Fix port collision bug, add --container-port flag

Port allocation:
- Use atomic flock-based allocation via /etc/ship/next_port
- Prevents race conditions when multiple deploys run concurrently
- Each app still gets its port stored in /etc/ship/ports/<name>

Docker container port:
- Add --container-port flag (default 80)
- Template now uses {{.ContainerPort}} instead of hardcoded 80
- Supports containers that listen on 8080, 3000, etc.

3 files changed, 39 insertions, 25 deletions

diff --git a/cmd/ship/deploy_impl_v2.go b/cmd/ship/deploy_impl_v2.go
index e2989b2..9ff674e 100644
--- a/cmd/ship/deploy_impl_v2.go
+++ b/cmd/ship/deploy_impl_v2.go
@@ -132,9 +132,14 @@ func deployDockerV2(ctx *deployContext) *output.ErrorResponse {
         }
 
         // Generate systemd unit
+        containerPort := ctx.Opts.ContainerPort
+        if containerPort == 0 {
+                containerPort = 80
+        }
         service, err := templates.DockerService(map[string]string{
-                "Name": name,
-                "Port": strconv.Itoa(port),
+                "Name":          name,
+                "Port":          strconv.Itoa(port),
+                "ContainerPort": strconv.Itoa(containerPort),
         })
         if err != nil {
                 return output.Err(output.ErrServiceFailed, "failed to generate systemd unit: "+err.Error())
@@ -281,38 +286,44 @@ func deployBinaryV2(ctx *deployContext) *output.ErrorResponse {
 }
 
 // allocatePort allocates or retrieves a port for a service
+// Uses atomic increment on /etc/ship/next_port to avoid collisions
 func allocatePort(client *ssh.Client, name string) (int, error) {
         portFile := fmt.Sprintf("/etc/ship/ports/%s", name)
 
-        // Try to read existing port
+        // Try to read existing port for this app
         out, err := client.Run(fmt.Sprintf("cat %s 2>/dev/null || echo ''", portFile))
         if err == nil && out != "" {
-                port, err := strconv.Atoi(out[:len(out)-1]) // Strip newline
-                if err == nil && port > 0 {
+                out = strings.TrimSpace(out)
+                if port, err := strconv.Atoi(out); err == nil && port > 0 {
                         return port, nil
                 }
         }
 
-        // Allocate new port
-        // Find highest used port and increment
-        out, err = client.RunSudo("mkdir -p /etc/ship/ports && ls /etc/ship/ports/ 2>/dev/null | xargs -I{} cat /etc/ship/ports/{} 2>/dev/null | sort -n | tail -1")
+        // Allocate new port atomically using flock
+        // This reads next_port, increments it, and writes back while holding a lock
+        allocScript := `
+flock -x /etc/ship/.port.lock sh -c '
+  mkdir -p /etc/ship/ports
+  PORT=$(cat /etc/ship/next_port 2>/dev/null || echo 9000)
+  echo $((PORT + 1)) > /etc/ship/next_port
+  echo $PORT
+'`
+        out, err = client.RunSudo(allocScript)
         if err != nil {
-                out = ""
+                return 0, fmt.Errorf("failed to allocate port: %w", err)
         }
 
-        nextPort := 9000
-        if out != "" {
-                if lastPort, err := strconv.Atoi(out[:len(out)-1]); err == nil {
-                        nextPort = lastPort + 1
-                }
+        port, err := strconv.Atoi(strings.TrimSpace(out))
+        if err != nil {
+                return 0, fmt.Errorf("invalid port allocated: %s", out)
         }
 
-        // Write port allocation
-        if err := client.WriteSudoFile(portFile, strconv.Itoa(nextPort)); err != nil {
+        // Write port allocation for this app
+        if err := client.WriteSudoFile(portFile, strconv.Itoa(port)); err != nil {
                 return 0, err
         }
 
-        return nextPort, nil
+        return port, nil
 }
 
 // setTTLV2 sets auto-expiry for a deploy
diff --git a/cmd/ship/deploy_v2.go b/cmd/ship/deploy_v2.go
index b636709..7d498b2 100644
--- a/cmd/ship/deploy_v2.go
+++ b/cmd/ship/deploy_v2.go
@@ -143,14 +143,15 @@ func deployV2(path string, opts deployV2Options) {
 }
 
 type deployV2Options struct {
-        Name    string
-        Host    string
-        Domain  string
-        Health  string
-        TTL     string
-        Env     []string
-        EnvFile string
-        Pretty  bool
+        Name          string
+        Host          string
+        Domain        string
+        Health        string
+        TTL           string
+        Env           []string
+        EnvFile       string
+        ContainerPort int // Port the container listens on (default 80 for Docker)
+        Pretty        bool
 }
 
 // deployContext holds all info needed for a deploy
diff --git a/cmd/ship/root_v2.go b/cmd/ship/root_v2.go
index 4101d4e..aa81d1e 100644
--- a/cmd/ship/root_v2.go
+++ b/cmd/ship/root_v2.go
@@ -43,6 +43,7 @@ func initV2() {
         rootV2Cmd.Flags().String("ttl", "", "Auto-delete after duration (e.g., 1h, 7d)")
         rootV2Cmd.Flags().StringArray("env", nil, "Environment variable (KEY=VALUE)")
         rootV2Cmd.Flags().String("env-file", "", "Path to .env file")
+        rootV2Cmd.Flags().Int("container-port", 80, "Port the container listens on (Docker only)")
 
         // Check for SHIP_PRETTY env var
         if os.Getenv("SHIP_PRETTY") == "1" {
@@ -78,6 +79,7 @@ func runDeployV2(cmd *cobra.Command, args []string) error {
         opts.TTL, _ = cmd.Flags().GetString("ttl")
         opts.Env, _ = cmd.Flags().GetStringArray("env")
         opts.EnvFile, _ = cmd.Flags().GetString("env-file")
+        opts.ContainerPort, _ = cmd.Flags().GetInt("container-port")
 
         // deployV2 handles all output and exits
         deployV2(path, opts)