/Go Engineering/Phase 4

Phase 4Days 16-20

Packages, Modules, I/O & CLI Engineering

Official module layout, files, JSON, configuration, and maintainable commands

Phase Goal

Organize a real Go module and build reliable file- and network-facing command-line tools.

Progress

Notes

Open the written lectures for this course before checking off the phase topics.

Projects

Research Archive Catalog CLI

Day 16: Packages, Modules & internal

Define Package boundaries and exported identifiers in plain language and explain the problem it solvesTrace what the Go compiler or runtime does when Package boundaries and exported identifiers is usedWrite a tiny example, then apply it to a realistic backend taskDiagnose the beginner failure mode for Package boundaries and exported identifiers and fix it deliberately

Define go mod init, go.mod, go.sum, and MVS in plain language and explain the problem it solvesTrace what the Go compiler or runtime does when go mod init, go.mod, go.sum, and MVS is usedWrite a tiny example, then apply it to a realistic backend taskDiagnose the beginner failure mode for go mod init, go.mod, go.sum, and MVS and fix it deliberately

Define cmd and internal layout from official guidance in plain language and explain the problem it solvesTrace what the Go compiler or runtime does when cmd and internal layout from official guidance is usedWrite a tiny example, then apply it to a realistic backend taskDiagnose the beginner failure mode for cmd and internal layout from official guidance and fix it deliberately

Define go list, go doc, dependencies, and avoiding package cycles in plain language and explain the problem it solvesTrace what the Go compiler or runtime does when go list, go doc, dependencies, and avoiding package cycles is usedWrite a tiny example, then apply it to a realistic backend taskDiagnose the beginner failure mode for go list, go doc, dependencies, and avoiding package cycles and fix it deliberately

Day 17: Files, Readers, Writers & bufio

Define io.Reader and io.Writer as composable contracts in plain language and explain the problem it solvesTrace what the Go compiler or runtime does when io.Reader and io.Writer as composable contracts is usedWrite a tiny example, then apply it to a realistic backend taskDiagnose the beginner failure mode for io.Reader and io.Writer as composable contracts and fix it deliberately

Define os.File lifecycle and defer Close in plain language and explain the problem it solvesTrace what the Go compiler or runtime does when os.File lifecycle and defer Close is usedWrite a tiny example, then apply it to a realistic backend taskDiagnose the beginner failure mode for os.File lifecycle and defer Close and fix it deliberately

Define Buffered I/O and scanner limits in plain language and explain the problem it solvesTrace what the Go compiler or runtime does when Buffered I/O and scanner limits is usedWrite a tiny example, then apply it to a realistic backend taskDiagnose the beginner failure mode for Buffered I/O and scanner limits and fix it deliberately

Define Paths, permissions, atomic writes, and cleanup in plain language and explain the problem it solvesTrace what the Go compiler or runtime does when Paths, permissions, atomic writes, and cleanup is usedWrite a tiny example, then apply it to a realistic backend taskDiagnose the beginner failure mode for Paths, permissions, atomic writes, and cleanup and fix it deliberately

Day 18: JSON, Tags & Validation Boundaries

Define encoding/json marshal and unmarshal in plain language and explain the problem it solvesTrace what the Go compiler or runtime does when encoding/json marshal and unmarshal is usedWrite a tiny example, then apply it to a realistic backend taskDiagnose the beginner failure mode for encoding/json marshal and unmarshal and fix it deliberately

Define Struct tags, omitempty, unknown fields, and optional values in plain language and explain the problem it solvesTrace what the Go compiler or runtime does when Struct tags, omitempty, unknown fields, and optional values is usedWrite a tiny example, then apply it to a realistic backend taskDiagnose the beginner failure mode for Struct tags, omitempty, unknown fields, and optional values and fix it deliberately

Define Streaming JSON with Encoder and Decoder in plain language and explain the problem it solvesTrace what the Go compiler or runtime does when Streaming JSON with Encoder and Decoder is usedWrite a tiny example, then apply it to a realistic backend taskDiagnose the beginner failure mode for Streaming JSON with Encoder and Decoder and fix it deliberately

Define Separating transport structs from domain structs in plain language and explain the problem it solvesTrace what the Go compiler or runtime does when Separating transport structs from domain structs is usedWrite a tiny example, then apply it to a realistic backend taskDiagnose the beginner failure mode for Separating transport structs from domain structs and fix it deliberately

Day 19: CLI Flags, Config & Graceful UX

Define flag package, subcommands, usage, and exit codes in plain language and explain the problem it solvesTrace what the Go compiler or runtime does when flag package, subcommands, usage, and exit codes is usedWrite a tiny example, then apply it to a realistic backend taskDiagnose the beginner failure mode for flag package, subcommands, usage, and exit codes and fix it deliberately

