Move libstatssocket from frameworks/base to system/core/

So that lmkd can build on PDK.

Bug: 79349329
Test: builds locally
Merged-In: I981e6ef9f9769b873640e5f169a9495ccea2f25c
Change-Id: I981e6ef9f9769b873640e5f169a9495ccea2f25c
(cherry picked from commit b13a102c0afec2c0a1fbdafb9a00e3d55450b28b)

5 files changed, 771 insertions, 0 deletions

diff --git a/libstats/Android.bp b/libstats/Android.bp
new file mode 100644
index 000000000..d58f29417
--- /dev/null
+++ b/libstats/Android.bp
@@ -0,0 +1,37 @@
+//
+// Copyright (C) 2018 The Android Open Source Project
+//
+// 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.
+//
+
+// ==========================================================
+// Native library to write stats log to statsd socket
+// ==========================================================
+cc_library_static {
+    name: "libstatssocket",
+    srcs: [
+        "stats_event_list.c",
+        "statsd_writer.c",
+    ],
+    cflags: [
+        "-Wall",
+        "-Werror",
+        "-DLIBLOG_LOG_TAG=1006",
+        "-DWRITE_TO_STATSD=1",
+        "-DWRITE_TO_LOGD=0",
+    ],
+    export_include_dirs: ["include"],
+    shared_libs: [
+        "liblog",
+    ],
+}
diff --git a/libstats/include/stats_event_list.h b/libstats/include/stats_event_list.h
new file mode 100644
index 000000000..5d174ae03
--- /dev/null
+++ b/libstats/include/stats_event_list.h
@@ -0,0 +1,250 @@
+/*
+ * Copyright (C) 2018, The Android Open Source Project
+ *
+ * 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.
+ */
+
+#ifndef ANDROID_STATS_LOG_STATS_EVENT_LIST_H
+#define ANDROID_STATS_LOG_STATS_EVENT_LIST_H
+
+#include <log/log_event_list.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+void reset_log_context(android_log_context ctx);
+int write_to_logger(android_log_context context, log_id_t id);
+
+#ifdef __cplusplus
+}
+#endif
+
+#ifdef __cplusplus
+/**
+ * A copy of android_log_event_list class.
+ *
+ * android_log_event_list is going to be deprecated soon, so copy it here to
+ * avoid creating dependency on upstream code. TODO(b/78304629): Rewrite this
+ * code.
+ */
+class stats_event_list {
+  private:
+    android_log_context ctx;
+    int ret;
+
+    stats_event_list(const stats_event_list&) = delete;
+    void operator=(const stats_event_list&) = delete;
+
+  public:
+    explicit stats_event_list(int tag) : ret(0) {
+        ctx = create_android_logger(static_cast<uint32_t>(tag));
+    }
+    explicit stats_event_list(log_msg& log_msg) : ret(0) {
+        ctx = create_android_log_parser(log_msg.msg() + sizeof(uint32_t),
+                                        log_msg.entry.len - sizeof(uint32_t));
+    }
+    ~stats_event_list() { android_log_destroy(&ctx); }
+
+    int close() {
+        int retval = android_log_destroy(&ctx);
+        if (retval < 0) {
+            ret = retval;
+        }
+        return retval;
+    }
+
+    /* To allow above C calls to use this class as parameter */
+    operator android_log_context() const { return ctx; }
+
+    /* return errors or transmit status */
+    int status() const { return ret; }
+
+    int begin() {
+        int retval = android_log_write_list_begin(ctx);
+        if (retval < 0) {
+            ret = retval;
+        }
+        return ret;
+    }
+    int end() {
+        int retval = android_log_write_list_end(ctx);
+        if (retval < 0) {
+            ret = retval;
+        }
+        return ret;
+    }
+
+    stats_event_list& operator<<(int32_t value) {
+        int retval = android_log_write_int32(ctx, value);
+        if (retval < 0) {
+            ret = retval;
+        }
+        return *this;
+    }
+
+    stats_event_list& operator<<(uint32_t value) {
+        int retval = android_log_write_int32(ctx, static_cast<int32_t>(value));
