rtc_base/flags.cc

/*
 *  Copyright 2006 The WebRTC Project Authors. All rights reserved.
 *
 *  Use of this source code is governed by a BSD-style license
 *  that can be found in the LICENSE file in the root of the source
 *  tree. An additional intellectual property rights grant can be found
 *  in the file PATENTS.  All contributing project authors may
 *  be found in the AUTHORS file in the root of the source tree.
 */

#include "rtc_base/flags.h"

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "rtc_base/checks.h"

namespace {
bool FlagEq(const char* arg, const char* flag) {
  // Compare two flags for equality.
  // 'arg' is the name of a flag passed via the command line and 'flag' is the
  // name of a flag defined with the DEFINE_* macros.
  // We compare the flags for equality, considering hyphens (-) and
  // underscores (_) to be equivalent, so that --flag-name and --flag_name both
  // match with --flag_name.
  while (*arg != '\0' && (*arg == *flag || (*arg == '-' && *flag == '_'))) {
    ++arg;
    ++flag;
  }
  return *arg == '\0' && *flag == '\0';
}
}  // namespace

namespace rtc {
// -----------------------------------------------------------------------------
// Implementation of Flag

Flag::Flag(const char* file,
           const char* name,
           const char* comment,
           Type type,
           void* variable,
           FlagValue default__)
    : file_(file),
      name_(name),
      comment_(comment),
      type_(type),
      variable_(reinterpret_cast<FlagValue*>(variable)),
      default_(default__) {
  FlagList::Register(this);
}

void Flag::SetToDefault() {
  // Note that we cannot simply do '*variable_ = default_;' since
  // flag variables are not really of type FlagValue and thus may
  // be smaller! The FlagValue union is simply 'overlayed' on top
  // of a flag variable for convenient access. Since union members
  // are guarantee to be aligned at the beginning, this works.
  switch (type_) {
    case Flag::BOOL:
      variable_->b = default_.b;
      return;
    case Flag::INT:
      variable_->i = default_.i;
      return;
    case Flag::FLOAT:
      variable_->f = default_.f;
      return;
    case Flag::STRING:
      variable_->s = default_.s;
      return;
  }
  FATAL() << "unreachable code";
}

static const char* Type2String(Flag::Type type) {
  switch (type) {
    case Flag::BOOL:
      return "bool";
    case Flag::INT:
      return "int";
    case Flag::FLOAT:
      return "float";
    case Flag::STRING:
      return "string";
  }
  FATAL() << "unreachable code";
}

static void PrintFlagValue(Flag::Type type, FlagValue* p) {
  switch (type) {
    case Flag::BOOL:
      printf("%s", (p->b ? "true" : "false"));
      return;
    case Flag::INT:
      printf("%d", p->i);
      return;
    case Flag::FLOAT:
      printf("%f", p->f);
      return;
    case Flag::STRING:
      printf("%s", p->s);
      return;
  }
  FATAL() << "unreachable code";
}

void Flag::Print(bool print_current_value) {
  printf("  --%s (%s)  type: %s  default: ", name_, comment_,
         Type2String(type_));
  PrintFlagValue(type_, &default_);
  if (print_current_value) {
    printf("  current value: ");
    PrintFlagValue(type_, variable_);
  }
  printf("\n");
}

// -----------------------------------------------------------------------------
// Implementation of FlagList

Flag* FlagList::list_ = nullptr;

FlagList::FlagList() {
  list_ = nullptr;
}

void FlagList::Print(const char* file, bool print_current_value) {
  // Since flag registration is likely by file (= C++ file),
  // we don't need to sort by file and still get grouped output.
  const char* current = nullptr;
  for (Flag* f = list_; f != nullptr; f = f->next()) {
    if (file == nullptr || file == f->file()) {
      if (current != f->file()) {
        printf("Flags from %s:\n", f->file());
        current = f->file();
      }
      f->Print(print_current_value);
    }
  }
}

