diff --git a/libstats/Android.bp b/libstats/Android.bp
index f5ee1da..c5d05ec 100644
--- a/libstats/Android.bp
+++ b/libstats/Android.bp
@@ -22,6 +22,7 @@
     srcs: [
         "stats_event_list.c",
         "statsd_writer.c",
+	"stats_event.c",
     ],
     host_supported: true,
     cflags: [
diff --git a/libstats/stats_event.c b/libstats/stats_event.c
new file mode 100644
index 0000000..e2f247a
--- /dev/null
+++ b/libstats/stats_event.c
@@ -0,0 +1,349 @@
+/*
+ * Copyright (C) 2019 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 "stats_event.h"
+#include <stdlib.h>
+#include <string.h>
+#include "include/stats_event_list.h"
+
+#define byte unsigned char
+
+#define STATS_EVENT_TAG 1937006964
+#define LOGGER_ENTRY_MAX_PAYLOAD 4068
+// Max payload size is 4 bytes less as 4 bytes are reserved for stats_eventTag.
+// See android_util_Stats_Log.cpp
+#define MAX_EVENT_PAYLOAD (LOGGER_ENTRY_MAX_PAYLOAD - 4)
+
+/* POSITIONS */
+#define POS_NUM_ELEMENTS 1
+#define POS_TIMESTAMP (POS_NUM_ELEMENTS + 1)
+#define POS_ATOM_ID (POS_TIMESTAMP + sizeof(byte) + sizeof(uint64_t))
+#define POS_FIRST_FIELD (POS_ATOM_ID + sizeof(byte) + sizeof(uint32_t))
+
+/* TYPE IDS */
+#define INT32_TYPE 0x00
+#define INT64_TYPE 0x01
+#define STRING_TYPE 0x02
+#define LIST_TYPE 0x03
+#define FLOAT_TYPE 0x04
+#define BOOL_TYPE 0x05
+#define BYTE_ARRAY_TYPE 0x06
+#define OBJECT_TYPE 0x07
+#define KEY_VALUE_PAIR_TYPE 0x08
+#define ATTRIBUTION_CHAIN_TYPE 0x09
+#define ERROR_TYPE 0x0F
+
+/* LIMITS */
+#define MAX_ANNOTATION_COUNT 15
+#define MAX_ANNOTATION_ID 127
+#define MAX_ATTRIBUTION_NODES 127
+#define MAX_NUM_ELEMENTS 127
+
+// The stats_event struct holds the serialized encoding of an event
+// within a buf. Also includes other required fields.
+struct stats_event {
+    byte buf[MAX_EVENT_PAYLOAD];
+    size_t bufPos;        // current write position within the buf
+    size_t lastFieldPos;  // location of last field within the buf
+    size_t size;          // number of valid bytes within buffer
+    uint32_t numElements;
+    uint32_t atomId;
+    uint64_t timestampNs;
+    uint32_t errors;
+    uint32_t tag;
+};
+
+struct stats_event* stats_event_obtain() {
+    struct stats_event* event = malloc(sizeof(struct stats_event));
+
+    memset(event->buf, 0, MAX_EVENT_PAYLOAD);
+    event->buf[0] = OBJECT_TYPE;
+
+    event->bufPos = POS_FIRST_FIELD;
+    event->lastFieldPos = 0;
+    event->size = 0;
+    event->numElements = 0;
+    event->atomId = 0;
+    event->timestampNs = 0;
+    event->errors = 0;
+    event->tag = STATS_EVENT_TAG;
+    return event;
+}
+
+void stats_event_release(struct stats_event* event) {
+    free(event);  // free is a no-op if event is NULL
+}
+
+void stats_event_set_timestamp_ns(struct stats_event* event, uint64_t timestampNs) {
+    if (event) event->timestampNs = timestampNs;
+}
+
+void stats_event_set_atom_id(struct stats_event* event, uint32_t atomId) {
+    if (event) event->atomId = atomId;
+}
+
+// Side-effect: modifies event->errors if the buffer would overflow
+static bool overflows(struct stats_event* event, size_t size) {
+    if (event->bufPos + size > MAX_EVENT_PAYLOAD) {
+        event->errors |= ERROR_OVERFLOW;
+        return true;
+    }
+    return false;
+}
+
+static size_t put_byte(struct stats_event* event, byte value) {
+    if (!overflows(event, sizeof(value))) {
+        event->buf[event->bufPos] = value;
+        return sizeof(byte);
+    }
+    return 0;
+}
+
+static size_t put_bool(struct stats_event* event, bool value) {
