plugins/experimental/http_stats/http_stats.cc

/** @file

  Stats Over HTTP as an origin intercept

  @section license License

  Licensed to the Apache Software Foundation (ASF) under one
  or more contributor license agreements.  See the NOTICE file
  distributed with this work for additional information
  regarding copyright ownership.  The ASF licenses this file
  to you 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 <cerrno>
#include <cinttypes>

#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <unistd.h>

#include <fstream>
#include <sstream>

#include <string>
#include <getopt.h>

#include <netinet/in.h>
#include <arpa/inet.h>

#include "ts/ts.h"
#include "ts/remap.h"

constexpr char PLUGIN[] = "http_stats";

static DbgCtl dbg_ctl{PLUGIN};

#define VDEBUG(fmt, ...) Dbg(dbg_ctl, fmt, ##__VA_ARGS__)

#if DEBUG
#define VERROR(fmt, ...) Dbg(dbg_ctl, fmt, ##__VA_ARGS__)
#else
#define VERROR(fmt, ...) TSError("[%s] %s: " fmt, PLUGIN, __FUNCTION__, ##__VA_ARGS__)
#endif

#define VIODEBUG(vio, fmt, ...)                                                                                              \
  VDEBUG("vio=%p vio.cont=%p, vio.cont.data=%p, vio.vc=%p " fmt, (vio), TSVIOContGet(vio), TSContDataGet(TSVIOContGet(vio)), \
         TSVIOVConnGet(vio), ##__VA_ARGS__)

static int StatCountBytes     = -1;
static int StatCountResponses = -1;

static int HTTPStatsInterceptHook(TSCont contp, TSEvent event, void *edata);
static int HTTPStatsTxnHook(TSCont contp, TSEvent event, void *edata);

struct HTTPStatsFormatter {
  HTTPStatsFormatter(bool csv, bool integer_counters, bool wrap_counters)
    : csv(csv), integer_counters(integer_counters), wrap_counters(wrap_counters)
  {
  }

  uint64_t    wrap_unsigned_counter(uint64_t value);
  std::string output();

  bool        csv              = false;
  bool        integer_counters = false;
  bool        wrap_counters    = false;
  std::string buf;
};

struct HTTPStatsConfig {
  explicit HTTPStatsConfig() {}

  ~HTTPStatsConfig()
  {
    if (cont) {
      TSContDestroy(cont);
    }
  }
  std::string mimeType;

  int  maxAge           = 0;
  bool csv              = false;
  bool integer_counters = false;
  bool wrap_counters    = false;

  TSCont cont{nullptr};
};

struct HTTPStatsRequest;

union argument_type {
  void             *ptr;
  intptr_t          ecode;
  TSVConn           vc;
  TSVIO             vio;
  TSHttpTxn         txn;
  HTTPStatsRequest *trq;

  argument_type(void *_p) : ptr(_p) {}
};

// This structure represents the state of a streaming I/O request. It
// is directional (ie. either a read or a write). We need two of these
// for each TSVConn; one to push data into the TSVConn and one to pull
// data out.
struct IOChannel {
  TSVIO            vio = nullptr;
  TSIOBuffer       iobuf;
  TSIOBufferReader reader;

  IOChannel() : iobuf(TSIOBufferSizedCreate(TS_IOBUFFER_SIZE_INDEX_32K)), reader(TSIOBufferReaderAlloc(iobuf)) {}
  ~IOChannel()
  {
    if (this->reader) {
      TSIOBufferReaderFree(this->reader);
    }

    if (this->iobuf) {
      TSIOBufferDestroy(this->iobuf);
    }
  }

  void
  read(TSVConn vc, TSCont contp)
  {
    this->vio = TSVConnRead(vc, contp, this->iobuf, INT64_MAX);
  }

  void
  write(TSVConn vc, TSCont contp)
  {
    this->vio = TSVConnWrite(vc, contp, this->reader, INT64_MAX);
  }
};

struct HTTPStatsHttpHeader {
  TSMBuffer    buffer;
  TSMLoc       header;
  TSHttpParser parser;

  HTTPStatsHttpHeader()
  {
    this->buffer = TSMBufferCreate();
    this->header = TSHttpHdrCreate(this->buffer);
    this->parser = TSHttpParserCreate();
  }

