add mastosan package to turn Mastodon HTML to Slackdown

Signed-off-by: Xe <me@christine.website>

13 files changed, 729 insertions, 2 deletions

diff --git a/flake.lock b/flake.lock
index 318c22a..587d3ab 100644
--- a/flake.lock
+++ b/flake.lock
@@ -94,9 +94,33 @@
         "gomod2nix": "gomod2nix",
         "nixpkgs": "nixpkgs",
         "portable-svc": "portable-svc",
+        "rust-overlay": "rust-overlay",
         "utils": "utils"
       }
     },
+    "rust-overlay": {
+      "inputs": {
+        "flake-utils": [
+          "utils"
+        ],
+        "nixpkgs": [
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1669084742,
+        "narHash": "sha256-aLYwYVnrmEE1LVqd17v99CuqVmAZQrlgi2DVTAs4wFg=",
+        "owner": "oxalica",
+        "repo": "rust-overlay",
+        "rev": "9652ef34c7439eca9f86cee11e94dbef5c9adb09",
+        "type": "github"
+      },
+      "original": {
+        "owner": "oxalica",
+        "repo": "rust-overlay",
+        "type": "github"
+      }
+    },
     "utils": {
       "locked": {
         "lastModified": 1659877975,
diff --git a/flake.nix b/flake.nix
index adb570e..33133a0 100644
--- a/flake.nix
+++ b/flake.nix
@@ -7,6 +7,12 @@
     portable-svc.url = "git+https://tulpa.dev/cadey/portable-svc.git?ref=main";
     ckiee.url = "github:ckiee/nixpkgs?ref=gpt2simple-py-init";
 
+    rust-overlay = {
+      url = "github:oxalica/rust-overlay";
+      inputs.nixpkgs.follows = "nixpkgs";
+      inputs.flake-utils.follows = "utils";
+    };
+
     gomod2nix = {
       url = "github:tweag/gomod2nix";
       inputs.nixpkgs.follows = "nixpkgs";
@@ -14,7 +20,7 @@
     };
   };
 
-  outputs = { self, nixpkgs, utils, gomod2nix, portable-svc, ckiee }@attrs:
+  outputs = { self, nixpkgs, utils, gomod2nix, portable-svc, ckiee, rust-overlay }@attrs:
     utils.lib.eachSystem [
       "x86_64-linux"
       "aarch64-linux"
@@ -31,7 +37,8 @@
             })
             gomod2nix.overlays.default
             portable-svc.overlay
-            (final: prev: self.packages.${system})
+            rust-overlay.overlays.default
+            #(final: prev: self.packages.${system})
           ];
         };
         ckieepkgs = import ckiee { inherit system; };
@@ -182,6 +189,17 @@
             pkg-config
             libaom
             libavif
+
+            cargo
+            cargo-watch
+            rustfmt
+            rust-analyzer
+            wasmtime
+            binaryen
+            (rust-bin.stable.latest.default.override {
+              extensions = [ "rust-src" ];
+              targets = [ "wasm32-wasi" ];
+            })
           ];
         };
       });
diff --git a/go.mod b/go.mod
index 060ea7c..bee3941 100644
--- a/go.mod
+++ b/go.mod
@@ -122,6 +122,7 @@ require (
 	github.com/tcnksm/go-httpstat v0.2.0 // indirect
 	github.com/templexxx/cpufeat v0.0.0-20180724012125-cef66df7f161 // indirect
 	github.com/templexxx/xor v0.0.0-20181023030647-4e92f724b73b // indirect
+	github.com/tetratelabs/wazero v1.0.0-pre.3 // indirect
 	github.com/tjfoc/gmsm v1.0.1 // indirect
 	github.com/u-root/uio v0.0.0-20220204230159-dac05f7d2cb4 // indirect
 	github.com/vishvananda/netlink v1.1.1-0.20211118161826-650dca95af54 // indirect
diff --git a/go.sum b/go.sum
index 66f7044..69f9165 100644
--- a/go.sum
+++ b/go.sum
@@ -395,6 +395,8 @@ github.com/templexxx/cpufeat v0.0.0-20180724012125-cef66df7f161 h1:89CEmDvlq/F7S
 github.com/templexxx/cpufeat v0.0.0-20180724012125-cef66df7f161/go.mod h1:wM7WEvslTq+iOEAMDLSzhVuOt5BRZ05WirO+b09GHQU=
 github.com/templexxx/xor v0.0.0-20181023030647-4e92f724b73b h1:mnG1fcsIB1d/3vbkBak2MM0u+vhGhlQwpeimUi7QncM=
 github.com/templexxx/xor v0.0.0-20181023030647-4e92f724b73b/go.mod h1:5XA7W9S6mni3h5uvOC75dA3m9CCCaS83lltmc0ukdi4=