+        if (retval < 0) {
+            ret = retval;
+        }
+        return *this;
+    }
+
+    stats_event_list& operator<<(bool value) {
+        int retval = android_log_write_int32(ctx, value ? 1 : 0);
+        if (retval < 0) {
+            ret = retval;
+        }
+        return *this;
+    }
+
+    stats_event_list& operator<<(int64_t value) {
+        int retval = android_log_write_int64(ctx, value);
+        if (retval < 0) {
+            ret = retval;
+        }
+        return *this;
+    }
+
+    stats_event_list& operator<<(uint64_t value) {
+        int retval = android_log_write_int64(ctx, static_cast<int64_t>(value));
+        if (retval < 0) {
+            ret = retval;
+        }
+        return *this;
+    }
+
+    stats_event_list& operator<<(const char* value) {
+        int retval = android_log_write_string8(ctx, value);
+        if (retval < 0) {
+            ret = retval;
+        }
+        return *this;
+    }
+
+#if defined(_USING_LIBCXX)
+    stats_event_list& operator<<(const std::string& value) {
+        int retval = android_log_write_string8_len(ctx, value.data(), value.length());
+        if (retval < 0) {
+            ret = retval;
+        }
+        return *this;
+    }
+#endif
+
+    stats_event_list& operator<<(float value) {
+        int retval = android_log_write_float32(ctx, value);
+        if (retval < 0) {
+            ret = retval;
+        }
+        return *this;
+    }
+
+    int write(log_id_t id = LOG_ID_EVENTS) {
+        /* facilitate -EBUSY retry */
+        if ((ret == -EBUSY) || (ret > 0)) {
+            ret = 0;
+        }
+        int retval = write_to_logger(ctx, id);
+        /* existing errors trump transmission errors */
+        if (!ret) {
+            ret = retval;
+        }
+        return ret;
+    }
+
+    /*
+     * Append<Type> methods removes any integer promotion
+     * confusion, and adds access to string with length.
+     * Append methods are also added for all types for
+     * convenience.
+     */
+
+    bool AppendInt(int32_t value) {
+        int retval = android_log_write_int32(ctx, value);
+        if (retval < 0) {
+            ret = retval;
+        }
+        return ret >= 0;
+    }
+
+    bool AppendLong(int64_t value) {
+        int retval = android_log_write_int64(ctx, value);
+        if (retval < 0) {
+            ret = retval;
+        }
+        return ret >= 0;
+    }
+
+    bool AppendString(const char* value) {
+        int retval = android_log_write_string8(ctx, value);
+        if (retval < 0) {
+            ret = retval;
+        }
+        return ret >= 0;
+    }
+
+    bool AppendString(const char* value, size_t len) {
+        int retval = android_log_write_string8_len(ctx, value, len);
+        if (retval < 0) {
+            ret = retval;
+        }
+        return ret >= 0;
+    }
+
+#if defined(_USING_LIBCXX)
+    bool AppendString(const std::string& value) {
+        int retval = android_log_write_string8_len(ctx, value.data(), value.length());
+        if (retval < 0) {
+            ret = retval;
+        }
+        return ret;
+    }
+
+    bool Append(const std::string& value) {
+        int retval = android_log_write_string8_len(ctx, value.data(), value.length());
+        if (retval < 0) {
+            ret = retval;
+        }
+        return ret;
+    }
+#endif
+
+    bool AppendFloat(float value) {
+        int retval = android_log_write_float32(ctx, value);
+        if (retval < 0) {
+            ret = retval;
+        }
+        return ret >= 0;
+    }
+
+    template <typename Tvalue>
+    bool Append(Tvalue value) {
+        *this << value;
+        return ret >= 0;
+    }
+
+    bool Append(const char* value, size_t len) {
+        int retval = android_log_write_string8_len(ctx, value, len);