  ~HTTPStatsHttpHeader()
  {
    if (this->parser) {
      TSHttpParserDestroy(this->parser);
    }

    TSHttpHdrDestroy(this->buffer, this->header);
    TSHandleMLocRelease(this->buffer, TS_NULL_MLOC, this->header);
    TSMBufferDestroy(this->buffer);
  }
};

struct HTTPStatsRequest {
  HTTPStatsRequest() {}

  off_t               nbytes     = 0; // Number of bytes to generate.
  unsigned            maxAge     = 0; // Max age for cache responses.
  unsigned            statusCode = 200;
  IOChannel           readio;
  IOChannel           writeio;
  HTTPStatsHttpHeader rqheader;

  std::string mimeType;
  std::string body;

  static HTTPStatsRequest *
  createHTTPStatsRequest(HTTPStatsConfig *cfg)
  {
    HTTPStatsRequest *shr = new HTTPStatsRequest;

    HTTPStatsFormatter fmtr(cfg->csv, cfg->integer_counters, cfg->wrap_counters);
    shr->body = fmtr.output();

    shr->nbytes     = shr->body.size();
    shr->mimeType   = cfg->mimeType;
    shr->statusCode = 200;
    shr->maxAge     = cfg->maxAge;

    return shr;
  }

  ~HTTPStatsRequest() = default;
};

// Destroy a HTTPStatsRequest, including the per-txn continuation.
static void
HTTPStatsRequestDestroy(HTTPStatsRequest *trq, TSVIO vio, TSCont contp)
{
  if (vio) {
    TSVConnClose(TSVIOVConnGet(vio));
  }

  TSContDestroy(contp);
  delete trq;
}

// NOTE: This will always append a new "field_name: value"
static void
HeaderFieldDateSet(const HTTPStatsHttpHeader &http, const char *field_name, int64_t field_len, time_t value)
{
  TSMLoc field;

  TSMimeHdrFieldCreateNamed(http.buffer, http.header, field_name, field_len, &field);
  TSMimeHdrFieldValueDateSet(http.buffer, http.header, field, value);
  TSMimeHdrFieldAppend(http.buffer, http.header, field);
  TSHandleMLocRelease(http.buffer, http.header, field);
}

// NOTE: This will always append a new "field_name: value"
static void
HeaderFieldIntSet(const HTTPStatsHttpHeader &http, const char *field_name, int64_t field_len, int64_t value)
{
  TSMLoc field;

  TSMimeHdrFieldCreateNamed(http.buffer, http.header, field_name, field_len, &field);
  TSMimeHdrFieldValueInt64Set(http.buffer, http.header, field, -1, value);
  TSMimeHdrFieldAppend(http.buffer, http.header, field);
  TSHandleMLocRelease(http.buffer, http.header, field);
}

// NOTE: This will always append a new "field_name: value"
static void
HeaderFieldStringSet(const HTTPStatsHttpHeader &http, const char *field_name, int64_t field_len, const char *value)
{
  TSMLoc field;

  TSMimeHdrFieldCreateNamed(http.buffer, http.header, field_name, field_len, &field);
  TSMimeHdrFieldValueStringSet(http.buffer, http.header, field, -1, value, -1);
  TSMimeHdrFieldAppend(http.buffer, http.header, field);
  TSHandleMLocRelease(http.buffer, http.header, field);
}

static TSReturnCode
WriteResponseHeader(HTTPStatsRequest *trq, TSHttpStatus status)
{
  HTTPStatsHttpHeader response;

  VDEBUG("writing response header");

  if (TSHttpHdrTypeSet(response.buffer, response.header, TS_HTTP_TYPE_RESPONSE) != TS_SUCCESS) {
    VERROR("failed to set type");
    return TS_ERROR;
  }
  if (TSHttpHdrVersionSet(response.buffer, response.header, TS_HTTP_VERSION(1, 1)) != TS_SUCCESS) {
    VERROR("failed to set HTTP version");
    return TS_ERROR;
  }
  if (TSHttpHdrStatusSet(response.buffer, response.header, status) != TS_SUCCESS) {
    VERROR("failed to set HTTP status");
    return TS_ERROR;
  }

