Compiling an Existing C Module to WebAssembly - WebAssembly
webp to wasm. the source for the webp codec is written in c and available on github as well as some extensive api documentation. that's a pretty good starting point. $ git clone https://github.com/webmproject/libwebp to start off simple, expose webpgetencoderversion() from encode.h to javascript by writing a c file called webp.c: #include "emscripten.h" #include "src/webp/encode.h" emscripten_keepalive int version() { return webpgetencoderversion(); } this is a good simple program to test whether you can get the source code of libwebp to compile, as it doesn't require any parameters or complex data structures to invoke this function. to compile this program, you need to tell the compiler where it can find libwebp's header files using the -i flag and also pass it all the c files of libwebp t...
... ctx = canvas.getcontext('2d'); ctx.drawimage(img, 0, 0); return ctx.getimagedata(0, 0, img.width, img.height); } now it's "only" a matter of copying the data from javascript into wasm. for that, you need to expose two additional functions — one that allocates memory for the image inside wasm and one that frees it up again: #include <stdlib.h> // required for malloc definition emscripten_keepalive uint8_t* create_buffer(int width, int height) { return malloc(width * height * 4 * sizeof(uint8_t)); } emscripten_keepalive void destroy_buffer(uint8_t* p) { free(p); } the create_buffer() function allocates a buffer for the rgba image — hence 4 bytes per pixel. the pointer returned by malloc() is the address of the first memory cell of that buffer. when the pointer is returned to javascr...
... the webp image. the result of the encoding operation is an output buffer and its length. because functions in c can't have arrays as return types (unless you allocate memory dynamically), this example resorts to a static global array. this may not be clean c. in fact, it relies on wasm pointers being 32 bits wide. ...
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PRSockOption
enumeration type used in the option field of prsocketoptiondata to form the name portion of a name-value pair. syntax #include <prio.h> typedef enum prsockoption { pr_sockopt_nonblocking, pr_sockopt_linger, pr_sockopt_reuseaddr, pr_sockopt_keepalive, pr_sockopt_recvbuffersize, pr_sockopt_sendbuffersize, pr_sockopt_iptimetolive, pr_sockopt_iptypeofservice, pr_sockopt_addmember, pr_sockopt_dropmember, pr_sockopt_mcastinterface, pr_sockopt_mcasttimetolive, pr_sockopt_mcastloopback, pr_sockopt_nodelay, pr_sockopt_maxsegment, pr_sockopt_last } prsockoption; enumerators the enumeration has the following enumerators: pr_sockopt_nonblocking nonblocking i/o. pr_sockopt_linger time to linger on close if data is present in the socket send buffer. pr_sockopt_reusea...
...e, pr_sockopt_mcasttimetolive, pr_sockopt_mcastloopback, pr_sockopt_nodelay, pr_sockopt_maxsegment, pr_sockopt_last } prsockoption; enumerators the enumeration has the following enumerators: pr_sockopt_nonblocking nonblocking i/o. pr_sockopt_linger time to linger on close if data is present in the socket send buffer. pr_sockopt_reuseaddr allow local address reuse. pr_sockopt_keepalive periodically test whether connection is still alive. pr_sockopt_recvbuffersize receive buffer size. pr_sockopt_sendbuffersize send buffer size. pr_sockopt_iptimetolive ip time-to-live. pr_sockopt_iptypeofservice ip type-of-service and precedence. pr_sockopt_addmember join an ip multicast group. pr_sockopt_dropmember leave an ip multicast group. pr_sockopt_mcastinterface ip multicas...