+        if (retval < 0) {
+            ret = retval;
+        }
+        return ret >= 0;
+    }
+
+    android_log_list_element read() { return android_log_read_next(ctx); }
+    android_log_list_element peek() { return android_log_peek_next(ctx); }
+};
+
+#endif
+#endif  // ANDROID_STATS_LOG_STATS_EVENT_LIST_H
diff --git a/libstats/stats_event_list.c b/libstats/stats_event_list.c
new file mode 100644
index 000000000..966bb08a2
--- /dev/null
+++ b/libstats/stats_event_list.c
@@ -0,0 +1,181 @@
+/*
+ * Copyright (C) 2018, The Android Open Source Project
+ *
+ * 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 "include/stats_event_list.h"
+
+#include <string.h>
+#include "statsd_writer.h"
+
+#define MAX_EVENT_PAYLOAD (LOGGER_ENTRY_MAX_PAYLOAD - sizeof(int32_t))
+
+typedef struct {
+    uint32_t tag;
+    unsigned pos;                                    /* Read/write position into buffer */
+    unsigned count[ANDROID_MAX_LIST_NEST_DEPTH + 1]; /* Number of elements   */
+    unsigned list[ANDROID_MAX_LIST_NEST_DEPTH + 1];  /* pos for list counter */
+    unsigned list_nest_depth;
+    unsigned len; /* Length or raw buffer. */
+    bool overflow;
+    bool list_stop; /* next call decrement list_nest_depth and issue a stop */
+    enum {
+        kAndroidLoggerRead = 1,
+        kAndroidLoggerWrite = 2,
+    } read_write_flag;
+    uint8_t storage[LOGGER_ENTRY_MAX_PAYLOAD];
+} android_log_context_internal;
+
+extern struct android_log_transport_write statsdLoggerWrite;
+
+static int __write_to_statsd_init(struct iovec* vec, size_t nr);
+static int (*write_to_statsd)(struct iovec* vec, size_t nr) = __write_to_statsd_init;
+
+// Similar to create_android_logger(), but instead of allocation a new buffer,
+// this function resets the buffer for resuse.
+void reset_log_context(android_log_context ctx) {
+    if (!ctx) {
+        return;
+    }
+    android_log_context_internal* context = (android_log_context_internal*)(ctx);
+    uint32_t tag = context->tag;
+    memset(context, 0, sizeof(android_log_context_internal));
+
+    context->tag = tag;
+    context->read_write_flag = kAndroidLoggerWrite;
+    size_t needed = sizeof(uint8_t) + sizeof(uint8_t);
+    if ((context->pos + needed) > MAX_EVENT_PAYLOAD) {
+        context->overflow = true;
+    }
+    /* Everything is a list */
+    context->storage[context->pos + 0] = EVENT_TYPE_LIST;
+    context->list[0] = context->pos + 1;
+    context->pos += needed;
+}
+
+int stats_write_list(android_log_context ctx) {
+    android_log_context_internal* context;
+    const char* msg;
+    ssize_t len;
+
+    context = (android_log_context_internal*)(ctx);
+    if (!context || (kAndroidLoggerWrite != context->read_write_flag)) {
+        return -EBADF;
+    }
+
+    if (context->list_nest_depth) {
+        return -EIO;
+    }
+
+    /* NB: if there was overflow, then log is truncated. Nothing reported */
+    context->storage[1] = context->count[0];
+    len = context->len = context->pos;
+    msg = (const char*)context->storage;
+    /* it's not a list */
+    if (context->count[0] <= 1) {
+        len -= sizeof(uint8_t) + sizeof(uint8_t);
+        if (len < 0) {
+            len = 0;
+        }
+        msg += sizeof(uint8_t) + sizeof(uint8_t);
+    }
+
+    struct iovec vec[2];
+    vec[0].iov_base = &context->tag;
+    vec[0].iov_len = sizeof(context->tag);
+    vec[1].iov_base = (void*)msg;
+    vec[1].iov_len = len;
+    return write_to_statsd(vec, 2);
+}
+
+int write_to_logger(android_log_context ctx, log_id_t id) {
+    int retValue = 0;
+
+    if (WRITE_TO_LOGD) {
+        retValue = android_log_write_list(ctx, id);
+    }
+
+    if (WRITE_TO_STATSD) {
+        // log_event_list's cast operator is overloaded.