  TSHttpHdrReasonSet(response.buffer, response.header, TSHttpHdrReasonLookup(status), -1);

  if (status == TS_HTTP_STATUS_OK) {
    // Set the Content-Length header.
    HeaderFieldIntSet(response, TS_MIME_FIELD_CONTENT_LENGTH, TS_MIME_LEN_CONTENT_LENGTH, trq->nbytes);

    // Set the Cache-Control header.
    if (trq->maxAge > 0) {
      char buf[64];

      snprintf(buf, sizeof(buf), "max-age=%u", trq->maxAge);
      HeaderFieldStringSet(response, TS_MIME_FIELD_CACHE_CONTROL, TS_MIME_LEN_CACHE_CONTROL, buf);
      HeaderFieldDateSet(response, TS_MIME_FIELD_LAST_MODIFIED, TS_MIME_LEN_LAST_MODIFIED, time(nullptr));

    } else {
      HeaderFieldStringSet(response, TS_MIME_FIELD_CACHE_CONTROL, TS_MIME_LEN_CACHE_CONTROL, "no-cache");
    }

    HeaderFieldStringSet(response, TS_MIME_FIELD_CONTENT_TYPE, TS_MIME_LEN_CONTENT_TYPE, trq->mimeType.c_str());
  }

  // Write the header to the IO buffer. Set the VIO bytes so that we can get a WRITE_COMPLETE
  // event when this is done.
  int hdrlen = TSHttpHdrLengthGet(response.buffer, response.header);

  TSHttpHdrPrint(response.buffer, response.header, trq->writeio.iobuf);
  TSVIONBytesSet(trq->writeio.vio, hdrlen);
  TSVIOReenable(trq->writeio.vio);

  TSStatIntIncrement(StatCountBytes, hdrlen);

  return TS_SUCCESS;
}

static bool
HTTPStatsParseRequest(HTTPStatsRequest *trq)
{
  const char *path;
  int         pathsz;

  // Make sure this is a GET request
  path = TSHttpHdrMethodGet(trq->rqheader.buffer, trq->rqheader.header, &pathsz);
  if (path != TS_HTTP_METHOD_GET) {
    VDEBUG("%.*s method is not supported", pathsz, path);
    return false;
  }

  return true;
}

// Handle events from TSHttpTxnServerIntercept. The intercept
// starts with TS_EVENT_NET_ACCEPT, and then continues with
// TSVConn events.
static int
HTTPStatsInterceptHook(TSCont contp, TSEvent event, void *edata)
{
  VDEBUG("HTTPStatsInterceptHook: %p ", edata);

  argument_type arg(edata);

  VDEBUG("contp=%p, event=%s (%d), edata=%p", contp, TSHttpEventNameLookup(event), event, arg.ptr);

  switch (event) {
  case TS_EVENT_NET_ACCEPT: {
    // TS_EVENT_NET_ACCEPT will be delivered when the server intercept
    // is set up by the core. We just need to allocate a stats_over_http2
    // request state and start reading the VC.
    HTTPStatsRequest *trq = static_cast<HTTPStatsRequest *>(TSContDataGet(contp));

    TSStatIntIncrement(StatCountResponses, 1);
    VDEBUG("allocated server intercept stats_over_http2 trq=%p", trq);

    // This continuation was allocated in HTTPStatsTxnHook. Reset the
    // data to keep track of this generator request.
    TSContDataSet(contp, trq);

    // Start reading the request from the server intercept VC.
    trq->readio.read(arg.vc, contp);
    VIODEBUG(trq->readio.vio, "started reading stats_over_http2 request");

    return TS_EVENT_NONE;
  }

  case TS_EVENT_NET_ACCEPT_FAILED: {
    // TS_EVENT_NET_ACCEPT_FAILED will be delivered if the
    // transaction is cancelled before we start tunnelling
    // through the server intercept. One way that this can happen
    // is if the intercept is attached early, and then we serve
    // the document out of cache.

    // There's nothing to do here except nuke the continuation
    // that was allocated in HTTPStatsTxnHook().

