also check that Wuffs’ output mimics (i.e. exactly matches) other libraries' output, such as giflib for GIF, libpng for PNG, etc.

If your library change is an optimization, run wuffs bench or wuffs bench -mimic both before and after your change to quantify the improvement. The mimic benchmark numbers shouldn‘t change if you’re only changing .wuffs code, but seeing zero change in those numbers is a coherence check on any unrelated system variance, such as software updates or virus checkers running in the background.