+    return put_byte(event, (byte)value);
+}
+
+static size_t put_int32(struct stats_event* event, int32_t value) {
+    if (!overflows(event, sizeof(value))) {
+        memcpy(&event->buf[event->bufPos], &value, sizeof(int32_t));
+        return sizeof(int32_t);
+    }
+    return 0;
+}
+
+static size_t put_int64(struct stats_event* event, int64_t value) {
+    if (!overflows(event, sizeof(value))) {
+        memcpy(&event->buf[event->bufPos], &value, sizeof(int64_t));
+        return sizeof(int64_t);
+    }
+    return 0;
+}
+
+static size_t put_float(struct stats_event* event, float value) {
+    if (!overflows(event, sizeof(value))) {
+        memcpy(&event->buf[event->bufPos], &value, sizeof(float));
+        return sizeof(float);
+    }
+    return 0;
+}
+
+static size_t put_byte_array(struct stats_event* event, void* buf, size_t size) {
+    if (!overflows(event, size)) {
+        memcpy(&event->buf[event->bufPos], buf, size);
+        return size;
+    }
+    return 0;
+}
+
+void stats_event_write_int32(struct stats_event* event, int32_t value) {
+    if (!event || event->errors) return;
+
+    event->lastFieldPos = event->bufPos;
+    event->bufPos += put_byte(event, INT32_TYPE);
+    event->bufPos += put_int32(event, value);
+    event->numElements++;
+}
+
+void stats_event_write_int64(struct stats_event* event, int64_t value) {
+    if (!event || event->errors) return;
+
+    event->lastFieldPos = event->bufPos;
+    event->bufPos += put_byte(event, INT64_TYPE);
+    event->bufPos += put_int64(event, value);
+    event->numElements++;
+}
+
+void stats_event_write_float(struct stats_event* event, float value) {
+    if (!event || event->errors) return;
+
+    event->lastFieldPos = event->bufPos;
+    event->bufPos += put_byte(event, FLOAT_TYPE);
+    event->bufPos += put_float(event, value);
+    event->numElements++;
+}
+
+void stats_event_write_bool(struct stats_event* event, bool value) {
+    if (!event || event->errors) return;
+
+    event->lastFieldPos = event->bufPos;
+    event->bufPos += put_byte(event, BOOL_TYPE);
+    event->bufPos += put_bool(event, value);
+    event->numElements++;
+}
+
+// Buf is assumed to be encoded using UTF8
+void stats_event_write_byte_array(struct stats_event* event, uint8_t* buf, uint32_t numBytes) {
+    if (!event || !buf || event->errors) return;
+
+    event->lastFieldPos = event->bufPos;
+    event->bufPos += put_byte(event, BYTE_ARRAY_TYPE);
+    event->bufPos += put_int32(event, numBytes);
+    event->bufPos += put_byte_array(event, buf, numBytes);
+    event->numElements++;
+}
+
+// Buf is assumed to be encoded using UTF8
+void stats_event_write_string8(struct stats_event* event, char* buf, uint32_t numBytes) {
+    if (!event || !buf || event->errors) return;
+
+    event->lastFieldPos = event->bufPos;
+    event->bufPos += put_byte(event, STRING_TYPE);
+    event->bufPos += put_int32(event, numBytes);
+    event->bufPos += put_byte_array(event, buf, numBytes);
+    event->numElements++;
+}
+
+// Side-effect: modifies event->errors if the attribution chain is too long
+static bool is_attribution_chain_too_long(struct stats_event* event, uint32_t numNodes) {
+    if (numNodes > MAX_ATTRIBUTION_NODES) {
+        event->errors |= ERROR_ATTRIBUTION_CHAIN_TOO_LONG;
+        return true;
+    }
+    return false;
+}
+
+// Tags are assumed to be encoded using UTF8
+void stats_event_write_attribution_chain(struct stats_event* event, uint32_t* uids, char** tags,
