feat: Allow emscripten users to define HTTP handler

c2pa_c_ffi/Cargo.toml

@@ -33,6 +33,7 @@ c2pa = { path = "../sdk", version = "0.78.4", default-features = false, features
     "file_io",
     "pdf",
 ] }
+libc = "0.2"
 scopeguard = "1.2.0"
 serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0"

c2pa_c_ffi/Makefile

@@ -17,7 +17,7 @@ endif
 
 TARGET_DIR ?= ../target
 
-CARGO_BUILD_FLAGS_EMSCRIPTEN = --release -p c2pa-c-ffi --no-default-features --features "rust_native_crypto"
+CARGO_BUILD_FLAGS_EMSCRIPTEN = --release -p c2pa-c-ffi --no-default-features --features "rust_native_crypto,file_io"
 CARGO_BUILD_FLAGS = --release -p c2pa-c-ffi --no-default-features --features "rust_native_crypto, add_thumbnails, http, file_io"
 
 IPHONEOS_DEPLOYMENT_TARGET ?= 15.0

c2pa_c_ffi/examples/CMakeLists.txt

@@ -0,0 +1,71 @@
+cmake_minimum_required(VERSION 3.13)
+project(C2PAEmscriptenExample)
+
+if(NOT EMSCRIPTEN)
+    message(FATAL_ERROR "This project requires Emscripten. Use: emcmake cmake")
+endif()
+
+set(CMAKE_CXX_STANDARD 17)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+
+# C2PA_ROOT must point to the cargo workspace root (where target/ lives).
+set(C2PA_ROOT "${CMAKE_CURRENT_SOURCE_DIR}/../.." CACHE PATH "Path to c2pa-rs workspace root")
+
+if(CMAKE_BUILD_TYPE STREQUAL "Debug")
+    set(C2PA_LIB_DIR "${C2PA_ROOT}/target/wasm32-unknown-emscripten/debug")
+else()
+    set(C2PA_LIB_DIR "${C2PA_ROOT}/target/wasm32-unknown-emscripten/release")
+endif()
+
+set(C2PA_LIBRARY "${C2PA_LIB_DIR}/libc2pa_c.a")
+
+if(NOT EXISTS "${C2PA_LIBRARY}")
+    message(FATAL_ERROR
+        "c2pa library not found: ${C2PA_LIBRARY}\n"
+        "Build it first:\n"
+        "  cargo +nightly build -Z build-std=std,panic_unwind \\\n"
+        "    -p c2pa-c-ffi --target wasm32-unknown-emscripten --release \\\n"
+        "    --no-default-features --features rust_native_crypto,file_io"
+    )
+endif()
+
+add_executable(c2pa_example emscripten_example.cpp)
+target_include_directories(c2pa_example PRIVATE ${C2PA_LIB_DIR})
+target_link_libraries(c2pa_example ${C2PA_LIBRARY})
+
+# -pthread and -fwasm-exceptions must match the Rust library's compile flags
+# (set in .cargo/config.toml for the wasm32-unknown-emscripten target).
+set(EMSCRIPTEN_LINK_FLAGS
+    "-pthread"
+    "-fwasm-exceptions"
+    "-s WASM=1"
+    "-s USE_PTHREADS=1"
+    "-s ALLOW_MEMORY_GROWTH=1"
+    "-s INITIAL_MEMORY=256MB"
+    "-s MAXIMUM_MEMORY=2GB"
+    "-s EXPORTED_FUNCTIONS=['_main']"
+    "-s EXPORTED_RUNTIME_METHODS=['ccall','cwrap','FS']"
+    "-s FETCH=1"
+    "-s ENVIRONMENT=node,worker"
+    "-s NODERAWFS=1"
+)
+
+if(CMAKE_BUILD_TYPE STREQUAL "Debug")
+    list(APPEND EMSCRIPTEN_LINK_FLAGS "-g" "-s ASSERTIONS=1" "-s SAFE_HEAP=1")
+else()
+    list(APPEND EMSCRIPTEN_LINK_FLAGS "-O3" "-s ASSERTIONS=0")
+endif()
+
+string(REPLACE ";" " " EMSCRIPTEN_LINK_FLAGS_STR "${EMSCRIPTEN_LINK_FLAGS}")
+set_target_properties(c2pa_example PROPERTIES
+    LINK_FLAGS "${EMSCRIPTEN_LINK_FLAGS_STR}"
+    SUFFIX ".js"
+)
+
+install(TARGETS c2pa_example RUNTIME DESTINATION bin)
+install(FILES
+    "${CMAKE_CURRENT_BINARY_DIR}/c2pa_example.js"
+    "${CMAKE_CURRENT_BINARY_DIR}/c2pa_example.wasm"
+    "${CMAKE_CURRENT_BINARY_DIR}/c2pa_example.worker.js"
+    DESTINATION bin
+)