+github.com/tetratelabs/wazero v1.0.0-pre.3 h1:Z5fbogMUGcERzaQb9mQU8+yJSy0bVvv2ce3dfR4wcZg=
+github.com/tetratelabs/wazero v1.0.0-pre.3/go.mod h1:M8UDNECGm/HVjOfq0EOe4QfCY9Les1eq54IChMLETbc=
 github.com/tjfoc/gmsm v1.0.1 h1:R11HlqhXkDospckjZEihx9SW/2VW0RgdwrykyWMFOQU=
 github.com/tjfoc/gmsm v1.0.1/go.mod h1:XxO4hdhhrzAd+G4CjDqaOkd0hUzmtPR/d3EiBBMn/wc=
 github.com/tmc/scp v0.0.0-20170824174625-f7b48647feef h1:7D6Nm4D6f0ci9yttWaKjM1TMAXrH5Su72dojqYGntFY=
diff --git a/web/mastosan/.cargo/config b/web/mastosan/.cargo/config
new file mode 100644
index 0000000..6b77899
--- /dev/null
+++ b/web/mastosan/.cargo/config
@@ -0,0 +1,2 @@
+[build]
+target = "wasm32-wasi"
diff --git a/web/mastosan/.gitignore b/web/mastosan/.gitignore
new file mode 100644
index 0000000..eb5a316
--- /dev/null
+++ b/web/mastosan/.gitignore
@@ -0,0 +1 @@
+target
diff --git a/web/mastosan/Cargo.lock b/web/mastosan/Cargo.lock
new file mode 100644
index 0000000..a3449fc
--- /dev/null
+++ b/web/mastosan/Cargo.lock
@@ -0,0 +1,496 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "ahash"
+version = "0.7.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fcb51a0695d8f838b1ee009b3fbf66bda078cd64590202a864a8f3e8c4315c47"
+dependencies = [
+ "getrandom 0.2.8",
+ "once_cell",
+ "version_check",
+]
+
+[[package]]
+name = "bitflags"
+version = "1.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bef38d45163c2f1dde094a7dfd33ccf595c92905c8f8f4fdc18d06fb1037718a"
+
+[[package]]
+name = "byteorder"
+version = "1.4.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "14c189c53d098945499cdfa7ecc63567cf3886b3332b312a5b4585d8d3a6a610"
+
+[[package]]
+name = "cfg-if"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "baf1de4339761588bc0619e3cbc0120ee582ebb74b53b4efbf79117bd2da40fd"
+
+[[package]]
+name = "convert_case"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6245d59a3e82a7fc217c5828a6692dbc6dfb63a0c8c90495621f7b9d79704a0e"
+
+[[package]]
+name = "cssparser"
+version = "0.27.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "754b69d351cdc2d8ee09ae203db831e005560fc6030da058f86ad60c92a9cb0a"
+dependencies = [
+ "cssparser-macros",
+ "dtoa-short",
+ "itoa",
+ "matches",
+ "phf",
+ "proc-macro2",
+ "quote",
+ "smallvec",
+ "syn",
+]
+
+[[package]]
+name = "cssparser-macros"
+version = "0.6.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dfae75de57f2b2e85e8768c3ea840fd159c8f33e2b6522c7835b7abac81be16e"
+dependencies = [
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "derive_more"
+version = "0.99.17"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4fb810d30a7c1953f91334de7244731fc3f3c10d7fe163338a35b9f640960321"
+dependencies = [
+ "convert_case",
+ "proc-macro2",
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+ "rustc_version",
+ "syn",
+]
+
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+
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+checksum = "bde03329ae10e79ede66c9ce4dc930aa8599043b0743008548680f25b91502d6"
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+checksum = "9852635589dc9f9ea1b6fe9f05b50ef208c85c834a562f0c6abb1c475736ec2b"
+dependencies = [
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+checksum = "c31b6d751ae2c7f11320402d34e41349dd1016f8d5d45e48c4312bc8625af50c"
+dependencies = [
+ "byteorder",
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+dependencies = [
+ "ahash",
+]
+
+[[package]]
+name = "itoa"
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+ "cfg-if",
+ "cssparser",
+ "encoding_rs",
+ "hashbrown",
+ "lazy_static",
+ "lazycell",
+ "memchr",
+ "safemem",
+ "selectors",
+ "thiserror",
+]
+
+[[package]]
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+ "lol_html",
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+ "bitflags",
+ "cssparser",
+ "derive_more",
+ "fxhash",
+ "log",