+                                         uint32_t* tagLengths, uint32_t numNodes) {
+    if (!event || event->errors) return;
+    if (is_attribution_chain_too_long(event, numNodes)) return;
+
+    event->lastFieldPos = event->bufPos;
+    event->bufPos += put_byte(event, ATTRIBUTION_CHAIN_TYPE);
+    event->bufPos += put_byte(event, (byte)numNodes);
+
+    for (int i = 0; i < numNodes; i++) {
+        event->bufPos += put_int32(event, uids[i]);
+        event->bufPos += put_int32(event, tagLengths[i]);
+        event->bufPos += put_byte_array(event, tags[i], tagLengths[i]);
+    }
+    event->numElements++;
+}
+
+// Side-effect: modifies event->errors if annotation does not follow field
+static bool does_annotation_follow_field(struct stats_event* event) {
+    if (event->lastFieldPos == 0) {
+        event->errors |= ERROR_ANNOTATION_DOES_NOT_FOLLOW_FIELD;
+        return false;
+    }
+    return true;
+}
+
+// Side-effect: modifies event->errors if annotation id is too large
+static bool is_valid_annotation_id(struct stats_event* event, uint32_t annotationId) {
+    if (annotationId > MAX_ANNOTATION_ID) {
+        event->errors |= ERROR_ANNOTATION_ID_TOO_LARGE;
+        return false;
+    }
+    return true;
+}
+
+// Side-effect: modifies event->errors if field has too many annotations
+static void increment_annotation_count(struct stats_event* event) {
+    byte fieldType = event->buf[event->lastFieldPos] & 0x0F;
+    byte oldAnnotationCount = event->buf[event->lastFieldPos] & 0xF0;
+    byte newAnnotationCount = oldAnnotationCount + 1;
+
+    if (newAnnotationCount > MAX_ANNOTATION_COUNT) {
+        event->errors |= ERROR_TOO_MANY_ANNOTATIONS;
+        return;
+    }
+
+    event->buf[event->lastFieldPos] = ((newAnnotationCount << 4) & 0xF0) | fieldType;
+}
+
+void stats_event_add_bool_annotation(struct stats_event* event, uint32_t annotationId, bool value) {
+    if (!event || event->errors) return;
+    if (!does_annotation_follow_field(event)) return;
+    if (!is_valid_annotation_id(event, annotationId)) return;
+
+    event->bufPos += put_byte(event, (byte)annotationId);
+    event->bufPos += put_byte(event, BOOL_TYPE);
+    event->bufPos += put_bool(event, value);
+    increment_annotation_count(event);
+}
+
+void stats_event_add_int32_annotation(struct stats_event* event, uint32_t annotationId,
+                                      int32_t value) {
+    if (!event || event->errors) return;
+    if (!does_annotation_follow_field(event)) return;
+    if (!is_valid_annotation_id(event, annotationId)) return;
+
+    event->bufPos += put_byte(event, (byte)annotationId);
+    event->bufPos += put_byte(event, INT32_TYPE);
+    event->bufPos += put_int32(event, value);
+    increment_annotation_count(event);
+}
+
+uint32_t stats_event_get_errors(struct stats_event* event) {
+    return event->errors;
+}
+
+static void build(struct stats_event* event) {
+    // store size before we modify bufPos
+    event->size = event->bufPos;
+
+    if (event->numElements > MAX_NUM_ELEMENTS) {
+        event->errors |= ERROR_TOO_MANY_FIELDS;
+    } else {
+        event->bufPos = POS_NUM_ELEMENTS;
+        put_byte(event, (byte)event->numElements);
+    }
+
+    if (event->timestampNs == 0) {
+        event->errors |= ERROR_NO_TIMESTAMP;
+    } else {
+        // Don't use the write functions since they short-circuit if there was
+        // an error previously. We, regardless, want to know the timestamp and
+        // atomId.
