src/core/channel/channel_stack.h

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 *
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 *
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#ifndef __GRPC_INTERNAL_CHANNEL_CHANNEL_STACK_H__
#define __GRPC_INTERNAL_CHANNEL_CHANNEL_STACK_H__

/* A channel filter defines how operations on a channel are implemented.
   Channel filters are chained together to create full channels, and if those
   chains are linear, then channel stacks provide a mechanism to minimize
   allocations for that chain.
   Call stacks are created by channel stacks and represent the per-call data
   for that stack. */

#include <stddef.h>

#include <grpc/grpc.h>
#include <grpc/support/log.h>
#include "src/core/transport/transport.h"

/* #define GRPC_CHANNEL_STACK_TRACE 1 */

typedef struct grpc_channel_element grpc_channel_element;
typedef struct grpc_call_element grpc_call_element;

/* Call operations - things that can be sent and received.

   Threading:
     SEND, RECV, and CANCEL ops can be active on a call at the same time, but
     only one SEND, one RECV, and one CANCEL can be active at a time.

   If state is shared between send/receive/cancel operations, it is up to
   filters to provide their own protection around that. */
typedef enum {
  /* send metadata to the channels peer */
  GRPC_SEND_METADATA,
  /* send a deadline */
  GRPC_SEND_DEADLINE,
  /* start a connection (corresponds to start_invoke/accept) */
  GRPC_SEND_START,
  /* send a message to the channels peer */
  GRPC_SEND_MESSAGE,
  /* send half-close to the channels peer */
  GRPC_SEND_FINISH,
  /* request that more data be allowed through flow control */
  GRPC_REQUEST_DATA,
  /* metadata was received from the channels peer */
  GRPC_RECV_METADATA,
  /* receive a deadline */
  GRPC_RECV_DEADLINE,
  /* the end of the first batch of metadata was received */
  GRPC_RECV_END_OF_INITIAL_METADATA,
  /* a message was received from the channels peer */
  GRPC_RECV_MESSAGE,
  /* half-close was received from the channels peer */
  GRPC_RECV_HALF_CLOSE,
  /* full close was received from the channels peer */
  GRPC_RECV_FINISH,
  /* the call has been abnormally terminated */
  GRPC_CANCEL_OP
} grpc_call_op_type;

/* The direction of the call.
   The values of the enums (1, -1) matter here - they are used to increment
   or decrement a pointer to find the next element to call */
typedef enum { GRPC_CALL_DOWN = 1, GRPC_CALL_UP = -1 } grpc_call_dir;

/* A single filterable operation to be performed on a call */
typedef struct {
  /* The type of operation we're performing */
  grpc_call_op_type type;
  /* The directionality of this call - does the operation begin at the bottom
     of the stack and flow up, or does the operation start at the top of the
     stack and flow down through the filters. */
  grpc_call_dir dir;

  /* Flags associated with this call: see GRPC_WRITE_* in grpc.h */
  gpr_uint32 flags;

  /* Argument data, matching up with grpc_call_op_type names */
  union {
    grpc_byte_buffer *message;
    grpc_mdelem *metadata;
    gpr_timespec deadline;
  } data;

  /* Must be called when processing of this call-op is complete.
     Signature chosen to match transport flow control callbacks */
  void (*done_cb)(void *user_data, grpc_op_error error);
  /* User data to be passed into done_cb */
  void *user_data;
} grpc_call_op;

/* returns a string representation of op, that can be destroyed with gpr_free */
char *grpc_call_op_string(grpc_call_op *op);

typedef enum {
  /* send a goaway message to remote channels indicating that we are going
     to disconnect in the future */
  GRPC_CHANNEL_GOAWAY,
  /* disconnect any underlying transports */
  GRPC_CHANNEL_DISCONNECT,
  /* transport received a new call */
  GRPC_ACCEPT_CALL,
  /* an underlying transport was closed */
  GRPC_TRANSPORT_CLOSED,
  /* an underlying transport is about to be closed */
  GRPC_TRANSPORT_GOAWAY
} grpc_channel_op_type;

/* A single filterable operation to be performed on a channel */
typedef struct {
  /* The type of operation we're performing */
  grpc_channel_op_type type;
  /* The directionality of this call - is it bubbling up the stack, or down? */
  grpc_call_dir dir;

  /* Argument data, matching up with grpc_channel_op_type names */
  union {
    struct {
      grpc_transport *transport;
      const void *transport_server_data;
    } accept_call;
    struct {
      grpc_status_code status;
      gpr_slice message;
    } goaway;
  } data;
} grpc_channel_op;

/* Channel filters specify:
   1. the amount of memory needed in the channel & call (via the sizeof_XXX
      members)
   2. functions to initialize and destroy channel & call data
      (init_XXX, destroy_XXX)
   3. functions to implement call operations and channel operations (call_op,
      channel_op)
   4. a name, which is useful when debugging

   Members are laid out in approximate frequency of use order. */
typedef struct {
  /* Called to eg. send/receive data on a call.
     See grpc_call_next_op on how to call the next element in the stack */
  void (*call_op)(grpc_call_element *elem, grpc_call_element *from_elem,
                  grpc_call_op *op);
  /* Called to handle channel level operations - e.g. new calls, or transport
     closure.
     See grpc_channel_next_op on how to call the next element in the stack */
  void (*channel_op)(grpc_channel_element *elem,
                     grpc_channel_element *from_elem, grpc_channel_op *op);

