Edge Cases

Cached Package with Modified ETag

Scenario: Cached package exists but ETag file doesn't match

Behavior:

• Re-download package
• Verify checksum
• Update cache and ETag

Interrupted Download

Scenario: Download interrupted mid-process

Behavior:

• Temporary directory removed on error
• Next run will re-attempt download
• Cached packages may be incomplete

Protection: Always use temporary directory first, then atomic move

Git Shallow Clone Limitations

Behavior: rebar3 uses --single-branch for optimization

Limitation: Cannot switch to other branches without re-cloning

Impact: Minimal; dependencies shouldn't change branches

SSH vs HTTPS Git URLs

SSH: git@github.com:user/repo.git HTTPS: https://github.com/user/repo.git

Differences:

• SSH requires SSH keys configured
• HTTPS may prompt for credentials
• Both work equivalently for fetching

Lock File: Both normalize to same format

Git Tag vs Branch vs Ref

Tag: Immutable reference to specific commit Branch: Mutable, points to latest commit on branch Ref: Direct commit SHA

Recommendation: Use tags for releases, refs for locking

Example:

{deps, [
    {cowboy, {git, "https://github.com/ninenines/cowboy.git", {tag, "2.9.0"}}}
]}.

Lock File Result:

{<<"cowboy">>, {git, "https://github.com/ninenines/cowboy.git",
                     {ref, "abc123..."}}, 0}

Note: Tag converted to ref in lock file

Local Git URLs

Format: file:///path/to/repo.git or /path/to/repo

Warning:

Local git resources (file:///...) are unsupported and may have odd behaviour.
Use remote git resources, or a plugin for local dependencies.

Recommendation: Use _checkouts/ for local development

Package Download with Slow Connection

Behavior: May timeout after default httpc timeout

Solution: Configure longer timeout in ~/.config/rebar3/rebar.config:

{hex, [
    {http_timeout, 120000}  % 120 seconds
]}.

Hex CDN Changes

Multiple CDNs Supported:

• Official: https://repo.hex.pm
• Mirrors: Various regions

Configuration: Use HEX_CDN environment variable

Example:

HEX_CDN=https://hexpm.example.com rebar3 compile

Transitive Dependencies of Git Deps

Scenario: Git dependency has its own dependencies

Behavior:

• After cloning Git dep, read its rebar.config
• Resolve its dependencies recursively
• Add to dependency tree

Example:

my_app → git_dep (Git)
git_dep → hex_dep (Hex)

Both fetched, Git first, then Hex