+        event->bufPos = POS_TIMESTAMP;
+        event->bufPos += put_byte(event, INT64_TYPE);
+        event->bufPos += put_int64(event, event->timestampNs);
+    }
+
+    if (event->atomId == 0) {
+        event->errors |= ERROR_NO_ATOM_ID;
+    } else {
+        event->bufPos = POS_ATOM_ID;
+        event->bufPos += put_byte(event, INT32_TYPE);
+        event->bufPos += put_int64(event, event->atomId);
+    }
+
+    // If there are errors, rewrite buffer
+    if (event->errors) {
+        event->bufPos = POS_NUM_ELEMENTS;
+        put_byte(event, (byte)3);
+
+        event->bufPos = POS_FIRST_FIELD;
+        event->bufPos += put_byte(event, ERROR_TYPE);
+        event->bufPos += put_int32(event, event->errors);
+        event->size = event->bufPos;
+    }
+}
+
+void stats_event_write(struct stats_event* event) {
+    if (!event) return;
+
+    build(event);
+
+    // prepare iovecs for write to statsd
+    struct iovec vecs[2];
+    vecs[0].iov_base = &event->tag;
+    vecs[0].iov_len = sizeof(event->tag);
+    vecs[1].iov_base = &event->buf;
+    vecs[1].iov_len = event->size;
+    write_to_statsd(vecs, 2);
+}
diff --git a/libstats/stats_event.h b/libstats/stats_event.h
new file mode 100644
index 0000000..16a04f8
--- /dev/null
+++ b/libstats/stats_event.h
@@ -0,0 +1,86 @@
+/*
+ * Copyright (C) 2019 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_H
+#define ANDROID_STATS_LOG_STATS_EVENT_H
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+
+/*
+ * Functionality to build and store the buffer sent over the statsd socket.
+ * This code defines and encapsulates the socket protocol.
+ *
+ * Usage:
+ *      struct stats_event* event = stats_event_obtain();
+ *
+ *      stats_event_set_timestamp_ns(event, timestampNs);
+ *      stats_event_set_atom_id(event, atomId);
+ *      stats_event_write_int32(event, 24);
+ *      stats_event_add_bool_annotation(event, 1, true); // annotations apply to the previous field
+ *      stats_event_add_int32_annotation(event, 2, 128);
+ *      stats_event_write_float(event, 2.0);
+ *
+ *      stats_event_write(event);
+ *      stats_event_release(event);
+ *
+ * Notes:
+ *    (a) write_<type>() and add_<type>_annotation() should be called in the order that fields
+ *        and annotations are defined in the atom.
+ *    (b) set_timestamp_ns() and set_atom_id() can be called anytime before stats_event_write().
+ *    (c) add_<type>_annotation() calls apply to the previous field.
+ *    (d) If errors occur, stats_event_write() will write a bitmask of the errors to the socket.
+ *    (e) Strings should be encoded using UTF8 and written using stats_event_write_string8().
+ */
+
+struct stats_event;
+
+/* ERRORS */
+#define ERROR_NO_TIMESTAMP 0x1
+#define ERROR_NO_ATOM_ID 0x2
+#define ERROR_OVERFLOW 0x4
+#define ERROR_ATTRIBUTION_CHAIN_TOO_LONG 0x8
+#define ERROR_ANNOTATION_DOES_NOT_FOLLOW_FIELD 0x10
+#define ERROR_INVALID_ANNOTATION_ID 0x20
+#define ERROR_ANNOTATION_ID_TOO_LARGE 0x40
+#define ERROR_TOO_MANY_ANNOTATIONS 0x80
+#define ERROR_TOO_MANY_FIELDS 0x100
+
+/* System API */
+struct stats_event* stats_event_obtain();
+void stats_event_write(struct stats_event* event);
+void stats_event_release(struct stats_event* event);
+
+void stats_event_set_atom_id(struct stats_event* event, const uint32_t atomId);
+void stats_event_set_timestamp_ns(struct stats_event* event, const uint64_t timestampNs);
+
+void stats_event_write_int32(struct stats_event* event, int32_t value);
+void stats_event_write_int64(struct stats_event* event, int64_t value);
+void stats_event_write_float(struct stats_event* event, float value);
+void stats_event_write_bool(struct stats_event* event, bool value);
+void stats_event_write_byte_array(struct stats_event* event, uint8_t* buf, uint32_t numBytes);
+void stats_event_write_string8(struct stats_event* event, char* buf, uint32_t numBytes);
+void stats_event_write_attribution_chain(struct stats_event* event, uint32_t* uids, char** tags,
+                                         uint32_t* tagLengths, uint32_t numNodes);
+
+void stats_event_add_bool_annotation(struct stats_event* event, uint32_t annotationId, bool value);
+void stats_event_add_int32_annotation(struct stats_event* event, uint32_t annotationId,
+                                      int32_t value);
+
+uint32_t stats_event_get_errors(struct stats_event* event);
+
+#endif  // ANDROID_STATS_LOG_STATS_EVENT_H