vendor/github.com/apigee-labs/transicator/pgoutput/transicator_output.c

/*
Copyright 2016 The Transicator Authors

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
#include <postgres.h>
#include <catalog/pg_type.h>
#include <access/xlogdefs.h>
#include <utils/builtins.h>
#include <utils/lsyscache.h>
#include <utils/memutils.h>
#include <replication/output_plugin.h>
#include <replication/logical.h>
#include <transicator.h>

/*
 * This plugin encodes logical encoding records into JSON. JSON is produced
 * using string concatenation -- after all, isn't that the point of JSON?
 *
 * Based largely on the "test_encoding.c" sample from the Postgres source.
 */

/* This is required by postgres. */
PG_MODULE_MAGIC;

extern void _PG_output_plugin_init(OutputPluginCallbacks *cb);

static void outputStart(
    struct LogicalDecodingContext *ctx,
    OutputPluginOptions *options,
    bool is_init
) {
  ListCell   *option;
  int binaryFormat = 0;
  DecodingState* state;

  foreach(option, ctx->output_plugin_options)
	{
		DefElem    *elem = lfirst(option);
    if (!strcmp(elem->defname, "protobuf")) {
      binaryFormat = 1;
    }
  }

  if (binaryFormat) {
    elog(LOG, "Logical decoding output in protobuf format");
  } else {
    elog(LOG, "Logical decoding output in JSON format");
  }

  /* Create state for decoding. */
  state = (DecodingState*)palloc(sizeof(DecodingState));
  /* Include a memory context that we will reset for each output run. */
  state->memCtx =
    AllocSetContextCreate(ctx->context, "transicator_output",
      ALLOCSET_DEFAULT_MINSIZE,
      ALLOCSET_DEFAULT_INITSIZE,
      ALLOCSET_DEFAULT_MAXSIZE);
  state->index = 0;
  state->isBinary = binaryFormat;

  if (binaryFormat) {
    options->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
  } else {
    options->output_type = OUTPUT_PLUGIN_TEXTUAL_OUTPUT;
  }

  ctx->output_plugin_private = state;
}


static void outputStop(
    struct LogicalDecodingContext *ctx
) {
  /* This will free all memory that we allocated. */
  DecodingState* state = (DecodingState*)(ctx->output_plugin_private);
  MemoryContextDelete(state->memCtx);
}

static bool outputFilter(
    struct LogicalDecodingContext *ctx,
    RepOriginId origin_id
) {
  /* False means yes */
  return FALSE;
}

static void outputBegin(
    struct LogicalDecodingContext* ctx,
    ReorderBufferTXN *txn
) {
  /* Reset "index" for start of new transaction */
  DecodingState* state = (DecodingState*)(ctx->output_plugin_private);
  state->index = 0;
}

static void outputCommit(
    struct LogicalDecodingContext* ctx,
    ReorderBufferTXN *txn,
    XLogRecPtr commitLSN
) {
}

static void outputChange(
    struct LogicalDecodingContext *ctx,
    ReorderBufferTXN *txn,
    Relation relation,
    ReorderBufferChange *change
) {
  MemoryContext oldMemCtx;
  DecodingState* state = (DecodingState*)(ctx->output_plugin_private);

  /* Switch to our private memory context so that we will not leak. */
  oldMemCtx = MemoryContextSwitchTo(state->memCtx);
  OutputPluginPrepareWrite(ctx, true);
  if (state->isBinary) {
    transicatorOutputChangeProto(ctx, txn, relation, change, state);
  } else {
    transicatorOutputChangeString(ctx, txn, relation, change, state);
  }
  OutputPluginWrite(ctx, true);

  /* Switch back to original context and release everything we "palloc"ed */
  MemoryContextSwitchTo(oldMemCtx);
  MemoryContextReset(state->memCtx);
}

void _PG_output_plugin_init(OutputPluginCallbacks *cb) {
  cb->startup_cb = outputStart;
  cb->shutdown_cb = outputStop;
  cb->begin_cb = outputBegin;
  cb->commit_cb = outputCommit;
  cb->change_cb = outputChange;
  cb->filter_by_origin_cb = outputFilter;
}

 /*
  * do a TransactionId -> txid conversion for an XID near the given epoch
  * NOTE: This is heavily borrowed from http://doxygen.postgresql.org/txid_8c.html#ab7c28f6665db1d30fcaf26c93d74a3aa
  */
 uint64 convert_xid(TransactionId xid)
 {
     uint64      epoch;
     uint32      current_epoch;
     TransactionId current_xid;


     /* return special xid's as-is */
     if (!TransactionIdIsNormal(xid))
         return (uint64) xid;

     GetNextXidAndEpoch(&current_xid, &current_epoch);

     /* xid can be on either side when near wrap-around */
     epoch = (uint64)current_epoch;
     if (xid > current_xid &&
         TransactionIdPrecedes(xid, current_xid))
         epoch--;
     else if (xid < current_xid &&
              TransactionIdFollows(xid, current_xid))
         epoch++;

     return (epoch << 32) | xid;
 }