chore(tools/journaldriver): Prepare tree for depot merge

2 files changed, 760 insertions, 0 deletions

diff --git a/tools/journaldriver/src/main.rs b/tools/journaldriver/src/main.rs
new file mode 100644
index 000000000000..a57bb3505ddc
--- /dev/null
+++ b/tools/journaldriver/src/main.rs
@@ -0,0 +1,665 @@
+// Copyright (C) 2018 Vincent Ambo <mail@tazj.in>
+//
+// journaldriver is free software: you can redistribute it and/or
+// modify it under the terms of the GNU General Public License as
+// published by the Free Software Foundation, either version 3 of the
+// License, or (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+//! This file implements journaldriver, a small application that
+//! forwards logs from journald (systemd's log facility) to
+//! Stackdriver Logging.
+//!
+//! Log entries are read continously from journald and are forwarded
+//! to Stackdriver in batches.
+//!
+//! Stackdriver Logging has a concept of monitored resources. In the
+//! simplest case this monitored resource will be the GCE instance on
+//! which journaldriver is running.
+//!
+//! Information about the instance, the project and required security
+//! credentials are retrieved from Google's metadata instance on GCP.
+//!
+//! To run journaldriver on non-GCP machines, users must specify the
+//! `GOOGLE_APPLICATION_CREDENTIALS`, `GOOGLE_CLOUD_PROJECT` and
+//! `LOG_NAME` environment variables.
+
+#[macro_use] extern crate failure;
+#[macro_use] extern crate log;
+#[macro_use] extern crate serde_derive;
+#[macro_use] extern crate serde_json;
+#[macro_use] extern crate lazy_static;
+
+extern crate chrono;
+extern crate env_logger;
+extern crate medallion;
+extern crate serde;
+extern crate systemd;
+extern crate ureq;
+
+use chrono::offset::LocalResult;
+use chrono::prelude::*;
+use failure::ResultExt;
+use serde_json::{from_str, Value};
+use std::env;
+use std::fs::{self, File, rename};
+use std::io::{self, Read, ErrorKind, Write};
+use std::mem;
+use std::path::PathBuf;
+use std::process;
+use std::time::{Duration, Instant};
+use systemd::journal::*;
+
+#[cfg(test)]
+mod tests;
+
+const LOGGING_SERVICE: &str = "https://logging.googleapis.com/google.logging.v2.LoggingServiceV2";
+const ENTRIES_WRITE_URL: &str = "https://logging.googleapis.com/v2/entries:write";
+const METADATA_TOKEN_URL: &str = "http://metadata.google.internal/computeMetadata/v1/instance/service-accounts/default/token";
+const METADATA_ID_URL: &str = "http://metadata.google.internal/computeMetadata/v1/instance/id";
+const METADATA_ZONE_URL: &str = "http://metadata.google.internal/computeMetadata/v1/instance/zone";
+const METADATA_PROJECT_URL: &str = "http://metadata.google.internal/computeMetadata/v1/project/project-id";
+
+/// Convenience type alias for results using failure's `Error` type.
+type Result<T> = std::result::Result<T, failure::Error>;
+
+/// Representation of static service account credentials for GCP.
+#[derive(Debug, Deserialize)]
+struct Credentials {
+    /// PEM encoded private key
+    private_key: String,
+
+    /// `kid` of this private key
+    private_key_id: String,
+
+    /// "email" address of the service account
+    client_email: String,
+}
+
+lazy_static! {
+    /// ID of the GCP project to which to send logs.
+    static ref PROJECT_ID: String = get_project_id();
+
+    /// Name of the log to write to (this should only be manually
+    /// configured if not running on GCP):
+    static ref LOG_NAME: String = env::var("LOG_NAME")
+        .unwrap_or("journaldriver".into());
+
+    /// Service account credentials (if configured)
+    static ref SERVICE_ACCOUNT_CREDENTIALS: Option<Credentials> =
+        env::var("GOOGLE_APPLICATION_CREDENTIALS").ok()
+        .and_then(|path| File::open(path).ok())
+        .and_then(|file| serde_json::from_reader(file).ok());
+
+    /// Descriptor of the currently monitored instance. Refer to the
+    /// documentation of `determine_monitored_resource` for more
+    /// information.
+    static ref MONITORED_RESOURCE: Value = determine_monitored_resource();
+
+    /// Path to the directory in which journaldriver should persist
+    /// its cursor state.