    HTTPStatsRequest *trq = static_cast<HTTPStatsRequest *>(TSContDataGet(contp));
    delete trq;

    TSContDestroy(contp);
    return TS_EVENT_NONE;
  }

  case TS_EVENT_VCONN_READ_READY: {
    argument_type        cdata    = TSContDataGet(contp);
    HTTPStatsHttpHeader &rqheader = cdata.trq->rqheader;

    VDEBUG("reading vio=%p vc=%p, trq=%p", arg.vio, TSVIOVConnGet(arg.vio), cdata.trq);

    TSIOBufferBlock blk;
    TSParseResult   result = TS_PARSE_CONT;

    for (blk = TSIOBufferReaderStart(cdata.trq->readio.reader); blk; blk = TSIOBufferBlockNext(blk)) {
      const char  *ptr;
      const char  *end;
      int64_t      nbytes;
      TSHttpStatus status = static_cast<TSHttpStatus>(cdata.trq->statusCode);

      ptr = TSIOBufferBlockReadStart(blk, cdata.trq->readio.reader, &nbytes);
      if (ptr == nullptr || nbytes == 0) {
        continue;
      }

      end    = ptr + nbytes;
      result = TSHttpHdrParseReq(rqheader.parser, rqheader.buffer, rqheader.header, &ptr, end);
      switch (result) {
      case TS_PARSE_ERROR:
        // If we got a bad request, just shut it down.
        VDEBUG("bad request on trq=%p, sending an error", cdata.trq);
        HTTPStatsRequestDestroy(cdata.trq, arg.vio, contp);
        return TS_EVENT_ERROR;

      case TS_PARSE_DONE:
        // Check the response.
        VDEBUG("parsed request on trq=%p, sending a response", cdata.trq);
        if (!HTTPStatsParseRequest(cdata.trq)) {
          status = TS_HTTP_STATUS_METHOD_NOT_ALLOWED;
        }

        // Start the vconn write.
        cdata.trq->writeio.write(TSVIOVConnGet(arg.vio), contp);
        TSVIONBytesSet(cdata.trq->writeio.vio, 0);

        if (WriteResponseHeader(cdata.trq, status) != TS_SUCCESS) {
          VERROR("failure writing response");
          return TS_EVENT_ERROR;
        }

        return TS_EVENT_NONE;

      case TS_PARSE_CONT:
        break;
      }
    }

    TSReleaseAssert(result == TS_PARSE_CONT);

    // Reenable the read VIO to get more events.
    TSVIOReenable(arg.vio);
    return TS_EVENT_NONE;
  }

  case TS_EVENT_VCONN_WRITE_READY: {
    argument_type cdata = TSContDataGet(contp);

    if (cdata.trq->nbytes) {
      int64_t nbytes = cdata.trq->nbytes;

      VIODEBUG(arg.vio, "writing %" PRId64 " bytes for trq=%p", nbytes, cdata.trq);

      nbytes = TSIOBufferWrite(cdata.trq->writeio.iobuf, cdata.trq->body.c_str(), nbytes);

      cdata.trq->nbytes -= nbytes;
      TSStatIntIncrement(StatCountBytes, nbytes);

      // Update the number of bytes to write.
      TSVIONBytesSet(arg.vio, TSVIONBytesGet(arg.vio) + nbytes);
      TSVIOReenable(arg.vio);
    }

    return TS_EVENT_NONE;
  }

  case TS_EVENT_ERROR:
  case TS_EVENT_VCONN_EOS: {
    argument_type cdata = TSContDataGet(contp);

    VIODEBUG(arg.vio, "received EOS or ERROR for trq=%p", cdata.trq);
    HTTPStatsRequestDestroy(cdata.trq, arg.vio, contp);
    return event == TS_EVENT_ERROR ? TS_EVENT_ERROR : TS_EVENT_NONE;
  }

  case TS_EVENT_VCONN_READ_COMPLETE:
    // We read data forever, so we should never get a READ_COMPLETE.
    VIODEBUG(arg.vio, "unexpected TS_EVENT_VCONN_READ_COMPLETE");
    return TS_EVENT_NONE;

  case TS_EVENT_VCONN_WRITE_COMPLETE: {
    argument_type cdata = TSContDataGet(contp);