c2pa_c_ffi/examples/README.md

@@ -0,0 +1,59 @@
+# C2PA Emscripten Example
+
+Demonstrates using the c2pa C library from C++ compiled with Emscripten.
+
+## Prerequisites
+
+**Rust nightly** (required to rebuild stdlib with `+atomics,+bulk-memory`):
+```bash
+rustup toolchain install nightly
+rustup target add --toolchain nightly wasm32-unknown-emscripten
+```
+
+**Emscripten SDK**:
+```bash
+git clone https://github.com/emscripten-core/emsdk.git
+cd emsdk && ./emsdk install latest && ./emsdk activate latest
+source ./emsdk_env.sh
+```
+
+## Build and Run
+
+```bash
+# Build (compiles Rust library + C++ example)
+./build_emscripten_example.sh release
+
+# Run with Node.js
+node target/emscripten-example/c2pa_example.js path/to/image.jpg
+```
+
+CMake alternative: `./build_cmake_example.sh Release`
+
+## Browser
+
+Output is a `.js` module. Browser use requires:
+- Running in a **Web Worker** (`EMSCRIPTEN_FETCH_SYNCHRONOUS` is not available on the main thread)
+- COOP/COEP headers for `SharedArrayBuffer`:
+  ```
+  Cross-Origin-Opener-Policy: same-origin
+  Cross-Origin-Embedder-Policy: require-corp
+  ```
+
+## What the Example Covers
+
+- **File read** — `c2pa_read_file`
+- **Stream API** — `c2pa_reader_from_stream` with in-memory read/seek callbacks
+- **Custom HTTP resolver** — `c2pa_http_resolver_create` + `c2pa_context_builder_set_http_resolver`, backed by `emscripten_fetch` for remote manifest fetching
+
+## Common Build Errors
+
+| Error | Fix |
+|-------|-----|
+| `--shared-memory is disallowed` | Use `cargo +nightly build -Z build-std=std,panic_unwind` |
+| `__cpp_exception` undefined | Add `-fwasm-exceptions` to your emcc command |
+| File not found at runtime | Add `-s NODERAWFS=1` for host filesystem access under Node.js |
+
+## Further Reading
+
+- [`EMSCRIPTEN_USAGE.md`](../EMSCRIPTEN_USAGE.md) — full integration guide
+- [`c2pa.h`](../../target/wasm32-unknown-emscripten/release/c2pa.h) — generated C API header

c2pa_c_ffi/examples/build_cmake_example.sh

@@ -0,0 +1,53 @@
+#!/bin/bash
+# CMake-based build for the Emscripten C++ example.
+#
+# Usage: ./build_cmake_example.sh [Release|Debug]  (default: Release)
+
+set -e
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+PROJECT_ROOT="$(dirname "$SCRIPT_DIR")"
+WORKSPACE_ROOT="$(dirname "$PROJECT_ROOT")"
+BUILD_TYPE="${1:-Release}"
+
+echo "Build type: $BUILD_TYPE"
+
+# Step 1: Build the Rust library (same as build_emscripten_example.sh).
+cd "$WORKSPACE_ROOT"
+
+if ! rustup toolchain list | grep -q '^nightly'; then
+    echo "Error: nightly toolchain not found. Run: rustup toolchain install nightly"
+    exit 1
+fi
+rustup target add --toolchain nightly wasm32-unknown-emscripten 2>/dev/null || true
+
+CARGO_FLAGS="-p c2pa-c-ffi --target wasm32-unknown-emscripten --no-default-features --features rust_native_crypto,file_io"
+if [ "$BUILD_TYPE" = "Debug" ]; then
+    cargo +nightly build -Z build-std=std,panic_unwind $CARGO_FLAGS
+else
+    cargo +nightly build -Z build-std=std,panic_unwind $CARGO_FLAGS --release
+fi
+echo "✓ Rust library built"
+
+# Step 2: Build with CMake + emcmake.
+if ! command -v emcc &>/dev/null; then
+    echo "Error: emcc not found. Install the Emscripten SDK and source emsdk_env.sh."
+    exit 1
+fi
+
+BUILD_DIR="$SCRIPT_DIR/build-emscripten-$BUILD_TYPE"
+rm -rf "$BUILD_DIR"
+mkdir -p "$BUILD_DIR"
+cd "$BUILD_DIR"
+
+emcmake cmake .. \
+    -DCMAKE_BUILD_TYPE="$BUILD_TYPE" \
+    -DC2PA_ROOT="$WORKSPACE_ROOT"
+
+emmake make -j"$(nproc 2>/dev/null || sysctl -n hw.ncpu 2>/dev/null || echo 4)"
+
+echo ""
+echo "✓ Build complete: $BUILD_DIR"
+echo ""
+echo "Run with Node.js:"
+echo "  node $BUILD_DIR/c2pa_example.js path/to/image.jpg"

