Serialize Data Formats

Select+impl right serialization format → correct encode/decode + perf awareness.

Use When

• Wire format for API
• Persist structured data → disk|object storage
• Exchange between langs
• Optimize size|speed
• Migrate formats

In

• Required: Data structure (schema|example)
• Required: Use case (API|storage|stream|analytics)
• Optional: Perf reqs (size|speed|schema enforce)
• Optional: Target lang|runtime constraints
• Optional: Human readability

Do

Step 1: Select Format

Decision tree:

1. Human edit? → YAML (config) | JSON (data)
2. Strict schema + fast RPC? → Protobuf
3. Smallest wire? → MessagePack | Protobuf
4. Columnar analytics? → Parquet
5. In-memory interchange? → Arrow
6. Legacy enterprise? → XML

→ Format selected w/ documented rationale.

If err: reqs conflict (human + fast) → prioritize primary use case + note tradeoff.

Step 2: JSON Serialize

import json
from datetime import datetime, date
from dataclasses import dataclass, asdict

@dataclass
class Measurement:
    sensor_id: str
    value: float
    unit: str
    timestamp: datetime

# Custom encoder for non-standard types
class CustomEncoder(json.JSONEncoder):
    def default(self, obj):
        if isinstance(obj, datetime):
            return obj.isoformat()
        if isinstance(obj, date):
            return obj.isoformat()
        if isinstance(obj, bytes):
            import base64
            return base64.b64encode(obj).decode('ascii')
        return super().default(obj)

# Serialize
measurement = Measurement("sensor-01", 23.5, "celsius", datetime.now())
json_str = json.dumps(asdict(measurement), cls=CustomEncoder, indent=2)

# Deserialize
data = json.loads(json_str)

# R: JSON with jsonlite
library(jsonlite)

# Serialize
df <- data.frame(sensor_id = "sensor-01", value = 23.5, unit = "celsius")
json_str <- jsonlite::toJSON(df, auto_unbox = TRUE, pretty = TRUE)

# Deserialize
df_back <- jsonlite::fromJSON(json_str)

→ Round-trip preserves all types accurately.

If err: type lost (dates → strings) → add explicit conversion in deserialize.

Step 3: Protobuf

.proto:

syntax = "proto3";
package sensors;

message Measurement {
  string sensor_id = 1;
  double value = 2;
  string unit = 3;
  int64 timestamp_ms = 4;  // Unix milliseconds
}

message MeasurementBatch {
  repeated Measurement measurements = 1;
}

Gen+use:

# Generate Python code
protoc --python_out=. sensors.proto

# Generate Go code
protoc --go_out=. sensors.proto

from sensors_pb2 import Measurement, MeasurementBatch
import time

# Serialize
m = Measurement(
    sensor_id="sensor-01",
    value=23.5,
    unit="celsius",
    timestamp_ms=int(time.time() * 1000)
)
binary = m.SerializeToString()  # Compact binary

# Deserialize
m2 = Measurement()
m2.ParseFromString(binary)

→ Binary 3-10x smaller than JSON.

If err: protoc unavail → lang-native lib (betterproto Py).

Step 4: MessagePack

import msgpack
from datetime import datetime

# Custom packing for datetime
def encode_datetime(obj):
    if isinstance(obj, datetime):
        return {"__datetime__": True, "s": obj.isoformat()}
    return obj

def decode_datetime(obj):
    if "__datetime__" in obj:
        return datetime.fromisoformat(obj["s"])
    return obj

data = {"sensor_id": "sensor-01", "value": 23.5, "ts": datetime.now()}

# Serialize (smaller than JSON, faster than JSON)
packed = msgpack.packb(data, default=encode_datetime)

# Deserialize
unpacked = msgpack.unpackb(packed, object_hook=decode_datetime, raw=False)

→ Output 15-30% smaller than JSON for typical payloads.

If err: lang lacks MessagePack → fallback JSON+gzip.

Step 5: Parquet (Columnar)

import pyarrow as pa
import pyarrow.parquet as pq
import pandas as pd

# Create data
df = pd.DataFrame({
    "sensor_id": ["s-01", "s-02", "s-01", "s-03"] * 1000,
    "value": [23.5, 18.2, 24.1, 19.8] * 1000,
    "unit": ["celsius"] * 4000,
    "timestamp": pd.date_range("2025-01-01", periods=4000, freq="min")
})

# Write Parquet (columnar, compressed)
table = pa.Table.from_pandas(df)
pq.write_table(table, "measurements.parquet", compression="snappy")

# Read Parquet (can read specific columns without loading all data)
table_back = pq.read_table("measurements.parquet", columns=["sensor_id", "value"])
df_subset = table_back.to_pandas()

# R: Parquet with arrow
library(arrow)

# Write
df <- data.frame(sensor_id = rep("s-01", 1000), value = rnorm(1000))
arrow::write_parquet(df, "measurements.parquet")

# Read (with column selection — only reads selected columns from disk)
df_back <- arrow::read_parquet("measurements.parquet", col_select = c("value"))

→ Parquet 5-20x smaller than CSV for tabular.

If err: Arrow unavail → fastparquet (Py)|CSV+gzip fallback.

Step 6: Compare Perf

import json, msgpack, time
import pyarrow as pa, pyarrow.parquet as pq

data = [{"id": i, "value": i * 0.1, "label": f"item-{i}"} for i in range(10000)]

# JSON
start = time.perf_counter()
json_bytes = json.dumps(data).encode()
json_time = time.perf_counter() - start

# MessagePack
start = time.perf_counter()
msgpack_bytes = msgpack.packb(data)
msgpack_time = time.perf_counter() - start

print(f"JSON:    {len(json_bytes):>8} bytes, {json_time*1000:.1f} ms")
print(f"MsgPack: {len(msgpack_bytes):>8} bytes, {msgpack_time*1000:.1f} ms")

→ Benchmarks guide format for prod.

If err: insufficient perf any format → consider compression (zstd, snappy) as orthogonal optimization.

Check

• Format matches use case (rationale documented)
• Round-trip preserves all types
• Edge cases: empty, null, Unicode, large nums
• Perf benchmarked for representative sizes
• Err handling for malformed (graceful fail)
• Schema documented (JSON Schema|.proto|equiv)

Traps

• Float precision: JSON = IEEE 754 doubles. String encoding for financial.
• Date/time: No native JSON datetime. Always document format (ISO 8601) + timezone.
• Schema evolution: Add|remove fields can break consumers. Protobuf good; JSON needs careful versioning.
• Binary in JSON: Base64 inflates ~33%. Binary format for binary-heavy.
• YAML security: Parsers may exec arbitrary code via !!python/object tags. Always safe loaders.

→

• design-serialization-schema — schema design, versioning, evolution
• implement-pharma-serialisation — pharma serialisation (diff domain, same naming)
• create-quarto-report — data output for reports