Optipng (#156)

* omg it’s compiling

* example actually works

* Expose compression level options

* Disable crypto and path module emulation in webpack

* Update README

* Remove small image

* Use -O3 on optipng

* Free memory after copy

* Handle unexpected file reader return types

* Rename level label to effort

codecs/optipng/optipng.cpp

@@ -0,0 +1,51 @@
+#include "emscripten/bind.h"
+#include "emscripten/val.h"
+
+#include <stdio.h>
+
+using namespace emscripten;
+
+extern "C" int main(int argc, char *argv[]);
+
+int version() {
+  // FIXME (@surma): Haven’t found a version in optipng :(
+  return 0;
+}
+
+struct OptiPngOpts {
+  int level;
+};
+
+uint8_t* result;
+val compress(std::string png, OptiPngOpts opts) {
+  FILE* infile = fopen("input.png", "wb");
+  fwrite(png.c_str(), png.length(), 1, infile);
+  fflush(infile);
+  fclose(infile);
+
+  char optlevel[8];
+  sprintf(&optlevel[0], "-o%d", opts.level);
+  char* args[] = {"optipng", optlevel, "-out", "output.png", "input.png"};
+  main(5, args);
+
+  FILE *outfile = fopen("output.png", "rb");
+  fseek(outfile, 0, SEEK_END);
+  int fsize = ftell(outfile);
+  result = (uint8_t*) malloc(fsize);
+  fseek(outfile, 0, SEEK_SET);
+  fread(result, fsize, 1, outfile);
+  return val(typed_memory_view(fsize, result));
+}
+
+void free_result() {
+  free(result);
+}
+
+EMSCRIPTEN_BINDINGS(my_module) {
+  value_object<OptiPngOpts>("OptiPngOpts")
+    .field("level", &OptiPngOpts::level);
+
+  function("version", &version);
+  function("compress", &compress);
+  function("free_result", &free_result);
+}