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41 lines
1.2 KiB
Markdown
41 lines
1.2 KiB
Markdown
## TCP echo server
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This is an example of a server which accepts connections on port 8080, and
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returns to the client anything it sends.
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```ts
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const listener = Deno.listen({ port: 8080 });
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console.log("listening on 0.0.0.0:8080");
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for await (const conn of listener) {
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Deno.copy(conn, conn);
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}
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```
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When this program is started, it throws PermissionDenied error.
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```shell
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$ deno run https://deno.land/std@$STD_VERSION/examples/echo_server.ts
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error: Uncaught PermissionDenied: network access to "0.0.0.0:8080", run again with the --allow-net flag
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► $deno$/dispatch_json.ts:40:11
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at DenoError ($deno$/errors.ts:20:5)
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...
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```
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For security reasons, Deno does not allow programs to access the network without
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explicit permission. To allow accessing the network, use a command-line flag:
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```shell
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deno run --allow-net https://deno.land/std@$STD_VERSION/examples/echo_server.ts
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```
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To test it, try sending data to it with netcat:
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```shell
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$ nc localhost 8080
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hello world
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hello world
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```
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Like the `cat.ts` example, the `copy()` function here also does not make
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unnecessary memory copies. It receives a packet from the kernel and sends back,
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without further complexity.
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