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implementation-guide.md

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Implementation Guide

uv_link_t behaves very similar to uv_stream_t. All uv_link_methods_t MUST conform to this semantics.

Error Codes

All error codes MUST be negative and be less than UV_ERRNO_MAX.

  • UV_ENOSYS SHOULD be returned if the particular method (e.g. shutdown or try_write)
  • UV_EAGAIN MUST be returned by uv_link_methods_t.try_write if the write could not be completed at the moment

uv_link_init()

Links start in non-reading mode, alloc_cb/read_cb MUST NOT be called until uv_link_read_start(link) will be invoked with zero return code.

uv_link_read_start()/uv_link_read_stop()

This switch link to and from the reading mode. After the switch to the reading mode either:

  • alloc_cb + read_cb will be invoked for a particular link (NOTE: read_cb MUST follow every alloc_cb)
  • read_cb(..., err, ...) will be called to indicate a error. In this case user MUST call uv_read_stop() on the error'ed link.

NOTE: buf argument of read_cb may be NULL in case of error.

NOTE: If alloc_cb sets buf->len = 0; - read_cb(..., UV_ENOBUFS, ...) MUST be called by a link implementation.

uv_link_close()

Links MAY be closed at any time, unless they are already closed or weren't initialized with uv_link_init(). However, the methods->close() may not be called immediately on uv_link_close() if close attempt is happening on the link's call stack:

static void read_cb(uv_link_t* link, ssize_t nread, uv_buf_t* buf) {
  uv_link_close(link, ...);
}

link->read_cb = read_cb;

uv_link_propagate_read_cb(link, UV_EOF, NULL);
/* link->methods->close() call will happen upon returning from
   `uv_link_propagate_read_cb` */

uv_link_t public APIs MUST NOT be used on a link after uv_link_close(link).

When several links are chained together, uv_link_close() SHOULD be called only on a last (leaf) link in a chain. Otherwise uv_link_t API is allowed to crash.

When closing leaf link in a chain:

  1. All links will be unchained
  2. Each link starting from the deepest link (from the leaf) will be closed one by one
  3. close_cb will be invoked upon close of all links in a chain