+        int ret = stats_write_list(ctx);
+        // In debugging phase, we may write to both logd and statsd. Prefer to
+        // return statsd socket write error code here.
+        if (ret < 0) {
+            retValue = ret;
+        }
+    }
+
+    return retValue;
+}
+
+/* log_init_lock assumed */
+static int __write_to_statsd_initialize_locked() {
+    if (!statsdLoggerWrite.open || ((*statsdLoggerWrite.open)() < 0)) {
+        if (statsdLoggerWrite.close) {
+            (*statsdLoggerWrite.close)();
+            return -ENODEV;
+        }
+    }
+    return 1;
+}
+
+static int __write_to_stats_daemon(struct iovec* vec, size_t nr) {
+    int ret, save_errno;
+    struct timespec ts;
+    size_t len, i;
+
+    for (len = i = 0; i < nr; ++i) {
+        len += vec[i].iov_len;
+    }
+    if (!len) {
+        return -EINVAL;
+    }
+
+    save_errno = errno;
+    clock_gettime(CLOCK_REALTIME, &ts);
+
+    ret = 0;
+
+    ssize_t retval;
+    retval = (*statsdLoggerWrite.write)(&ts, vec, nr);
+    if (ret >= 0) {
+        ret = retval;
+    }
+
+    errno = save_errno;
+    return ret;
+}
+
+static int __write_to_statsd_init(struct iovec* vec, size_t nr) {
+    int ret, save_errno = errno;
+
+    statsd_writer_init_lock();
+
+    if (write_to_statsd == __write_to_statsd_init) {
+        ret = __write_to_statsd_initialize_locked();
+        if (ret < 0) {
+            statsd_writer_init_unlock();
+            errno = save_errno;
+            return ret;
+        }
+
+        write_to_statsd = __write_to_stats_daemon;
+    }
+
+    statsd_writer_init_unlock();
+
+    ret = write_to_statsd(vec, nr);
+    errno = save_errno;
+    return ret;
+}
\ No newline at end of file
diff --git a/libstats/statsd_writer.c b/libstats/statsd_writer.c
new file mode 100644
index 000000000..9953bba2e
--- /dev/null
+++ b/libstats/statsd_writer.c
@@ -0,0 +1,260 @@
+/*
+ * Copyright (C) 2018, The Android Open Source Project
+ *
+ * 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 "statsd_writer.h"
+
+#include <cutils/sockets.h>
+#include <endian.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <inttypes.h>
+#include <poll.h>
+#include <private/android_filesystem_config.h>
+#include <private/android_logger.h>
+#include <stdarg.h>
+#include <stdatomic.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/un.h>
+#include <time.h>
+#include <unistd.h>
+
+/* branchless on many architectures. */
+#define min(x, y) ((y) ^ (((x) ^ (y)) & -((x) < (y))))
+
+static pthread_mutex_t log_init_lock = PTHREAD_MUTEX_INITIALIZER;
+
+void statsd_writer_init_lock() {
+    /*
+     * If we trigger a signal handler in the middle of locked activity and the
+     * signal handler logs a message, we could get into a deadlock state.