+ "matches",
+ "phf",
+ "phf_codegen",
+ "precomputed-hash",
+ "servo_arc",
+ "smallvec",
+ "thin-slice",
+]
+
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+
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+ "proc-macro2",
+ "quote",
+ "unicode-ident",
+]
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+ "thiserror-impl",
+]
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+[[package]]
+name = "thiserror-impl"
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+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
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+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cccddf32554fecc6acb585f82a32a72e28b48f8c4c1883ddfeeeaa96f7d8e519"
+
+[[package]]
+name = "wasi"
+version = "0.11.0+wasi-snapshot-preview1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
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diff --git a/web/mastosan/Cargo.toml b/web/mastosan/Cargo.toml
new file mode 100644
index 0000000..3aba4e8
--- /dev/null
+++ b/web/mastosan/Cargo.toml
@@ -0,0 +1,15 @@
+[package]
+name = "mastosan"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+lol_html = "0.3"
+
+[profile.release]
+lto = true
+opt-level = "z"
+panic = "abort"
+
diff --git a/web/mastosan/README.md b/web/mastosan/README.md
new file mode 100644
index 0000000..f3c5a00
--- /dev/null
+++ b/web/mastosan/README.md
@@ -0,0 +1,24 @@
+# mastosan
+
+Package mastosan takes Mastodon flavored HTML and emits Slack-flavored
+markdown.
+
+It works by using an embedded Rust program compiled to WebAssembly. At
+the time of writing this adds an extra 0.2 seconds to compile and run the
+WebAssembly module, but this can probably be fixed with aggressive sync.Once
+caching should this prove a problem in the real world.
+
+Building this Rust program outside of Nix flakes is UNSUPPORTED.
+
+To build the Rust module from inside the Nix flake:
+
+    cargo install wasm-snip
+    cargo build --release
+    wasm-opt -Oz -o ./testdata/mastosan-pre-snip.wasm
+    wasm-snip --skip-producers-section --snip-rust-panicking-code -i ./testdata/mastosan-pre-snip.wasm ./testdata/mastosan.wasm
+    rm ./testdata/mastosan-pre-snip.wasm
+
+This adds about two megabytes to the resulting binary, including the AOT
+WebAssembly runtime wazero: https://wazero.io/
+
+
diff --git a/web/mastosan/mastosan.go b/web/mastosan/mastosan.go
new file mode 100644
index 0000000..87bee1d
--- /dev/null
+++ b/web/mastosan/mastosan.go
@@ -0,0 +1,64 @@
+// Package mastosan takes Mastodon flavored HTML and emits Slack-flavored
+// markdown.
+//
+// It works by using an embedded Rust program compiled to WebAssembly. At
+// the time of writing this adds an extra 0.2 seconds to compile and run the
+// WebAssembly module, but this can probably be fixed with aggressive sync.Once
+// caching should this prove a problem in the real world.
+//
+// Building this Rust program outside of Nix flakes is UNSUPPORTED.
+//
+// To build the Rust module from inside the Nix flake:
+//
+//     cargo install wasm-snip
+//     cargo build --release
+//     wasm-opt -Oz -o ./testdata/mastosan-pre-snip.wasm
+//     wasm-snip --skip-producers-section --snip-rust-panicking-code -i ./testdata/mastosan-pre-snip.wasm ./testdata/mastosan.wasm
+//     rm ./testdata/mastosan-pre-snip.wasm
+//
+// This adds about two megabytes to the resulting binary, including the AOT
+// WebAssembly runtime wazero: https://wazero.io/
+package mastosan
+
+import (
+	"bytes"
+	"context"
+	_ "embed"
+	"log"
+	"strings"
+
+	"github.com/tetratelabs/wazero"
+	"github.com/tetratelabs/wazero/imports/wasi_snapshot_preview1"
+)
+
+//go:embed testdata/mastosan.wasm
+var mastosanWasm []byte
+
+// HTML2Slackdown converts a string full of HTML text to slack-flavored markdown.