+    static ref CURSOR_DIR: PathBuf = env::var("CURSOR_POSITION_DIR")
+        .unwrap_or("/var/lib/journaldriver".into())
+        .into();
+
+    /// Path to the cursor position file itself.
+    static ref CURSOR_FILE: PathBuf = {
+        let mut path = CURSOR_DIR.clone();
+        path.push("cursor.pos");
+        path
+    };
+
+    /// Path to the temporary file used for cursor position writes.
+    static ref CURSOR_TMP_FILE: PathBuf = {
+        let mut path = CURSOR_DIR.clone();
+        path.push("cursor.tmp");
+        path
+    };
+}
+
+/// Convenience helper for retrieving values from the metadata server.
+fn get_metadata(url: &str) -> Result<String> {
+    let response = ureq::get(url)
+        .set("Metadata-Flavor", "Google")
+        .timeout_connect(5000)
+        .timeout_read(5000)
+        .call();
+
+    if response.ok() {
+        // Whitespace is trimmed to remove newlines from responses.
+        let body = response.into_string()
+            .context("Failed to decode metadata response")?
+            .trim().to_string();
+
+        Ok(body)
+    } else {
+        let status = response.status_line().to_string();
+        let body = response.into_string()
+            .unwrap_or_else(|e| format!("Metadata body error: {}", e));
+        bail!("Metadata failure: {} ({})", body, status)
+    }
+}
+
+/// Convenience helper for determining the project ID.
+fn get_project_id() -> String {
+    env::var("GOOGLE_CLOUD_PROJECT")
+        .map_err(Into::into)
+        .or_else(|_: failure::Error| get_metadata(METADATA_PROJECT_URL))
+        .expect("Could not determine project ID")
+}
+
+/// Determines the monitored resource descriptor used in Stackdriver
+/// logs. On GCP this will be set to the instance ID as returned by
+/// the metadata server.
+///
+/// On non-GCP machines the value is determined by using the
+/// `GOOGLE_CLOUD_PROJECT` and `LOG_STREAM` environment variables.
+///
+/// [issue #4]: https://github.com/tazjin/journaldriver/issues/4
+fn determine_monitored_resource() -> Value {
+    if let Ok(log) = env::var("LOG_STREAM") {
+        // The special value `global` is recognised as a log stream name that
+        // results in a `global`-type resource descriptor. This is useful in
+        // cases where Stackdriver Error Reporting is intended to be used on
+        // a non-GCE instance. See [issue #4][] for details.
+        if log == "global" {
+            return json!({
+                "type": "global",
+                "labels": {
+                    "project_id": PROJECT_ID.as_str(),
+                }
+            });
+        }
+
+        json!({
+            "type": "logging_log",
+            "labels": {
+                "project_id": PROJECT_ID.as_str(),
+                "name": log,
+            }
+        })
+    } else {
+        let instance_id = get_metadata(METADATA_ID_URL)
+            .expect("Could not determine instance ID");
+
+        let zone = get_metadata(METADATA_ZONE_URL)
+            .expect("Could not determine instance zone");
+
+        json!({
+            "type": "gce_instance",
+            "labels": {
+                "project_id": PROJECT_ID.as_str(),
+                "instance_id": instance_id,
+                "zone": zone,
+            }
+        })
+    }
+}
+
+/// Represents the response returned by the metadata server's token
+/// endpoint. The token is normally valid for an hour.
+#[derive(Deserialize)]
+struct TokenResponse {
+    expires_in: u64,
+    access_token: String,
+}
+
+/// Struct used to store a token together with a sensible
+/// representation of when it expires.
+struct Token {
+    token: String,
+    fetched_at: Instant,
+    expires: Duration,
+}
+
+impl Token {
+    /// Does this token need to be renewed?
+    fn is_expired(&self) -> bool {
+        self.fetched_at.elapsed() > self.expires
+    }
+}
+
+/// Retrieves a token from the GCP metadata service. Retrieving these
+/// tokens requires no additional authentication.
+fn get_metadata_token() -> Result<Token> {
+    let body = get_metadata(METADATA_TOKEN_URL)?;
+    let token: TokenResponse = from_str(&body)?;
+
+    debug!("Fetched new token from metadata service");
+
+    Ok(Token {
+        fetched_at: Instant::now(),
+        expires: Duration::from_secs(token.expires_in / 2),
+        token: token.access_token,
+    })
+}
+
+/// Signs a token using static client credentials configured for a
+/// service account. This service account must have been given the
+/// `Log Writer` role in Google Cloud IAM.
