fix(udp): expose UDP ports properly#3485
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mdelapenya merged 2 commits intotestcontainers:mainfrom Nov 5, 2025
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Summary by CodeRabbitBug Fixes
Tests
WalkthroughA fix is applied to the Changes
Estimated code review effort🎯 3 (Moderate) | ⏱️ ~25 minutes
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Pre-merge checks and finishing touches✅ Passed checks (2 passed)
✨ Finishing touches
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@blueprismo i think we need to update the tests for the new condition. Can you take a look? 🙏 |
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What does this PR do?
Fixes UDP port exposure.
Problem:
When using ExposedPorts: []string{"8080/udp"} in testcontainers-go, the MappedPort() function always returned "0/udp" instead of the actual mapped host port (e.g., "55051/udp"). This made it impossible to connect to UDP services running in containers.
Root Cause:
The issue was in the mergePortBindings() function in lifecycle.go. When nat.ParsePortSpecs() processes exposed port specifications like 8080/udp, it creates PortBinding structs with empty HostPort fields ({HostIP: "", HostPort: ""})
Docker interprets these differently:
HostPort: "" (empty) → "Don't bind this port to any host port" → results in port 0
HostPort: "0" → "Bind this port to a random available host port" → proper allocation
Solution:
Modified mergePortBindings() to convert empty HostPort values to "0" for automatic port allocation:
Why is it important?
To support UDP connections correctly as now they aren't useful (at least with random port allocatio
Related issues
Follows: #3484