+//
+// Internally this works by taking that HTML and piping it to a small Rust program
+// using lol_html to parse the HTML and rejigger it into slack-flavored markdown.
+// This has an added latency of about 0.2 seconds per invocation, but this is as
+// fast as I can make it for now.
+func HTML2Slackdown(ctx context.Context, text string) (string, error) {
+	r := wazero.NewRuntime(ctx)
+	defer r.Close(ctx)
+
+	fout := &bytes.Buffer{}
+	fin := bytes.NewBufferString(text)
+
+	config := wazero.NewModuleConfig().WithStdout(fout).WithStdin(fin).WithArgs("mastosan")
+
+	wasi_snapshot_preview1.MustInstantiate(ctx, r)
+
+	code, err := r.CompileModule(ctx, mastosanWasm)
+	if err != nil {
+		log.Panicln(err)
+	}
+
+	if _, err = r.InstantiateModule(ctx, code, config); err != nil {
+		return "", err
+	}
+
+	return strings.TrimSpace(fout.String()), nil
+}
diff --git a/web/mastosan/mastosan_test.go b/web/mastosan/mastosan_test.go
new file mode 100644
index 0000000..efdec88
--- /dev/null
+++ b/web/mastosan/mastosan_test.go
@@ -0,0 +1,32 @@
+package mastosan
+
+import (
+	"context"
+	"testing"
+	"time"
+)
+
+func TestHTML2Slackdown(t *testing.T) {
+	for _, tt := range []struct {
+		name     string
+		inp, out string
+	}{
+		{"basic mention", `<p>test mention <span class="h-card"><a href="https://vt.social/@xe" class="u-url mention">@<span>xe</span></a></span> so I can see what HTML mastodon makes</p>`, "test mention <https://vt.social/@xe|@xe> so I can see what HTML mastodon makes"},
+	} {
+		t.Run(tt.name, func(t *testing.T) {
+			ctx, cancel := context.WithTimeout(context.Background(), time.Second)
+			defer cancel()
+			result, err := HTML2Slackdown(ctx, tt.inp)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			if tt.out != result {
+				t.Logf("inp: %s", tt.inp)
+				t.Logf("out: %q", tt.out)
+				t.Logf("got: %q", result)
+				t.Fatal("output did not match what was expected")
+			}
+		})
+	}
+}
diff --git a/web/mastosan/src/main.rs b/web/mastosan/src/main.rs
new file mode 100644
index 0000000..7535129
--- /dev/null
+++ b/web/mastosan/src/main.rs
@@ -0,0 +1,48 @@
+use lol_html::{element, html_content::ContentType, HtmlRewriter, Settings};
+use std::io::{self, prelude::*, stdin, stdout};
+
+fn main() -> io::Result<()> {
+    let mut output = Vec::new();
+    let mut rewriter = HtmlRewriter::new(
+        Settings {
+            element_content_handlers: vec![
+                element!("span", |el| {
+                    el.remove_and_keep_content();
+                    Ok(())
+                }),
+                element!("p", |el| {
+                    el.append("\n\n", ContentType::Html);
+                    el.remove_and_keep_content();
+                    Ok(())
+                }),
+                element!("br", |el| {
+                    el.append("\n\n", ContentType::Html);
+                    el.remove_and_keep_content();
+                    Ok(())
+                }),
+                element!("a[href]", |el| {
+                    let href = el.get_attribute("href").unwrap();
+                    el.prepend(&format!("<{href}|"), ContentType::Html);
+                    el.append(">", ContentType::Html);
+                    el.remove_and_keep_content();
+
+                    Ok(())
+                }),
+            ],
+            ..Settings::default()
+        },
+        |c: &[u8]| output.extend_from_slice(c),
+    );
+
+    let mut input = Vec::new();
+    let mut fin = stdin().lock();
+    fin.read_to_end(&mut input)?;
+
+    rewriter.write(&input).unwrap();
+    rewriter.end().unwrap();
+
+    let mut fout = stdout().lock();
+    fout.write(&output)?;
+
+    Ok(())
+}
diff --git a/web/mastosan/testdata/mastosan.wasm b/web/mastosan/testdata/mastosan.wasm
new file mode 100644
index 0000000..59f88d0
--- /dev/null
+++ b/web/mastosan/testdata/mastosan.wasm