Define Configuration precedence: flags, environment, file, defaults in plain language and explain the problem it solvesTrace what the Go compiler or runtime does when Configuration precedence: flags, environment, file, defaults is usedWrite a tiny example, then apply it to a realistic backend taskDiagnose the beginner failure mode for Configuration precedence: flags, environment, file, defaults and fix it deliberately

Define Signals and context-aware cancellation preview in plain language and explain the problem it solvesTrace what the Go compiler or runtime does when Signals and context-aware cancellation preview is usedWrite a tiny example, then apply it to a realistic backend taskDiagnose the beginner failure mode for Signals and context-aware cancellation preview and fix it deliberately

Define Actionable errors, stdout versus stderr, and scripting contracts in plain language and explain the problem it solvesTrace what the Go compiler or runtime does when Actionable errors, stdout versus stderr, and scripting contracts is usedWrite a tiny example, then apply it to a realistic backend taskDiagnose the beginner failure mode for Actionable errors, stdout versus stderr, and scripting contracts and fix it deliberately

Day 20: Mini Project — Research Archive Catalog CLI

Define Walk an archive and stream file metadata and hashes in plain language and explain the problem it solvesTrace what the Go compiler or runtime does when Walk an archive and stream file metadata and hashes is usedWrite a tiny example, then apply it to a realistic backend taskDiagnose the beginner failure mode for Walk an archive and stream file metadata and hashes and fix it deliberately

Define Versioned JSON catalog and deterministic output in plain language and explain the problem it solvesTrace what the Go compiler or runtime does when Versioned JSON catalog and deterministic output is usedWrite a tiny example, then apply it to a realistic backend taskDiagnose the beginner failure mode for Versioned JSON catalog and deterministic output and fix it deliberately

Define Report duplicates, drift, missing metadata, and unreadable files in plain language and explain the problem it solvesTrace what the Go compiler or runtime does when Report duplicates, drift, missing metadata, and unreadable files is usedWrite a tiny example, then apply it to a realistic backend taskDiagnose the beginner failure mode for Report duplicates, drift, missing metadata, and unreadable files and fix it deliberately

Define Project requirements, atomic output, and install docs in plain language and explain the problem it solvesTrace what the Go compiler or runtime does when Project requirements, atomic output, and install docs is usedWrite a tiny example, then apply it to a realistic backend taskDiagnose the beginner failure mode for Project requirements, atomic output, and install docs and fix it deliberately

Capstone

Research Archive Catalog CLI

Create and audit a deterministic catalog for a field-research archive, recording paths, sizes, media types, checksums, and required sidecar metadata.

Streaming inspection without loading files into memory
Atomic versioned catalog writes
Distinct exit codes for drift, invalid metadata, and I/O failure

Phase Complete!

After this phase, you'll be able to:

Package boundaries and exported identifiers
go mod init, go.mod, go.sum, and MVS
cmd and internal layout from official guidance
go list, go doc, dependencies, and avoiding package cycles
io.Reader and io.Writer as composable contracts
os.File lifecycle and defer Close
Buffered I/O and scanner limits
Paths, permissions, atomic writes, and cleanup

You can apply Phase 4 skills in a finished, explainable Go project.

Back to all phases

Phase Goal

Day 16: Packages, Modules & internal

Package boundaries and exported identifiers

go mod init, go.mod, go.sum, and MVS

cmd and internal layout from official guidance

go list, go doc, dependencies, and avoiding package cycles

Day 17: Files, Readers, Writers & bufio

io.Reader and io.Writer as composable contracts

os.File lifecycle and defer Close

Buffered I/O and scanner limits

Paths, permissions, atomic writes, and cleanup

Day 18: JSON, Tags & Validation Boundaries

encoding/json marshal and unmarshal

Struct tags, omitempty, unknown fields, and optional values

Streaming JSON with Encoder and Decoder

Separating transport structs from domain structs

Day 19: CLI Flags, Config & Graceful UX

flag package, subcommands, usage, and exit codes

Configuration precedence: flags, environment, file, defaults

Signals and context-aware cancellation preview

Actionable errors, stdout versus stderr, and scripting contracts

Day 20: Mini Project — Research Archive Catalog CLI

Walk an archive and stream file metadata and hashes

Versioned JSON catalog and deterministic output

Report duplicates, drift, missing metadata, and unreadable files

Project requirements, constraints & review

Research Archive Catalog CLI

Phase Complete!