    // If we still have bytes to write, kick off a new write operation, otherwise
    // we are done and we can shut down the VC.
    if (cdata.trq->nbytes) {
      cdata.trq->writeio.write(TSVIOVConnGet(arg.vio), contp);
      TSVIONBytesSet(cdata.trq->writeio.vio, cdata.trq->nbytes);
    } else {
      VIODEBUG(arg.vio, "TS_EVENT_VCONN_WRITE_COMPLETE %" PRId64 " todo", TSVIONTodoGet(arg.vio));
      HTTPStatsRequestDestroy(cdata.trq, arg.vio, contp);
    }

    return TS_EVENT_NONE;
  }

  case TS_EVENT_TIMEOUT: {
    return TS_EVENT_NONE;
  }

  case TS_EVENT_VCONN_INACTIVITY_TIMEOUT:
    VERROR("unexpected event %s (%d) edata=%p", TSHttpEventNameLookup(event), event, arg.ptr);
    return TS_EVENT_ERROR;

  default:
    VERROR("unexpected event %s (%d) edata=%p", TSHttpEventNameLookup(event), event, arg.ptr);
    return TS_EVENT_ERROR;
  }
}

static void
HTTPStatsSetupIntercept(HTTPStatsConfig *cfg, TSHttpTxn txn)
{
  HTTPStatsRequest *req = HTTPStatsRequest::createHTTPStatsRequest(cfg);
  if (req == nullptr) {
    VERROR("could not create request!");
    return;
  }

  TSCont cnt = TSContCreate(HTTPStatsInterceptHook, TSMutexCreate());
  TSContDataSet(cnt, req);

  TSHttpTxnServerIntercept(cnt, txn);

  return;
}

// Handle events that occur on the TSHttpTxn.
static int
HTTPStatsTxnHook(TSCont contp, TSEvent event, void *edata)
{
  argument_type arg(edata);

  VDEBUG("contp=%p, event=%s (%d), edata=%p", contp, TSHttpEventNameLookup(event), event, edata);

  switch (event) {
  case TS_EVENT_HTTP_CACHE_LOOKUP_COMPLETE: {
    int         method_length, status;
    TSMBuffer   bufp;
    TSMLoc      hdr_loc;
    const char *method;

    if (TSHttpTxnCacheLookupStatusGet(arg.txn, &status) != TS_SUCCESS) {
      VERROR("failed to get client request handle");
      goto done;
    }

    if (TSHttpTxnClientReqGet(arg.txn, &bufp, &hdr_loc) != TS_SUCCESS) {
      VERROR("Couldn't retrieve client request header");
      goto done;
    }

    method = TSHttpHdrMethodGet(bufp, hdr_loc, &method_length);
    if (nullptr == method) {
      VERROR("Couldn't retrieve client request method");
      goto done;
    }

    if (status != TS_CACHE_LOOKUP_HIT_FRESH || method != TS_HTTP_METHOD_GET) {
      HTTPStatsSetupIntercept(static_cast<HTTPStatsConfig *>(TSContDataGet(contp)), arg.txn);
    }

    break;
  }

  default:
    VERROR("unexpected event %s (%d)", TSHttpEventNameLookup(event), event);
    break;
  }

done:
  TSHttpTxnReenable(arg.txn, TS_EVENT_HTTP_CONTINUE);
  return TS_EVENT_NONE;
}

TSReturnCode
TSRemapInit(TSRemapInterface * /* api_info */, char * /* errbuf */, int /* errbuf_size */)
{
  if (TSStatFindName("stats_over_http2.response_bytes", &StatCountBytes) == TS_ERROR) {
    StatCountBytes =
      TSStatCreate("stats_over_http2.response_bytes", TS_RECORDDATATYPE_COUNTER, TS_STAT_NON_PERSISTENT, TS_STAT_SYNC_SUM);
  }

  if (TSStatFindName("stats_over_http2.response_count", &StatCountResponses) == TS_ERROR) {
    StatCountResponses =
      TSStatCreate("stats_over_http2.response_count", TS_RECORDDATATYPE_COUNTER, TS_STAT_NON_PERSISTENT, TS_STAT_SYNC_COUNT);
  }
  return TS_SUCCESS;
}

TSRemapStatus
TSRemapDoRemap(void *ih, TSHttpTxn rh, TSRemapRequestInfo * /* rri ATS_UNUSED */)
{
  const TSHttpStatus txnstat = TSHttpTxnStatusGet(rh);
  if (txnstat != TS_HTTP_STATUS_NONE && txnstat != TS_HTTP_STATUS_OK) {
    VDEBUG("transaction status_code=%d already set; skipping processing", static_cast<int>(txnstat));
    return TSREMAP_NO_REMAP;
  }

