Re-support WASM via simple stub headers

libsecp256k1 really only barely uses libc at all, and in practice,
things like memcpy/memcmp get optimized into something other than a
libc call. Thus, if we provide simple stub headers, things seem to
work with wasm-pack just fine.

Author: TheBlueMatt

.travis.yml

@@ -1,19 +1,24 @@
 language: rust
-# cache:
-#   directories:
-#   - cargo_web
+cache:
+  directories:
+  - wasm
 
 rust:
   - stable
   - beta
   - nightly
   - 1.22.0
+distro: bionic
 os:
  - linux
  - windows
 
 addons:
   chrome: stable
+  apt:
+    packages:
+      - clang-9
+      - nodejs
 
 matrix:
   exclude:
@@ -46,8 +51,10 @@ script:
     cd no_std_test &&
     cargo run --release | grep -q "Verified Successfully";
     fi
-  - #if [ ${TRAVIS_RUST_VERSION} == "stable" -a "$TRAVIS_OS_NAME" = "linux" ]; then
-    #CARGO_TARGET_DIR=cargo_web cargo install --verbose --force cargo-web &&
-    #cargo web build --verbose --target=asmjs-unknown-emscripten &&
-    #cargo web test --verbose --target=asmjs-unknown-emscripten;
-    #fi
+  - if [ ${TRAVIS_RUST_VERSION} == "stable" -a "$TRAVIS_OS_NAME" = "linux" ]; then
+    clang --version &&
+    CARGO_TARGET_DIR=wasm cargo install --verbose --force wasm-pack &&
+    sed -i 's/\[lib\]/[lib]\ncrate-type = ["cdylib", "rlib"]/' Cargo.toml &&
+    CC=clang-9 wasm-pack build &&
+    CC=clang-9 wasm-pack test --node;
+    fi

Cargo.toml

@@ -46,6 +46,10 @@ rand_core = "0.4"
 serde_test = "1.0"
 bitcoin_hashes = "0.7"
 
+[target.wasm32-unknown-unknown.dev-dependencies]
+wasm-bindgen-test = "0.3"
+rand = { version = "0.6", features = ["wasm-bindgen"] }
+
 [dependencies.rand]
 version = "0.6"
 optional = true

secp256k1-sys/build.rs

@@ -84,6 +84,10 @@ fn main() {
                    .define("USE_SCALAR_8X32", Some("1"));
     }
 
+    if env::var("TARGET").unwrap() == "wasm32-unknown-unknown" {
+        base_config.include("wasm-sysroot");
+    }
+
     // secp256k1
     base_config.file("depend/secp256k1/contrib/lax_der_parsing.c")
                .file("depend/secp256k1/src/secp256k1.c")

secp256k1-sys/wasm-sysroot/stdio.h

@@ -0,0 +1,4 @@
+#include <stddef.h>
+void *memset(void *s, int c, size_t n);
+void *memcpy(void *dest, const void *src, size_t n);
+int memcmp(const void *s1, const void *s2, size_t n);

secp256k1-sys/wasm-sysroot/stdlib.h

@@ -1060,6 +1060,33 @@ mod tests {
         assert_tokens(&sig.compact(), &[Token::BorrowedBytes(&SIG_BYTES[..])]);
         assert_tokens(&sig.readable(), &[Token::BorrowedStr(SIG_STR)]);
     }
+
+    // For WASM, just run through our general tests in this file all at once.
+    #[cfg(target_arch = "wasm32")]
+    extern crate wasm_bindgen_test;
+    #[cfg(target_arch = "wasm32")]
+    use self::wasm_bindgen_test::*;
+    #[cfg(target_arch = "wasm32")]
+    #[wasm_bindgen_test]
+    fn stuff() {
+        test_manual_create_destroy();
+        test_raw_ctx();
+        // Note that, sadly, WASM doesn't currently properly unwind panics, so use of the library
+        // via unsafe primitives may cause abort() instead of catch-able panics.
+        /*assert!(std::panic::catch_unwind(|| {
+            test_panic_raw_ctx();
+        }).is_err());*/
+        test_preallocation();
+        capabilities();
+        signature_serialize_roundtrip();
+        signature_display();
+        signature_lax_der();
+        sign_and_verify();
+        sign_and_verify_extreme();
+        sign_and_verify_fail();
+        test_bad_slice();
+        test_low_s();
+    }
 }
 
 #[cfg(all(test, feature = "unstable"))]