+///
+/// The process for creating and signing these tokens is described
+/// here:
+///
+/// https://developers.google.com/identity/protocols/OAuth2ServiceAccount#jwt-auth
+fn sign_service_account_token(credentials: &Credentials) -> Result<Token> {
+    use medallion::{Algorithm, Header, Payload};
+
+    let iat = Utc::now();
+    let exp = iat.checked_add_signed(chrono::Duration::seconds(3600))
+        .ok_or_else(|| format_err!("Failed to calculate token expiry"))?;
+
+    let header = Header {
+        alg: Algorithm::RS256,
+        headers: Some(json!({
+            "kid": credentials.private_key_id,
+        })),
+    };
+
+    let payload: Payload<()> = Payload {
+        iss: Some(credentials.client_email.clone()),
+        sub: Some(credentials.client_email.clone()),
+        aud: Some(LOGGING_SERVICE.to_string()),
+        iat: Some(iat.timestamp() as u64),
+        exp: Some(exp.timestamp() as u64),
+        ..Default::default()
+    };
+
+    let token = medallion::Token::new(header, payload)
+        .sign(credentials.private_key.as_bytes())
+        .context("Signing service account token failed")?;
+
+    debug!("Signed new service account token");
+
+    Ok(Token {
+        token,
+        fetched_at: Instant::now(),
+        expires: Duration::from_secs(3000),
+    })
+}
+
+/// Retrieve the authentication token either by using static client
+/// credentials, or by talking to the metadata server.
+///
+/// Which behaviour is used is controlled by the environment variable
+/// `GOOGLE_APPLICATION_CREDENTIALS`, which should be configured to
+/// point at a JSON private key file if service account authentication
+/// is to be used.
+fn get_token() -> Result<Token> {
+    if let Some(credentials) = SERVICE_ACCOUNT_CREDENTIALS.as_ref() {
+        sign_service_account_token(credentials)
+    } else {
+        get_metadata_token()
+    }
+}
+
+/// This structure represents the different types of payloads
+/// supported by journaldriver.
+///
+/// Currently log entries can either contain plain text messages or
+/// structured payloads in JSON-format.
+#[derive(Debug, Serialize, PartialEq)]
+#[serde(untagged)]
+enum Payload {
+    TextPayload {
+        #[serde(rename = "textPayload")]
+        text_payload: String,
+    },
+    JsonPayload {
+        #[serde(rename = "jsonPayload")]
+        json_payload: Value,
+    },
+}
+
+/// Attempt to parse a log message as JSON and return it as a
+/// structured payload. If parsing fails, return the entry in plain
+/// text format.
+fn message_to_payload(message: Option<String>) -> Payload {
+    match message {
+        None => Payload::TextPayload { text_payload: "empty log entry".into() },
+        Some(text_payload) => {
+            // Attempt to deserialize the text payload as a generic
+            // JSON value.
+            if let Ok(json_payload) = serde_json::from_str::<Value>(&text_payload) {
+                // If JSON-parsing succeeded on the payload, check
+                // whether we parsed an object (Stackdriver does not
+                // expect other types of JSON payload) and return it
+                // in that case.
+                if json_payload.is_object() {
+                    return Payload::JsonPayload { json_payload }
+                }
+            }
+
+            Payload::TextPayload { text_payload }
+        }
+    }
+}
+
+/// Attempt to parse journald's microsecond timestamps into a UTC
+/// timestamp.
+///
+/// Parse errors are dismissed and returned as empty options: There
+/// simply aren't any useful fallback mechanisms other than defaulting
+/// to ingestion time for journaldriver's use-case.
+fn parse_microseconds(input: String) -> Option<DateTime<Utc>> {
+    if input.len() != 16 {
+        return None;
+    }
+
+    let seconds: i64 = (&input[..10]).parse().ok()?;
+    let micros: u32 = (&input[10..]).parse().ok()?;
+
+    match Utc.timestamp_opt(seconds, micros * 1000) {
+        LocalResult::Single(time) => Some(time),
+        _ => None,
+    }
+}
+
+/// Converts a journald log message priority to a
+/// Stackdriver-compatible severity number.
+///
+/// Both Stackdriver and journald specify equivalent
+/// severities/priorities. Conveniently, the names are the same.
+/// Inconveniently, the numbers are not.