  HTTPStatsConfig *cfg = static_cast<HTTPStatsConfig *>(ih);

  if (!cfg) {
    VERROR("No remap context available, check code / config");
    TSHttpTxnStatusSet(rh, TS_HTTP_STATUS_INTERNAL_SERVER_ERROR, PLUGIN);
    return TSREMAP_NO_REMAP;
  }

  if (!cfg->maxAge) {
    TSHttpTxnConfigIntSet(rh, TS_CONFIG_HTTP_CACHE_HTTP, 0);
    HTTPStatsSetupIntercept(static_cast<HTTPStatsConfig *>(ih), rh);
  } else {
    TSHttpTxnHookAdd(rh, TS_HTTP_CACHE_LOOKUP_COMPLETE_HOOK, static_cast<HTTPStatsConfig *>(ih)->cont);
  }

  return TSREMAP_NO_REMAP; // This plugin never rewrites anything.
}

TSReturnCode
TSRemapNewInstance(int argc, char *argv[], void **ih, char * /* errbuf ATS_UNUSED */, int /* errbuf_size ATS_UNUSED */)
{
  static const struct option longopt[] = {
    {"csv",              no_argument,       nullptr, 'c' },
    {"integer-counters", no_argument,       nullptr, 'i' },
    {"wrap-counters",    no_argument,       nullptr, 'w' },
    {"max-age",          required_argument, nullptr, 'a' },
    {nullptr,            no_argument,       nullptr, '\0'}
  };

  HTTPStatsConfig *cfg = new HTTPStatsConfig;

  // argv contains the "to" and "from" URLs. Skip the first so that the
  // second one poses as the program name.
  --argc;
  ++argv;
  optind = 0;

  while (true) {
    int opt = getopt_long(argc, (char *const *)argv, "ciw", longopt, nullptr);

    switch (opt) {
    case 'i':
      cfg->integer_counters = true;
      break;
    case 'w':
      cfg->wrap_counters = true;
      break;
    case 'c':
      cfg->csv = true;
      break;
    case 'a':
      cfg->maxAge = atoi(optarg);
      break;
    }
    if (opt == -1) {
      break;
    }
  }

  if (cfg->csv) {
    cfg->mimeType = "text/csv";
  } else {
    cfg->mimeType = "application/json";
  }

  // Finally, create the continuation to use for this remap rule, tracking the config as cont data.
  cfg->cont = TSContCreate(HTTPStatsTxnHook, nullptr);
  TSContDataSet(cfg->cont, cfg);

  *ih = static_cast<void *>(cfg);

  return TS_SUCCESS;
}

void
TSRemapDeleteInstance(void *ih)
{
  HTTPStatsConfig *cfg = static_cast<HTTPStatsConfig *>(ih);
  delete cfg;
}

// This wraps uint64_t values to the int64_t range to fit into a Java long. Java 8 has an unsigned long which
// can interoperate with a full uint64_t, but it's unlikely that much of the ecosystem supports that yet.
uint64_t
HTTPStatsFormatter::wrap_unsigned_counter(uint64_t value)
{
  if (wrap_counters) {
    return (value > INT64_MAX) ? value % INT64_MAX : value;
  }
  return value;
};

#define APPEND(b, a) b += a
#define APPEND_STAT_JSON(c, a, fmt, v)                                           \
  do {                                                                           \
    char b[256];                                                                 \
    if (snprintf(b, sizeof(b), "\"%s\": \"" fmt "\",\n", a, v) < (int)sizeof(b)) \
      APPEND(c->buf, b);                                                         \
  } while (0)
#define APPEND_STAT_JSON_NUMERIC(f, a, fmt, v)                                       \
  do {                                                                               \
    char b[256];                                                                     \
    if (f->integer_counters) {                                                       \
      if (snprintf(b, sizeof(b), "\"%s\": " fmt ",\n", a, v) < (int)sizeof(b)) {     \
        APPEND(f->buf, b);                                                           \
      }                                                                              \
    } else {                                                                         \
      if (snprintf(b, sizeof(b), "\"%s\": \"" fmt "\",\n", a, v) < (int)sizeof(b)) { \
        APPEND(f->buf, b);                                                           \
      }                                                                              \
    }                                                                                \
  } while (0)