  /* sizeof(per call data) */
  size_t sizeof_call_data;
  /* Initialize per call data.
     elem is initialized at the start of the call, and elem->call_data is what
     needs initializing.
     The filter does not need to do any chaining.
     server_transport_data is an opaque pointer. If it is NULL, this call is
     on a client; if it is non-NULL, then it points to memory owned by the
     transport and is on the server. Most filters want to ignore this
     argument.*/
  void (*init_call_elem)(grpc_call_element *elem,
                         const void *server_transport_data);
  /* Destroy per call data.
     The filter does not need to do any chaining */
  void (*destroy_call_elem)(grpc_call_element *elem);

  /* sizeof(per channel data) */
  size_t sizeof_channel_data;
  /* Initialize per-channel data.
     elem is initialized at the start of the call, and elem->channel_data is
     what needs initializing.
     is_first, is_last designate this elements position in the stack, and are
     useful for asserting correct configuration by upper layer code.
     The filter does not need to do any chaining */
  void (*init_channel_elem)(grpc_channel_element *elem,
                            const grpc_channel_args *args,
                            grpc_mdctx *metadata_context, int is_first,
                            int is_last);
  /* Destroy per channel data.
     The filter does not need to do any chaining */
  void (*destroy_channel_elem)(grpc_channel_element *elem);

  /* The name of this filter */
  const char *name;
} grpc_channel_filter;

/* A channel_element tracks its filter and the filter requested memory within
   a channel allocation */
struct grpc_channel_element {
  const grpc_channel_filter *filter;
  void *channel_data;
};

/* A call_element tracks its filter, the filter requested memory within
   a channel allocation, and the filter requested memory within a call
   allocation */
struct grpc_call_element {
  const grpc_channel_filter *filter;
  void *channel_data;
  void *call_data;
};

/* A channel stack tracks a set of related filters for one channel, and
   guarantees they live within a single malloc() allocation */
typedef struct {
  size_t count;
  /* Memory required for a call stack (computed at channel stack
     initialization) */
  size_t call_stack_size;
} grpc_channel_stack;

/* A call stack tracks a set of related filters for one call, and guarantees
   they live within a single malloc() allocation */
typedef struct { size_t count; } grpc_call_stack;

/* Get a channel element given a channel stack and its index */
grpc_channel_element *grpc_channel_stack_element(grpc_channel_stack *stack,
                                                 size_t i);
/* Get the last channel element in a channel stack */
grpc_channel_element *grpc_channel_stack_last_element(
    grpc_channel_stack *stack);
/* Get a call stack element given a call stack and an index */
grpc_call_element *grpc_call_stack_element(grpc_call_stack *stack, size_t i);

/* Determine memory required for a channel stack containing a set of filters */
size_t grpc_channel_stack_size(const grpc_channel_filter **filters,
                               size_t filter_count);
/* Initialize a channel stack given some filters */
void grpc_channel_stack_init(const grpc_channel_filter **filters,
                             size_t filter_count, const grpc_channel_args *args,
                             grpc_mdctx *metadata_context,
                             grpc_channel_stack *stack);
/* Destroy a channel stack */
void grpc_channel_stack_destroy(grpc_channel_stack *stack);

/* Initialize a call stack given a channel stack. transport_server_data is
   expected to be NULL on a client, or an opaque transport owned pointer on the
   server. */
void grpc_call_stack_init(grpc_channel_stack *channel_stack,
                          const void *transport_server_data,
                          grpc_call_stack *call_stack);
/* Destroy a call stack */
void grpc_call_stack_destroy(grpc_call_stack *stack);

/* Call the next operation (depending on call directionality) in a call stack */
void grpc_call_next_op(grpc_call_element *elem, grpc_call_op *op);
/* Call the next operation (depending on call directionality) in a channel
   stack */
void grpc_channel_next_op(grpc_channel_element *elem, grpc_channel_op *op);

/* Given the top element of a channel stack, get the channel stack itself */
grpc_channel_stack *grpc_channel_stack_from_top_element(
    grpc_channel_element *elem);
/* Given the top element of a call stack, get the call stack itself */
grpc_call_stack *grpc_call_stack_from_top_element(grpc_call_element *elem);

void grpc_call_log_op(char *file, int line, gpr_log_severity severity,
                      grpc_call_element *elem, grpc_call_op *op);

void grpc_call_element_send_metadata(grpc_call_element *cur_elem,
                                     grpc_mdelem *elem);
void grpc_call_element_send_cancel(grpc_call_element *cur_elem);

#ifdef GRPC_CHANNEL_STACK_TRACE
#define GRPC_CALL_LOG_OP(sev, elem, op) grpc_call_log_op(sev, elem, op)
#else
#define GRPC_CALL_LOG_OP(sev, elem, op) \
  do {                                  \
  } while (0)
#endif

#endif  /* __GRPC_INTERNAL_CHANNEL_CHANNEL_STACK_H__ */