+///
+/// For more information on the journald priorities, consult these
+/// man-pages:
+///
+/// * systemd.journal-fields(7) (section 'PRIORITY')
+/// * sd-daemon(3)
+/// * systemd.exec(5) (section 'SyslogLevelPrefix')
+///
+/// Note that priorities can be logged by applications via the prefix
+/// concept described in these man pages, without interfering with
+/// structured JSON-payloads.
+///
+/// For more information on the Stackdriver severity levels, please
+/// consult Google's documentation:
+///
+/// https://cloud.google.com/logging/docs/reference/v2/rest/v2/LogEntry#LogSeverity
+///
+/// Any unknown priority values result in no severity being set.
+fn priority_to_severity(priority: String) -> Option<u32> {
+    match priority.as_ref() {
+        "0" => Some(800), // emerg
+        "1" => Some(700), // alert
+        "2" => Some(600), // crit
+        "3" => Some(500), // err
+        "4" => Some(400), // warning
+        "5" => Some(300), // notice
+        "6" => Some(200), // info
+        "7" => Some(100), // debug
+        _ => None,
+    }
+}
+
+/// This structure represents a log entry in the format expected by
+/// the Stackdriver API.
+#[derive(Debug, Serialize)]
+#[serde(rename_all = "camelCase")]
+struct LogEntry {
+    labels: Value,
+
+    #[serde(skip_serializing_if = "Option::is_none")]
+    timestamp: Option<DateTime<Utc>>,
+
+    #[serde(flatten)]
+    payload: Payload,
+
+    // https://cloud.google.com/logging/docs/reference/v2/rest/v2/LogEntry#LogSeverity
+    #[serde(skip_serializing_if = "Option::is_none")]
+    severity: Option<u32>,
+}
+
+impl From<JournalRecord> for LogEntry {
+    // Converts from the fields contained in a journald record to the
+    // representation required by Stackdriver Logging.
+    //
+    // The fields are documented in systemd.journal-fields(7).
+    fn from(mut record: JournalRecord) -> LogEntry {
+        // The message field is technically just a convention, but
+        // journald seems to default to it when ingesting unit
+        // output.
+        let payload = message_to_payload(record.remove("MESSAGE"));
+
+        // Presumably this is always set, but who can be sure
+        // about anything in this world.
+        let hostname = record.remove("_HOSTNAME");
+
+        // The unit is seemingly missing on kernel entries, but
+        // present on all others.
+        let unit = record.remove("_SYSTEMD_UNIT");
+
+        // The source timestamp (if present) is specified in
+        // microseconds since epoch.
+        //
+        // If it is not present or can not be parsed, journaldriver
+        // will not send a timestamp for the log entry and it will
+        // default to the ingestion time.
+        let timestamp = record
+            .remove("_SOURCE_REALTIME_TIMESTAMP")
+            .and_then(parse_microseconds);
+
+        // Journald uses syslogd's concept of priority. No idea if this is
+        // always present, but it's optional in the Stackdriver API, so we just
+        // omit it if we can't find or parse it.
+        let severity = record
+            .remove("PRIORITY")
+            .and_then(priority_to_severity);
+
+        LogEntry {
+            payload,
+            timestamp,
+            labels: json!({
+                "host": hostname,
+                "unit": unit.unwrap_or_else(|| "syslog".into()),
+            }),
+            severity,
+        }
+    }
+}
+
+/// Attempt to read from the journal. If no new entry is present,
+/// await the next one up to the specified timeout.
+fn receive_next_record(timeout: Duration, journal: &mut Journal)
+                       -> Result<Option<JournalRecord>> {
+    let next_record = journal.next_record()?;
+    if next_record.is_some() {
+        return Ok(next_record);
+    }
+
+    Ok(journal.await_next_record(Some(timeout))?)
+}
+
+/// This function starts a double-looped, blocking receiver. It will
+/// buffer messages for half a second before flushing them to
+/// Stackdriver.
+fn receiver_loop(mut journal: Journal) -> Result<()> {
+    let mut token = get_token()?;
+
+    let mut buf: Vec<LogEntry> = Vec::new();
+    let iteration = Duration::from_millis(500);
+
+    loop {
+        trace!("Beginning outer iteration");
+        let now = Instant::now();
+
+        loop {
+            if now.elapsed() > iteration {
+                break;
+            }
+
+            if let Ok(Some(entry)) = receive_next_record(iteration, &mut journal) {
+                trace!("Received a new entry");
+                buf.push(entry.into());
+            }
+        }
+
+        if !buf.is_empty() {
+            let to_flush = mem::replace(&mut buf, Vec::new());
+            flush(&mut token, to_flush, journal.cursor()?)?;
+        }
+
+        trace!("Done outer iteration");
+    }
+}
+
+/// Writes the current cursor into `/var/journaldriver/cursor.pos`. To
+/// avoid issues with journaldriver being terminated while the cursor
+/// is still being written, this will first write the cursor into a
+/// temporary file and then move it.