Compiling a New C/C++ Module to WebAssembly - WebAssembly
usually easier to use the provided html template. emscripten requires a large variety of javascript "glue" code to handle memory allocation, memory leaks, and a host of other problems calling a custom function defined in c if you have a function defined in your c code that you want to call as needed from javascript, you can do this using the emscripten ccall() function, and the emscripten_keepalive declaration (which adds your functions to the exported functions list (see why do functions in my c/c++ source code vanish when i compile to javascript, and/or i get no functions to process?)). let's look at how this works. to start with, save the following code as hello3.c in a new directory: #include <stdio.h> #include <emscripten/emscripten.h> int main(int argc, char ** argv) { p...
...functions in my c/c++ source code vanish when i compile to javascript, and/or i get no functions to process?)). let's look at how this works. to start with, save the following code as hello3.c in a new directory: #include <stdio.h> #include <emscripten/emscripten.h> int main(int argc, char ** argv) { printf("hello world\n"); } #ifdef __cplusplus extern "c" { #endif void emscripten_keepalive myfunction(int argc, char ** argv) { printf("myfunction called\n"); } #ifdef __cplusplus } #endif by default, emscripten-generated code always just calls the main() function, and other functions are eliminated as dead code. putting emscripten_keepalive before a function name stops this from happening. you also need to import the emscripten.h library to use emscripten_keepalive. note...

HTTP delegation
t support both strategies.) the logical http server session object is expected to remain valid until explicitly destroyed (sec_httpserver_freesessionfcn). should the application be unable to keep a physical connection alive all the time, the application is expected to create new connections automatically. nss may choose to repeatedly call a "network connection keep alive" function (sec_httpserver_keepalivesessionfcn) on the server session object, giving application code a chance to do whatever is required. for each individual http request, nss will request the creation of a "http request object" (sec_httprequest_createfcn). no full uri is provided as a parameter. instead, the parameters are a server session object (that carries host and port information already) and the request path. in our example...

HTTP delegation
t support both strategies.) the logical http server session object is expected to remain valid until explicitly destroyed (sec_httpserver_freesessionfcn). should the application be unable to keep a physical connection alive all the time, the application is expected to create new connections automatically. nss may choose to repeatedly call a "network connection keep alive" function (sec_httpserver_keepalivesessionfcn) on the server session object, giving application code a chance to do whatever is required. for each individual http request, nss will request the creation of a "http request object" (sec_httprequest_createfcn). no full uri is provided as a parameter. instead, the parameters are a server session object (that carries host and port information already) and the request path. in our example...

PerformanceEventTiming - Web APIs
ce: true}); // sends the passed data to an analytics endpoint. this code // uses `/analytics`; you can replace it with your own url. function sendtoanalytics(data) { const body = json.stringify(data); // use `navigator.sendbeacon()` if available, falling back to `fetch()`. (navigator.sendbeacon && navigator.sendbeacon('/analytics', body)) || fetch('/analytics', {body, method: 'post', keepalive: true}); } // use a try/catch instead of feature detecting `first-input` // support, since some browsers throw when using the new `type` option. // https://bugs.webkit.org/show_bug.cgi?id=209216 try { function onfirstinputentry(entry) { // only report fid if the page wasn't hidden prior to // the entry being dispatched. this typically happens when a // page is loaded in a backgroun...

WindowOrWorkerGlobalScope.fetch() - Web APIs
:client, or an empty string. referrerpolicy specifies the referrer policy to use for the request. may be one of no-referrer, no-referrer-when-downgrade, same-origin, origin, strict-origin, origin-when-cross-origin, strict-origin-when-cross-origin, or unsafe-url. integrity contains the subresource integrity value of the request (e.g., sha256-bpfbw7ivv8q2jlit13fxdyae2tjllusrsz273h2nfse=). keepalive the keepalive option can be used to allow the request to outlive the page. fetch with the keepalive flag is a replacement for the navigator.sendbeacon() api. signal an abortsignal object instance; allows you to communicate with a fetch request and abort it if desired via an abortcontroller. return value a promise that resolves to a response object. exceptions aborterror the requ...

Synchronous and asynchronous requests - Web APIs
n be useful, for example in order to interact with the server in the background, or to preload content. see using web workers for examples and details. adapting sync xhr use cases to the beacon api there are some cases in which the synchronous usage of xmlhttprequest is not replaceable, like during the unload, beforeunload, and pagehide events. you should consider using the fetch() api with the keepalive flag. when fetch with keepalive isn't available, you can consider using the navigator.sendbeacon() api, which can support these use cases while typically delivering a good ux. the following example shows theoretical analytics code that attempts to submit data to a server by using a synchronous xmlhttprequest in an unload handler. this results in the unloading of the page to be delayed. window.a...