+     */
+    pthread_mutex_lock(&log_init_lock);
+}
+
+int statd_writer_trylock() {
+    return pthread_mutex_trylock(&log_init_lock);
+}
+
+void statsd_writer_init_unlock() {
+    pthread_mutex_unlock(&log_init_lock);
+}
+
+static int statsdAvailable();
+static int statsdOpen();
+static void statsdClose();
+static int statsdWrite(struct timespec* ts, struct iovec* vec, size_t nr);
+
+struct android_log_transport_write statsdLoggerWrite = {
+    .name = "statsd",
+    .sock = -EBADF,
+    .available = statsdAvailable,
+    .open = statsdOpen,
+    .close = statsdClose,
+    .write = statsdWrite,
+};
+
+/* log_init_lock assumed */
+static int statsdOpen() {
+    int i, ret = 0;
+
+    i = atomic_load(&statsdLoggerWrite.sock);
+    if (i < 0) {
+        int sock = TEMP_FAILURE_RETRY(socket(PF_UNIX, SOCK_DGRAM | SOCK_CLOEXEC | SOCK_NONBLOCK, 0));
+        if (sock < 0) {
+            ret = -errno;
+        } else {
+            struct sockaddr_un un;
+            memset(&un, 0, sizeof(struct sockaddr_un));
+            un.sun_family = AF_UNIX;
+            strcpy(un.sun_path, "/dev/socket/statsdw");
+
+            if (TEMP_FAILURE_RETRY(
+                    connect(sock, (struct sockaddr*)&un, sizeof(struct sockaddr_un))) < 0) {
+                ret = -errno;
+                switch (ret) {
+                    case -ENOTCONN:
+                    case -ECONNREFUSED:
+                    case -ENOENT:
+                        i = atomic_exchange(&statsdLoggerWrite.sock, ret);
+                    /* FALLTHRU */
+                    default:
+                        break;
+                }
+                close(sock);
+            } else {
+                ret = atomic_exchange(&statsdLoggerWrite.sock, sock);
+                if ((ret >= 0) && (ret != sock)) {
+                    close(ret);
+                }
+                ret = 0;
+            }
+        }
+    }
+
+    return ret;
+}
+
+static void __statsdClose(int negative_errno) {
+    int sock = atomic_exchange(&statsdLoggerWrite.sock, negative_errno);
+    if (sock >= 0) {
+        close(sock);
+    }
+}
+
+static void statsdClose() {
+    __statsdClose(-EBADF);
+}
+
+static int statsdAvailable() {
+    if (atomic_load(&statsdLoggerWrite.sock) < 0) {
+        if (access("/dev/socket/statsdw", W_OK) == 0) {
+            return 0;
+        }
+        return -EBADF;
+    }
+    return 1;
+}
+
+static int statsdWrite(struct timespec* ts, struct iovec* vec, size_t nr) {
+    ssize_t ret;
+    int sock;
+    static const unsigned headerLength = 1;
+    struct iovec newVec[nr + headerLength];
+    android_log_header_t header;
+    size_t i, payloadSize;
+    static atomic_int dropped;
+
+    sock = atomic_load(&statsdLoggerWrite.sock);
+    if (sock < 0) switch (sock) {
+            case -ENOTCONN:
+            case -ECONNREFUSED:
+            case -ENOENT:
+                break;
+            default:
+                return -EBADF;
+        }
+    /*
+     *  struct {
+     *      // what we provide to socket
+     *      android_log_header_t header;
+     *      // caller provides
+     *      union {
+     *          struct {
+     *              char     prio;
+     *              char     payload[];
+     *          } string;
+     *          struct {
+     *              uint32_t tag
+     *              char     payload[];
+     *          } binary;
+     *      };
+     *  };
+     */
+
+    header.tid = gettid();
+    header.realtime.tv_sec = ts->tv_sec;
+    header.realtime.tv_nsec = ts->tv_nsec;
+
+    newVec[0].iov_base = (unsigned char*)&header;
+    newVec[0].iov_len = sizeof(header);
+
+    // If we dropped events before, try to tell statsd.