+fn persist_cursor(cursor: String) -> Result<()> {
+    // This code exists to aid in tracking down if there are other
+    // causes of issue #2 than what has already been taken care of.
+    //
+    // One theory is that journald (or the Rust library to interface
+    // with it) may occasionally return empty cursor strings. If this
+    // is ever the case, we would like to know about it.
+    if cursor.is_empty() {
+        error!("Received empty journald cursor position, refusing to persist!");
+        error!("Please report this message at https://github.com/tazjin/journaldriver/issues/2");
+        return Ok(())
+    }
+
+    let mut file = File::create(&*CURSOR_TMP_FILE)
+        .context("Failed to create cursor file")?;
+
+    write!(file, "{}", cursor).context("Failed to write cursor file")?;
+
+    rename(&*CURSOR_TMP_FILE, &*CURSOR_FILE)
+        .context("Failed to move cursor file")
+        .map_err(Into::into)
+}
+
+/// Flushes all drained records to Stackdriver. Any Stackdriver
+/// message can at most contain 1000 log entries which means they are
+/// chunked up here.
+///
+/// In some cases large payloads seem to cause errors in Stackdriver -
+/// the chunks are therefore made smaller here.
+///
+/// If flushing is successful the last cursor position will be
+/// persisted to disk.
+fn flush(token: &mut Token,
+         entries: Vec<LogEntry>,
+         cursor: String) -> Result<()> {
+    if token.is_expired() {
+        debug!("Refreshing Google metadata access token");
+        let new_token = get_token()?;
+        mem::replace(token, new_token);
+    }
+
+    for chunk in entries.chunks(750) {
+        let request = prepare_request(chunk);
+        if let Err(write_error) = write_entries(token, request) {
+            error!("Failed to write {} entries: {}", chunk.len(), write_error)
+        } else {
+            debug!("Wrote {} entries to Stackdriver", chunk.len())
+        }
+    }
+
+    persist_cursor(cursor)
+}
+
+/// Convert a slice of log entries into the format expected by
+/// Stackdriver. This format is documented here:
+///
+/// https://cloud.google.com/logging/docs/reference/v2/rest/v2/entries/write
+fn prepare_request(entries: &[LogEntry]) -> Value {
+    json!({
+        "logName": format!("projects/{}/logs/{}", PROJECT_ID.as_str(), LOG_NAME.as_str()),
+        "resource": &*MONITORED_RESOURCE,
+        "entries": entries,
+        "partialSuccess": true
+    })
+}
+
+/// Perform the log entry insertion in Stackdriver Logging.
+fn write_entries(token: &Token, request: Value) -> Result<()> {
+    let response = ureq::post(ENTRIES_WRITE_URL)
+        .set("Authorization", format!("Bearer {}", token.token).as_str())
+        // The timeout values are set relatively high, not because of
+        // an expectation of Stackdriver being slow but just to
+        // eventually hit an error case in case of network troubles.
+        // Presumably no request in a functioning environment will
+        // ever hit these limits.
+        .timeout_connect(2000)
+        .timeout_read(5000)
+        .send_json(request);
+
+    if response.ok() {
+        Ok(())
+    } else {
+        let status = response.status_line().to_string();
+        let body = response.into_string()
+            .unwrap_or_else(|_| "no response body".into());
+        bail!("Write failure: {} ({})", body, status)
+    }
+}
+
+/// Attempt to read the initial cursor position from the configured
+/// file. If there is no initial cursor position set, read from the
+/// tail of the log.
+///
+/// The only "acceptable" error when reading the cursor position is
+/// the cursor position file not existing, other errors are fatal
+/// because they indicate a misconfiguration of journaldriver.
+fn initial_cursor() -> Result<JournalSeek> {
+    let read_result: io::Result<String> = (|| {
+        let mut contents = String::new();
+        let mut file = File::open(&*CURSOR_FILE)?;
+        file.read_to_string(&mut contents)?;
+        Ok(contents.trim().into())
+    })();
+
+    match read_result {
+        Ok(cursor) => Ok(JournalSeek::Cursor { cursor }),
+        Err(ref err) if err.kind() == ErrorKind::NotFound => {
+            info!("No previous cursor position, reading from journal tail");
+            Ok(JournalSeek::Tail)
+        },
+        Err(err) => {
+            (Err(err).context("Could not read cursor position"))?