c2pa_c_ffi/examples/build_emscripten_example.sh

@@ -0,0 +1,85 @@
+#!/bin/bash
+# Builds the c2pa Rust library for wasm32-unknown-emscripten, then compiles
+# the C++ example with emcc.
+#
+# Usage: ./build_emscripten_example.sh [release|debug]  (default: release)
+
+set -e
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+PROJECT_ROOT="$(dirname "$SCRIPT_DIR")"
+WORKSPACE_ROOT="$(dirname "$PROJECT_ROOT")"
+BUILD_TYPE="${1:-release}"
+
+echo "Build type: $BUILD_TYPE"
+
+# Step 1: Build the Rust library.
+# Nightly + -Z build-std is required so stdlib is rebuilt with
+# +atomics,+bulk-memory, matching USE_PTHREADS=1.
+cd "$WORKSPACE_ROOT"
+
+if ! rustup toolchain list | grep -q '^nightly'; then
+    echo "Error: nightly toolchain not found. Run: rustup toolchain install nightly"
+    exit 1
+fi
+rustup target add --toolchain nightly wasm32-unknown-emscripten 2>/dev/null || true
+
+CARGO_FLAGS="-p c2pa-c-ffi --target wasm32-unknown-emscripten --no-default-features --features rust_native_crypto,file_io"
+if [ "$BUILD_TYPE" = "debug" ]; then
+    cargo +nightly build -Z build-std=std,panic_unwind $CARGO_FLAGS
+    LIB_DIR="$WORKSPACE_ROOT/target/wasm32-unknown-emscripten/debug"
+else
+    cargo +nightly build -Z build-std=std,panic_unwind $CARGO_FLAGS --release
+    LIB_DIR="$WORKSPACE_ROOT/target/wasm32-unknown-emscripten/release"
+fi
+
+C2PA_LIB="$LIB_DIR/libc2pa_c.a"
+C2PA_HEADER="$LIB_DIR/c2pa.h"
+
+[ -f "$C2PA_LIB" ]    || { echo "Error: library not found: $C2PA_LIB"; exit 1; }
+[ -f "$C2PA_HEADER" ] || { echo "Error: header not found: $C2PA_HEADER"; exit 1; }
+echo "✓ Rust library: $C2PA_LIB"
+
+# Step 2: Compile the C++ example.
+if ! command -v emcc &>/dev/null; then
+    echo "Error: emcc not found. Install the Emscripten SDK and source emsdk_env.sh."
+    exit 1
+fi
+
+OUTPUT_DIR="$WORKSPACE_ROOT/target/emscripten-example"
+mkdir -p "$OUTPUT_DIR"
+
+if [ "$BUILD_TYPE" = "debug" ]; then
+    OPT_FLAGS="-g -s ASSERTIONS=1 -s SAFE_HEAP=1"
+else
+    OPT_FLAGS="-O3 -s ASSERTIONS=0"
+fi
+
+# -pthread and -fwasm-exceptions must match how the Rust library was compiled
+# (see .cargo/config.toml for the wasm32-unknown-emscripten target).
+emcc "$SCRIPT_DIR/emscripten_example.cpp" \
+    -I"$LIB_DIR" \
+    "$C2PA_LIB" \
+    -o "$OUTPUT_DIR/c2pa_example.js" \
+    -pthread \
+    -fwasm-exceptions \
+    -s WASM=1 \
+    -s USE_PTHREADS=1 \
+    -s ALLOW_MEMORY_GROWTH=1 \
+    -s INITIAL_MEMORY=256MB \
+    -s MAXIMUM_MEMORY=2GB \
+    -s EXPORTED_FUNCTIONS='["_main"]' \
+    -s EXPORTED_RUNTIME_METHODS='["ccall","cwrap","FS"]' \
+    -s FETCH=1 \
+    -s ENVIRONMENT='node,worker' \
+    -s NODERAWFS=1 \
+    -std=c++17 \
+    $OPT_FLAGS
+
+echo ""
+echo "✓ Build complete: $OUTPUT_DIR/c2pa_example.js"
+echo ""
+echo "Run with Node.js:"
+echo "  node $OUTPUT_DIR/c2pa_example.js path/to/image.jpg"
+echo ""
+echo "Note: the HTTP resolver example requires a Web Worker in the browser."