#define APPEND_STAT_CSV(f, a, fmt, v)                                  \
  do {                                                                 \
    char b[256];                                                       \
    if (snprintf(b, sizeof(b), "%s," fmt "\n", a, v) < (int)sizeof(b)) \
      APPEND(f->buf, b);                                               \
  } while (0)
#define APPEND_STAT_CSV_NUMERIC(f, a, fmt, v)                            \
  do {                                                                   \
    char b[256];                                                         \
    if (snprintf(b, sizeof(b), "%s," fmt "\n", a, v) < (int)sizeof(b)) { \
      APPEND(f->buf, b);                                                 \
    }                                                                    \
  } while (0)

static void
json_out_stat(TSRecordType /* rec_type ATS_UNUSED */, void *edata, int /* registered ATS_UNUSED */, const char *name,
              TSRecordDataType data_type, TSRecordData *datum)
{
  HTTPStatsFormatter *fmtr = static_cast<HTTPStatsFormatter *>(edata);

  switch (data_type) {
  case TS_RECORDDATATYPE_COUNTER:
    APPEND_STAT_JSON_NUMERIC(fmtr, name, "%" PRIu64, fmtr->wrap_unsigned_counter(datum->rec_counter));
    break;
  case TS_RECORDDATATYPE_INT:
    APPEND_STAT_JSON_NUMERIC(fmtr, name, "%" PRIu64, fmtr->wrap_unsigned_counter(datum->rec_int));
    break;
  case TS_RECORDDATATYPE_FLOAT:
    APPEND_STAT_JSON_NUMERIC(fmtr, name, "%f", datum->rec_float);
    break;
  case TS_RECORDDATATYPE_STRING:
    APPEND_STAT_JSON(fmtr, name, "%s", datum->rec_string);
    break;
  default:
    Dbg(dbg_ctl, "unknown type for %s: %d", name, data_type);
    break;
  }
}

static void
csv_out_stat(TSRecordType /* rec_type ATS_UNUSED */, void *edata, int /* registered ATS_UNUSED */, const char *name,
             TSRecordDataType data_type, TSRecordData *datum)
{
  HTTPStatsFormatter *fmtr = static_cast<HTTPStatsFormatter *>(edata);

  switch (data_type) {
  case TS_RECORDDATATYPE_COUNTER:
    APPEND_STAT_CSV_NUMERIC(fmtr, name, "%" PRIu64, fmtr->wrap_unsigned_counter(datum->rec_counter));
    break;
  case TS_RECORDDATATYPE_INT:
    APPEND_STAT_CSV_NUMERIC(fmtr, name, "%" PRIu64, fmtr->wrap_unsigned_counter(datum->rec_int));
    break;
  case TS_RECORDDATATYPE_FLOAT:
    APPEND_STAT_CSV_NUMERIC(fmtr, name, "%f", datum->rec_float);
    break;
  case TS_RECORDDATATYPE_STRING:
    APPEND_STAT_CSV(fmtr, name, "%s", datum->rec_string);
    break;
  default:
    Dbg(dbg_ctl, "unknown type for %s: %d", name, data_type);
    break;
  }
}

std::string
HTTPStatsFormatter::output()
{
  if (csv) {
    TSRecordDump(static_cast<TSRecordType>(TS_RECORDTYPE_PLUGIN | TS_RECORDTYPE_NODE | TS_RECORDTYPE_PROCESS), csv_out_stat, this);
    APPEND_STAT_CSV(this, "version", "%s", TSTrafficServerVersionGet());
  } else {
    APPEND(buf, "{ \"global\": {\n");

    TSRecordDump(static_cast<TSRecordType>(TS_RECORDTYPE_PLUGIN | TS_RECORDTYPE_NODE | TS_RECORDTYPE_PROCESS), json_out_stat, this);

    APPEND(buf, "\"server\": \"");
    APPEND(buf, TSTrafficServerVersionGet());
    APPEND(buf, "\"\n");
    APPEND(buf, "  }\n}\n");
  }
  return buf;
}