+    if (sock >= 0) {
+        int32_t snapshot = atomic_exchange_explicit(&dropped, 0, memory_order_relaxed);
+        if (snapshot) {
+            android_log_event_int_t buffer;
+            header.id = LOG_ID_STATS;
+            buffer.header.tag = htole32(LIBLOG_LOG_TAG);
+            buffer.payload.type = EVENT_TYPE_INT;
+            buffer.payload.data = htole32(snapshot);
+
+            newVec[headerLength].iov_base = &buffer;
+            newVec[headerLength].iov_len = sizeof(buffer);
+
+            ret = TEMP_FAILURE_RETRY(writev(sock, newVec, 2));
+            if (ret != (ssize_t)(sizeof(header) + sizeof(buffer))) {
+                atomic_fetch_add_explicit(&dropped, snapshot, memory_order_relaxed);
+            }
+        }
+    }
+
+    header.id = LOG_ID_STATS;
+
+    for (payloadSize = 0, i = headerLength; i < nr + headerLength; i++) {
+        newVec[i].iov_base = vec[i - headerLength].iov_base;
+        payloadSize += newVec[i].iov_len = vec[i - headerLength].iov_len;
+
+        if (payloadSize > LOGGER_ENTRY_MAX_PAYLOAD) {
+            newVec[i].iov_len -= payloadSize - LOGGER_ENTRY_MAX_PAYLOAD;
+            if (newVec[i].iov_len) {
+                ++i;
+            }
+            break;
+        }
+    }
+
+    /*
+     * The write below could be lost, but will never block.
+     *
+     * ENOTCONN occurs if statsd has died.
+     * ENOENT occurs if statsd is not running and socket is missing.
+     * ECONNREFUSED occurs if we can not reconnect to statsd.
+     * EAGAIN occurs if statsd is overloaded.
+     */
+    if (sock < 0) {
+        ret = sock;
+    } else {
+        ret = TEMP_FAILURE_RETRY(writev(sock, newVec, i));
+        if (ret < 0) {
+            ret = -errno;
+        }
+    }
+    switch (ret) {
+        case -ENOTCONN:
+        case -ECONNREFUSED:
+        case -ENOENT:
+            if (statd_writer_trylock()) {
+                return ret; /* in a signal handler? try again when less stressed
+                             */
+            }
+            __statsdClose(ret);
+            ret = statsdOpen();
+            statsd_writer_init_unlock();
+
+            if (ret < 0) {
+                return ret;
+            }
+
+            ret = TEMP_FAILURE_RETRY(writev(atomic_load(&statsdLoggerWrite.sock), newVec, i));
+            if (ret < 0) {
+                ret = -errno;
+            }
+        /* FALLTHRU */
+        default:
+            break;
+    }
+
+    if (ret > (ssize_t)sizeof(header)) {
+        ret -= sizeof(header);
+    } else if (ret == -EAGAIN) {
+        atomic_fetch_add_explicit(&dropped, 1, memory_order_relaxed);
+    }
+
+    return ret;
+}
diff --git a/libstats/statsd_writer.h b/libstats/statsd_writer.h
new file mode 100644
index 000000000..82e14e04f
--- /dev/null
+++ b/libstats/statsd_writer.h
@@ -0,0 +1,43 @@
+/*
+ * Copyright (C) 2018, The Android Open Source Project
+ *
+ * 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.
+ */
+
+#ifndef ANDROID_STATS_LOG_STATS_WRITER_H
+#define ANDROID_STATS_LOG_STATS_WRITER_H
+
+#include <pthread.h>
+#include <stdatomic.h>
+#include <sys/socket.h>
+
+/**
+ * Internal lock should not be exposed. This is bad design.
+ * TODO: rewrite it in c++ code and encapsulate the functionality in a
+ * StatsdWriter class.
+ */
+void statsd_writer_init_lock();
+int statsd_writer_init_trylock();
+void statsd_writer_init_unlock();
+
+struct android_log_transport_write {
+    const char* name; /* human name to describe the transport */
+    atomic_int sock;
+    int (*available)(); /* Does not cause resources to be taken */
+    int (*open)();      /* can be called multiple times, reusing current resources */
+    void (*close)();    /* free up resources */
+    /* write log to transport, returns number of bytes propagated, or -errno */
+    int (*write)(struct timespec* ts, struct iovec* vec, size_t nr);
+};
+
+#endif  // ANDROID_STATS_LOG_STATS_WRITER_H