add script and now.sh function to edit pg_dump output (close #1861) (#1884)

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### Description
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This PR adds a bash script and a serverless function to clean up the output of `pg_dump` so that it can be used as a migration file for Hasura. This can be later integrated with the CLI so that the cleanup is handled by CLI.

### Affected components 
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- Scripts

### Related Issues
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<!-- Add the issue number below (e.g. #234) -->
#1861 
### Solution and Design
<!-- How is this issue solved/fixed? What is the design? -->
<!-- It's better if we elaborate -->
- A serverless function written in Go gets the SQL content though HTTP POST.
- A set of pre-defined lines are removed from this SQL string.
- SQL comments are removed using regex matching.
- Postgres triggers created by Hasura for use with event triggers are removed with regex matching.
- Empty newlines are removed by regex matching.
- Resulting string is returned in the HTTP response.
### Steps to test and verify
<!-- If this is a feature, what are the steps to try them out? -->
<!-- If this is a bug-fix, how do we verify the fix? -->
```bash
curl --data-binary @filename.sql https://hasura-edit-pg-dump.now.sh > newfile.sql
```

### Limitations, known bugs & workarounds
<!-- Limitations of the PR, known bugs and suggested workarounds -->
NA
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scripts/edit-pg-dump/README.md

@@ -0,0 +1,23 @@
+# hasura-edit-pg-dump
+
+This is a serverless function written in Go and deployed onto now.sh which can
+takes the output SQL from `pg_dump` and clean it up so that it can be used as a
+migration file with Hasura.
+
+1. SQL front matter, like `SET` statements are removed.
+2. Comments and empty newlines are removed.
+3. Postgres triggers created by Hasura are removed.
+
+This app is available at https://hasura-edit-pg-dump.now.sh
+
+Usage:
+
+```bash
+curl --data-binary @file.sql https://hasura-edit-pg-dump.now.sh > cleaned.sql
+```
+
+A bash version is also available:
+
+```bash
+./edit-pg-dump.sh filename.sql
+```

scripts/edit-pg-dump/edit-pg-dump.sh

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+#! /usr/bin/env bash
+#
+# Usage: ./edit-pg-dump.sh <file-name.sql>
+#
+
+if [ "$#" -ne 1 ]; then
+    echo "Invalid usage: ./edit-pg-dump.sh <file-name.sql>"
+fi
+
+filename=$1
+
+if [ ! -f $filename ] || [ "$filename" == "" ]; then
+    echo "file $filename does not exist"
+    exit 1
+fi
+
+echo "making a copy"
+cp $filename $filename.backup
+
+echo "processing file"
+
+# delete all comments
+
+sed -i '/^--/d' $filename
+
+# delete front matter
+
+read -r -d '' lines << EOF
+SET statement_timeout = 0;
+SET lock_timeout = 0;
+SET idle_in_transaction_session_timeout = 0;
+SET client_encoding = 'UTF8';
+SET standard_conforming_strings = on;
+SELECT pg_catalog.set_config('search_path', '', false);
+SET check_function_bodies = false;
+SET client_min_messages = warning;
+SET row_security = off;
+SET default_tablespace = '';
+SET default_with_oids = false;
+EOF
+
+while read -r line; do
+    sed -i '/^'"$line"'$/d' $filename
+done <<< $lines
+
+# delete notify triggers
+
+sed -i -E '/^CREATE TRIGGER "?notify_hasura_\w+"? AFTER \w+ ON "?\w+"?\."?\w+"? FOR EACH ROW EXECUTE PROCEDURE "?hdb_views"?\."?notify_hasura_\w+"?\(\);$/d' $filename
+
+# delete empty lines
+
+sed -i '/^[[:space:]]*$/d' $filename
+
+echo "done"

scripts/edit-pg-dump/index.go

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+package main
+
+import (
+	"fmt"
+	"io/ioutil"
+	"net/http"
+	"regexp"
+	"strings"
+)
+
+var frontMatter = []string{
+	"SET statement_timeout = 0;",
+	"SET lock_timeout = 0;",
+	"SET idle_in_transaction_session_timeout = 0;",
+	"SET client_encoding = 'UTF8';",
+	"SET standard_conforming_strings = on;",
+	"SELECT pg_catalog.set_config('search_path', '', false);",
+	"SET check_function_bodies = false;",
+	"SET client_min_messages = warning;",
+	"SET row_security = off;",
+	"SET default_tablespace = '';",
+	"SET default_with_oids = false;",
+}
+
+const helpStr = `POST the SQL file contents to this URL:
+
+curl --data-binary @filename.sql https://hasura-edit-pg-dump.now.sh > newfile.sql`
+
+// Handler is the now.sh serverless handler
+func Handler(w http.ResponseWriter, r *http.Request) {
+
+	// if method is not POST, respond with help message
+	if r.Method != "POST" {
+		fmt.Fprintf(w, helpStr)
+		return
+	}
+
+	// build the regular expression for matching empty newlines
+	emptyNewlineRe, err := regexp.Compile(`(?m)^\s*$[\r\n]*`)
+	if err != nil {
+		http.Error(w, err.Error(), 500)
+		return
+	}
+
+	// build the regular expression for matching SQL comments
+	commentsRe, err := regexp.Compile(`(?m)^--.*$`)
+	if err != nil {
+		http.Error(w, err.Error(), 500)
+		return
+	}
+
+	// build the regular expression for matching triggers created by Hasura
+	triggerRe, err := regexp.Compile(`(?m)^CREATE TRIGGER "?notify_hasura_\w+"? AFTER \w+ ON "?\w+"?\."?\w+"? FOR EACH ROW EXECUTE PROCEDURE "?hdb_views"?\."?notify_hasura_\w+"?\(\);$`)
+	if err != nil {
+		http.Error(w, err.Error(), 500)
+		return
+	}
+
+	// read the POST body
+	body, err := ioutil.ReadAll(r.Body)
+	if err != nil {
+		http.Error(w, err.Error(), 500)
+		return
+	}
+
+	// convert bytes to string
+	bodyStr := string(body)
+
+	// remove the SQL front matter
+	for _, l := range frontMatter {
+		bodyStr = strings.Replace(bodyStr, l, "", 1)
+	}
+
+	// replace the regex matches
+	bodyStr = commentsRe.ReplaceAllLiteralString(bodyStr, "")
+	bodyStr = triggerRe.ReplaceAllLiteralString(bodyStr, "")
+	bodyStr = emptyNewlineRe.ReplaceAllLiteralString(bodyStr, "\n")
+
+	// prefix a message
+	bodyStr = "--\r\n-- SQL edited by https://hasura-edit-pg-dump.now.sh\r\n--\r\n" + bodyStr
+
+	// respond with the edited string
+	fmt.Fprintf(w, bodyStr)
+}

scripts/edit-pg-dump/now.json

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+{
+  "version": 2,
+  "name": "hasura-edit-pg-dump",
+  "alias": "hasura-edit-pg-dump.now.sh",
+  "builds": [{ "src": "index.go", "use": "@now/go" }]
+}