New command: check (#901)

#### Description

This PR adds a new dummy command called `check`. It will run the
preflight checks before `run`/`snapshot`.
The actual checks will come in multiple follow-up PRs.

When invoking `check` all checks are executed. If you want to run a only
a portion of the checks, you will be able to provide flags to filter.

```
$ pgstream check --connectivity
```

```
$ pgstream check --replication
```

```
$ pgstream check --access
```

```
$ pgstream check --connectivity --replication
```

##### Help
```
$ pgstream check --help
Runs pre-migration checks to catch blocking issues before snapshot/run

Usage:
  pgstream check [flags]

Examples:

      pgstream check -c pg2pg.env
      pgstream check -c pg2pg.yaml --json

Flags:
  -h, --help                  help for check
      --json                  Output the check report in JSON format
      --postgres-url string   Source postgres URL to run checks against
      --target-url string     Target URL to run checks against
```

##### Example outputs

```
# Run against a config file
$ pgstream check -c pg2pg.yaml
 SUCCESS  no checks to run

# Run with env-var-driven config
$ PGSTREAM_POSTGRES_LISTENER_URL="postgres://user:pw@source:5432/app" pgstream check
 SUCCESS  no checks to run

# Run with flags
$ pgstream check \
    --postgres-url "postgres://user:pw@source:5432/app" \
    --target-url   "postgres://user:pw@target:5432/app"
 SUCCESS  no checks to run

# JSON output (no findings to report yet)
$ pgstream check -c pg2pg.yaml --json
 SUCCESS  no checks to run
```

#### Related Issue(s)

- Related to #897

#### Type of Change

Please select the relevant option(s):

- [ ] 🐛 Bug fix (non-breaking change that fixes an issue)
- [x] ✨ New feature (non-breaking change that adds functionality)
- [ ] 💥 Breaking change (fix or feature that would cause existing
functionality to not work as expected)
- [ ] 📚 Documentation update
- [ ] 🔧 Refactoring (no functional changes)
- [ ] ⚡ Performance improvement
- [ ] 🧪 Test coverage improvement
- [ ] 🔨 Build/CI changes
- [ ] 🧹 Code cleanup

#### Testing

- [ ] Unit tests added/updated
- [ ] Integration tests added/updated
- [x] Manual testing performed
- [x] All existing tests pass

#### Checklist

- [x] Code follows project style guidelines
- [x] Self-review completed
- [x] Code is well-commented
- [x] Documentation updated where necessary


#### Additional Notes

<!-- Any context or special instructions for reviewers -->

Author: kvch

cli-definition.json

@@ -1,6 +1,31 @@
 {
   "name": "pgstream",
   "commands": [
+    {
+      "name": "check",
+      "short": "Runs pre-migration checks to catch blocking issues before snapshot/run",
+      "use": "check",
+      "example": "\n\tpgstream check -c pg2pg.env\n\tpgstream check -c pg2pg.yaml --json\n\t",
+      "flags": [
+        {
+          "name": "json",
+          "description": "Output the check report in JSON format",
+          "default": "false"
+        },
+        {
+          "name": "postgres-url",
+          "description": "Source postgres URL to run checks against",
+          "default": ""
+        },
+        {
+          "name": "target-url",
+          "description": "Target URL to run checks against",
+          "default": ""
+        }
+      ],
+      "subcommands": [],
+      "args": []
+    },
     {
       "name": "destroy",
       "short": "It destroys any pgstream setup, removing the replication slot and all the relevant tables/functions/triggers, along with the internal pgstream schema",

cmd/check_cmd.go

@@ -0,0 +1,58 @@
+// SPDX-License-Identifier: Apache-2.0
+
+package cmd
+
+import (
+	"fmt"
+
+	"github.com/pterm/pterm"
+	"github.com/spf13/cobra"
+	"github.com/spf13/viper"
+
+	"github.com/xataio/pgstream/cmd/config"
+)
+
+var checkCmd = &cobra.Command{
+	Use:     "check",
+	Short:   "Runs pre-migration checks to catch blocking issues before snapshot/run",
+	PreRunE: checkFlagBinding,
+	RunE: func(cmd *cobra.Command, args []string) error {
+		sp, _ := pterm.DefaultSpinner.WithText("running pgstream checks...").Start()
+
+		err := func() error {
+			streamConfig, err := config.ParseStreamConfig()
+			if err != nil {
+				return fmt.Errorf("parsing stream config: %w", err)
+			}
+			_ = streamConfig
+
+			// TODO: run checks. See https://github.com/xataio/pgstream/issues/897 for the
+			// list of checks to implement.
+
+			sp.Success("no checks to run")
+			return nil
+		}()
+		if err != nil {
+			sp.Fail(err.Error())
+		}
+
+		return err
+	},
+	Example: `
+	pgstream check -c pg2pg.env
+	pgstream check -c pg2pg.yaml --json
+	`,
+}
+
+func checkFlagBinding(cmd *cobra.Command, _ []string) error {
+	// to be able to overwrite configuration with flags when yaml config file is
+	// provided
+	viper.BindPFlag("source.postgres.url", cmd.Flags().Lookup("postgres-url"))
+	viper.BindPFlag("target.postgres.url", cmd.Flags().Lookup("target-url"))
+
+	// to be able to overwrite configuration with flags when env config file is
+	// provided or when no configuration is provided
+	viper.BindPFlag("PGSTREAM_POSTGRES_LISTENER_URL", cmd.Flags().Lookup("postgres-url"))
+	viper.BindPFlag("PGSTREAM_POSTGRES_WRITER_TARGET_URL", cmd.Flags().Lookup("target-url"))
+	return nil
+}

cmd/root_cmd.go

@@ -115,6 +115,11 @@ func Prepare() *cobra.Command {
 	validateSchemaCmd.Flags().Bool("json", false, "Output the validation status in JSON format")
 	validateCmd.AddCommand(validateSchemaCmd)
 
+	// check cmd
+	checkCmd.Flags().String("postgres-url", "", "Source postgres URL to run checks against")
+	checkCmd.Flags().String("target-url", "", "Target URL to run checks against")
+	checkCmd.Flags().Bool("json", false, "Output the check report in JSON format")
+
 	// Flag binding for root cmd
 	rootFlagBinding(rootCmd)
 
@@ -126,6 +131,7 @@ func Prepare() *cobra.Command {
 	rootCmd.AddCommand(snapshotCmd)
 	rootCmd.AddCommand(statusCmd)
 	rootCmd.AddCommand(validateCmd)
+	rootCmd.AddCommand(checkCmd)
 	return rootCmd
 }