Flag* FlagList::Lookup(const char* name) {
  Flag* f = list_;
  while (f != nullptr && !FlagEq(name, f->name()))
    f = f->next();
  return f;
}

void FlagList::SplitArgument(const char* arg,
                             char* buffer,
                             int buffer_size,
                             const char** name,
                             const char** value,
                             bool* is_bool) {
  *name = nullptr;
  *value = nullptr;
  *is_bool = false;

  if (*arg == '-') {
    // find the begin of the flag name
    arg++;  // remove 1st '-'
    if (*arg == '-')
      arg++;  // remove 2nd '-'
    if (arg[0] == 'n' && arg[1] == 'o' && Lookup(arg + 2)) {
      arg += 2;  // remove "no"
      *is_bool = true;
    }
    *name = arg;

    // find the end of the flag name
    while (*arg != '\0' && *arg != '=')
      arg++;

    // get the value if any
    if (*arg == '=') {
      // make a copy so we can NUL-terminate flag name
      int n = static_cast<int>(arg - *name);
      RTC_CHECK_LT(n, buffer_size);
      memcpy(buffer, *name, n * sizeof(char));
      buffer[n] = '\0';
      *name = buffer;
      // get the value
      *value = arg + 1;
    }
  }
}

int FlagList::SetFlagsFromCommandLine(int* argc,
                                      const char** argv,
                                      bool remove_flags) {
  // parse arguments
  for (int i = 1; i < *argc; /* see below */) {
    int j = i;  // j > 0
    const char* arg = argv[i++];

    // split arg into flag components
    char buffer[1024];
    const char* name;
    const char* value;
    bool is_bool;
    SplitArgument(arg, buffer, sizeof buffer, &name, &value, &is_bool);

    if (name != nullptr) {
      // lookup the flag
      Flag* flag = Lookup(name);
      if (flag == nullptr) {
        fprintf(stderr, "Error: unrecognized flag %s\n", arg);
        return j;
      }

      // if we still need a flag value, use the next argument if available
      if (flag->type() != Flag::BOOL && value == nullptr) {
        if (i < *argc) {
          value = argv[i++];
        } else {
          fprintf(stderr, "Error: missing value for flag %s of type %s\n", arg,
                  Type2String(flag->type()));
          return j;
        }
      }

      // set the flag
      char empty[] = {'\0'};
      char* endp = empty;
      switch (flag->type()) {
        case Flag::BOOL:
          *flag->bool_variable() = !is_bool;
          break;
        case Flag::INT:
          *flag->int_variable() = strtol(value, &endp, 10);
          break;
        case Flag::FLOAT:
          *flag->float_variable() = strtod(value, &endp);
          break;
        case Flag::STRING:
          *flag->string_variable() = value;
          break;
      }

      // handle errors
      if ((flag->type() == Flag::BOOL && value != nullptr) ||
          (flag->type() != Flag::BOOL && is_bool) || *endp != '\0') {
        fprintf(stderr, "Error: illegal value for flag %s of type %s\n", arg,
                Type2String(flag->type()));
        return j;
      }

      // remove the flag & value from the command
      if (remove_flags)
        while (j < i)
          argv[j++] = nullptr;
    }
  }

  // shrink the argument list
  if (remove_flags) {
    int j = 1;
    for (int i = 1; i < *argc; i++) {
      if (argv[i] != nullptr)
        argv[j++] = argv[i];
    }
    *argc = j;
  }

  // parsed all flags successfully
  return 0;
}

void FlagList::Register(Flag* flag) {
  RTC_DCHECK(flag);
  RTC_DCHECK_GT(strlen(flag->name()), 0);
  // NOTE: Don't call Lookup() within Register because it accesses the name_
  // of other flags in list_, and if the flags are coming from two different
  // compilation units, the initialization order between them is undefined, and
  // this will trigger an asan initialization-order-fiasco error.
  flag->next_ = list_;
  list_ = flag;
}

}  // namespace rtc