--- /dev/null
+/*
+ * sel.h: subsystem to manage the grubby details of a select loop,
+ * buffering data to write, and performing the actual writes and
+ * reads.
+ */
+
+#ifndef FIXME_SEL_H
+#define FIXME_SEL_H
+
+typedef struct sel sel;
+typedef struct sel_wfd sel_wfd;
+typedef struct sel_rfd sel_rfd;
+
+/*
+ * Callback called when some data is written to a wfd. "bufsize"
+ * is the remaining quantity of data buffered in that wfd.
+ */
+typedef void (*sel_written_fn_t)(sel_wfd *wfd, size_t bufsize);
+
+/*
+ * Callback called when an error occurs on a wfd, preventing
+ * further writing to it. "error" is the errno value.
+ */
+typedef void (*sel_writeerr_fn_t)(sel_wfd *wfd, int error);
+
+/*
+ * Callback called when some data is read from an rfd. On EOF,
+ * this will be called with len==0.
+ */
+typedef void (*sel_readdata_fn_t)(sel_rfd *rfd, void *data, size_t len);
+
+/*
+ * Callback called when an error occurs on an rfd, preventing
+ * further reading from it. "error" is the errno value.
+ */
+typedef void (*sel_readerr_fn_t)(sel_rfd *rfd, int error);
+
+/*
+ * Create a sel structure, which will oversee a select loop.
+ *
+ * "ctx" is user-supplied data stored in the sel structure; it can
+ * be read and written with sel_get_ctx() and sel_set_ctx().
+ */
+sel *sel_new(void *ctx);
+
+/*
+ * Add a new fd for writing. Returns a sel_wfd which identifies
+ * that fd in the sel structure, e.g. for putting data into its
+ * output buffer.
+ *
+ * "ctx" is user-supplied data stored in the sel structure; it can
+ * be read and written with sel_wfd_get_ctx() and sel_wfd_set_ctx().
+ *
+ * "written" and "writeerr" are called from the event loop when
+ * things happen.
+ *
+ * The fd passed in can be -1, in which case it will be assumed to
+ * be unwritable at all times. An actual fd can be passed in later
+ * using sel_wfd_setfd.
+ */
+sel_wfd *sel_wfd_add(sel *sel, int fd,
+ sel_written_fn_t written, sel_writeerr_fn_t writeerr,
+ void *ctx);
+
+/*
+ * Add a new fd for reading. Returns a sel_rfd which identifies
+ * that fd in the sel structure.
+ *
+ * "ctx" is user-supplied data stored in the sel structure; it can
+ * be read and written with sel_rfd_get_ctx() and sel_rfd_set_ctx().
+ *
+ * "readdata" and "readerr" are called from the event loop when
+ * things happen. "ctx" is passed to both of them.
+ */
+sel_rfd *sel_rfd_add(sel *sel, int fd,
+ sel_readdata_fn_t readdata, sel_readerr_fn_t readerr,
+ void *ctx);
+
+/*
+ * Write data into the output buffer of a wfd. Returns the new
+ * size of the output buffer. (You can call it with len==0 if you
+ * just want to know the buffer size; in that situation data==NULL
+ * is also safe.)
+ */
+size_t sel_write(sel_wfd *wfd, const void *data, size_t len);
+
+/*
+ * Freeze and unfreeze an rfd. When frozen, sel will temporarily
+ * not attempt to read from it, but all its state is retained so
+ * it can be conveniently unfrozen later. (You might use this
+ * facility, for instance, if what you were doing with the
+ * incoming data could only accept it at a certain rate: freeze
+ * the rfd when you've got lots of backlog, and unfreeze it again
+ * when things get calmer.)
+ */
+void sel_rfd_freeze(sel_rfd *rfd);
+void sel_rfd_unfreeze(sel_rfd *rfd);
+
+/*
+ * Delete a wfd structure from its containing sel. Returns the
+ * underlying fd, which the client may now consider itself to own
+ * once more.
+ */
+int sel_wfd_delete(sel_wfd *wfd);
+
+/*
+ * Delete an rfd structure from its containing sel. Returns the
+ * underlying fd, which the client may now consider itself to own
+ * once more.
+ */
+int sel_rfd_delete(sel_rfd *rfd);
+
+/*
+ * NOT IMPLEMENTED YET: useful functions here might be ones which
+ * enumerated all the wfds/rfds in a sel structure in some
+ * fashion, so you could go through them and remove them all while
+ * doing sensible things to them. Or, at the very least, just
+ * return an arbitrary one of the wfds/rfds.
+ */
+
+/*
+ * Free a sel structure and all its remaining wfds and rfds.
+ */
+void sel_free(sel *sel);
+
+/*
+ * Read and write the ctx parameters in sel, sel_wfd and sel_rfd.
+ */
+void *sel_get_ctx(sel *sel);
+void sel_set_ctx(sel *sel, void *ctx);
+void *sel_wfd_get_ctx(sel_wfd *wfd);
+void sel_wfd_set_ctx(sel_wfd *wfd, void *ctx);
+void *sel_rfd_get_ctx(sel_rfd *rfd);
+void sel_rfd_set_ctx(sel_rfd *rfd, void *ctx);
+
+/*
+ * Run one iteration of the sel event loop, calling callbacks as
+ * necessary. Returns zero on success; in the event of a fatal
+ * error, returns the errno value.
+ *
+ * "timeout" is a value in microseconds to limit the length of the
+ * select call. Less than zero means to wait indefinitely.
+ */
+int sel_iterate(sel *sel, long timeout);
+
+/*
+ * Change the underlying fd in a wfd. If set to -1, no write
+ * attempts will take place and the wfd's buffer will simply store
+ * everything passed to sel_write(). If later set to something
+ * other than -1, all that buffered data will become eligible for
+ * real writing.
+ */
+void sel_wfd_setfd(sel_wfd *wfd, int fd);
+
+/*
+ * Change the underlying fd in a rfd. If set to -1, no read
+ * attempts will take place.
+ */
+void sel_rfd_setfd(sel_rfd *rfd, int fd);
+
+#endif /* FIXME_SEL_H */
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