+        }
+    }
+}
+
+fn main () {
+    env_logger::init();
+
+    // The directory in which cursor positions are persisted should
+    // have been created:
+    if !CURSOR_DIR.exists() {
+        error!("Cursor directory at '{:?}' does not exist", *CURSOR_DIR);
+        process::exit(1);
+    }
+
+    let cursor_position_dir = CURSOR_FILE.parent()
+        .expect("Invalid cursor position file path");
+
+    fs::create_dir_all(cursor_position_dir)
+        .expect("Could not create directory to store cursor position in");
+
+    let mut journal = Journal::open(JournalFiles::All, false, true)
+        .expect("Failed to open systemd journal");
+
+    let seek_position = initial_cursor()
+        .expect("Failed to determine initial cursor position");
+
+    match journal.seek(seek_position) {
+        Ok(cursor) => info!("Opened journal at cursor '{}'", cursor),
+        Err(err) => {
+            error!("Failed to set initial journal position: {}", err);
+            process::exit(1)
+        }
+    }
+
+    receiver_loop(journal).expect("log receiver encountered an unexpected error");
+}
diff --git a/tools/journaldriver/src/tests.rs b/tools/journaldriver/src/tests.rs
new file mode 100644
index 000000000000..779add7a7012
--- /dev/null
+++ b/tools/journaldriver/src/tests.rs
@@ -0,0 +1,95 @@
+use super::*;
+use serde_json::to_string;
+
+#[test]
+fn test_text_entry_serialization() {
+    let entry = LogEntry {
+        labels: Value::Null,
+        timestamp: None,
+        payload: Payload::TextPayload {
+            text_payload: "test entry".into(),
+        },
+        severity: None,
+    };
+
+    let expected = "{\"labels\":null,\"textPayload\":\"test entry\"}";
+    let result = to_string(&entry).expect("serialization failed");
+
+    assert_eq!(expected, result, "Plain text payload should serialize correctly")
+}
+
+#[test]
+fn test_json_entry_serialization() {
+    let entry = LogEntry {
+        labels: Value::Null,
+        timestamp: None,
+        payload: Payload::JsonPayload {
+            json_payload: json!({
+                "message": "JSON test"
+            })
+        },
+        severity: None,
+    };
+
+    let expected = "{\"labels\":null,\"jsonPayload\":{\"message\":\"JSON test\"}}";
+    let result = to_string(&entry).expect("serialization failed");
+
+    assert_eq!(expected, result, "JSOn payload should serialize correctly")
+}
+
+#[test]
+fn test_plain_text_payload() {
+    let message = "plain text payload".into();
+    let payload = message_to_payload(Some(message));
+    let expected = Payload::TextPayload {
+        text_payload: "plain text payload".into(),
+    };
+
+    assert_eq!(expected, payload, "Plain text payload should be detected correctly");
+}
+
+#[test]
+fn test_empty_payload() {
+    let payload = message_to_payload(None);
+    let expected = Payload::TextPayload {
+        text_payload: "empty log entry".into(),
+    };
+
+    assert_eq!(expected, payload, "Empty payload should be handled correctly");
+}
+
+#[test]
+fn test_json_payload() {
+    let message = "{\"someKey\":\"someValue\", \"otherKey\": 42}".into();
+    let payload = message_to_payload(Some(message));
+    let expected = Payload::JsonPayload {
+        json_payload: json!({
+            "someKey": "someValue",
+            "otherKey": 42
+        })
+    };
+
+    assert_eq!(expected, payload, "JSON payload should be detected correctly");
+}
+
+#[test]
+fn test_json_no_object() {
+    // This message can be parsed as valid JSON, but it is not an
+    // object - it should be returned as a plain-text payload.
+    let message = "42".into();
+    let payload = message_to_payload(Some(message));
+    let expected = Payload::TextPayload {
+        text_payload: "42".into(),
+    };
+
+    assert_eq!(expected, payload, "Non-object JSON payload should be plain text");
+}
+
+#[test]
+fn test_parse_microseconds() {
+    let input: String = "1529175149291187".into();
+    let expected: DateTime<Utc> = "2018-06-16T18:52:29.291187Z"
+        .to_string().parse().unwrap();
+
+    assert_eq!(Some(expected), parse_microseconds(input));
+}